Lithium-ion battery using a cross-linked separator

Abstract

The present invention relates to a lithium ion battery using a crosslinked separator and provides a separator for a power storage device and a method for producing the same. The separator for a power storage device is characterized in that it contains a silane-modified polyolefin and initiates a silane crosslinking reaction of the silane-modified polyolefin when in contact with an electrolyte.

Description

[0001] This application is a divisional application of an application filed on October 11, 2019, with application number 201980007742.8 and invention name “Lithium-ion battery using a cross-linked separator”. Technical Field

[0002] The present invention relates to a separator for an electricity storage device, a cross-linking method thereof, an assembly kit for an electricity storage device, a method for producing an electricity storage device, and the like. Background Art

[0003] Microporous membranes are widely used as membranes for separating various substances, selectively permeating separation membranes, and separators. Examples of their applications include microfiltration membranes, separators for fuel cells and capacitors, substrates for functional membranes that incorporate functional materials into their pores to achieve new functions, and separators for power storage devices. Among these, polyolefin microporous membranes are particularly suitable as separators for lithium-ion batteries, which are widely used in laptop computers, mobile phones, digital cameras, and the like.

[0004] In order to ensure the safety of the battery, the separator is required to take into account both the activation of the shutdown function and the increase in the membrane rupture temperature. For example, Patent Document 1 describes the adjustment of the high-order physical properties of the polyolefin resin, which is an essential component of the separator for lithium-ion batteries. In addition, as shown in Patent Document 2, it is known that in a specific crystallinity and gel fraction region, the shutdown function can suppress the heat caused by the short circuit inside the battery, and on the other hand, even if a high-temperature area is generated locally in the battery cell, the membrane will not rupture (breakdown above 170°C), thereby ensuring the safety of the battery. Regarding Patent Documents 1 and 2, in more detail, it has been gradually discovered experimentally that by constructing a silane cross-linked portion (gel structure) in a polyolefin separator, high-temperature membrane rupture properties can be exhibited.

[0005] For example, Patent Documents 1 to 6 describe silane crosslinked structures formed by contacting a separator containing silane-modified polyolefin with water. Patent Document 8 describes a crosslinked structure formed by ring-opening norbornene by irradiation with ultraviolet rays, electron beams, etc. Patent Document 9 describes a separator having an insulating layer with a (meth)acrylic copolymer having a crosslinked structure, a styrene-butadiene rubber binder, etc. In addition, for example, a separator is proposed in which the thickness ratio of the A layer having a shutdown characteristic to the B layer containing an aramid resin and an inorganic material is adjusted to within a specified range (see Patent Document 11).

[0006] Regarding the components used in lithium-ion batteries, positive electrodes, negative electrode materials, electrolytes and separators are used. Among these components, the separator is required to be inactive to electrochemical reactions or surrounding components based on its characteristics as an insulating material. On the other hand, the negative electrode material of lithium-ion batteries established a technology for suppressing the decomposition of the electrolyte on the negative electrode surface by forming a solid electrolyte interface (SEI) by utilizing the chemical reaction during the initial charge at the beginning of its development (non-patent document 1). In addition, it has been reported that even if a polyolefin resin is used as a separator, an oxidation reaction is induced on the positive electrode surface at high voltage, and the separator becomes black and the surface deteriorates.

[0007] Based on this concept, separator materials for power storage devices employ chemical structures that are inactive to electrochemical and other chemical reactions. Consequently, the development and practical application of polyolefin-based microporous membranes have been extensively pursued. However, even with improvements to the mechanical microporous structure of separators using polyolefins as the resin, performance improvements are limited. For example, due to the thermal stability of separators above the melting point of polyolefins and the electronegativity of the olefin units, the separators lack sufficient affinity for the electrolyte and sufficient electrolyte retention, making it difficult to achieve satisfactory permeability of lithium ions or their solvated ion clusters within the separator.

[0008] Thus, due to the above-mentioned limitations, the current situation cannot be expected to satisfy the high-speed charge and discharge and heat-resistant stability required in modern battery development.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 9-216964

[0012] Patent Document 2: International Publication No. 97 / 44839

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 11-144700

[0014] Patent Document 4: Japanese Patent Application Laid-Open No. 11-172036

[0015] Patent Document 5: Japanese Patent Application Laid-Open No. 2001-176484

[0016] Patent Document 6: Japanese Patent Application Laid-Open No. 2000-319441

[0017] Patent Document 7: Japanese Patent Application Laid-Open No. 2017-203145

[0018] Patent Document 8: Japanese Patent Application Laid-Open No. 2011-071128

[0019] Patent Document 9: Japanese Patent Application Laid-Open No. 2014-056843

[0020] Patent Document 10: Japanese Patent Application Laid-Open No. 10-261435

[0021] Patent Document 11: Japanese Patent Application Laid-Open No. 2007-299612

[0022] Patent Document 12: International Publication No. 2010 / 134585

[0023] Patent Document 13: Japanese Patent Application Laid-Open No. 2016-072150

[0024] Non-patent literature

[0025] Non-Patent Document 1: Lithium Ion Secondary Battery (2nd Edition) Published by Nikkan Kogyo Shimbun

[0026] Non-Patent Literature 2: Basic Polymer Chemistry, published by Tokyo Chemical Industry Summary of the Invention

[0027] Problems to be solved by the invention

[0028] In recent years, the high output and high energy density of lithium-ion secondary batteries for use in mobile devices or vehicles are being developed. On the other hand, miniaturization of battery cells and stable cycle discharge and charge performance during long-term use are required. Therefore, as the separator used, a thin film (for example, less than 15 μm) and high-quality material (for example, with uniform physical properties and no resin agglomerates) is required. Furthermore, the level of battery safety is more stringent than before. As also described in Patent Documents 1 and 2, a shutdown function and high-temperature film rupture properties are required, and the development of a resin composition and a manufacturing method for separators that can be stably produced is expected. In this regard, as the level of the shutdown temperature, the lower the temperature than 150°C, the better. In addition, as the level of the film rupture temperature, the higher the temperature, the better.

[0029] For example, the method described in Patent Document 3 uses a cross-linking catalyst masterbatch during the extrusion process to carry out a cross-linking reaction of silane-modified polyethylene in an extruder, but the generation of resin agglomerates also occurs, which reduces the uniformity of the physical properties of the separator. In response to this method, the methods described in Patent Documents 4, 5, and 6 respond by setting a plasticizer extraction process or a silane glue cross-linking process, or controlling the gel fraction of the resin film, or forming the uncross-linked resin with hot water and then dehydrating it. In addition, Patent Document 7 proposes to provide a heat-resistant resin microporous membrane, which is excellent in low thermal shrinkage, low fluidity, and resistance to melt fracture by adjusting the gel fraction of the polyolefin microporous membrane, the storage modulus at a temperature of 40°C to 250°C in the dynamic viscoelasticity (DMA) measurement, the maximum shrinkage based on thermomechanical analysis (TMA), and the amount of free radicals measured by electron spin resonance (ESR).

[0030] Furthermore, with regard to separators for storage devices, from the perspectives of dimensional stability, maintaining the shutdown function and increasing the membrane rupture temperature, dimensional stability, etc., it has been proposed to configure an inorganic porous layer containing inorganic particles such as calcined kaolin and boehmite and a resin binder on the surface of at least one side of a polyolefin microporous membrane (Patent Documents 12 and 13).

[0031] However, the method disclosed in Patent Document 4 does not allow for sufficient silane crosslinking reaction, making it difficult to achieve high-temperature film breakage resistance. The plasticizer extraction steps described in Patent Documents 3 and 4 utilize a tin(II)-based crosslinking catalyst, allowing for crosslinking reaction, but there is a risk of residual crosslinking catalyst.

[0032] The heat-resistant resin microporous membrane described in Patent Document 7 is obtained by applying a photopolymerizable coating liquid to a membrane that has been porous by a dry process. In addition, Example 5 of Patent Document 7 adds a low-molecular-weight silane coupling agent such as γ-methacryloxypropyltrimethoxysilane to the porous membrane. However, if a low-molecular-weight silane coupling agent is used in a wet porous process, it is expected that the low-molecular-weight silane coupling agent will easily react or bind with the plasticizer used for the porous process, rather than binding with the resin of the porous membrane. Furthermore, batteries equipped with a heat-resistant resin microporous membrane as described in Patent Document 7 as a separator have poor cycle characteristics. In addition, during long-term use, unpredictable side reactions may be induced in the battery, which may reduce battery safety.

[0033] In addition, the coating layer of patent documentation 7 is recorded in that after the compound with polymerizable functional group is applied to the resin porous film, it is formed by external stimulation with cross-linking reaction, so it is expected that liquid will invade a part of the resin porous film while the coating layer is applied, and after the cross-linking reaction is carried out, it is expected that their mixed region will also be formed near the interface of the coating layer and the resin porous film. Thus, good TMA thermal shrinkage performance can be obtained, but the reduction of the battery cycle characteristics caused by the blockage of the resin porous film or the reduction of the fusing (closing) performance of the melting phenomenon with the resin porous film can be expected. And then, in the composite microporous film obtained by the method recorded in patent documentation 7, a small amount of free radical species compound is detected by ESR, due to residue, when the composite microporous film is assembled into a battery, free radical reaction is carried out with other components, particularly with electrolyte, it is expected that the chain reaction of the electrolyte decomposition is expected, and it is thought that the battery performance can be significantly deteriorated.

[0034] Furthermore, the microporous membranes and separators recorded in patent documents 1, 2, and 7 lack research on inorganic porous layers comprising inorganic particles and resin binders configured on their surfaces. The existing separators having an inorganic porous layer on a microporous membrane appear to have increased film breakage temperatures on the temperature-resistance curve of an electrical storage device. However, in reality, resin sometimes dissolves from the microporous membrane into the inorganic porous layer, so it is expected that the membrane as a whole of the separator will be reduced in weight and the resulting reduction in stress tolerance. Therefore, although the multilayer porous membranes recorded in patent documents 12 and 13 have a polyolefin microporous membrane and an inorganic porous layer, there is room for research on both the low-temperature shutdown function and the high-temperature film breakage property of a separator for an electrical storage device, or on improving the cycle characteristics and battery nailing safety of an electrical storage device.

[0035] Furthermore, batteries using separators such as those described in Patent Documents 3 to 7 have poor cycle characteristics. Furthermore, during long-term use, unpredictable side reactions may be induced in the battery, leading to a risk of reduced battery safety.

[0036] Conventional molded products, such as hot water pipes, require a tin (Sn) catalyst to be added to the extruder during the extrusion process. Meanwhile, the wet manufacturing process for separators for power storage devices typically includes extrusion and sheet forming, stretching, plasticizer extraction (porization), heat treatment, and coiling. Therefore, if silane crosslinking is promoted within the extruder during the sheet forming process, the gelled portion can be degraded, and stretching of the silane-crosslinked polyolefin is difficult in the subsequent stretching process. Therefore, there is still room for research on new separators for power storage devices that are suitable for manufacturing processes.

[0037] Furthermore, the crosslinking methods described in Patent Documents 1 to 6, 8, and 9 are all performed intermittently during the separator film formation process or immediately after separator production. Therefore, after the crosslinked structure described in Patent Documents 1 to 6, 8, and 9 is formed, the separator must be coated and slit. This increases internal stress during the subsequent electrode lamination and winding process, potentially causing deformation in the resulting battery. For example, if the crosslinked structure is formed by heating, the internal stress of the separator containing this crosslinked structure may increase at room or normal temperatures.

[0038] Furthermore, when forming a crosslinked structure by irradiation with light such as ultraviolet rays or electron beams, the irradiation may be uneven, resulting in an inhomogeneous crosslinked structure. This is believed to be because the periphery of the crystal portion of the resin constituting the separator is easily crosslinked by electron beams.

[0039] It should be noted that Patent Document 10 describes a technique for improving the cycle characteristics of lithium-ion secondary batteries by adding succinimides or the like to an electrolyte solution. However, the technique described in Patent Document 10 does not achieve improved cycle characteristics by specifying the structure of a separator.

[0040] Furthermore, the separators for electricity storage devices described in Patent Documents 1, 2, and 11 still have room for improvement in terms of achieving improved performance of the electricity storage devices.

[0041] In view of the above problems, the present invention aims to provide a separator for a storage device that can achieve both shutdown function and high-temperature rupture resistance, ensuring the safety, output and / or cycle stability of the storage device, as well as a new cross-linking method suitable for its manufacturing process or an assembly kit or manufacturing method for the storage device.

[0042] Solutions for solving problems

[0043] The above problems are solved by the following technical means. [1]

[0045] A separator for an electricity storage device, comprising a silane-modified polyolefin, wherein a silane cross-linking reaction of the silane-modified polyolefin is initiated when the separator comes into contact with an electrolyte. [2]

[0047] The separator for a power storage device according to item 1, wherein the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst for cross-linking the silane-modified polyolefin. [3]

[0049] The separator for an electricity storage device according to item 1 or 2, further comprising polyethylene in addition to the silane-modified polyolefin. [4]

[0051] The separator for a power storage device according to item 3, wherein a mass ratio of the silane-modified polyolefin to the polyethylene (mass of the silane-modified polyolefin / mass of the polyethylene) is 0.05 / 0.95 to 0.40 / 0.60. [5]

[0053] A separator for an electrical storage device, comprising 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, wherein the storage modulus change ratio (R ΔE’ ) is 1.5 to 20 times:

[0054] R ΔE’ =E' S / E' j (1)

[0055] {where, E' j is the storage modulus of the separator for the power storage device before the cross-linking reaction of the silane-modified polyolefin, measured at 160° C. to 220° C., and E′ S is the storage modulus of the separator for the power storage device after the cross-linking reaction of the silane-modified polyolefin, measured at 160° C. to 220° C., and is E′ j or E' S The measurement conditions of the storage modulus E' are defined by the following configurations (i) to (iv).

[0056] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0057] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0058] Sample film thickness: 5μm to 50μm

[0059] Measuring temperature range: -50~225℃

[0060] Heating rate: 10℃ / min

[0061] Measuring frequency: 1Hz

[0062] Deformation mode: Sine wave stretching mode (Linear tension)

[0063] Initial value of static tensile load: 0.5N

[0064] Initial gap distance (at 25°C): 25mm

[0065] Automatic strain adjustment: Enabled (range: amplitude 0.05-25%, sine wave load 0.02-5N).

[0066] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load.

[0067] (iii) The sinusoidal wave tensile mode refers to measuring the vibration stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal wave tensile mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a manner that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a manner that the sinusoidal wave load is within 5N and the increase in the amplitude value is within 25%.

[0068] (iv) Calculate the storage modulus E' based on the relationship between the obtained sinusoidal wave load and the amplitude value and the following formula:

[0069] σ * =σ0·Exp[i(ωt+δ)],

[0070] ε * =ε0·Exp(iωt),

[0071] σ * =E * ·ε *

[0072] E * =E'+iE"

[0073] (where σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[0074] Vibration stress: Sine wave load / initial cross-sectional area

[0075] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[0076] Sine wave load: The difference between the measured vibration stress and the static tensile load). [6]

[0078] A separator for an electrical storage device, comprising 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, wherein the loss modulus change ratio (R ΔE” ) is 1.5 to 20 times:

[0079] R ΔE” =E” S / E” j (3)

[0080] {where, E” j is the loss modulus of the separator for the power storage device before the cross-linking reaction of the silane-modified polyolefin, measured at 160°C to 220°C, and E" S The loss modulus of the separator for the power storage device after the cross-linking reaction of the silane-modified polyolefin is measured at 160°C to 220°C, and is E" j or E" S The measurement conditions of the loss modulus E" are specified by the following constitutions (i) to (iv).

[0081] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0082] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0083] Sample film thickness: 5μm to 50μm

[0084] Measuring temperature range: -50~225℃

[0085] Heating rate: 10℃ / min

[0086] Measuring frequency: 1Hz

[0087] Deformation mode: Sine wave stretching mode (Linear tension)

[0088] Initial value of static tensile load: 0.5N

[0089] Initial gap distance (at 25°C): 25mm

[0090] Automatic strain adjustment: Enabled (range: amplitude 0.05-25%, sine wave load 0.02-5N).

[0091] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load.

[0092] (iii) The sinusoidal wave tensile mode refers to measuring the vibration stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal wave tensile mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a manner that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a manner that the sinusoidal wave load is within 5N and the increase in the amplitude value is within 25%.

[0093] (iv) Calculate the loss modulus E″ based on the relationship between the obtained sinusoidal wave load and amplitude value and the following formula:

[0094] σ * =σ0·Exp[i(ωt+δ)],

[0095] ε * =ε0·Exp(iωt),

[0096] σ * =E * ·ε *

[0097] E * =E'+iE"

[0098] (where σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[0099] Vibration stress: Sine wave load / initial cross-sectional area

[0100] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[0101] Sine wave load: The difference between the measured vibration stress and the static tensile load). [7]

[0103] A separator for an electricity storage device, characterized in that a silane cross-linking reaction of a silane-modified polyolefin occurs when the separator comes into contact with an electrolyte. [8]

[0105] A separator for an electric storage device, comprising 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, wherein the mixed storage modulus ratio (R E’mix) is 1.5 to 20 times:

[0106] R E’mix =E' a / E'0 (2)

[0107] {where, E' a is the storage modulus of the separator for a power storage device measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for a power storage device not containing the silane-modified polyolefin measured at 160°C to 220°C, and E' a The measurement conditions of the storage elastic modulus E' or E'0 are defined by the following configurations (i) to (iv).

[0108] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0109] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0110] Sample film thickness: 5μm to 50μm

[0111] Measuring temperature range: -50~225℃

[0112] Heating rate: 10℃ / min

[0113] Measuring frequency: 1Hz

[0114] Deformation mode: Sine wave stretching mode (Linear tension)

[0115] Initial value of static tensile load: 0.5N

[0116] Initial gap distance (at 25°C): 25mm

[0117] Automatic strain adjustment: Enabled (range: amplitude 0.05-25%, sine wave load 0.02-5N).

[0118] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load.

[0119] (iii) The sinusoidal wave tensile mode refers to measuring the vibration stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal wave tensile mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a manner that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a manner that the sinusoidal wave load is within 5N and the increase in the amplitude value is within 25%.

[0120] (iv) Calculate the storage modulus E' based on the relationship between the obtained sinusoidal wave load and the amplitude value and the following formula:

[0121] σ * =σ0·Exp[i(ωt+δ)],

[0122] ε * =ε0·Exp(iωt),

[0123] σ * =E * ·ε *

[0124] E * =E'+iE"

[0125] (where σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[0126] Vibration stress: Sine wave load / initial cross-sectional area

[0127] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[0128] Sine wave load: The difference between the measured vibration stress and the static tensile load). [9]

[0130] A separator for an electric storage device, comprising 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, wherein the mixed loss modulus ratio (R E”mix ) is 1.5 to 20.0 times:

[0131] R E”mix =E” a / E"0 (4)

[0132] {where, E” a is the loss modulus of the separator for the power storage device measured at 160°C to 220°C, and E"0 is the loss modulus of the separator for the power storage device without the silane-modified polyolefin measured at 160°C to 220°C, and E" a The measurement conditions of the loss modulus E" or E"0 are defined by the following configurations (i) to (iv).

[0133] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0134] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0135] Sample film thickness: 5μm to 50μm

[0136] Measuring temperature range: -50~225℃

[0137] Heating rate: 10℃ / min

[0138] Measuring frequency: 1Hz

[0139] Deformation mode: Sine wave stretching mode (Linear tension)

[0140] Initial value of static tensile load: 0.5N

[0141] Initial gap distance (at 25°C): 25mm

[0142] Automatic strain adjustment: Enabled (range: amplitude 0.05-25%, sine wave load 0.02-5N).

[0143] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load.

[0144] (iii) The sinusoidal wave tensile mode refers to measuring the vibration stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal wave tensile mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a manner that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a manner that the sinusoidal wave load is within 5N and the increase in the amplitude value is within 25%.

[0145] (iv) Calculate the loss modulus E″ based on the relationship between the obtained sinusoidal wave load and amplitude value and the following formula:

[0146] σ * =σ0·Exp[i(ωt+δ)],

[0147] ε * =ε0·Exp(iωt),

[0148] σ * =E * ·ε *

[0149] E * =E'+iE"

[0150] (where σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[0151] Vibration stress: Sine wave load / initial cross-sectional area

[0152] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[0153] Sine wave load: The difference between the measured vibration stress and the static tensile load).

[10]

[0155] The separator for a power storage device according to item 8 or 9, wherein the separator for a power storage device not containing the silane-modified polyolefin is a microporous membrane made of a silane-unmodified polyolefin having a degree of gelation of 0% to 10%.

[11]

[0157] A separator for an electrical storage device, comprising 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, wherein the separator has a transition temperature between a rubbery flat region and a crystalline melt flow region in the temperature variation of the storage modulus of the separator.

[12]

[0159] A separator for an electricity storage device, comprising a polyolefin microporous membrane,

[0160] In the solid viscoelasticity measurement of the separator for the electricity storage device at a temperature of -50°C to 250°C,

[0161] The minimum storage modulus is 1.0MPa to 10MPa, the maximum storage modulus is 100MPa to 10,000MPa, and

[0162] The minimum loss modulus is 0.1MPa~10MPa, and the maximum loss modulus is 10MPa~10,000MPa.

[0163] The conditions for the solid viscoelasticity measurement for measuring the storage modulus and the loss modulus are defined by the following configurations (i) to (iv):

[0164] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0165] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0166] Sample thickness: 200 μm to 400 μm (If the thickness of a single sample is less than 200 μm, dynamic viscoelasticity measurement is performed by stacking multiple samples so that the total thickness falls within the range of 200 μm to 400 μm.)

[0167] ·Measurement temperature range: -50℃~250℃

[0168] Heating rate: 10℃ / min

[0169] Measuring frequency: 1Hz

[0170] Deformation mode: Sine wave stretching mode (Linear tension)

[0171] Initial value of static tensile load: 0.2N

[0172] Initial gap distance (at 25°C): 10mm

[0173] Automatic strain adjustment: Disabled.

[0174] (ii) the static tensile load refers to the median value between the maximum stress and the minimum stress under each period of motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load;

[0175] (iii) the sinusoidal wave tensile mode refers to measuring the vibration stress while performing periodic motion at a fixed amplitude of 0.1%. In the sinusoidal wave tensile mode, the vibration stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal wave load is within 5%. When the sinusoidal wave load is 0.1 N or less, the vibration stress is measured while keeping the static tensile load fixed at 0.1 N.

[0176] (iv) Calculate the storage modulus and loss modulus based on the relationship between the obtained sinusoidal wave load and the amplitude value and the following formula:

[0177] σ * =σ0·Exp[i(ωt+δ)],

[0178] ε * =ε0·Exp(iωt),

[0179] σ * =E * ·ε *

[0180] E * =E'+iE"

[0181] {where, σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[0182] Vibration stress: Sine wave load / initial cross-sectional area

[0183] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[0184] Sine wave load: The difference between the measured vibration stress and the static tensile load.

[13]

[0186] A separator for an electricity storage device, comprising a polyolefin microporous membrane, wherein, in a solid viscoelasticity measurement of the separator from the membrane softening transition temperature to the membrane rupture temperature, the separator has an average storage modulus of 1.0 MPa to 12 MPa and an average loss modulus of 0.5 MPa to 10 MPa.

[14]

[0188] The separator for a power storage device according to item 13, wherein in the solid viscoelasticity measurement, the film softening transition temperature is 140° C. to 150° C., and the film rupture temperature is 180° C. or higher.

[15]

[0190] The separator for a power storage device according to any one of items 12 to 14, comprising a silane-modified polyolefin and a polyolefin other than the silane-modified polyolefin.

[16]

[0192] The separator for a power storage device according to item 15, comprising 5% by mass to 40% by mass of a silane-modified polyolefin and 60% by mass to 95% by mass of a polyolefin other than the silane-modified polyolefin.

[17]

[0194] A separator for an electricity storage device, characterized in that the separator comprises a polyolefin, wherein the polyolefin has one or more functional groups and

[0195] After being housed in a power storage device, (1) the functional groups undergo a condensation reaction, (2) the functional groups react with chemical substances within the power storage device, or (3) the functional groups react with other types of functional groups, thereby forming a cross-linked structure.

[18]

[0197] The separator for an electricity storage device according to item 17, wherein the chemical substance is any of an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof contained in the electricity storage device.

[19]

[0199] A separator for an electricity storage device, comprising a polyolefin and having an amorphous portion cross-linked structure in which amorphous portions of the polyolefin are cross-linked.

[20]

[0201] The separator for an electric storage device according to item 19, wherein the separator for an electric storage device has a hybrid storage modulus ratio (R E’X ) is 1.5 to 20 times:

[0202] R E’X =E' Z / E' Z0 (1)

[0203] {where, E' Z The storage modulus is measured in a temperature range of 160°C to 300°C after the cross-linking reaction of the separator for the power storage device is carried out in the power storage device, and

[0204] E' Z0 The storage modulus is the storage modulus measured in the temperature range of 160° C. to 300° C. before the separator for the electricity storage device is incorporated into the electricity storage device. [twenty one]

[0206] The separator for an electric storage device according to item 19 or 20, wherein the separator for an electric storage device has a mixed loss modulus ratio (R E”X ) is 1.5 to 20 times:

[0207] R E”X =E” Z / E” Z0 (3)

[0208] {where, E” Z The loss modulus is measured in a temperature range of 160°C to 300°C after the cross-linking reaction of the separator for the power storage device is carried out in the power storage device, and

[0209] E” Z0 The loss modulus is measured in the temperature range of 160° C. to 300° C. before the separator for an electricity storage device is incorporated into the electricity storage device. [twenty two]

[0211] The separator for a power storage device according to any one of items 19 to 21, wherein the amorphous portion is selectively cross-linked. [twenty three]

[0213] The separator for an electric storage device according to any one of items 17 to 22, wherein the separator for an electric storage device has a hybrid storage modulus ratio (R E’mix ) is 1.5 to 20 times:

[0214] R E’mix =E' / E'0 (2)

[0215] {wherein, E' is the storage modulus measured at 160°C to 300°C when the separator for a power storage device has a cross-linked amorphous portion structure, and

[0216] E'0 is the storage modulus of the separator for a power storage device having no crosslinked structure in the amorphous portion, measured at 160° C. to 300° C. [twenty four]

[0218] The separator for an electric storage device according to any one of items 17 to 23, wherein the separator for an electric storage device has a mixed loss modulus ratio (R E”mix ) is 1.5 to 20 times:

[0219] R E”mix =E” / E”0 (4)

[0220] {wherein, E" is the loss modulus measured at 160°C to 300°C when the separator for a power storage device has a cross-linked amorphous portion structure, and

[0221] E"0 is the loss modulus of the separator for a power storage device having no crosslinked structure in the amorphous portion, measured at 160° C. to 300° C.

[25]

[0223] The separator for a power storage device according to any one of items 17 to 24, wherein the polyolefin is polyethylene.

[26]

[0225] The separator for a power storage device according to any one of items 17 to 25, wherein the polyolefin is a functional group-modified polyolefin or a polyolefin obtained by copolymerizing a monomer having a functional group.

[27]

[0227] The separator for a power storage device according to any one of items 17 to 26, wherein the cross-linked structure is formed by a reaction via any of a covalent bond, a hydrogen bond, and a coordinate bond.

[28]

[0229] The separator for a power storage device according to item 27, wherein the reaction via a covalent bond is at least one selected from the group consisting of the following reactions (I) to (IV):

[0230] (I) condensation reaction of multiple identical functional groups;

[0231] (II) reactions between multiple different functional groups;

[0232] (III) chain condensation reaction between the functional group and the electrolyte; and

[0233] (IV) Reaction of functional groups with additives.

[29]

[0235] The separator for an electricity storage device according to item 27, wherein

[0236] The aforementioned reaction via coordination bonds is the following reaction (V):

[0237] (V) A reaction in which a plurality of identical functional groups undergo cross-linking via coordination bonds with metal ions.

[30]

[0239] The separator for an electricity storage device according to item 28, wherein the reaction (I) and / or (II) is catalytically promoted by chemical substances inside the electricity storage device.

[31]

[0241] The separator for a power storage device according to Item 28, wherein the reaction (I) is a condensation reaction of a plurality of silanol groups.

[32]

[0243] The separator for a power storage device according to item 28, wherein the reaction (IV) is a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between the compound Rx constituting the separator for a power storage device and the compound Ry constituting the additive, the compound Rx having a functional group x, and the compound Ry having a linking reaction unit y1.

[33]

[0245] The separator for an electricity storage device according to item 32, wherein

[0246] The above reaction (IV) is a nucleophilic substitution reaction.

[0247] The functional group x of the aforementioned compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH, and

[0248] The linking reaction unit y1 of the compound Ry is at least two selected from the group consisting of CH3SO2-, CF3SO2-, ArSO2-, CH3SO3-, CF3SO3-, ArSO3-, and monovalent groups represented by the following formulae (y1-1) to (y1-6):

[0249]

[0250] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0251]

[0252] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0253]

[0254] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0255]

[0256] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0257]

[0258] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0259]

[0260] {wherein, X is a hydrogen atom or a monovalent substituent.}

[34]

[0262] The separator for an electricity storage device according to item 32 or 33, wherein

[0263] The above reaction (IV) is a nucleophilic substitution reaction.

[0264] The aforementioned compound Ry further comprises a chain unit y2 based on the aforementioned linking reaction unit y1, and

[0265] The chain unit y2 is at least one selected from the group consisting of divalent groups represented by the following formulae (y2-1) to (y2-6):

[0266]

[0267] {wherein, m is an integer from 0 to 20, and n is an integer from 1 to 20.}

[0268]

[0269] {wherein, n is an integer from 1 to 20.}

[0270]

[0271] {wherein, n is an integer from 1 to 20.}

[0272]

[0273] {wherein, n is an integer from 1 to 20.}

[0274]

[0275] {wherein, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer of 1 to 20.}

[0276]

[0277] {wherein, X is an alkylene group having 1 to 20 carbon atoms or an arylene group,

[0278] And n is an integer from 1 to 20.}.

[35]

[0280] The separator for an electricity storage device according to item 32, wherein

[0281] The above reaction (IV) is a nucleophilic addition reaction.

[0282] The functional group x of the aforementioned compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH, and

[0283] The linking reaction unit y1 of the compound Ry is at least one selected from the group consisting of groups represented by the following formulae (Ay1-1) to (Ay1-6):

[0284]

[0285] {wherein, R is a hydrogen atom or a monovalent organic group.}

[0286]

[36]

[0288] The separator for an electricity storage device according to item 32, wherein

[0289] The above reaction (IV) is a ring-opening reaction.

[0290] The functional group x of the aforementioned compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH, and

[0291] The linking reaction unit y1 of the aforementioned compound Ry is at least two groups represented by the following formula (ROy1-1):

[0292]

[0293] {wherein, each of the multiple Xs is independently a hydrogen atom or a monovalent substituent.}

[37]

[0295] The separator for a power storage device according to item 29, wherein in the following reaction (V), the metal ion is selected from the group consisting of Zn 2+ 、Mn 2+ 、Co 3+ 、Ni 2+ He Li + At least one of the groups consisting of.

[38]

[0297] A separator for a storage device, comprising a silane-modified polyolefin, having a first porous layer (layer A) capable of forming a cross-linked structure and a second porous layer (layer B) comprising inorganic particles, wherein the thermal shrinkage at 150°C after forming the cross-linked structure is greater than or equal to 0.02 times and less than or equal to 0.91 times the thermal shrinkage at 150°C before forming the cross-linked structure.

[39]

[0299] The separator for an electricity storage device according to item 38, wherein the cross-linked structure in the layer A is formed by an acid, an alkali, swelling, or a compound generated in the electricity storage device.

[40]

[0301] A separator for an electrical storage device, comprising:

[0302] Microporous membrane comprising silane-modified polyolefin, and

[0303] An inorganic porous layer comprising inorganic particles and a resin binder is disposed on at least one surface of the microporous membrane.

[41]

[0305] The separator for a power storage device according to item 40, wherein the content of the inorganic particles in the inorganic porous layer is 5% by weight to 99% by weight.

[42]

[0307] The separator for a power storage device according to item 40 or 41, wherein the content of the silane-modified polyolefin in the microporous membrane is 0.5% by weight to 40% by weight.

[43]

[0309] The separator for a storage battery device according to any one of items 40 to 42, wherein the inorganic particles are at least one selected from the group consisting of aluminum oxide (Al2O3), silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand and glass fiber.

[44]

[0311] The separator for a power storage device according to any one of items 40 to 43, wherein the resin binder has a glass transition temperature (Tg) of -50°C to 100°C.

[45]

[0313] The separator for an electricity storage device according to any one of items 40 to 44, wherein a silane cross-linking reaction of the silane-modified polyolefin is initiated when the separator for an electricity storage device comes into contact with an electrolyte solution.

[46]

[0315] The separator for an electricity storage device according to any one of items 40 to 45, wherein

[0316] When the inorganic porous layer is removed and the separator for the electricity storage device is measured, the storage modulus change ratio (R △E’ ) is 1.5 to 20 times:

[0317] R △E’ =E' S / E' j (1A)

[0318] {where, E' j is the storage modulus of the separator for the power storage device before the cross-linking reaction of the silane-modified polyolefin, measured at 160° C. to 220° C., and E′ SThe storage modulus of the separator for a power storage device after the cross-linking reaction of the silane-modified polyolefin is measured at 160° C. to 220° C.

[0319] and / or the loss modulus change ratio (R △E ”) is 1.5 to 20 times:

[0320] R △E” =E” S / E” j (1B)

[0321] {where, E” j is the loss modulus of the separator for the power storage device before the cross-linking reaction of the silane-modified polyolefin, measured at 160°C to 220°C, and E" S The loss modulus of the separator for a power storage device after the cross-linking reaction of the silane-modified polyolefin is measured at 160° C. to 220° C.

[47]

[0323] The separator for an electricity storage device according to any one of items 40 to 46, wherein

[0324] When the inorganic porous layer is removed and the separator for the electricity storage device is measured, the hybrid storage modulus ratio (R E’mix ) is 1.5 to 20 times:

[0325] R E’mix =E' / E'0 (2A)

[0326] {wherein, E' is the storage modulus of the aforementioned separator for a power storage device measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for a power storage device not containing the aforementioned silane-modified polyolefin measured at 160°C to 220°C.},

[0327] and / or the hybrid loss modulus ratio (R E”mix ) is 1.5 to 20 times:

[0328] R E”mix =E” / E”0 (2B)

[0329] {wherein, E″ is the loss modulus of the aforementioned separator for a power storage device measured at 160° C. to 220° C., and E″0 is the loss modulus of a separator for a power storage device not containing the aforementioned silane-modified polyolefin measured at 160° C. to 220° C.}.

[48]

[0331] The separator for an electricity storage device according to any one of items 40 to 47, wherein the transition temperature between the rubbery flat region and the crystalline melt flow region in the temperature change of the storage modulus of the separator for an electricity storage device is 135°C to 150°C.

[49]

[0333] An electricity storage device comprising an electrode, the separator for an electricity storage device according to any one of items 1 to 48, and a non-aqueous electrolyte.

[50]

[0335] A power storage device includes a separator containing polyethylene and an electrolyte or an additive, wherein functional group-modified polyethylene or functional group-grafted copolymerized polyethylene reacts with chemical substances contained in the electrolyte or the additive to form a cross-linked structure.

[51]

[0337] A method for producing a separator for an electricity storage device, which is the method for producing a separator for an electricity storage device according to any one of items 1 to 50, comprising the following steps:

[0338] (1) a sheet forming step of extruding a mixture of silane-modified polyolefin, polyethylene, and a plasticizer, cooling and solidifying the mixture, and forming the mixture into a sheet to obtain a sheet;

[0339] (2) a stretching step of stretching the sheet in at least one uniaxial direction to obtain a stretched product;

[0340] (3) a porous body forming step of extracting the plasticizer from the stretched product in the presence of an extraction solvent to make the stretched product porous to form a porous body; and

[0341] (4) A heat treatment step of subjecting the porous body to heat treatment.

[52]

[0343] A method for manufacturing a separator for an electricity storage device, comprising the following steps:

[0344] (1) a sheet forming step, wherein the silane-modified polyolefin, polyethylene, and plasticizer are extruded into a sheet by an extruder, cooled and solidified, and processed into a sheet-shaped body;

[0345] (2) a stretching step of biaxially stretching the sheet-like formed body at an area ratio of 20 to 250 times to form a stretched article;

[0346] (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body;

[0347] (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing the porous body in the width direction to obtain a heat-treated porous body;

[0348] (8B) a coating step of forming an inorganic porous layer comprising inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinking precursor;

[0349] (9) An assembling step of housing a laminate of the electrode and the silane crosslinking precursor or a wound body thereof, and a non-aqueous electrolyte in an outer shell, and bringing the silane crosslinking precursor into contact with the non-aqueous electrolyte.

[53]

[0351] A power storage device assembly kit includes the following two elements:

[0352] (1) An outer casing accommodating a laminate or a wound body of an electrode and the separator for an electricity storage device according to any one of items 1 to 48; and

[0353] (2) A container containing a non-aqueous electrolyte.

[54]

[0355] The electricity storage device assembly kit according to item 53, wherein the non-aqueous electrolyte solution contains a lithium salt containing fluorine (F).

[55]

[0357] The electricity storage device assembly kit according to item 53 or 54, wherein the non-aqueous electrolyte solution contains lithium hexafluorophosphate (LiPF6).

[56]

[0359] The electricity storage device assembly kit according to any one of items 53 to 55, wherein the non-aqueous electrolyte is an acid solution and / or an alkaline solution.

[57]

[0361] A method for manufacturing an electricity storage device, comprising the following steps:

[0362] a step of preparing the electricity storage device assembly kit according to any one of items 53 to 56, and

[0363] The step of initiating a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator for the electricity storage device in the element (1) of the electricity storage device assembly kit into contact with the non-aqueous electrolyte in the element (2).

[58]

[0365] The method for manufacturing an electricity storage device according to item 57, further comprising the following step:

[0366] a step of connecting a lead terminal to the electrode of the element (1), and

[0367] A step of performing at least one cycle of charge and discharge.

[59]

[0369] A method for producing an electricity storage device using a separator containing polyolefin.

[0370] The polyolefin comprises one or more functional groups, and the method includes the following cross-linking steps:

[0371] The crosslinked structure is formed by (1) causing the functional groups to undergo a condensation reaction, (2) causing the functional groups to react with chemical substances within the power storage device, or (3) causing the functional groups to react with other types of functional groups.

[60]

[0373] The method for producing an electricity storage device according to item 59, wherein the cross-linking step is performed at a temperature of 5°C to 90°C.

[0374] Effects of the Invention

[0375] According to the present invention, it is possible to provide a power storage device and its assembly kit that can achieve both low-temperature shutdown function and high-temperature rupture resistance of a separator for a power storage device, suppress the generation of unmelted resin agglomerates during its manufacturing process, thereby contributing to productivity and economy, and further have good cycle characteristics and high safety.

[0376] Furthermore, according to the present invention, crosslinking can be eliminated during or immediately after the film formation process, thereby suppressing increases in internal stress in the separator and deformation of the battery device after fabrication. Furthermore, even without the use of high energies such as light irradiation or heating, a crosslinking structure can be imparted to the separator, reducing crosslinking unevenness. Furthermore, according to the present invention, crosslinking is formed not only within the separator but also between the separator and the electrode, or between the separator and the solid electrolyte interface (SEI). This improves the strength between the various components of the battery device, suppresses gaps between the separator and the electrode due to expansion and contraction during charging and discharging of the battery device, and significantly improves long-term cycling stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0377] Figure 1 This is an example of a graph used to illustrate the relationship between temperature and storage modulus. It compares the storage moduli of a standard film and a cross-linked film in the temperature range of -50°C to 225°C, and shows the transition temperature between the rubbery flat region and the crystalline melt flow region.

[0378] Figure 2 This is an example of a graph used to illustrate the relationship between temperature and loss modulus. It compares the loss modulus of a standard film and a cross-linked film in the temperature range of -50°C to 225°C, and shows the transition temperature between the rubbery flat region and the crystalline melt flow region.

[0379] Figure 3 This is a graph showing the relationship between temperature and resistance of an electricity storage device including the separator obtained in Example I-1.

[0380] Figure 4 These are graphs for explaining the relationship among temperature, gap distance, storage modulus, and loss modulus in viscoelasticity measurement of a separator for a power storage device, and illustrate graph (a) of Example II-1 and graph (b) of Comparative Example II-1.

[0381] Figure 5 This is a graph for determining the film softening transition temperature based on temperature, gap distance, and first-order derivative of gap displacement in viscoelasticity measurement of a separator for a power storage device, and illustrates graph (a) of Example II-1 and graph (b) of Comparative Example II-1.

[0382] Figure 6 This is a schematic diagram for explaining a crystalline polymer having a high-order structure divided into crystalline lamellae (crystal portion), an amorphous portion, and an intermediate layer portion therebetween.

[0383] Figure 7 This is a schematic diagram used to illustrate the crystal growth of polyolefin molecules.

[0384] Figure 8 This is a graph showing the strain amount and crystal fraction ratio for illustrating changes in the X-ray crystal structure during a tensile fracture test of a film according to one embodiment of the present invention.

[0385] Figure 9 This is an example of a graph used to illustrate the relationship between temperature and storage modulus. It compares the storage moduli of a standard film and a cross-linked film in the temperature range of -50°C to 310°C, and shows the transition temperature between the rubbery flat region and the crystalline melt flow region.

[0386] Figure 10 This is an example of a graph used to illustrate the relationship between temperature and loss modulus. It compares the loss modulus of a standard film and a cross-linked film in the temperature range of -50°C to 310°C, and shows the transition temperature between the rubbery flat region and the crystalline melt flow region.

[0387] Figure 11 Silane-modified polyolefin raw material 1 obtained using polyolefin 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b).

[0388] Figure 12 Silane-modified polyolefin raw material 2 obtained using polyolefin 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b).

[0389] Figure 13 The separator obtained in Example I-1 is in a state before cross-linking. 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b). DETAILED DESCRIPTION

[0390] Hereinafter, specific embodiments of the present invention (hereinafter referred to as "embodiments") will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist thereof.

[0391] In this specification, "to" means that the numerical values ​​at both ends are included as the upper limit and lower limit. In addition, in this specification, the upper limit and lower limit of the numerical range can be combined arbitrarily. For example, the upper limit of a preferred numerical range can be combined with the lower limit of a more preferred numerical range, and conversely, the upper limit of a more preferred numerical range can be combined with the lower limit of the preferred numerical range.

[0392] It should be noted that, in this specification, the terms "on" and "formed on the surface of" do not limit the positional relationship of the components to "directly above." For example, the phrases "layer B formed on layer A" and "layer B formed on the surface of layer A" do not exclude the inclusion of any layer between layer A and layer B that does not belong to either layer.

[0393] The properties of only the microporous membrane described below can be measured after removing layers other than the microporous membrane (for example, an inorganic porous layer) from the separator for a power storage device.

[0394] <Separator for power storage device>

[0395] One embodiment of the present invention is a separator for a power storage device (hereinafter referred to as a "separator"). Since separators are required to have both insulation and ion permeability, they generally include insulating materials such as paper, polyolefin nonwoven fabrics, or resin microporous membranes having a porous structure. In particular, in lithium-ion batteries, polyolefin microporous membranes are preferred, as they provide a dense and uniform porous structure that is resistant to redox degradation and provides a separator.

[0396] Here, the microporous membrane refers to a membrane (thin film) formed of a porous body, and the average pore diameter thereof is preferably 10 nm to 500 nm, more preferably 30 nm to 100 nm.

[0397] When the power storage device includes a separator, the separator can be removed from the power storage device.

[0398] <First, Second, Third, Fourth and Fifth Embodiments>

[0399] The separator of the first embodiment comprises a silane-modified polyolefin and may, if desired, comprise another polyolefin. When the separator of the first embodiment comes into contact with the electrolyte, a silane cross-linking reaction of the silane-modified polyolefin contained in the separator begins. Since the separator of the first embodiment can cross-link the silane-modified polyolefin while in contact with the electrolyte, the timing of cross-linking can be controlled. Consequently, the cross-linking reaction can be performed during the manufacturing process of the power storage device, rather than during the separator manufacturing process.

[0400] The separator of the second embodiment is characterized in that a silane crosslinking reaction of the silane-modified polyolefin occurs when in contact with an electrolyte. The second embodiment does not require the presence of a silane-modified polyolefin in the separator, the location of the residual silane-modified polyolefin, or whether the silane crosslinking reaction begins initially, occurs sequentially, or occurs continuously when in contact with the electrolyte. As long as the silane crosslinking reaction is observed when the separator is in contact with the electrolyte, the silane crosslinking reaction of the silane-modified polyolefin in the separator of the second embodiment occurs when in contact with the electrolyte, control of the crosslinking timing can be achieved without being affected by the manufacturing or use process of the separator.

[0401] The separators of the first and second embodiments promote a cross-linking reaction when the electrolyte is injected into the outer casing housing the separator. This helps prevent production defects during the manufacturing process, thereby achieving safety and high output in the energy storage device manufacturing process. From the perspective of the separator's ingredients and the timing of the cross-linking reaction, it is preferred that the silane cross-linking reaction of the silane-modified polyolefin begin when the separator is mixed with or in contact with the electrolyte.

[0402] The separator of the third embodiment comprises 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the examples, the storage modulus change ratio (R) defined by the following formula (1) is: ΔE’ ) is 1.5 to 20 times:

[0403] R ΔE’ =E' S / E' j (1)

[0404] {where, E' j is the storage modulus of the separator for a power storage device before the cross-linking reaction of the silane-modified polyolefin is measured at 160°C to 220°C, and E' S The storage modulus of the separator for a power storage device after cross-linking reaction of the silane-modified polyolefin is measured at 160°C to 220°C.

[0405] and / or the loss modulus change ratio (R ΔE”) is 1.5 to 20 times:

[0406] R ΔE” =E” S / E” j (3)

[0407] {where, E” j is the loss modulus of the separator for the power storage device before the cross-linking reaction of the silane-modified polyolefin, measured at 160°C to 220°C, and E" S The loss modulus of the separator for a power storage device after the cross-linking reaction of the silane-modified polyolefin is measured at 160° C. to 220° C.

[0408] In the third embodiment, the storage modulus change ratio (R ΔE’ ) and / or loss modulus change ratio (R ΔE” ) is within the range of 1.5 to 20 times, which can achieve both the shutdown function and high temperature resistance to film rupture. ΔE’ ) and / or loss modulus change ratio (R ΔE” ) is preferably 2 to 18 times. j and E' S and E” j and E” S The storage modulus or loss modulus is the average value of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160-220°C. In addition, when the separator is in the form of a laminated film, only the porous film containing silane-modified polyolefin is taken out from the laminated film to measure the storage modulus E'. j and E' S and loss modulus E" j and E” S .

[0409] The separator of the fourth embodiment comprises 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the examples, the mixed storage modulus ratio (R E’mix ) is 1.5 to 20 times:

[0410] R E’mix =E' a / E'0 (2)

[0411] {where, E' a is the storage modulus of the separator for a power storage device measured at 160° C. to 220° C., and E′0 is the storage modulus of the separator for a power storage device not containing silane-modified polyolefin measured at 160° C. to 220° C.

[0412] and / or the hybrid loss modulus ratio (R E”mix ) is 1.5 to 20.0 times:

[0413] R E”mix =E” a / E"0 (4)

[0414] {where, E” a is the loss modulus of the separator for a power storage device measured at 160° C. to 220° C., and E″0 is the loss modulus of a separator for a power storage device not containing the silane-modified polyolefin measured at 160° C. to 220° C.

[0415] In the fourth embodiment, by making the mixed storage modulus ratio (R E’mix ) and / or hybrid loss modulus ratio (R E”mix ) is within the range of 1.5 to 20.0 times, which can achieve both the shutdown function and high temperature resistance to film rupture. E’mix ) and / or hybrid loss modulus ratio (R E”mix ) is preferably 2 to 18 times. a and E'0 and E" a E' and E'0 are respectively the average values ​​of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160 to 220°C. In addition, when the separator is in the form of a laminated film, only the porous film containing silane-modified polyolefin is taken out from the laminated film to measure the storage modulus E' a and E'0 and loss modulus E" a and E”0.

[0416] The separator of the fifth embodiment comprises 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the embodiment, in the temperature change of its storage modulus or loss modulus, the transition temperature between the rubbery flat region and the crystalline melt flow region is 135°C to 150°C. The fifth embodiment can achieve both the shutdown function and the high-temperature rupture resistance by making the transition temperature between the rubbery flat region and the crystalline melt flow region within the range of 135°C to 150°C. The transition temperature between the rubbery flat region and the crystalline melt flow region is preferably 137°C to 147°C, more preferably 140°C to 145°C, and further preferably 140°C to 143°C. It should be noted that when the separator is in the form of a laminated film, only the porous film containing the silane-modified polyolefin is taken out from the laminate to measure the transition temperature between the rubbery flat region and the crystalline melt flow region.

[0417] <Sixth and Seventh Embodiments>

[0418] The separator of the sixth embodiment includes a polyolefin having one or more functional groups. After being housed in a power storage device, the functional groups of the polyolefin undergo a crosslinking structure by (1) condensation reaction among themselves, (2) reaction between the functional groups of the polyolefin and chemical substances within the power storage device, or (3) reaction between the functional groups of the polyolefin and other types of functional groups. It is believed that the functional groups contained in the polyolefin constituting the separator do not enter the crystalline portion of the polyolefin but crosslink in the amorphous portion. Therefore, after being housed in the power storage device, the separator of the sixth embodiment forms a crosslinking structure by utilizing the surrounding environment or chemical substances within the power storage device, thereby suppressing the increase of internal stress or deformation of the manufactured power storage device.

[0419] On the other hand, if a cross-linking reaction is performed before being housed in a power storage device, and if winding and slitting processes are performed, the effects of stress such as tension generated during these processes will remain. In this case, if these stresses are released after the power storage device is assembled, they may cause deformation of the electrode winding, etc., or damage due to stress concentration, which is not preferred.

[0420] In the sixth embodiment, (1) the condensation reaction between functional groups of the polyolefin may be, for example, a reaction between two or more functional groups A contained in the polyolefin via a covalent bond. (3) The reaction between a functional group of the polyolefin and another type of functional group may be, for example, a reaction between functional group A and functional group B contained in the polyolefin via a covalent bond.

[0421] Furthermore, in the reaction (2) between the functional groups of the polyolefin and the chemical substances within the power storage device, for example, the functional group A contained in the polyolefin can form a covalent bond or a coordinate bond with any of the electrolyte, electrolyte solution, electrode active material, additive, or decomposition products thereof contained in the power storage device. Furthermore, due to reaction (2), a cross-linked structure is formed not only within the separator but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), thereby improving the strength between the multiple components of the power storage device.

[0422] The separator of the seventh embodiment comprises a polyolefin and has an amorphous crosslinked structure formed by crosslinking the amorphous portion of the polyolefin. It is believed that the functional groups contained in the polyolefin constituting the separator do not enter the crystalline portion of the polyolefin, but are crosslinked in the amorphous portion. Therefore, compared to existing crosslinked separators that are easily crosslinked in the crystalline portion and its surrounding area, the separator of the seventh embodiment can achieve both shutdown function and high-temperature rupture resistance while suppressing the increase in internal stress or deformation of the produced power storage device, thereby ensuring the safety of the power storage device. From the same perspective, the amorphous portion of the polyolefin contained in the separator of the seventh embodiment is preferably selectively crosslinked, and more preferably significantly crosslinked compared to the crystalline portion.

[0423] The cross-linking reaction mechanism and cross-linking structure of the seventh embodiment are not yet clear, but the present inventors have the following assumptions.

[0424] (1) Crystal structure in high-density polyethylene microporous membrane

[0425] Polyolefin resins such as high-density polyethylene Figure 6 As shown in the figure, crystalline polymers generally have a high-order structure consisting of crystalline lamellae (crystal part), amorphous part, and intermediate layer part between them. In the crystalline part and the intermediate layer between the crystalline part and the amorphous part, the polymer chain mobility is low and difficult to cut, but relaxation can be observed in the 0-120°C range during solid viscoelasticity measurement. On the other hand, the polymer chain mobility in the amorphous part is very high and can be observed in the -150--100°C range during solid viscoelasticity measurement. This is closely related to the relaxation of free radicals, free radical transfer reactions, cross-linking reactions, etc., which will be described later.

[0426] Furthermore, the polyolefin molecules constituting the crystals are not single, e.g. Figure 7 As an example, after multiple polymer chains form small lamellae, the lamellae aggregate to form crystals. This phenomenon is difficult to observe directly. In recent years, it has been clarified through academic research through simulation. It should be noted that here, crystal refers to the smallest crystal unit measured by X-ray structure analysis, which is the unit that can be used to calculate the crystallite size. In this way, although it is a crystal part (inside the lamellae), it is predicted that there is a part in the crystal that is not constrained and has slightly higher mobility.

[0427] (2) Cross-linking reaction mechanism based on electron beams

[0428] Next, the reaction mechanism of electron beam cross-linking (hereinafter abbreviated as EB cross-linking) for polymers is as follows. (i) irradiation of electron beams from tens of kGy to hundreds of kGy, (ii) penetration of electron beams into the reaction object (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 based on free radicals and movement of active sites, (v) cross-linking reaction or polyene formation based on recombination between free radicals. Here, regarding the free radicals generated in the crystal part, they exist for a long time due to poor movement, and impurities and the like cannot enter the crystal, so the probability of reaction and extinction is low. This type of free radical species is called a stable free radical (Stable Radical), which remains for a long time for several months, and its lifespan is clarified by ESR measurement. As a result, it is believed that the cross-linking reaction in the crystal is poor. However, the free radicals generated by the unconstrained molecular chains that exist slightly inside the crystal or the crystal-amorphous intermediate layer portion on the periphery have a slightly longer lifespan. These free radical species are called persistent radicals, and they are thought to undergo cross-linking reactions between molecular chains with high probability in a mobile environment. On the other hand, the amorphous portion, due to its extremely high mobility, produces free radical species with a short lifetime. It is thought that not only cross-linking reactions between molecular chains but also polyene reactions within a single molecular chain occur with high probability.

[0429] As described above, it can be inferred that in the microscopic field of view at the crystal level, the cross-linking reaction based on EB cross-linking exists locally inside the crystal or in its periphery.

[0430] (3) Cross-linking reaction mechanism based on chemical reaction

[0431] In the seventh embodiment of the present invention, it is preferred to use a functional group in the polyolefin resin and a chemical substance contained in the electricity storage device, or a chemical substance contained in the electricity storage device as a catalyst.

[0432] As previously mentioned, polyolefin resins contain both crystalline and amorphous portions. However, due to steric hindrance, the aforementioned functional groups are localized in the amorphous portion and not present within the crystals. This is well known; while methyl units, which are slightly present in polyethylene chains, sometimes enter the crystals, grafts, which are bulkier than ethyl groups, do not (Non-Patent Document 2). Therefore, crosslinking points based on reactions different from electron beam crosslinking, are only localized in the amorphous portion.

[0433] (4) Relationship between differences in cross-linking structure and effects

[0434] As described above, the crosslinking reaction based on the chemical reaction inside the battery used in the seventh embodiment of the present invention produces different morphologies of the reaction products. In the research leading to the present invention, the following experiments were conducted to clarify the crosslinking structure and the changes in the physical properties of the microporous membrane that accompany this structural change.

[0435] First, the mechanical properties of the film were studied by tensile fracture tests. In addition, while conducting the tensile fracture tests, the crystal structure changes were analyzed by in-situ X-ray structural analysis using radioactive light. Figure 8 As shown in FIG. 1 , with the film that is not implemented EB cross-linking or chemical cross-linking (before) as a benchmark, the EB cross-linked film increases as the strain amount, and the segmentation of the crystalline portion is suppressed. This is because the crystalline portion or the periphery are selectively cross-linked. Thereupon, Young's modulus and breaking strength are significantly improved, and high mechanical strength can be shown. On the other hand, the chemical cross-linked film is not seen in the segmentation of the crystal before and after the cross-linking reaction, so it is suggested that the amorphous portion is selectively cross-linked. In addition, before and after the cross-linking reaction, there is no change in mechanical strength.

[0436] Next, the behavior of the two when the crystals melted was studied by the melting / melting fracture characteristic test. As a result, the melting temperature of the film treated with EB cross-linking increased significantly, and the melting fracture temperature rose to above 200°C. On the other hand, it was confirmed that the melting temperature of the chemically cross-linked film did not change before and after the cross-linking treatment, and the melting fracture temperature rose to above 200°C. It is therefore believed that in the melting (shutdown) characteristics generated by crystal melting, the EB cross-linked film is cross-linked around the crystal part, so the increase in melting temperature and the decrease in melting speed are the reasons. On the other hand, it is judged that the chemically cross-linked film does not have a cross-linked structure in the crystal part, so it will not change the shutdown characteristics. In addition, in the high temperature range of around 200°C, since both have a cross-linked structure after the crystal melts, the resin material as a whole can be stabilized in a gel state, and good melting fracture characteristics can be obtained.

[0437] The above understandings are summarized in the table below.

[0438] [Table 1]

[0439]

[0440] The separator of the seventh embodiment has a cross-linked structure in the amorphous part, and has both a shutdown function and a high-temperature rupture resistance. Regarding the viscoelasticity measurement (version 2) described in the examples, the hybrid storage modulus ratio (R E’X ):

[0441] R E’X =E' Z / E'Z0 (1)

[0442] {where, E' Z The storage modulus is measured in a temperature range of 160°C to 300°C after the cross-linking reaction of the separator for the power storage device is carried out in the power storage device, and

[0443] E' Z0 The storage modulus is the storage modulus measured in the temperature range of 160°C to 300°C before the separator for the electricity storage device is incorporated into the electricity storage device.

[0444] and / or the hybrid loss modulus ratio (R E”X ):

[0445] R E”X =E” Z / E” Z0 (3)

[0446] {where, E” Z The loss modulus is measured in a temperature range of 160°C to 300°C after the cross-linking reaction of the separator for the power storage device is carried out in the power storage device, and

[0447] E” Z0 The loss modulus is measured in the temperature range of 160°C to 300°C before the separator for a power storage device is incorporated into the power storage device.

[0448] It is preferably 1.5 to 20 times, more preferably 3 to 18 times. Z and E' Z0 and E” Z and E” Z0 The storage modulus or loss modulus is the average value of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160°C to 300°C. In addition, when the separator is in the form of a laminated film, only the polyolefin porous film is taken out from the laminated film to measure the storage modulus E'. Z and E' Z0 and loss modulus E" Z and E” Z0 .

[0449] The separators of the sixth and seventh embodiments have the following characteristics: from the viewpoint of forming a cross-linked structure of the amorphous part, achieving both shutdown function and high-temperature rupture resistance, etc., with respect to the viscoelasticity measurement (version 2) described in the examples, the hybrid storage modulus ratio (R E’mix ):

[0450] R E’mix =E' / E'0 (2)

[0451] {wherein, E' is the storage modulus of the separator for a power storage device having a cross-linked amorphous portion structure measured at 160°C to 300°C, and

[0452] E'0 is the storage modulus of the separator for a power storage device having no crosslinked structure in the amorphous portion measured at 160°C to 300°C.

[0453] and / or the hybrid loss modulus ratio (R E”mix ):

[0454] R E”mix =E” / E”0 (4)

[0455] {wherein, E" is the loss modulus measured at 160°C to 300°C when the separator for a power storage device has a cross-linked amorphous portion structure, and

[0456] E"0 is the loss modulus of the separator for a power storage device having no crosslinked structure in the amorphous portion measured at 160°C to 300°C.

[0457] It is preferably 1.5 times to 20 times, more preferably 3 times to 19 times, and further preferably 5 times to 18 times. It should be noted that E' and E'0 as well as E" and E"0 are respectively the average values ​​of the storage modulus or loss modulus measured within the set temperature range of the measuring device when 160°C to 300°C is set as the widest temperature range. In addition, when the separator is in the form of a laminated film, only the polyolefin porous film is taken out from the laminated film to measure the storage modulus E' and E'0 and the loss modulus E" and E"0.

[0458] <Eighth Embodiment>

[0459] [Viscoelastic behavior (viscoelasticity measurement version 3 described in the examples)]

[0460] The separator of the eighth embodiment includes a polyolefin microporous membrane, and in the viscoelasticity measurement (version 3) described in the examples, the minimum value (E') of the storage modulus (E') in the solid viscoelasticity measurement at a temperature of -50°C to 250°C is min ) is 1.0MPa~10MPa, the maximum value of E' (E' max ) is 100 MPa to 10,000 MPa, and / or the minimum value (E") of the loss modulus (E") min ) is 0.1MPa~10MPa, the maximum value of E” (E” max ) is 10MPa~10,000MPa. If 1.0MPa≤E' min ≤10MPa and 100MPa≤E' max≤10,000MPa, and / or 0.1MPa≤E” min ≤10MPa and 10MPa≤E” max If the pressure is within the range of ≤10,000 MPa, not only is there a tendency to achieve both the shut-down function of the separator and the resistance to high-temperature membrane rupture, but also production defects can be avoided in the manufacturing process of the separator or the power storage device, thus achieving the stability and safety of the power storage device. From these perspectives, it is preferred that 1.1 MPa ≤ E' min ≤9.0MPa and / or 150MPa≤E' max ≤9,500MPa, more preferably 1.2MPa≤E' min ≤8.0MPa and / or 233MPa≤E' max ≤9,000MPa. In addition, preferably 0.2MPa≤E" min ≤9.0MPa and / or 56MPa≤E” max ≤9,000MPa, more preferably 0.4MPa≤E" min ≤8.0MPa and / or 74MPa≤E” max ≤8,000MPa.

[0461] In the solid viscoelasticity measurement (version 3), the average E' (E' ave ) is preferably 1.0 MPa to 12 MPa, more preferably 1.2 MPa to 10 MPa, further preferably 1.8 MPa to 8.2 MPa, and / or average E" (E" ave ) is preferably 0.5 MPa to 10 MPa, more preferably 0.8 MPa to 8.2 MPa or 0.9 MPa to 3.2 MPa. If E' and / or E" are within the above numerical ranges at temperatures from the membrane softening transition temperature to the membrane rupture temperature, the cycle stability and safety of the power storage device equipped with the separator tend to be improved.

[0462] In the solid viscoelasticity measurement (version 3), from the perspective of achieving both shutdown function and high-temperature membrane rupture resistance, the separator comprising a polyolefin microporous membrane preferably has a membrane softening transition temperature of 140°C to 150°C, more preferably 141°C to 149°C or 146°C to 149°C, and / or a membrane rupture temperature of 180°C or higher, more preferably 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, or 240°C or higher, and even more preferably 250°C or higher. There is no upper limit to the membrane rupture temperature, and it is understood in the art that membrane rupture can occur even at temperatures above 250°C.

[0463] The conditions for measuring E' and E" in the solid viscoelasticity measurement (version 3) of the separator are described in the examples. When the separator is in the form of a laminated film, only the polyolefin microporous membrane is removed from the laminated film, and E' and E" of the removed polyolefin microporous membrane are measured. In addition, when the thickness of a single polyolefin microporous membrane is less than 200 μm, dynamic viscoelasticity measurement (version 3) is performed by stacking multiple polyolefin microporous membranes or folding a single polyolefin microporous membrane so that the total thickness is within the range of 200 μm to 400 μm.

[0464] To achieve both low-temperature shutdown performance and high-temperature membrane rupture resistance, while also improving the cycle characteristics and safety of the power storage device, the separators of the first to eighth embodiments may include: a microporous membrane; and an inorganic porous layer comprising inorganic particles and a resin binder, disposed on at least one surface of the microporous membrane. The separator may be a composite of the microporous membrane as a substrate and the inorganic coating layer.

[0465] <Ninth embodiment>

[0466] A separator according to a ninth embodiment includes:

[0467] A microporous membrane comprising a silane-modified polyolefin; and

[0468] An inorganic porous layer comprising inorganic particles and a resin binder is disposed on at least one surface of a microporous membrane.

[0469] The separator of the ninth embodiment may include layers other than the microporous membrane and the inorganic porous layer, as desired.

[0470] In the ninth embodiment, the combination of a microporous membrane comprising a silane-modified polyolefin and an inorganic porous layer tends to achieve both a shutdown function at temperatures below 150°C and membrane rupture resistance at higher temperatures, thereby improving the cycle characteristics and battery nail puncture safety of the battery device. It is speculated that because the silane-modified polyolefin in the microporous membrane is silane-crosslinked, once silane crosslinking occurs, the viscosity of the resin in the microporous membrane may increase. Therefore, when a battery device including the separator of the ninth embodiment is subjected to abnormally high temperatures and a compressive force is applied between the multiple electrodes, the crosslinked, high-viscosity resin is less likely to flow into the inorganic layer (i.e., less likely to integrate), thereby ensuring sufficient gaps between the electrodes and suppressing battery short circuits.

[0471] The separator of the ninth embodiment preferably initiates a silane crosslinking reaction of the silane-modified polyolefin when in contact with the electrolyte. More preferably, when in contact with the electrolyte, the silane crosslinking reaction is observed when the separator is in contact with the electrolyte, whether it is initially initiated, occurs sequentially, or occurs continuously. By the silane crosslinking reaction of the silane-modified polyolefin occurring when the separator is in contact with the electrolyte, not only can the crosslinking time point of the separator be controlled, thus avoiding production defects in the separator manufacturing process, but also safety and high output can be achieved in the manufacturing process of the storage device. In addition, by bringing the separator into contact with the electrolyte, crosslinking reactions other than the silane crosslinking reaction can be initiated.

[0472] The separator of the ninth embodiment Regarding the viscoelasticity measurement (version 1) described in the examples, when the inorganic porous layer is removed from the separator and the measurement is performed, the storage modulus change ratio (R △E’ ) is 1.5 to 20 times:

[0473] R △E’ =E' S / E' j (1A)

[0474] {where, E' j is the storage modulus of the separator for a power storage device before the cross-linking reaction of the silane-modified polyolefin is measured at 160°C to 220°C, and E' S The storage modulus of the separator for a power storage device after the silane-modified polyolefin undergoes a cross-linking reaction, measured at 160° C. to 220° C.

[0475] and / or preferably the loss modulus change ratio (R △E ”) is 1.5 to 20 times:

[0476] R △E” =E” S / E” j (1B)

[0477] {where, E” j The loss modulus of the separator for a storage device before the cross-linking reaction of the silane-modified polyolefin is measured at 160°C to 220°C, and E" S This is the loss modulus of a separator for a power storage device after a cross-linking reaction of a silane-modified polyolefin, measured at 160°C to 220°C.

[0478] By changing the storage modulus ratio (R △E’ ) and / or loss modulus change ratio (R △E” ) is in the range of 1.5 to 20 times, which makes it easy to take into account both the shutdown function and the high temperature resistance to film rupture.ΔE’ ) and / or loss modulus change ratio (R ΔE” ) is more preferably 2 to 18 times. j and E' S and E” j and E” S The storage modulus or loss modulus is the average value of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160-220°C. In addition, when the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, only the microporous film containing silane-modified polyolefin is taken out from the laminated film or composite film to measure the storage modulus E' of the microporous film containing silane-modified polyolefin. j and E' S and loss modulus E" j and E” S .

[0479] The separator of the ninth embodiment Regarding the viscoelasticity measurement (version 1) described in the examples, when the inorganic porous layer is removed from the separator for measurement, the hybrid storage modulus ratio (R E’mix ) is 1.5 to 20 times:

[0480] R E’mix =E' / E'0 (2A)

[0481] {wherein, E' is the storage modulus of the separator for a power storage device measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for a power storage device not containing silane-modified polyolefin measured at 160°C to 220°C.},

[0482] and / or preferably a hybrid loss modulus ratio (R E”mix ) is 1.5 to 20 times:

[0483] R E”mix =E” / E”0 (2B)

[0484] {wherein, E″ is the loss modulus of the separator for a power storage device measured at 160° C. to 220° C., and E″0 is the loss modulus of the separator for a power storage device not containing silane-modified polyolefin measured at 160° C. to 220° C.}.

[0485] By making the mixed storage modulus ratio (R E’mix ) and / or hybrid loss modulus ratio (R E”mix ) is within the range of 1.5 to 20 times, which makes it easy to take into account both the shutdown function and the high temperature resistance to film rupture. E’mix ) and / or hybrid loss modulus ratio (R E”mix) is more preferably 2 times to 18 times. It should be noted that E' and E'0 as well as E" and E"0 are respectively the average values ​​of the storage modulus or loss modulus measured within the set temperature range of the measuring device when 160 to 220°C is set as the widest temperature range. In addition, when the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, only the microporous film containing silane-modified polyolefin is taken out from the laminated film or the composite film to measure the storage modulus E' and E'0 and the loss modulus E" and E"0 of the microporous film containing silane-modified polyolefin. It should be noted that the separator for a storage device that does not contain silane-modified polyolefin is described in detail in the embodiment project.

[0486] The separator of the ninth embodiment preferably has a transition temperature between the rubber-like flat region and the crystalline melt flow region in the temperature change of its storage modulus from the perspective of taking into account both the shutdown function and the high-temperature rupture resistance. The transition temperature between the rubber-like flat region and the crystalline melt flow region is preferably 135°C to 150°C. The transition temperature between the rubber-like flat region and the crystalline melt flow region is preferably 137°C to 147°C, more preferably 140°C to 145°C, and further preferably 140°C to 143°C. It should be noted that when the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, only the microporous film containing silane-modified polyolefin is taken out from the laminate or the composite film to measure the transition temperature of the microporous film containing silane-modified polyolefin.

[0487] <Tenth embodiment>

[0488] The separator for a power storage device according to the tenth embodiment (hereinafter also referred to as "separator") comprises a first porous layer (layer A) comprising a silane-modified polyolefin capable of forming a crosslinked structure, and a second porous layer (layer B) comprising inorganic particles. Layers A and B are each a single layer or multiple layers. Layer B is formed only on one surface of layer A or on both surfaces.

[0489] In LIBs, a representative example of a power storage device, lithium (Li) ions move back and forth between the positive and negative electrodes. Therefore, placing a separator consisting of layers A and B between the positive and negative electrodes allows for faster movement of Li ions between the electrodes while preventing contact between them.

[0490] (Thickness ratio)

[0491] The A layer functions as a cross-linked microporous membrane, and the B layer functions as an inorganic porous layer formed on the microporous membrane.

[0492] Here, the ratio (TA / TB) of the thickness of layer A (TA) to the thickness of layer B (TB) is preferably 0.22 or more and 14 or less. If the ratio (TA / TB) is 0.22 or more, the proportion of layer A in the separator can be sufficiently ensured, and the function of layer A can be exerted. On the other hand, if the ratio (TA / TB) is 14 or less, the proportion of layer B in the separator can be sufficiently ensured, and the function of layer B can be exerted.

[0493] By specifying the structures of layer A and layer B and setting their ratio (TA / TB) within the above range, a separator capable of improving the cycle characteristics and safety of a power storage device can be provided. Such a separator can be suitably used as a constituent material of LIBs for mobile device or vehicle applications, for example.

[0494] From the viewpoint of the above-mentioned effects, the ratio (TA / TB) is preferably 0.8 or more, more preferably 1.0 or more. On the other hand, the ratio (TA / TB) is preferably 5.5 or less, more preferably 3.2 or less.

[0495] The ratio (TA / TB) can be set to, for example, less than 2.5, less than 2.0, or less than 1.0. In this case, the thickness of layer A (TA) is less than 2.5 times the thickness of layer B (TB), or less than the thickness of layer B (TB), making it easy to reduce the thickness of layer A and even the separator.

[0496] The total thickness (TA + TB) of layer A and layer B is preferably 3.0 μm or more and 22 μm or less. If the total thickness (TA + TB) is 3.0 μm or more, the membrane strength of the separator tends to be improved. On the other hand, if the total thickness (TA + TB) is 22 μm or less, the ion permeability of the separator tends to be improved.

[0497] From the viewpoint of the above effects, the total thickness (TA+TB) is more preferably 3.5 μm or more, and further preferably 4.0 μm or more. On the other hand, the total thickness (TA+TB) is more preferably 20 μm or less, and further preferably 18 μm or less.

[0498] The total thickness (TA+TB) can be set to, for example, less than 11 μm, 10 μm or less, or 8 μm or less. Even such a thin separator can improve the cycle characteristics and safety of the power storage device within the scope of the present invention.

[0499] The ratio (TA / TB) and the total thickness (TA+TB) can be measured by the methods described in the Examples section, and can be controlled by adjusting the thickness (TA) and / or the thickness (TB). The A layer and the B layer will be described later.

[0500] (Shutdown temperature and melt fracture temperature)

[0501] Regarding layer A, the shutdown temperature (sometimes called the melting temperature) measured based on resistance under a pressure of 0.1 MPa to 10.0 MPa (preferably 10 MPa) is 130°C to 160°C and the melt fracture temperature (sometimes called the film rupture temperature) is preferably 200°C or above.

[0502] If the shutdown temperature is 130°C or higher, unnecessary activation of the shutdown function during normal operation of the power storage device can be avoided, thereby ensuring sufficient output characteristics of the power storage device. On the other hand, if the shutdown temperature is 160°C or lower, the shutdown function can be appropriately activated during abnormal operation of the power storage device.

[0503] Furthermore, if the shutdown temperature is 200° C. or higher, abnormal reactions of the power storage device can be stopped before reaching an ultrahigh temperature region, and melt-breakage of the separator during abnormal reactions of the power storage device can be prevented.

[0504] That is, by ensuring that the shutdown temperature and melt-rupture temperature meet the above conditions, a separator can be provided that provides an electricity storage device with excellent heat resistance, closed-cell characteristics (shutdown function), and melt-rupture characteristics (melt-rupture function), while also ensuring mechanical properties, ion permeability, etc. for the separator itself. Therefore, by having a separator whose shutdown temperature and melt-rupture temperature meet the above conditions, the electricity storage device can achieve improved cycle characteristics and safety.

[0505] From the viewpoint of the above effects, the shutdown temperature is preferably higher than 130°C, more preferably 135°C or higher, and even more preferably 136°C or higher. On the other hand, the shutdown temperature is preferably 150°C or lower, more preferably 148°C or lower, and even more preferably 146°C or lower.

[0506] Likewise, from the viewpoint of the above-mentioned effects, the melt fracture temperature is preferably 175°C or higher, more preferably 178°C or higher, and even more preferably 180°C or higher. On the other hand, the melt fracture temperature is preferably 230°C or lower, more preferably 225°C or lower, and even more preferably 220°C or lower.

[0507] Even if the melt fracture temperature cannot be accurately measured in a range exceeding 200°C, the above-mentioned condition of "melt fracture temperature is 200°C or higher" is satisfied as long as the temperature is 200°C or higher.

[0508] The "shutdown temperature" and "melt-rupture temperature" in this specification refer to values ​​obtained by measuring the electrical resistance under the aforementioned pressure. Specifically, while applying the aforementioned pressure to a stack comprising a positive electrode, a separator, and a negative electrode, the temperature of the stack is increased, and the shutdown temperature and melt-rupture temperature are derived based on the resulting increase in AC resistance (AC resistance between the electrodes). In the tenth embodiment, the temperature at which the AC resistance first exceeds a predetermined reference value (e.g., 1000Ω) is set as the shutdown temperature, and the temperature at which the AC resistance, after further heating, drops below the aforementioned reference value (e.g., 1000Ω) is set as the melt-rupture temperature.

[0509] The stack can be pressurized using a hydraulic jack, but is not limited thereto, and known pressurizing means other than the hydraulic jack can be used. In addition, the stack can be heated using an aluminum heater, but is not limited thereto, and known heating means other than the aluminum heater can be used.

[0510] The shutdown temperature and melt fracture temperature can be measured by the method described in the Examples section, and can also be controlled by adjusting the composition of the A layer or the production method.

[0511] (Heat shrinkage at 150°C)

[0512] In layer A, the thermal shrinkage rate (T2) at 150°C after forming its crosslinked structure is 0.02 times or more and 0.91 times or less of the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure. In other words, the ratio (T2 / T1) of the thermal shrinkage rate (T2) at 150°C after forming the crosslinked structure to the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure is 0.02 or more and 0.91 or less. The thermal shrinkage rate used here is the larger value of the thermal shrinkage rate of layer A in the machine direction (MD) or the thermal shrinkage rate of layer A in the width direction (TD).

[0513] Because layer A can form a cross-linked structure based on silane-modified polyolefin, it is possible to focus on the changes in its thermal shrinkage before and after cross-linking.

[0514] If the ratio (T2 / T1) is 0.02 or greater, the occurrence of short circuits can be effectively suppressed, thereby reliably preventing a temperature rise in the entire power storage device and the resulting smoke and, ultimately, fire. On the other hand, if the ratio (T2 / T1) is 0.91 or less, it can be determined that the crosslinking reaction in layer A has successfully and sufficiently progressed. In other words, if the ratio (T2 / T1) is within this range, a separator for a power storage device can be provided that improves the cycle characteristics and safety of the power storage device.

[0515] Therefore, from the viewpoint of the above-mentioned effects, the ratio (T2 / T1) is preferably 0.03 or more, more preferably 0.05 or more, and even more preferably 0.07 or more. On the other hand, the ratio (T2 / T1) is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.4 or less.

[0516] The thermal shrinkage ratio (T1) at 150° C. before forming a cross-linked structure is preferably 70% or less, more preferably 60% or less.

[0517] Furthermore, the thermal shrinkage (T2) at 150°C after forming a cross-linked structure is preferably 60% or less, more preferably 50% or less. However, since the formation of a cross-linked structure tends to reduce the thermal shrinkage compared to before the formation of the cross-linked structure, the thermal shrinkage (T2) is generally smaller than the thermal shrinkage (T1).

[0518] The heat shrinkage at 150° C. can be measured by the method described in the Examples section, and can also be controlled by adjusting the structure of the A layer or the production method.

[0519] The separators of the various embodiments described above can be interchanged or combined with one another. The separator of the ninth or tenth embodiment described above can include layers other than the microporous membrane and the inorganic porous layer, as desired. The components of the separators of the first to tenth embodiments are described below.

[0520] [Microporous membrane]

[0521] The microporous membrane can be formed of polyolefin or modified polyolefin.

[0522] The microporous membrane contains silane-modified polyolefin and may contain other polyolefins as desired. Due to the silane crosslinking property of the silane-modified polyolefin, the microporous membrane can undergo a crosslinking reaction during the separator manufacturing process.

[0523] The polyolefin contained in the microporous membrane is not particularly limited, and for example, a homopolymer of ethylene or propylene or a copolymer formed by at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and norbornene can be listed. Among these, from the perspective of being able to perform heat setting (sometimes abbreviated as "HS") at a higher temperature without clogging the hole, high-density polyethylene (homopolymer) or low-density polyethylene, more preferably high-density polyethylene (homopolymer) can be used. It should be noted that the polyolefin can be used alone or in combination of two or more.

[0524] Microporous membranes are preferably manufactured using both silane-modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) as raw materials to achieve resistance to redox degradation and a dense, uniform porous structure. Ultra-high molecular weight polyethylene (UHMWPE) generally has a weight-average molecular weight of 1,000,000 or greater. More preferably, in the manufacture of microporous membranes or separators, the weight ratio of silane-modified polyolefin to UHMWPE (silane-modified polyolefin weight / UHMWPE weight) is 0.05 / 0.95 to 0.40 / 0.60.

[0525] The content of the polyolefin contained in the microporous membrane is preferably 50% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, preferably 80% by weight or more and 100% by weight or less. In addition, the microporous membrane preferably includes a polyolefin having a weight average molecular weight of 100,000 or more and less than 1,000,000 (relative to the polyolefin as a whole, preferably 40% by weight or more, more preferably 80% by weight or more). The weight average molecular weight of the polyolefin is more preferably 120,000 or more and less than 950,000, and further preferably 130,000 or more and less than 930,000. By using a polyolefin having a weight average molecular weight of 100,000 or more and less than 1,000,000, there is a tendency to easily maintain safety in the early stage of the relaxation of the shrinkage of the polymer in the heating test of the storage device, etc., especially in the heating safety test. By adjusting the weight-average molecular weight of the microporous membrane to less than 1,000,000, it is possible to suppress poor extrusion forming (film graining) known as melt fracture. On the other hand, by adjusting the weight-average molecular weight of the microporous membrane to 100,000 or more, it is possible to suppress the transfer of depressions when the microporous membrane is wound onto a core (winding core).

[0526] The viscosity average molecular weight of the microporous membrane when the inorganic porous layer is removed and the crosslinking treatment is not performed is preferably 100,000 to 1,200,000, more preferably 150,000 to 800,000, from the viewpoint of preventing the generation of polymer powder due to frictional shear during the roll conveyance of the separator.

[0527] The thickness of the microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, and further preferably 3.0 μm or more, 4.0 μm or more, or 4.5 μm or more. By making the thickness of the microporous membrane 1.0 μm or more, there is a tendency for the membrane strength to be further improved. In addition, the thickness of the microporous membrane is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less, 22 μm or less, or 19 μm or less. By making the thickness of the microporous membrane 500 μm or less, there is a tendency for the ion permeability to be further improved. The thickness of the microporous membrane can be measured by the method described in the Examples.

[0528] In the case where the microporous membrane is a separator used in a lithium-ion secondary battery with a relatively high capacity in recent years, the thickness of the microporous membrane is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, further preferably 18 μm or less, and particularly preferably 16 μm or less. In this case, by making the thickness of the microporous membrane 25 μm or less, there is a tendency for the permeability to be further improved. In this case, the lower limit of the thickness of the microporous membrane may be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, 6.0 μm or more, or 7.5 μm or more.

[0529] From the perspective of the high-temperature rupture resistance of the separator for the power storage device and the safety of the power storage device, the microporous membrane as the separator is preferably such that, when measured by thermomechanical analysis (TMA), the melting and rupture temperature is preferably 180°C to 220°C, more preferably 180°C to 200°C. Generally, when the power storage device generates heat due to an unexpected runaway reaction, the polyolefin-made separator for the power storage device melts at a low temperature (e.g., below 150°C), stopping the movement of Li ions and the associated discharge inside or outside the power storage device at an early stage. Then, the power storage device is cooled as a whole by natural cooling using external air or refrigerant, which can prevent the ignition of the electrolyte or the exothermic reaction of the decomposition of the electrolyte, and it is expected to ensure safety. However, the runaway reaction occurring in the above-mentioned power storage device is not stopped by the melting of the separator, and continues to generate heat, causing the separator to melt and rupture, making it impossible to ensure the safety of the device. Therefore, it is important that the separator does not melt and rupture until the entire power storage device is fully cooled. Furthermore, if the temperature rises to an ultra-high temperature of 220°C or above, the decomposition reaction of the electrolyte or electrolyte will proceed rapidly, and the decomposition products will cause corrosion reactions on the electrodes, further generating heat and causing explosions. In this case, the separator can prevent the corrosion reaction by melting and breaking the membrane, penetrating into both electrodes to coat the active material.

[0530] [First porous layer (layer A)]

[0531] Layer A comprises a silane-modified polyolefin, which can form a cross-linked structure. To ensure resistance to oxidation-reduction degradation and a dense and uniform porous structure, Layer A preferably further comprises polyethylene as a polyolefin different from the silane-modified polyolefin. It should be noted that Layer A may contain components other than the silane-modified polyolefin and polyethylene.

[0532] Examples of the polyolefin constituting the silane-modified polyolefin in layer A include homopolymers of ethylene or propylene; copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these polyolefins, ethylene homopolymers (polyethylene) are preferred, with high-density polyethylene and / or low-density polyethylene being more preferred, and high-density polyethylene being even more preferred, from the perspective of avoiding pore clogging and enabling heat setting at higher temperatures. One polyolefin may be used alone or in combination of two or more.

[0533] The layer A may contain a polymer (other polymer) that is neither silane-modified polyolefin nor polyethylene, within a range that does not excessively impair the effects of the present invention.

[0534] The weight average molecular weight of the entire A layer is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

[0535] (Thickness of layer A)

[0536] The thickness (TA) of layer A is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 3 μm or more. If the thickness (TA) is 1 μm or more, there is a tendency for the membrane strength to be further improved. On the other hand, the thickness (TA) is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less. If the thickness (TA) is 500 μm or less, there is a tendency for the ion permeability to be further improved. It should be noted that the thickness (TA) can be set to, for example, 1.00 μm or more, 2.00 μm or more, or 3.00 μm or more.

[0537] In the case where the separator is a LIB separator, the thickness (TA) is preferably less than 22 μm, more preferably less than 21 μm, and further preferably less than 20.5 μm. In the case where the separator is a LIB separator, the upper limit of the thickness (TA) can be set to less than 13 μm or less than 8.5 μm. If the thickness (TA) is less than 25 μm, there is a tendency for the permeability to be further improved. It should be noted that the thickness (TA) can be set to, for example, less than 22.00 μm, less than 21.00 μm, less than 20.00 μm, less than 13.00 μm or less than 8.50. The lower limit of the thickness (TA) can be the same as above.

[0538] The thickness (TA) can be measured by the method described in the Examples section, and can also be controlled by changing the stretching ratio of the A layer, for example.

[0539] When layer A is a single layer, the thickness of layer A is regarded as thickness (TA). When layer A is a multilayer, the total thickness of the multilayer A layer is regarded as thickness (TA).

[0540] (Film rupture temperature of layer A)

[0541] The film rupture temperature of the A layer measured by thermomechanical analysis (TMA) is preferably 180° C. or higher and 220° C. or lower.

[0542] Even if an unexpected runaway reaction causes abnormal heating of the power storage device, the separator's shutdown function can be expected to stop the movement of Li ions and the associated discharge within or outside the power storage device. The refrigerant can then be used to cool the entire power storage device, ensuring safety. Furthermore, by keeping the membrane rupture temperature within the aforementioned range, even if the entire power storage device is not sufficiently cooled, or if it reaches an extremely high temperature, the separator can melt and rupture, permeating both electrodes and coating the active material, thereby easily suppressing further heating.

[0543] The film rupture temperature can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0544] (Porosity of the microporous membrane or layer A)

[0545] The porosity of the microporous membrane or layer A is preferably 20% or greater, more preferably 25% or greater, and even more preferably 28% or greater, 30% or greater, 32% or greater, or 35% or greater. A porosity of 20% or greater tends to further improve the ability to follow the rapid migration of Li ions. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and even more preferably 60% or less. A porosity of 90% or less tends to further improve membrane strength and further suppress self-discharge.

[0546] The porosity can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0547] (Air permeability of microporous membrane or layer A)

[0548] The air permeability of the microporous membrane or layer A is preferably 1 second / 100 cm 3 More than 50 seconds / 100 cm 3 More than 55 seconds / 100 cm 3 More preferably, it is more than 70 seconds, more than 90 seconds or more than 110 seconds. If the air permeability is 1 second / 100cm 3 Above 400 sec / 100 cm, there is a tendency for the balance of film thickness, porosity and average pore size to be further improved. On the other hand, the air permeability is preferably 400 sec / 100 cm 3 Less than 300 seconds / 100cm, more preferably less than 300 seconds / 100cm 3 , more preferably 270 seconds / 100cm 3 If the air permeability is 400 seconds / 100cm 3 Below this level, the ion permeability tends to further increase.

[0549] The air permeability can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0550] (Puncture strength of microporous membrane or layer A)

[0551] As the puncture strength of the microporous membrane or the A layer, it is preferably 200gf / 20μm or more, more preferably 300gf / 20μm or more. If the puncture strength is 200gf / 20μm or more, even if the active material or the like falls off when the separator and the stack of electrodes are wound, it is easy to suppress the rupture of the film caused by the falling active material or the like. In addition, it is easy to reduce the possibility of short circuit due to expansion and contraction of the electrode accompanying charge and discharge. On the other hand, the puncture strength is preferably 4000gf / 20μm or less, more preferably 3800gf / 20μm or less. If the puncture strength is 3500gf / 20μm or less, it is easy to reduce thermal shrinkage during heating.

[0552] The puncture strength can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0553] [Tensile strength of microporous membrane or layer A]

[0554] The tensile strength of the microporous membrane or layer A is preferably 1000 kgf / cm in both the MD (longitudinal direction of the membrane or layer A, machine direction or processing direction) and the TD (direction perpendicular to the MD, width direction of the membrane or layer A). 2 More than 1050kgf / cm 2 More than 1100 kgf / cm 2 By making the tensile strength 1000kgf / cm 2 As described above, there is a tendency that the breakage during slitting or winding of the power storage device is further suppressed, and short circuits caused by foreign matter in the power storage device are further suppressed. On the other hand, the tensile strength is preferably 5000 kgf / cm 2 Below, more preferably 4500kgf / cm 2 Below, more preferably 4000kgf / cm 2 By making the tensile strength 5000kgf / cm 2 Next, during the heating test, the microporous membrane or the A layer is relaxed early to reduce the shrinkage force, and as a result, there is a tendency that safety is improved.

[0555] [Tensile elastic modulus of the microporous membrane or layer A]

[0556] The tensile modulus of the microporous film or A layer is preferably less than 120N / cm in both directions of MD and TD, more preferably less than 100N / cm, and further preferably less than 90N / cm. The tensile modulus of 120N / cm or less indicates that the separator for lithium ion secondary battery is not extremely oriented. In a heating test, for example, when a blocking agent such as polyethylene melts and shrinks, stress relaxation occurs in the early polyethylene, thereby suppressing the shrinkage of the separator in the battery and easily preventing the short circuit between the electrodes (i.e., the safety of the separator during heating can be improved). This low tensile modulus is easily achieved by including a polyethylene having a weight average molecular weight of less than 500,000 in the polyolefin forming the microporous film or A layer. On the other hand, the lower limit of the tensile modulus is not particularly limited, and is preferably more than 10N / cm, more preferably more than 30N / cm, and further preferably more than 50N / cm. The tensile modulus can be appropriately adjusted by adjusting the degree of stretching in the manufacturing process, or by relaxing after stretching as needed.

[0557] <Polyolefin>

[0558] The polyolefin is not particularly limited, and examples thereof include homopolymers of ethylene or propylene, or copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these, high-density polyethylene or low-density polyethylene is preferred, with high-density polyethylene being more preferred, from the perspective of being able to perform heat setting (sometimes abbreviated as "HS") at higher temperatures without clogging the pores. It should be noted that the polyolefin may be used alone or in combination of two or more.

[0559] In addition, the separator preferably includes a polyolefin having a weight average molecular weight (Mw) of less than 2,000,000, and relative to the entire polyolefin, more preferably includes a polyolefin having Mw of less than 2,000,000 at a ratio of 40% by mass or more, further preferably at a ratio of 80% by mass or more. By using a polyolefin having Mw of less than 2,000,000, there is a tendency to easily maintain safety in a heating test of a storage device, such as relaxation of the shrinkage of the polymer occurring in the early stage, particularly in a heating safety test. It should be noted that, when using a polyolefin having Mw of less than 2,000,000, compared with a polyolefin having a weight average molecular weight of more than 1,000,000, there is a tendency that the elastic modulus in the thickness direction of the obtained microporous film becomes smaller, so that a microporous film having a concave and convex shape that is easier to transfer to a core can be obtained. The weight average molecular weight of the entire polyolefin microporous membrane constituting the separator is preferably 100,000 or more and 2,000,000 or less, and more preferably 150,000 or more and 1,500,000 or less.

[0560] (Polyolefins having one or more functional groups)

[0561] From the perspective of the formation of a cross-linked structure, resistance to redox degradation, and a dense and uniform porous structure, the separator is a polyolefin having one or more functional groups, preferably including a functional group-modified polyolefin or a polyolefin obtained by copolymerizing a monomer having a functional group. It should be noted that in this specification, the functional group-modified polyolefin refers to a substance obtained by connecting a functional group after manufacturing a polyolefin. The functional group is connected to the polyolefin skeleton or can be introduced into a comonomer, preferably participating in the selective cross-linking of the amorphous portion of the polyolefin, for example, it can be selected from at least one of a carboxyl group, a hydroxyl group, a carbonyl group, a polymerizable unsaturated hydrocarbon group, an isocyanate group, an epoxy group, a silanol group, a hydrazide group, a carbodiimide group, an oxazoline group, an acetoacetyl group, an aziridine group, an ester group, an active ester group, a carbonate group, an azido group, a chain or cyclic hydrocarbon group containing heteroatoms, an amino group, a thiol group, a metal chelate group, and a halogen-containing group.

[0562] From the perspectives of separator strength, ion permeability, resistance to redox degradation, and a dense and uniform porous structure, the separator preferably comprises both a polyolefin having one or more functional groups and a silane-unmodified polyethylene. When a polyolefin having one or more functional groups and a silane-unmodified polyethylene are used in combination, the mass ratio of the polyolefin having one or more functional groups to the silane-unmodified polyethylene in the separator (mass of the polyolefin having one or more functional groups / mass of the silane-unmodified polyethylene) is preferably 0.05 / 0.95 to 0.80 / 0.20.

[0563] (cross-linked structure)

[0564] The crosslinked structure of the separator contributes to the balance between the separator's shutdown function and high-temperature rupture resistance, as well as the safety of the battery device. It is preferably formed in the amorphous portion of the polyolefin contained in the separator. The crosslinked structure can be formed, for example, by a reaction involving covalent bonds, hydrogen bonds, or coordination bonds. The reaction involving covalent bonds is preferably at least one selected from the group consisting of the following reactions (I) to (IV):

[0565] (I) Condensation reaction of multiple identical functional groups

[0566] (II) Reactions between multiple functional groups

[0567] (III) Chain condensation reaction between functional groups and electrolyte

[0568] (IV) Chain condensation reaction between functional groups and additives.

[0569] Furthermore, the reaction via a coordination bond is preferably the following reaction (V):

[0570] (V) A reaction in which a plurality of identical functional groups undergo cross-linking via coordination bonds with eluted metal ions.

[0571] Reaction (I)

[0572] The first functional group of the separator is denoted as A. The principle diagram and specific examples of reaction (I) are shown below.

[0573] Schematic diagram of the principle of reaction (I)

[0574]

[0575] Examples of functional group A:

[0576] Silanol group, etc.

[0577] Specific example of reaction (I)

[0578]

[0579] {wherein, R is an alkyl group or heteroalkyl group having 1 to 20 carbon atoms, which may have a substituent.}

[0580] In the case where the functional group A used to carry out reaction (I) is a silanol group, the polyolefin contained in the separator is preferably silane-grafted modified. The silane-grafted modified polyolefin is composed of a structure in which the main chain is a polyolefin and an alkoxysilyl group is grafted on the main chain. It should be noted that, for example, alkoxides replaced by the above-mentioned alkoxysilyl groups can include methoxides, ethanolates, butoxides, etc. For example, in the above formula, R can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, etc. In addition, the main chain and the graft are connected by a covalent bond, and structures such as alkyl, ether, glycol or ester can be listed. Taking into account the manufacturing process of the separator of this embodiment, the ratio of silicon to carbon (Si / C) of the silane-grafted modified polyolefin in the stage before the cross-linking treatment step is preferably 0.2 to 1.8%, and more preferably 0.5 to 1.7%.

[0581] The preferred density of the silane grafted modified polyolefin is 0.90 to 0.96 g / cm 3, and the melt mass flow rate (MFR) at 190°C is 0.2 to 5 g / min. From the perspective of suppressing the generation of resin agglomerates in the manufacturing process of the separator and maintaining the silane cross-linking property until it comes into contact with the electrolyte, the silane grafted modified polyolefin is preferably not a masterbatch resin containing a dehydration condensation catalyst. Dehydration condensation catalysts are also known to function as catalysts for the siloxane bond formation reaction of alkoxysilyl-containing resins. In this specification, a substance obtained by adding a dehydration condensation catalyst (for example, containing an organic metal catalyst) to an alkoxysilyl-containing resin or other mixed resin in advance and mixing in a continuous process of resin mixing using an extruder is referred to as a masterbatch resin.

[0582] Reaction (II)

[0583] The first functional group of the separator is represented by A, and the second functional group is represented by B. The principle diagram and specific examples of reaction (II) are shown below.

[0584] Schematic diagram of the principle of reaction (II)

[0585]

[0586] Examples of combinations of functional groups A and B:

[0587] Hydroxyl and carboxyl groups (esterification);

[0588] Carbonyl and alkyl (aldol condensation);

[0589] Halogen and carboxyl group (intramolecular condensation);

[0590] Alkoxy and alkyl (Claisen reaction);

[0591] Carbonyl and anhydride groups (Perkin reaction);

[0592] amino and halogen;

[0593] Isocyanate groups and hydroxyl groups (forming urethane bonds); and

[0594]

[0595] (Oxazoline) and hydroxyl groups

[0596] Specific example 1 of reaction (II):

[0597]

[0598] Specific example 2 of reaction (II):

[0599]

[0600] Reaction (I) and reaction (II) may be catalytically promoted, for example, by chemical substances within the power storage device assembled with the separator. The chemical substances may be, for example, the electrolyte, electrolyte solution, electrode active material, additives, or decomposition products thereof contained in the power storage device.

[0601] Reaction (III)

[0602] The first functional group of the separator is represented by A, and the electrolyte is represented by Sol. The principle diagram and specific examples of reaction (III) are shown below.

[0603] Schematic diagram of the principle of reaction (III)

[0604]

[0605] Examples of functional group A:

[0606] Hydroxyl, carboxyl, amino, carbonyl, ether, isocyanate, etc.

[0607] Examples of electrolytes:

[0608] Electrolyte: LiPF6, LiBF4, LiN(SO2CF3)2, LiSO3CF3, LiBC4O8(LiBOB), etc.

[0609] Non-aqueous solvents: ethylene carbonate, ethyl methyl carbonate or mixtures thereof

[0610] Specific example 1 of reaction (III):

[0611]

[0612] Specific example 2 of reaction (III):

[0613]

[0614] Reaction (IV)

[0615] The principle diagram of reaction (IV) is shown below, where the first functional group of the separator is represented by A, the second functional group introduced as desired is represented by B, and the additive is represented by Add.

[0616]

[0617] Reaction (IV) is preferably a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between the compound Rx constituting the separator and the compound Ry constituting the additive (Add), from the perspective of forming a covalent bond represented by a dotted line in the above schematic diagram. Compound Rx can be a polyolefin contained in the separator, such as polyethylene or polypropylene. The polyolefin is preferably modified with a functional group x, such as at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH.

[0618] Since multiple compounds Rx are cross-linked via compound Ry as an additive, compound Ry preferably has two or more linking reaction units y1. Multiple linking reaction units y1 can be any structure or group as long as they can undergo a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction with the functional group x of compound Rx. They can be substituted or unsubstituted, can contain heteroatoms or inorganic substances, and can be the same or different from each other. In addition, when compound Ry has a chain structure, multiple linking reaction units y1 can each independently be a terminal group, or be introduced into the main chain, or be a side chain or pendant group.

[0619] In the case where reaction (IV) is a nucleophilic substitution reaction, as an example only, the functional group x of compound Rx is regarded as a nucleophilic group, and the linking reaction unit y1 of compound Ry is regarded as a leaving group for explanation below. However, in this embodiment, both the functional group x and the linking reaction unit y1 can form a leaving group depending on their nucleophilicity.

[0620] From the perspective of a nucleophilic agent, the functional group x of the compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of oxygen-based nucleophilic groups include hydroxyl groups, alkoxy groups, ether groups, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophilic groups include ammonium groups, primary amino groups, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of sulfur-based nucleophilic groups include -SH and thioether groups, with -SH being preferred.

[0621] When reaction (IV) is a nucleophilic substitution reaction, from the perspective of the leaving group, the linking reaction unit y1 of the compound Ry is preferably an alkylsulfonyl group such as CH3SO2-, CH3CH2SO2-; an arylsulfonyl group (-ArSO2-); a halogenated alkylsulfonyl group such as CF3SO2-, CCl3SO2-; an alkylsulfonate group such as CH3SO3-, CH3CH2SO3-; an arylsulfonate group (ArSO3-); a halogenated alkylsulfonate group such as CF3SO3-, CCl3SO3-; and a heterocyclic group, which can be used alone or in combination of multiple groups. As heteroatoms contained in the heterocycle, nitrogen atoms, oxygen atoms, sulfur atoms, etc. can be listed, among which nitrogen atoms are preferred from the perspective of leaving properties. As leaving groups containing nitrogen atoms in the heterocycle, monovalent groups represented by the following formulas (y1-1) to (y1-6) are preferred:

[0622]

[0623] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0624]

[0625] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0626]

[0627] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0628]

[0629] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0630]

[0631] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0632]

[0633] {wherein, X is a hydrogen atom or a monovalent substituent.}

[0634] In formulae (y1-1) to (y1-6), X is a hydrogen atom or a monovalent substituent. Examples of the monovalent substituent include an alkyl group, a halogenated alkyl group, an alkoxy group, and a halogen atom.

[0635] When reaction (IV) is a nucleophilic substitution reaction and compound Ry has a chain structure, compound Ry preferably has, in addition to the linking reaction unit y1, at least one selected from the group consisting of divalent groups represented by the following formulae (y2-1) to (y2-6) as a chain unit y2:

[0636]

[0637] {wherein, m is an integer from 0 to 20, and n is an integer from 1 to 20.}

[0638]

[0639] {wherein, n is an integer from 1 to 20.}

[0640]

[0641] {wherein, n is an integer from 1 to 20.}

[0642]

[0643] {wherein, n is an integer from 1 to 20.}

[0644]

[0645] {wherein, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer of 1 to 20.}

[0646]

[0647] {wherein, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer of 1 to 20.}

[0648] Furthermore, in the case where the compound Ry contains a plurality of chain units y2, they may be the same as or different from each other, and their arrangement may be block or random.

[0649] In formula (y2-1), m is an integer of 0 to 20, and from the perspective of the cross-linked network, it is preferably 1 to 18. In formulas (y2-1) to (y2-6), n is an integer of 1 to 20, and from the perspective of the cross-linked network, it is preferably 2 to 19 or 3 to 16. In formulas (y2-5) to (y2-6), X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and from the perspective of the stability of the chain structure, it is preferably a methylene group, an ethylene group, an n-propylene group, an n-butylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, an n-dodecylene group, an o-phenylene group, an m-phenylene group, or a p-phenylene group.

[0650] When reaction (IV) is a nucleophilic substitution reaction, preferred combinations of the linking reaction unit y1 and the chain unit y2 of the functional group x of the compound Rx and the compound Ry are shown in Tables 2 to 4 below.

[0651] [Table 2]

[0652] Nucleophilic substitution reaction (preferred combination I)

[0653]

[0654] [Table 3]

[0655] Nucleophilic substitution reaction (preferred combination II)

[0656]

[0657] [Table 4]

[0658] Nucleophilic substitution reaction (preferred combination III)

[0659]

[0660] As a specific example 1 of the nucleophilic substitution reaction, the following shows that the functional group x of the polyolefin is -NH2, the linking reaction unit y1 of the additive (compound Ry) is a skeleton derived from succinimide, and the chain unit y2 is -(O-C2H5) n -The reaction principle diagram.

[0661] Specific example 1:

[0662]

[0663] As a specific example 2 of the nucleophilic substitution reaction, the following is a reaction principle diagram when the functional group x of the polyolefin is -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 o-phenylene.

[0664] Specific example 2:

[0665]

[0666] When reaction (IV) is a nucleophilic addition reaction, the functional group x of compound Rx and the linking reaction unit y1 of compound Ry can undergo an addition reaction. In the nucleophilic addition reaction, the functional group x of compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of oxygen-based nucleophilic groups include hydroxyl groups, alkoxy groups, ether groups, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophilic groups include ammonium groups, primary amino groups, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of sulfur-based nucleophilic groups include -SH and thioether groups, with -SH being preferred.

[0667] In the nucleophilic addition reaction, the linking reaction unit y1 of the compound Ry is preferably at least one selected from the group consisting of groups represented by the following formulae (Ay1-1) to (Ay1-6), from the viewpoint of addition reactivity and availability of raw materials:

[0668]

[0669] {wherein, R is a hydrogen atom or a monovalent organic group.}

[0670]

[0671]

[0672] In formula (Ay1-4), R is a hydrogen atom or a monovalent organic group, preferably a hydrogen atom, C 1～20 The alkyl group, alicyclic group or aromatic group is more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group or a phenyl group.

[0673] When reaction (IV) is a nucleophilic addition reaction, preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 of compound Ry are shown in Tables 5 and 6 below.

[0674] [Table 5]

[0675] Nucleophilic addition reaction (preferred combination I)

[0676]

[0677] [Table 6]

[0678] Nucleophilic addition reaction (preferred combination II)

[0679]

[0680] As a specific example of the nucleophilic addition reaction, a reaction principle diagram is shown below when the functional group x of the separator is -OH and the linking reaction unit y1 of the additive (compound Ry) is -NCO.

[0681] Specific examples:

[0682]

[0683] 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, the ring structure on the linking reaction unit y1 side is preferably opened. From the same perspective, the linking reaction unit y1 is more preferably an epoxy group, and compound Ry further preferably has at least two epoxy groups, and is even more preferably a diepoxide.

[0684] When reaction (IV) is a ring-opening reaction, the functional group x of the 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 the compound Ry is preferably at least two groups represented by the following formula (ROy1-1):

[0685]

[0686] {wherein, each of the multiple Xs is independently a hydrogen atom or a monovalent substituent.}

[0687] In formula (ROy1-1), each of the plurality of Xs is independently a hydrogen atom or a monovalent substituent, preferably a hydrogen atom, C 1～20 Alkyl, alicyclic or aromatic groups, more preferably hydrogen, methyl, ethyl, cyclohexyl or phenyl. In the epoxy ring-opening reaction, preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 of compound Ry are shown in Table 7 below.

[0688] [Table 7]

[0689] Epoxy ring-opening reaction (preferred combination)

[0690]

[0691] Reaction (V)

[0692] The first functional group of the separator is denoted as A, and the metal ion is denoted as M. n+ , a schematic diagram of the principle of reaction (V) and an example of functional group A are shown below.

[0693] Schematic diagram of the principle of reaction (V)

[0694]

[0695] Examples of functional group A: -CHO, -COOH, anhydride, -COO - wait

[0696] In the above schematic diagram, the metal ion M n+ Preferred metal ions eluted from the power storage device (hereinafter also referred to as eluted metal ions) may be, for example, metal ions selected from the group consisting of Zn 2+ 、Mn 2+ 、Co 3+ 、Ni 2+ He Li + At least one of the group consisting of. The following example shows that the functional group A is -COO - The coordination bond when .

[0697]

[0698] The following shows that the functional group A is -COOH and the eluted metal ion is Zn 2+ Specific schematic diagram of the reaction (V).

[0699]

[0700] In the above-mentioned principle diagram, hydrofluoric acid (HF) may be derived from any of the electrolyte, electrolyte solution, electrode active material, additives, decomposed products, or water-absorbed products thereof contained in the power storage device, for example, depending on the charge and discharge cycle of the power storage device.

[0701] <Silane-modified polyolefin>

[0702] Silane-modified polyolefins have a structure in which the main chain is a polyolefin and alkoxysilyl groups are grafted onto the main chain. Silane-modified polyolefins can be obtained by grafting alkoxysilyl groups onto the main chain of a non-silane-modified polyolefin.

[0703] It is presumed that alkoxysilyl groups undergo hydrolysis with water, converting to silanol groups and undergoing a crosslinking reaction to form siloxane bonds (see the following formula; the ratio of T1 structure, T2 structure, and T3 structure is arbitrary). Examples of alkoxides substituted with alkoxysilyl groups include methoxides, ethoxides, and butoxides. In the following formula, R includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl.

[0704]

[0705] The main chain and the grafts are connected by covalent bonds. Examples of the structures forming these covalent bonds include alkyl groups, ethers, glycols, and esters. Before the crosslinking reaction, the silane-modified polyolefin has a modification ratio of silanol units to the main chain ethylene units of less than 2%.

[0706] The preferred density of the silane grafted modified polyolefin is 0.90 to 0.96 g / cm 3The melt flow rate (MFR) at 190° C. is 0.2 to 5 g / min.

[0707] The amount of the silane-modified polyolefin is preferably 0.5% by mass or more or 3% by mass or more, more preferably 4% by mass or more, and further preferably 5% by mass or more or 6% by mass or more, based on the total amount of the microporous membrane or layer A, from the perspective of achieving the effect of the present invention. From the perspective of the cyclability and safety of the power storage device, the amount of the silane-modified polyolefin is preferably 40% by mass or less, more preferably 38% by mass or less, based on the total amount of the microporous membrane. In addition, the amount of the silane-modified polyolefin can be set to 30% by mass or more or 50% by mass or more, and can further be set to 100% by mass, based on the total amount of layer A.

[0708] The cross-linked structure in the microporous membrane or layer A is preferably formed by a compound generated in the electricity storage device.

[0709] That is, when the separator comes into contact with the non-aqueous electrolyte during the manufacturing process of the electricity storage device, a cross-linked structure having oligosiloxane bonds formed by swelling of the microporous membrane or layer A and / or by compounds generated within the electricity storage device is also preferably a cross-linked structure within the microporous membrane or layer A. In this case, the cross-linked structure is a cross-linked structure obtained by actively promoting the cross-linking reaction during the manufacturing process of the electricity storage device, while the cross-linking reaction is not actively promoted during the manufacturing process of the separator. Therefore, the self-crosslinking property of the separator can be maintained until it is housed in the electricity storage device.

[0710] From the perspective of suppressing the formation of resin agglomerates during the manufacturing process of the separator and maintaining silane crosslinking properties until contact with the electrolyte, the silane-modified polyolefin is preferably not a masterbatch resin containing a dehydration condensation catalyst. Dehydration condensation catalysts are also known to function as catalysts for the siloxane bond formation reaction of alkoxysilyl-containing resins. In this specification, a substance obtained by adding a dehydration condensation catalyst (e.g., containing an organic metal catalyst) to an alkoxysilyl-containing resin or other mixed resin in advance and mixing in a continuous process having a resin mixing step using an extruder is referred to as a masterbatch resin.

[0711] (Polyethylene)

[0712] In this specification, the polyethylene that may be further contained in addition to the silane-modified polyolefin (polyethylene further contained in the microporous membrane or layer A as a polyolefin different from the silane-modified polyolefin) refers to polyethylene that is a homopolymer having a weight-average molecular weight of 100,000 to 10,000,000 or a copolymer containing an alkane unit.

[0713] When the microporous membrane or layer A further contains polyethylene as a polyolefin different from the silane-modified polyolefin, the content thereof is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the silane-modified polyolefin and the polyethylene. When the polyethylene content is 20% by mass or more, it tends to be easier to ensure resistance to oxidation-reduction degradation and to ensure a dense and uniform porous structure.

[0714] On the other hand, the polyethylene content is preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. If the polyethylene content is 97% by mass or less, the content of the silane-modified polyolefin in the microporous membrane or layer A can be ensured.

[0715] (Detection Method of Silane-Modified Polyolefin Contained in Separator)

[0716] When the silane-modified polyolefin contained in the separator is cross-linked, it is insoluble or has insufficient solubility in organic solvents, making it difficult to directly measure the content of the silane-modified polyolefin from the separator. In this case, as a pretreatment of the sample, methyl orthoformate, which does not cause side reactions, is used to decompose the siloxane bonds into methoxysilanols, and then solution NMR measurement is performed to detect the silane-modified polyolefin contained in the separator. Pretreatment experiments can be carried out with reference to Japanese Patent Nos. 3529854 and 3529858.

[0717] Specifically, the method for detecting the silane-modified polyolefin contained in the separator can effectively utilize the silane-modified polyolefin as a raw material used in the production of the separator. 1 H or 13 C NMR identification. 1 H and 13 An example of a method for measuring C by NMR will be described.

[0718] ( 1 H NMR determination)

[0719] The sample was dissolved in o-dichlorobenzene-d4 at 140°C to obtain a proton resonance frequency of 600 MHz. 1 H-NMR spectrum. 1 The measurement conditions of H-NMR are as follows.

[0720] Device: AVANCE NEO 600 manufactured by Bruker

[0721] Sample tube diameter: 5mmφ

[0722] Solvent: o-dichlorobenzene-d4

[0723] Measurement temperature: 130°C

[0724] Pulse angle: 30°

[0725] Pulse waiting time: 1sec

[0726] Cumulative times: more than 1000 times

[0727] Sample concentration: 1wt / vol%

[0728] ( 13 C NMR determination)

[0729] The sample was dissolved in o-dichlorobenzene-d4 at 140°C to obtain 13 C-NMR spectrum. 13 The measurement conditions of C-NMR are as follows.

[0730] Device: AVANCE NEO 600 manufactured by Bruker

[0731] Sample tube diameter: 5mmφ

[0732] Solvent: o-dichlorobenzene-d4

[0733] Measurement temperature: 130°C

[0734] Pulse angle: 30°

[0735] Pulse waiting time: 5sec

[0736] Cumulative times: more than 10,000 times

[0737] Sample concentration: 10wt / vol%

[0738] Figure 11 and 12 It uses 2 kinds of polyolefins, silane-modified polyolefin raw materials 1 and 2. 1 H and 13 C-NMR spectra, and raw materials 1 and 2 have different melt indexes (MI), C3 grafting amounts, C4 grafting amounts and / or silanol modification amounts.

[0739] Figure 11 of 1 H and 13 C-NMR measurement conditions are as follows.

[0740] ( 1 H-NMR measurement conditions)

[0741] Device: Bruker Avance NEO 600

[0742] Observation core: 1 H

[0743] Observation frequency: 600MHz

[0744] Pulse program: zg30

[0745] Pulse waiting time: 1sec

[0746] Cumulative times: 1024 times

[0747] Measurement temperature: 130°C

[0748] Chemical shift reference: 7.219 ppm (o-DCBz)

[0749] Solvent: o-dichlorobenzene-d4

[0750] Sample concentration: 1wt / vol%

[0751] Sample tube: 5mmφ

[0752] ( 13 C-NMR measurement conditions)

[0753] Device: Bruker Avance NEO 600

[0754] Observation core: 13 C

[0755] Observation frequency: 150.91MHz

[0756] Pulse program: zgpg30

[0757] Pulse waiting time: 5sec

[0758] Cumulative times: 24,000 or 12,800 times

[0759] Measurement temperature: 130°C

[0760] Chemical shift reference: 132.39 ppm (o-DCBz)

[0761] Solvent: o-dichlorobenzene-d4

[0762] Sample concentration: 10wt / vol%

[0763] Sample tube: 5mmφ

[0764] Figure 12 of 1 H and 13 C-NMR measurement conditions are as follows.

[0765] ( 1 H-NMR measurement conditions)

[0766] Device: Bruker Avance NEO 600

[0767] Observation core: 1 H

[0768] Observation frequency: 600MHz

[0769] Pulse program: zg30

[0770] Pulse waiting time: 1sec

[0771] Cumulative times: 1024 times

[0772] Measurement temperature: 130°C

[0773] Chemical shift reference: 7.219 ppm (o-DCBz)

[0774] Solvent: o-dichlorobenzene-d4

[0775] Sample concentration: 1wt / vol%

[0776] Sample tube: 5mmφ

[0777] ( 13 C-NMR measurement conditions)

[0778] Device: Bruker Avance NEO 600

[0779] Observation core: 13 C

[0780] Observation frequency: 150.91MHz

[0781] Pulse program: zgpg30

[0782] Pulse waiting time: 5sec

[0783] Cumulative times: 12800 times

[0784] Measurement temperature: 130°C

[0785] Chemical shift reference: 132.39 ppm (o-DCBz)

[0786] Solvent: o-dichlorobenzene-d4

[0787] Sample concentration: 10wt / vol%

[0788] Sample tube: 5mmφ

[0789] Figure 13 It is used in Example I-1 described later. Figure 11 The separator made of the silane-modified polyolefin raw material 1 is in a state before cross-linking. 1 H and 13 C-NMR spectrum. Figure 13 of 1 H and 13 C-NMR measurement conditions are as follows.

[0790] ( 1 H-NMR measurement conditions)

[0791] Device: Bruker Avance NEO 600

[0792] Observation core: 1 H

[0793] Observation frequency: 600MHz

[0794] Pulse program: zg30

[0795] Pulse waiting time: 1sec

[0796] Cumulative times: 1024 times

[0797] Measurement temperature: 130°C

[0798] Chemical shift reference: 7.219 ppm (o-DCBz)

[0799] Solvent: o-dichlorobenzene-d4

[0800] Sample concentration: 1wt / vol%

[0801] Sample tube: 5mmφ

[0802] ( 13 C-NMR measurement conditions)

[0803] Device: Bruker Avance NEO 600

[0804] Observation core: 13 C

[0805] Observation frequency: 150.91MHz

[0806] Pulse program: zgpg30

[0807] Pulse waiting time: 5sec

[0808] Cumulative times: 24,000 or 12,800 times

[0809] Measurement temperature: 130°C

[0810] Chemical shift reference: 132.39 ppm (o-DCBz)

[0811] Solvent: o-dichlorobenzene-d4

[0812] Sample concentration: 10wt / vol%

[0813] Sample tube: 5mmφ

[0814] In addition, for the separator in the cross-linked state, after the pre-treatment described above, it can be Figure 13 The same NMR measurement was performed (not shown).

[0815] like Figures 11-13 As shown, through 1 H and / or 13 C NMR measurement can confirm the amount of silane unit modification in the silane-modified polyolefin, the amount of alkyl modification of the polyolefin, etc. in the polyolefin raw material, and can identify the content of (-CH 2 -Si: 1 H, 0.69ppm, t; 13 C, 6.11ppm,s).

[0816] [Combination of Microporous Membrane and Inorganic Porous Layer]

[0817] The combination of a microporous membrane comprising a silane-modified polyolefin and an inorganic porous layer has a tendency to take into account both the shutdown function at temperatures lower than 150°C and the membrane rupture property at higher temperatures, and to improve the cycle characteristics of the storage device and the safety of battery nail penetration. It is speculated that since the silane-modified polyolefin in the microporous membrane is silane cross-linked, if silane cross-linking occurs, the viscosity of the resin in the microporous membrane is sometimes increased. Therefore, when the storage device including the separator is abnormally high in temperature, if a compressive force is applied between the multiple electrodes, the cross-linked high-viscosity resin is difficult to flow into the inorganic layer (i.e., difficult to integrate), which can fully ensure the gap between the electrodes and suppress battery short circuits.

[0818] [Inorganic porous layer]

[0819] The inorganic porous layer is a layer containing inorganic particles and a resin binder, and may further contain a dispersant for dispersing the inorganic particles in the binder resin, if desired.

[0820] The thickness of the inorganic porous layer is preferably 0.5 μm to 10 μm, 0.5 μm to 7 μm, 0.5 μm to 5 μm, or 0.5 μm to 4 μm from the perspective of ion permeability of the separator and charge / discharge capacity or cycle stability of the power storage device. The thickness of the inorganic porous layer can be determined by the method described in the Examples.

[0821] [Second porous layer (layer B)]

[0822] Layer B contains inorganic particles. Layer B may further contain a resin binder. In the case where layer B contains inorganic particles and a resin binder, layer B may be the inorganic porous layer described above. It should be noted that layer B may contain components other than the inorganic particles and the resin binder.

[0823] (Thickness of layer B)

[0824] The thickness (TB) of the B layer is preferably 0.2 μm or more, more preferably 0.5 μm or more. If the thickness (TB) is 0.5 μm or more, there is a tendency for the mechanical strength to be further improved. On the other hand, the thickness (TB) is preferably less than 22 μm, more preferably less than 20 μm, and further preferably less than 15 μm. If the thickness (TB) is 30 μm or less, the volume occupied by the separator in the power storage device is reduced, so there is a tendency to be advantageous in terms of high capacity of the power storage device. In addition, it is also preferred from the perspective of preventing the air permeability of the separator from increasing excessively. It should be noted that the thickness (TB) can be set to, for example, 0.50 μm or more, 0.80 μm or more, or 1.00 μm or more, and can also be set to less than 22.00 μm, less than 20.00 μm, or less than 15.00 μm.

[0825] The thickness (TB) can be measured by the method described in the Examples section, and can also be controlled by changing the amount of coating liquid (slurry) applied for forming the B layer.

[0826] When the B layer is a single layer, the thickness of the B layer is regarded as the above-mentioned “thickness (TB)”. When the B layer is a multi-layer layer, the total thickness of the multi-layer B layer is regarded as the above-mentioned “thickness (TB)”.

[0827] When the B layer is disposed on both one side and the other side of the A layer, the total thickness of the B layer disposed on the one side and the B layer disposed on the other side is regarded as the above-mentioned "thickness (TB)".

[0828] (Inorganic particles)

[0829] Examples of the inorganic particles include: inorganic oxides (oxide-based ceramics) such as aluminum oxide (Al2O3), silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; inorganic nitrides (nitride-based ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide (AlO(OH)), potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and quartz sand; and glass fibers. These may be used alone or in combination of two or more.

[0830] The amount of the inorganic particles is preferably 5% by mass or more, or 20% by mass or more, and more preferably 30% by mass or more, based on the total amount of the inorganic porous layer or layer B, from the perspective of ensuring heat resistance. The amount of the inorganic particles can be set to 50% by mass or more, more than 80% by mass, or 85% by mass or more, based on the total amount of the inorganic porous layer or layer B. On the other hand, the amount of the inorganic particles is preferably 99.9% by mass or less, and more preferably 99.5% by mass or less, or 99% by mass or less.

[0831] The amount of the inorganic particles can be set to, for example, 20.00 mass % or more, 30.00 mass % or more, 50.00 mass % or more, more than 80.00 mass % or 85.00 mass % or more, and can be set to 99.90 mass % or less or 99.50 mass % or less.

[0832] Examples of the shape of the inorganic particles include flakes, scales, needles, columns, spheres, polyhedrons, spindles, and blocks. A plurality of inorganic particles having these shapes may be used in combination.

[0833] The number average particle size of the inorganic particles is, for example, more than 0.01 μm, more than 0.1 μm or more than 0.3 μm, preferably more than 0.5 μm. On the other hand, the number average particle size is, for example, less than 10.0 μm, less than 9.0 μm or less than 6.0 μm, preferably less than 2.5 μm, more preferably less than 2.0 μm, and further preferably less than 1.5 μm. From the perspective of improving safety during short circuit, the number average particle size of the inorganic particles is preferably adjusted to within the above range. As a method for adjusting the number average particle size of the inorganic particles, a method for crushing the inorganic particles using a suitable pulverizing device such as a ball mill, a bead mill, a jet mill, etc. can be listed.

[0834] Regarding the particle size distribution of the inorganic particles, the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 7 μm or less. In addition, the ratio of maximum particle size / average particle size is preferably 50 or less, more preferably 30 or less, and further preferably 20 or less. From the perspective of suppressing thermal shrinkage at high temperatures, it is preferred to adjust the particle size distribution of the inorganic particles to within the above range. In addition, there may be multiple particle size peaks between the maximum particle size and the minimum particle size. It should be noted that, as a method for adjusting the particle size distribution of the inorganic particles, for example, there can be listed: a method of crushing the inorganic filler using a ball mill, a bead mill, a jet mill, etc. and adjusting it to the desired particle size distribution, a method of mixing a plurality of fillers having multiple particle size distributions after preparing them, etc.

[0835] (resin binder)

[0836] The resin binder comprises a resin that binds the inorganic particles together. The glass transition temperature (Tg) of the resin binder is preferably -50°C to 100°C, more preferably -35°C to 95°C, from the perspective of ensuring adhesion to the inorganic particles and stability of the inorganic porous layer or layer B during the separator manufacturing process, the electricity storage device manufacturing process, or the charge and discharge process.

[0837] The glass transition temperature is determined based on the DSC curve obtained in differential scanning calorimetry (DSC). Specifically, the temperature of the intersection of the straight line obtained by extending the baseline of the low temperature side in the DSC curve to the high temperature side and the tangent line at the inflection point of the step-like change portion of the glass transition can be used as the glass transition temperature. In more detail, it can be determined according to the method described in the embodiment. In addition, "glass transition" refers to the heat change generated on the heat-absorbing side in the DSC, which is accompanied by the change in the state of the polymer as the test piece. This heat change is observed as a step-like change in the DSC curve. "Step-like change" means the part from the baseline of the previous low temperature side to the baseline moving to the new high temperature side in the DSC curve. It should be noted that the combination of step-like change and peak is also included in the step-like change. Furthermore, "inflection point" means the point at which the slope of the DSC curve of the step-like change portion reaches the maximum. In addition, at the step-like change portion, when the upper side is the heating side, it can also be expressed as the point at which the convex curve changes to the concave curve. The "peak" represents the portion of the DSC curve where the curve leaves the baseline on the low temperature side and returns to the same baseline. The "baseline" represents the DSC curve in the temperature range where the test piece does not undergo transformation or reaction.

[0838] Examples of the resin binder include the following 1) to 7) and these can be used alone or in combination of two or more.

[0839] 1) Polyolefins: such as polyethylene, polypropylene, ethylene propylene rubber and their modifications;

[0840] 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene-styrene copolymers and their hydrogenates;

[0841] 3) Acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;

[0842] 4) Polyvinyl alcohol resins: such as polyvinyl alcohol and polyvinyl acetate;

[0843] 5) Fluorine-containing resins: such as PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer;

[0844] 6) Cellulose derivatives: such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; and

[0845] 7) Resins having a melting point and / or glass transition temperature of 180°C or higher or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide and polyester.

[0846] These types of resin binders can be obtained by using desired monomers as raw materials according to known production methods such as emulsion polymerization or solution polymerization. In the polymerization, the polymerization temperature, the pressure during polymerization, the method of adding monomers, and the additives used (polymerization initiator, molecular weight modifier, pH adjuster, etc.) are not limited.

[0847] The amount of the resin binder is, for example, 0.5% by mass or more or 1.0% by mass or more, based on the total amount of the inorganic porous layer or layer B, and is, for example, 50% by mass or less or 30% by mass or less. Furthermore, as described above, the resin binder is an optional component of layer B, and thus the amount of the resin binder contained in layer B can be set to less than 20% by mass, less than 15% by mass, or 0% by mass, based on the total amount of layer B. Reducing the amount of the resin binder contained in layer B allows for a corresponding increase in the amount of the inorganic particles contained in layer B.

[0848] (Dispersant)

[0849] Dispersant is a material that is adsorbed on the surface of inorganic particles in the slurry for forming the inorganic porous layer or the B layer, and that stabilizes the inorganic particles by electrostatic rebound, etc., and can be, for example, a polycarboxylate, a sulfonate, a polyoxyether, a surfactant, etc. In the inorganic porous layer or the B layer, in addition to the above-mentioned components, within the scope of its effect, it can further contain other components that are usually added in water-based coatings, etc. As this other component, it is not particularly limited, and for example, thickener, film-forming aid, plasticizer, cross-linking agent, antifreeze, defoamer, dye, preservative, ultraviolet absorber, light stabilizer, etc. can be listed. These other components can be used alone or in combination of two or more.

[0850] (additive)

[0851] The microporous membrane, inorganic porous layer, layer A, and / or layer B may contain known additives as needed. Examples of these additives include: organic metal catalysts (dehydration condensation catalysts); plasticizers; antioxidants such as phenolic, phosphorus, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; thickeners; film-forming aids; crosslinking agents; antifreeze agents; defoaming agents; preservatives; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; dyes; and coloring pigments.

[0852] Furthermore, layer B may contain a crosslinking agent. The crosslinking agent may contain a reactive group with the inorganic particles.

[0853] <Physical Properties of Separators>

[0854] When the separator is used in a higher capacity lithium-ion secondary battery, the overall thickness of the separator is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, further preferably 18 μm or less, and particularly preferably 16 μm or less. By making the separator film thickness 25 μm or less, there is a tendency for ion permeability to be further improved. The lower limit of the overall separator film thickness can be, for example, 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, 6.0 μm or more, or 7.5 μm or more.

[0855] The air permeability of the separator is preferably 50 seconds / 100 cm 3 ~400 seconds / 100cm 3 , more preferably 75 seconds / 100cm 3 ~275 seconds / 100cm 3 , more preferably 100 sec / 100 cm 3 ~200 seconds / 100cm 3 If the separator is 50 seconds / 100cm 3 If the air permeability is above 400 seconds / 100cm, it has appropriate mechanical strength. 3 An air permeability below 500 nm is preferred because it improves battery characteristics from the perspective of permeability.

[0856] [Electricity Storage Device Assembly Kit]

[0857] Another aspect of the present invention provides an electric storage device assembly kit including the above-described separator for an electric storage device. The electric storage device assembly kit includes the following two elements:

[0858] (A) an outer case accommodating a laminate or a wound body of electrodes and the separator for a power storage device according to each embodiment described above; and

[0859] (B) A container containing a non-aqueous electrolyte.

[0860] When using the energy storage device assembly kit, a cross-linked structure is formed within the separator by bringing the separator in element (A) into contact with the non-aqueous electrolyte in element (B), bringing the electrolyte into contact with the stack or wound body within the outer casing, and / or by continuously subjecting the assembled energy storage device to charge and discharge cycles. This allows for a energy storage device that achieves both safety and output.

[0861] Although we do not wish to be bound by theory, it is believed that when the electrolyte or electrolyte solution contacts the electrode and / or when the storage device is charged or discharged, a substance that catalyzes the crosslinking reaction or a substance having a functional group that forms part of the crosslinking structure is present in the electrolyte solution, inside the outer shell, or on the surface of the electrode. These substances dissolve in the electrolyte solution, swell and diffuse uniformly into the amorphous portion of the polyolefin, thereby uniformly promoting the crosslinking reaction of the laminate or wound body containing the separator. The substance that catalyzes the crosslinking reaction can be in the form of an acid solution or a film. In the case where the electrolyte contains lithium hexafluorophosphate (LiPF6), it can be hydrogen fluoride (HF) or a fluorine-containing organic compound derived from hydrogen fluoride (HF). The substance having a functional group that forms part of the crosslinking structure can be, for example, a compound having functional groups A and / or B described above, the electrolyte solution itself, various additives, etc.

[0862] From the perspective of promoting the cross-linking reaction of the separator, the non-aqueous electrolyte contained in element (2) can be a fluorine (F)-containing lithium salt such as LiPF6 that produces HF, an electrolyte with non-shared electron pairs such as LiN(SO2CF3)2, LiSO3CF3, or LiBF4, LiBC4O8 (LiBOB), etc.

[0863] From the perspective of promoting the cross-linking reaction of the separator, the power storage device assembly kit may include, as an accessory (or element (C)), another container for storing a catalyst for promoting the cross-linking reaction, such as a mixture of an organic metal catalyst and water, an acid solution, an alkaline solution, etc.

[0864] [Electricity Storage Device]

[0865] The separator described above can be used in an electrical storage device. The electrical storage device comprises a positive electrode, a negative electrode, a separator of the present embodiment disposed between the positive and negative electrodes, an electrolyte, and additives as desired. Once the separator is housed in the device housing, the functional group-modified polyethylene or the functional group-grafted copolymer polyethylene reacts with the chemical substances contained in the electrolyte or the additives to form a cross-linked structure, thereby forming a cross-linked structure in the manufactured electrical storage device. The functional group-modified polyethylene or the functional group-grafted copolymer polyethylene is not limited and can be derived from a polyolefin raw material of the microporous membrane or from a polyolefin modified in the manufacturing process of the microporous membrane.

[0866] Specific examples of the power storage device 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-hydrogen batteries, nickel-cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, zinc-air batteries, etc. Among these, from the perspective of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-hydrogen batteries, or lithium ion capacitors are preferred, and lithium batteries or lithium ion secondary batteries are more preferred.

[0867] Examples of the additives include a dehydration condensation catalyst, metal soaps such as calcium stearate or zinc stearate, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and a coloring pigment.

[0868] [Lithium-ion secondary battery]

[0869] A lithium-ion secondary battery is a storage battery that uses a lithium transition metal oxide such as lithium cobalt oxide or lithium cobalt composite oxide as the positive electrode, a carbon material such as graphite or black lead as the negative electrode, and an organic solvent containing a lithium salt such as LiPF6 as the electrolyte. The electrolyte described above can also be used in lithium-ion secondary batteries in power storage device assembly kits.

[0870] During charge and discharge of a lithium-ion secondary battery, ionized lithium reciprocates between electrodes. Separators are placed between the electrodes to prevent contact between the electrodes while allowing the ionized lithium to move at a relatively high speed.

[0871] <Method for Manufacturing Separator for Electricity Storage Device>

[0872] Another embodiment of the present invention is a method for manufacturing a separator for a power storage device. The separator manufacturing method may include, for example, a step for manufacturing a microporous membrane or layer A, and, if desired, a step for manufacturing an inorganic porous layer on the microporous membrane, or a step for manufacturing layer B on layer A. Unless otherwise specified, the materials used in the separator manufacturing method may be those described in the first to tenth embodiments.

[0873] <Eleventh Embodiment>

[0874] The manufacturing method of the separator of the eleventh embodiment is described below for a microporous membrane (flat membrane), but it is not intended to exclude forms other than flat membranes. The manufacturing method of the microporous membrane of the eleventh embodiment includes the following steps:

[0875] (1) Sheet forming process;

[0876] (2) stretching process;

[0877] (3) a porous body forming step; and

[0878] (4) Heat treatment process.

[0879] By carrying out steps (1) to (4), the above-described layer A can also be formed.

[0880] The method for manufacturing the separator of the eleventh embodiment may further include the following steps in addition to steps (1) to (4) as desired:

[0881] (8B) a coating step of forming an inorganic porous layer comprising inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinking precursor;

[0882] (9) An assembling step of housing a laminate of the electrode and the silane crosslinking precursor or a wound body thereof, and a non-aqueous electrolyte in an outer shell, and bringing the silane crosslinking precursor into contact with the non-aqueous electrolyte.

[0883] In the eleventh embodiment, after the microporous membrane that maintains silane crosslinking properties is coated with an inorganic porous layer in step (8B), the separator in the storage device is brought into contact with the electrolyte in step (9), thereby improving the stress tolerance of the storage device and the separator therein, thereby enabling the cycle stability and safety of the storage device to be achieved.

[0884] The method for producing the microporous membrane of the eleventh embodiment may include, as desired, a kneading step before the sheet forming step (1) and / or a winding / slitting step after the heat treatment step (3). However, from the perspective of maintaining silane crosslinking until contact with the electrolyte, it is preferred not to include a silane crosslinking treatment step. The silane crosslinking treatment step is generally a step of contacting a treated object comprising a silane-modified polyolefin with a mixture containing an organometallic catalyst and water, or immersing the object in an alkaline solution or an acid solution to cause a silane dehydration condensation reaction to form oligosiloxane bonds.

[0885] The metal containing the organometallic catalyst can be, for example, at least one selected from the group consisting of scandium, titanium, vanadium, copper, zinc, aluminum, zirconium, palladium, gallium, tin and lead. Regarding containing organometallic catalysts, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, etc. can be listed, and it is known that these substances can overwhelmingly promote the reaction rate based on the reaction mechanism proposed by Weij et al. (FW van. der. Weij: Macromol. Chem., 181, 2541, 1980.). In addition, in recent years, in order to avoid the health hazards to the environment and human body caused by organotin, it is known that the Lewis function of the chelate complex of copper and / or titanium can be combined with an organic base to promote the reaction of the formation of siloxane bonds between the alkoxysilyl groups in the same manner as the organotin complex.

[0886] The alkaline solution has a pH exceeding 7 and may contain, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, amine compounds, etc. Among these, from the perspectives of safety of the power storage device and silane crosslinking, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0887] The pH of the acid solution is less than 7, and it may contain, for example, an inorganic acid, an organic acid, etc. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0888] The kneading step uses a kneader. In this embodiment, the silane-modified polyolefin, optionally a plasticizer, or an inorganic material, can be kneaded with other polyolefins. From the perspective of suppressing the formation of resin aggregates during the manufacturing process and maintaining silane crosslinking properties until contact with the electrolyte, it is preferable not to add a masterbatch resin containing a dehydration condensation catalyst to the kneaded product.

[0889] There are no particular limitations on the plasticizer, and examples include organic compounds that can form a uniform solution with polyolefins at a temperature below the boiling point. More specifically, examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, paraffin oil, etc. Among these, paraffin oil and dioctyl phthalate are preferred. One type of plasticizer can be used alone, or two or more types can be used in combination. The proportion of the plasticizer is not particularly limited. From the perspective of the porosity of the resulting microporous membrane, the proportion of the polyolefin and silane-modified polyolefin, as needed, relative to the total mass, is preferably 20% by mass or more, and from the perspective of the viscosity during melt mixing, it is preferably 90% by mass or less.

[0890] The sheet forming step is a step of extruding the resulting kneaded product, or a mixture of the silane-grafted modified polyolefin, polyethylene, and plasticizer, cooling and solidifying it, and then forming it into a sheet to obtain a sheet. The sheet forming method is not particularly limited, and examples thereof include methods of solidifying the melted, kneaded, and extruded melt by compression cooling. Examples of cooling methods include methods of direct contact with a cooling medium such as cold air or cooling water, and methods of contact with a refrigerant-cooled roller and / or press. The method of contact with a refrigerant-cooled roller and / or press is preferred due to its excellent film thickness controllability.

[0891] From the perspective of resin agglomerates in the separator or the maximum internal heating rate, in the sheet forming process, the mass ratio of silane-modified polyolefin to polyethylene (mass of silane-modified polyolefin / mass of polyethylene) is preferably 0.05 / 0.95 to 0.4 / 0.6, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0892] From the perspective of suppressing thermal runaway during destruction of the storage device while having low-temperature shutdown properties below 150°C and resistance to film rupture at high temperatures of 180-220°C and improving safety, it is preferred that the silane-modified polyolefin in the sheet forming process is not a masterbatch resin containing a dehydration condensation catalyst for cross-linking the silane-modified polyolefin before the sheet forming process.

[0893] The stretching process is a process of extracting plasticizers and / or inorganic materials from the resulting sheet as needed and further stretching the sheet in one or more directions. Examples of sheet stretching methods include: MD uniaxial stretching using a roller stretcher, TD uniaxial stretching using a stenter, sequential biaxial stretching using a roller stretcher and a stenter or a combination of a stenter and a stenter, and simultaneous biaxial stretching using a simultaneous biaxial stenter or inflation molding. From the perspective of obtaining a more uniform film, simultaneous biaxial stretching is preferred. From the perspective of achieving uniformity in film thickness, tensile elongation, porosity, and average pore size, the total surface ratio is preferably 8 times or more, more preferably 15 times or more, and even more preferably 20 times or more or 30 times or more. By making the total surface ratio 8 times or more, there is a tendency to easily obtain sheets with high strength and good thickness distribution. In addition, from the perspective of preventing fracture, the surface ratio can be 250 times or less.

[0894] The porous body forming process is a process of extracting the plasticizer from the stretched product after the stretching process and making the stretched product porous. There is no particular limitation on the method for extracting the plasticizer, and examples thereof include: a method of immersing the stretched product in an extraction solvent, a method of spraying the stretched product with an extraction solvent, etc. There is no particular limitation on the extraction solvent, and examples thereof include: a solvent that is a poor solvent for polyolefins and a good solvent for plasticizers and / or inorganic materials, and has a boiling point lower than the melting point of polyolefins. There is no particular limitation on such an extraction solvent, and examples thereof include: hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropyl alcohol; ketones such as acetone and 2-butanone; alkaline water, etc. One type of extraction solvent may be used alone, or two or more types may be used in combination.

[0895] The heat treatment process is to extract plasticizer from the sheet as needed after the stretching process, further heat-treat and obtain the process of microporous membrane.As the method for heat treatment, it is not particularly limited, for example, the heat setting method utilizing stenter and / or roller stretching machine to stretch and relax operation etc. can be listed. Relaxation operation refers to the shrinking operation carried out with specified temperature and relaxation rate along the machine direction (MD) and / or width direction (TD) of film. Relaxation rate refers to the value obtained by dividing the MD size of the film before the operation with the MD size of the film after the relaxation operation, or the value obtained by dividing the TD size of the film before the operation with the TD size after the relaxation operation, or when relaxing along MD and TD both sides, refers to the value obtained by multiplying the relaxation rate of MD by the relaxation rate of TD.

[0896] [Inorganic porous layer coating step]

[0897] The inorganic porous layer coating step (8B) is a step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the microporous membrane obtained above. The coating step (8B) can be performed while maintaining the silane crosslinking property of the silane-modified polyolefin.

[0898] The above-described layer B can also be formed by performing the coating step (8B). As a method for forming the layer B, a known manufacturing method can be adopted. As a method for producing a laminate comprising the layer A and the layer B, for example, there can be cited: a method of applying a slurry containing inorganic particles to the layer A, a method of laminating the raw materials of the layer B and the raw materials of the layer A by co-extrusion, a method of laminating the layers A and B after separately producing them, etc.

[0899] The inorganic porous layer can be formed, for example, by applying a slurry containing inorganic particles, a resin binder, water or an aqueous solvent (e.g., a mixture of water and alcohol), and an optional dispersant to at least one surface of the microporous membrane. The inorganic particles, resin binder, and dispersant can be as described in the first to tenth embodiments.

[0900] The solvent contained in the slurry is preferably one that can uniformly and stably disperse or dissolve the inorganic particles. Examples of such solvents include N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, dichloromethane, and hexane.

[0901] Examples of methods for preparing the slurry containing inorganic particles include mechanical stirring methods using a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roller mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a stirring blade.

[0902] Examples of the coating method for the slurry containing inorganic particles include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air knife coater method, doctor blade coater method, rod coater method, extrusion coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0903] Methods for removing the solvent from the coating film include drying at a temperature below the melting point of the material constituting the microporous membrane, drying under reduced pressure at low temperature, etc. In addition, a portion of the solvent may remain as long as it does not significantly affect the device characteristics.

[0904] [Winding / Slitting Process]

[0905] The winding step is a step of slitting the obtained microporous membrane or the microporous membrane coated with the inorganic porous layer as needed and winding the resulting membrane around a predetermined core.

[0906] [Electricity Storage Device Assembly Process]

[0907] The power storage device assembly process is a process that includes laminating a separator precursor (hereinafter referred to as a silane crosslinking precursor) that maintains silane crosslinkability with an electrode to form a laminate, further winding the laminate to form a wound body as desired, and housing the laminate or wound body and a non-aqueous electrolyte in an outer shell, so that the silane crosslinking precursor and the non-aqueous electrolyte are in contact. The power storage device assembly process can suppress film loss of the microporous membrane, maintain its morphology, and inhibit the infiltration of polyolefin resin from the microporous membrane into the inorganic porous layer, thereby improving the stress tolerance of the power storage device or separator.

[0908] The silane-modified polyolefin is cross-linked during or after the electricity storage device assembly step (9), thereby being compatible with existing electricity storage device manufacturing processes and inducing a silane cross-linking reaction of the separator after the electricity storage device is manufactured, thereby improving the safety of the electricity storage device.

[0909] In the assembly process of the power storage device, from the perspective of electrolyte handling, it is preferred to place the stack or wound body in the outer shell and then inject the non-aqueous electrolyte into the outer shell, or to inject the electrolyte into the outer shell and then place the stack or wound body in the outer shell.

[0910] From the perspective of promoting the cross-linking reaction of the separator, the electrolyte of the non-aqueous electrolyte can be a fluorine (F)-containing lithium salt such as LiPF6 that produces hydrogen fluoride (HF), an electrolyte with non-shared electron pairs such as LiN(SO2CF3)2, LiSO3CF3, or LiBF4, LiBC4O8 (LiBOB), etc.

[0911] Although we do not wish to be bound by theory, it is presumed that the methoxysilane grafted portion is converted into silanol by the trace amount of water contained in the storage device (water contained in components such as the electrodes, separators, and electrolyte), undergoes a cross-linking reaction, and changes into a siloxane bond. In addition, it is believed that once the electrolyte or electrolyte comes into contact with the electrode, a substance that catalyzes the silane cross-linking reaction is generated in the electrolyte or on the electrode surface. These substances dissolve in the electrolyte and evenly swell and diffuse into the amorphous part of the polyolefin in which the silane-modified grafted portion is present, thereby uniformly promoting the cross-linking reaction of the laminate or wound body containing the separator. The substance that catalyzes the silane cross-linking reaction can be in the form of an acid solution or a film. In the case where the electrolyte contains lithium hexafluorophosphate (LiPF6), it can be HF generated by the reaction of LiPF6 with water, or a fluorine-containing organic substance derived from HF.

[0912] From the perspective of the efficiency of the silane cross-linking reaction, it is preferred that, after the stack or wound body and the non-aqueous electrolyte are housed within the outer casing of the electrical storage device, lead terminals are connected to the electrodes and at least one cycle of charge and discharge is performed. It is believed that through the charge and discharge cycles, a substance that catalyzes the silane cross-linking reaction is generated in the electrolyte or on the electrode surface, thereby achieving the silane cross-linking reaction. The cyclic charge and discharge can be carried out by known methods and apparatus, specifically the methods described in the Examples.

[0913] [Method for Manufacturing Electricity Storage Device]

[0914] Another embodiment of the present invention is a method for manufacturing a power storage device.

[0915] <Twelfth embodiment>

[0916] The method for manufacturing the power storage device according to the twelfth embodiment includes the following steps:

[0917] (1) a step of preparing the above-described power storage device assembly kit;

[0918] (II) a step of initiating a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator in the element (1) of the electricity storage device assembly kit into contact with the non-aqueous electrolyte in the element (2);

[0919] (III) a step of connecting a lead terminal to the electrode of element (1) as desired; and

[0920] (IV) If desired, a step of performing at least one cycle of charge and discharge.

[0921] In addition to using the separator for the storage device of this embodiment, steps (I) to (IV) can be carried out by methods known in the technical field. In addition, in steps (I) to (IV), positive electrodes, negative electrodes, electrolytes, outer shells and charging and discharging devices known in the technical field can be used.

[0922] For step (I), a longitudinal separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be manufactured. Next, in step (I), the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator can be stacked in the order of positive electrode-separator-negative electrode-separator, and wound into a circular or flat spiral to obtain a wound body. In steps (II) and (III), the wound body is placed in a device can (such as a battery can) and further injected with a non-aqueous electrolyte to manufacture a power storage device. In addition, the power storage device can also be manufactured by placing a wound body made by folding the electrodes and separators into a device container (such as an aluminum film) and injecting a non-aqueous electrolyte.

[0923] At this time, the wound body may be pressed. Specifically, a separator and an electrode including a current collector and an active material layer formed on at least one surface of the current collector may be stacked and pressed.

[0924] Regarding the pressing temperature, as a temperature at which adhesion can be effectively exhibited, for example, it is preferably 20°C or higher. In addition, from the perspective of suppressing clogging or thermal shrinkage of the pores in the separator caused by hot pressing, the pressing temperature is preferably lower than the melting point of the material contained in the microporous membrane, and more preferably 120°C or lower. From the perspective of suppressing clogging of the pores in the separator, the pressing pressure is preferably 20 MPa or lower. Regarding the pressing time, when using roller pressing, it can be less than 1 second or several hours of surface pressure. From the perspective of productivity, it is preferably 2 hours or less.

[0925] The above-described manufacturing process can suppress the back pressure during the press-forming of the wound body composed of electrodes and separators, thereby suppressing the reduction in yield during the device assembly process and shortening the production process time, which is preferable.

[0926] From the perspective of reliably performing the silane crosslinking reaction of the separator after step (II), it is preferred to perform steps (III) and (IV). It is believed that through the charge and discharge cycle, a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte or on the electrode surface, thereby achieving the silane crosslinking reaction.

[0927] For example, in the manufacturing method of the separator, when the manufacturing method of the A layer described above does not include a silane cross-linking treatment process, the cross-linking reaction can be actively promoted by bringing the separator into contact with a non-aqueous electrolyte. Although it is not desired to be constrained theoretically, it is presumed that the silane-modified grafted portion is converted into silanol due to the trace amount of water contained in the storage device (water slightly contained in the electrode, separator, non-aqueous electrolyte, etc.), undergoes a cross-linking reaction, and changes into a siloxane bond. In addition, it is believed that once the non-aqueous electrolyte contacts the electrode, a substance that catalyzes the silane cross-linking reaction is generated in the non-aqueous electrolyte or on the surface of the electrode. It is believed that this substance that catalyzes the silane cross-linking reaction dissolves in the non-aqueous electrolyte, uniformly swells and diffuses into the amorphous part of the polyolefin in which the silane-modified grafted portion exists, thereby uniformly promoting the cross-linking reaction of the laminate or wound body containing the separator.

[0928] The substance that catalyzes the silane crosslinking reaction can be in the form of an acid solution or a film. When the electrolyte contains lithium hexafluorophosphate (LiPF6), hydrogen fluoride (HF) or fluorinated organic compounds derived from hydrogen fluoride (HF) generated by the reaction of LiPF6 with water are considered substances that catalyze the silane crosslinking reaction (compounds generated within the battery device).

[0929] <Thirteenth embodiment>

[0930] The thirteenth embodiment is a method for producing a power storage device using a separator containing a polyolefin having one or more functional groups, and includes the following steps:

[0931] The crosslinking step is to form a crosslinked structure by (1) causing a condensation reaction between functional groups, (2) causing the functional groups to react with chemical substances inside the power storage device, or (3) causing the functional groups of the polyolefin to react with other types of functional groups.

[0932] The cross-linking step can be carried out in the same manner as the reaction for forming the cross-linked structure of the separator described above. Furthermore, since the cross-linking step can be carried out using the compounds within the power storage device and the environment surrounding the device, it does not require excessive conditions such as electron beams or high temperatures exceeding 100°C. Mild conditions such as temperatures of 5°C to 90°C and / or ambient atmosphere can be employed.

[0933] By performing a cross-linking step in the manufacturing process of the storage device, the formation of the cross-linking structure can be omitted during the film-forming process of the separator or immediately after it is completed, and the stress and strain after the storage device is manufactured can be relaxed or eliminated, and / or the separator can be given a cross-linking structure even without using higher energies such as light irradiation or heating, thereby reducing uneven cross-linking, the generation of unmelted resin agglomerates, and the burden on the environment.

[0934] In the cross-linking process, by (2) reacting the functional groups with chemical substances inside the storage device, or (3) reacting the functional groups of the polyolefin with functional groups of other types, 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), thereby improving the strength between the multiple components of the storage device.

[0935] The separator described above is compatible with existing electricity storage device manufacturing processes because the silane-modified polyolefin undergoes crosslinking when in contact with the electrolyte. The silane crosslinking reaction can be initiated after the electricity storage device is manufactured, thereby improving the safety of the electricity storage device.

[0936] Example

[0937] The present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples unless it exceeds the scope of the present invention. It should be noted that the physical properties in the Examples were measured by the following methods.

[0938] <Weight Average Molecular Weight>

[0939] Using ALC / GPC 150C (trademark) manufactured by Waters, standard polystyrene was measured under the following conditions to create a calibration curve. Chromatograms were also measured under the same conditions for each of the following polymers, and the weight average molecular weight of each polymer was calculated based on the calibration curve according to the following method.

[0940] Chromatography columns: 2 GMH6-HT (trademark) + 2 GMH6-HTL (trademark) manufactured by Tosoh Corporation

[0941] Mobile phase: o-dichlorobenzene

[0942] Detector: Differential refractometer

[0943] Flow rate: 1.0ml / min

[0944] Column temperature: 140°C

[0945] Sample concentration: 0.1wt%

[0946] (Weight average molecular weight of polyethylene)

[0947] The weight average molecular weight was calculated by multiplying each molecular weight component in the obtained calibration curve by 0.43 (Q factor of polyethylene / Q factor of polystyrene=17.7 / 41.3) to obtain a polyethylene-equivalent molecular weight distribution curve.

[0948] (Weight average molecular weight of resin composition)

[0949] The weight average molecular weight was calculated in the same manner as in the case of polyethylene, except that the Q factor value of the polyolefin having the largest mass fraction was used.

[0950] <Viscosity Average Molecular Weight (Mv)>

[0951] The intrinsic viscosity [η] at 135° C. in a decalin solvent was determined based on ASTM-D4020. The Mv of the polyethylene was calculated according to the following formula.

[0952] [η] = 6.77 × 10 -4 Mv 0.67

[0953] <Melt Flow Rate (MFR) (g / 10min)>

[0954] The weight of the resin extruded for 10 minutes at 190° C. and a load of 2.16 kg was determined as the MFR value using a melt flow rate meter (MELT INDEXER F-F01) manufactured by Toyo Seiki Co., Ltd.

[0955] <Determination of Glass Transition Temperature>

[0956] An appropriate amount of an aqueous dispersion containing a resin sample (solids content = 38-42 wt%, pH = 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes to obtain a dry film. Approximately 17 mg of this dry film was placed in an aluminum container for measurement, and DSC curves under a nitrogen atmosphere and DSC curves were obtained using a DSC analyzer (Shimadzu Corporation, Model "DSC6220"). The measurement conditions were as follows.

[0957] The first heating program: Start from 70℃ and increase the temperature at a rate of 15℃ per minute. After reaching 110℃, maintain it for 5 minutes.

[0958] Second cooling program: Start from 110℃ and cool down at a rate of 40℃ per minute. After reaching -50℃, maintain for 5 minutes.

[0959] The third temperature increase program was to increase the temperature from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third temperature increase.

[0960] The intersection of the base line (a straight line obtained by extending the base line in the obtained DSC curve toward the high temperature side) and the tangent line at the inflection point (the point where the upward convex curve changes to a downward convex curve) is defined as the glass transition temperature (Tg).

[0961] <Film Thickness (μm)>

[0962] Using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, Ltd., the film thickness of the microporous membrane or the separator is measured at a room temperature of 23 ± 2°C and a relative humidity of 60%. Specifically, the film thickness at 5 points is measured at substantially equal intervals along the entire width in the TD direction, and the average value thereof is obtained. The thickness of the inorganic porous layer can be calculated by subtracting the thickness of the microporous membrane from the thickness of the separator composed of the microporous membrane and the inorganic porous layer.

[0963] <The thickness of layer A (TA) and the thickness of layer B (TB)>

[0964] Using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, Ltd., the thickness of layer A (TA) is measured at a room temperature of 23 ± 2°C and a relative humidity of 60%. Specifically, the film thickness at 5 points is measured at substantially equal intervals along the entire width in the TD direction, and the average value thereof is obtained. In addition, by the same method, the thickness of the laminate including layer A and layer B is obtained. Then, the thickness of layer B (TB) is obtained by subtracting the thickness of layer A (TA) from the thickness of the obtained laminate.

[0965] The thickness of the obtained laminate is regarded as the total thickness of layer A and layer B (TA + TB). In addition, by dividing the thickness (TA) by the thickness (TB), the thickness ratio (TA / TB) is obtained.

[0966] <Porosity (%)>[[ID= thirteen]]

[0967] (i) Calculated based on the density of the mixed composition

[0968] A 10 cm × 10 cm square sample is cut from the microporous membrane, and its volume (cm 3 ) and mass (g) are obtained. Based on these and the density (g / cm 3 ), the porosity is calculated using the following formula. Note that the density of the mixed composition is a value calculated and obtained based on the respective densities and mixing ratios of the raw materials used.

[0969] Porosity (%) = (Volume - Mass / Density of mixed composition) / Volume × 100

[0970] (ii) Calculated based on the film density

[0971] Alternatively, the porosity of the microporous membrane is calculated from the volume, mass, and film density (g / cm 3 ) using the following formula.

[0972] Porosity (%) = (Volume - Mass / Film density) / Volume × 100

[0973] Note that in the present invention, the film density refers to the value measured by the D) density gradient tube method described in JIS K7112 (1999).

[0974] (iii) Porosity of Layer A

[0975] Cut a 10 cm × 10 cm square sample from Layer A, and find its volume (cm 3 ) and mass (g). Based on these and density (g / cm 3 ), use the following formula to calculate the porosity. The density of the mixed composition is the value calculated and obtained based on the respective densities and mixing ratios of the raw materials used.

[0976] Porosity (%) = (Volume - Mass / Density of the mixed composition) / Volume × 100

[0977] <Air permeability (sec / 100 cm 3 )>

[0978] According to JIS P - 8117 (2009), use a GURLEY type air permeability meter, G - B2 (trademark) manufactured by Toyo Seiki Co., Ltd. to measure the air permeability of the sample or Layer A.

[0979] <Puncture strength of Layer A>

[0980] Use a hand - held compression tester KES - G5 (model) manufactured by KATO TECH Co., Ltd. Fix Layer A with a sample holder having a diameter of 11.3 mm at the opening. Then, for the central part of the fixed Layer A, use a needle with a tip curvature radius of 0.5 mm, and perform a puncture test at a puncture speed of 2 mm / second in an atmosphere of 25°C to measure the maximum puncture load. Convert this maximum puncture load to a value equivalent to a thickness of 20 μm, and use this value as the puncture strength (gf / 20 μm). In the case where the thermoplastic polymer exists only on one side of the substrate, the needle can be punctured from the side where the thermoplastic polymer exists.

[0981] <Quantification of resin condensates in the separator>

[0982] The resin condensates in the separator are defined as regions that are opaque and have an area of 100 μm in length × 100 μm in width or more when observing the separator obtained through the film - forming process of the following Examples and Comparative Examples using a transmission - type optical microscope. In the observation based on the transmission - type optical microscope, measure the number of resin condensates per 1000 m 2 separator area.

[0983] <Storage modulus, loss modulus and transition temperature (version 1)>

[0984] The dynamic viscoelasticity of the separator is measured using a dynamic viscoelasticity measuring device. The storage modulus (E'), loss modulus (E"), and the transition temperature between the rubbery flat region and the crystalline melt flow region can be calculated. The storage modulus change ratio (R ΔE’ ) According to the following formula (1), the mixed storage modulus ratio (R E’mix ) According to the following formula (2), the loss modulus change ratio (R ΔE” ) According to the following formula (3), the mixed loss modulus ratio (R E”mix ) were calculated according to the following formula (4). It should be noted that the measurement conditions are as follows (i) to (iv).

[0985] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[0986] Atmosphere: Nitrogen

[0987] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[0988] Sample film thickness: 5μm to 50μm

[0989] Measuring temperature range: -50~225℃

[0990] Heating rate: 10℃ / min

[0991] Measurement frequency: 1 Hz

[0992] Deformation mode: Sine wave stretching mode (Linear tension)

[0993] Initial value of static tensile load: 0.5N

[0994] Initial gap distance (at 25°C): 25mm

[0995] Automatic strain adjustment: Enabled (range: amplitude 0.05-25%, sine wave load 0.02-5N).

[0996] (ii) The static tensile load refers to the median value between the maximum stress and the minimum stress under each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load.

[0997] (iii) Sine wave tension mode measures vibration stress while performing periodic motion at a fixed amplitude of 0.2%. In this mode, the gap distance and static tensile load are varied to maintain the difference between the static tensile load and the sinusoidal load within 20%. For sinusoidal loads below 0.02 N, the amplitude is increased to maintain the amplitude within 25% while maintaining the load within 5 N.

[0998] (iv) Calculate the storage modulus and loss modulus based on the relationship between the obtained sinusoidal wave load and amplitude and the following formula:

[0999] σ * =σ0·Exp[i(ωt+δ)],

[1000] ε * =ε0·Exp(iωt),

[1001] σ * =E * ·ε *

[1002] E * =E'+iE"

[1003] {where, σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[1004] Vibration stress: Sine wave load / initial cross-sectional area

[1005] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[1006] Sine wave load: The difference between the measured vibration stress and the static tensile load.

[1007] E' S and E' j and E” S and E” j The average value of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelasticity measurement data is used. a and E'0 and E" a The average value of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelasticity measurement data is used as E"0.

[1008] R ΔE’ =E'S / E' j (1) Comparison before and after battery installation

[1009] R E’mix =E' a / E'0 (2) Comparison of with and without silane crosslinking

[1010] R ΔE” =E” S / E” j (3) Comparison before and after battery installation

[1011] R E”mix =E” a / E”0 (4) Comparison of with and without silane crosslinking

[1012] An example of a graph for explaining the relationship between temperature and storage modulus is shown in Figure 1 .like Figure 1 As shown in FIG, the storage modulus of the standard film (separator for storage device without silane-modified polyolefin) and the cross-linked film in the temperature range of -50°C to 225°C can be compared. Figure 1 The transition temperature between the rubbery flat region and the crystalline melt flow region is determined in the figure. The transition temperature is the temperature at the intersection of a straight line extending the high temperature side baseline toward the low temperature side and a tangent line drawn at the inflection point of the curve of the crystalline melt change portion.

[1013] An example of a graph for explaining the relationship between temperature and loss modulus is shown in Figure 2 . Figure 2 The loss modulus of the standard film (separator for storage device without silane-modified polyolefin) and the cross-linked film in the temperature range of -50℃ to 220℃ is compared. Figure 1 The same method is used to determine the transition temperature. In this technical field, the storage modulus and loss modulus can be interchanged according to the following formula:

[1014] tanδ=E” / E'

[1015] {wherein, tanδ represents the loss tangent, E' represents the storage modulus, and E" represents the loss modulus.}

[1016] It should be noted that the mixed storage modulus ratio (R E’mix ) or mixed loss modulus ratio (R E”mix ) was measured, as a separator for a power storage device containing no silane-modified polyolefin, a microporous membrane made of a silane-unmodified polyolefin having a gelation degree of approximately 0% was used. a ,E'0,E” aWhen no sample fracture (sudden decrease in elastic modulus) was observed at 160°C to 220°C, the average value of the temperature at 160°C to 220°C was used for calculation. When the sample fractured at 160°C to 220°C, the average value of the temperature from 160°C to the fracture point was used for calculation. For example, Figure 1 and 2 The standard film shown breaks down at 207°C.

[1017] <Storage modulus, loss modulus, and transition temperature (version 2)>

[1018] The dynamic viscoelasticity of the separator is measured using a dynamic viscoelasticity measuring device, and the storage modulus (E'), loss modulus (E"), and the transition temperature between the rubbery flat region and the crystalline melt flow region can be calculated. The storage modulus change ratio (R ΔE’X ) According to the following formula (1), the mixed storage modulus ratio (R E’mix ) According to the following formula (2), the mixed loss modulus ratio (R E”X ) According to the following formula (3), the mixed loss modulus ratio (R E”mix ) were calculated according to the following formula (4). It should be noted that the measurement conditions were an RSA-G2 dynamic viscoelasticity measuring apparatus manufactured by TA Instruments, with a measurement frequency of 1 Hz, a strain of 0.2%, and a temperature range of -50°C to 310°C under a nitrogen atmosphere. Other conditions were determined according to version 1 above. Storage modulus and loss modulus E' Z and E' Z0 and E” Z and E” Z0 The average value of each storage modulus or each loss modulus at 160°C to 300°C in the dynamic viscoelasticity measurement data is used. E' and E'0 as well as E" and E"0 are the average values ​​of each storage modulus or each loss modulus at 160°C to 300°C in the dynamic viscoelasticity measurement data.

[1019] R ΔE’X =E' Z / E' Z0 (1) Comparison before and after battery installation

[1020] R E’mix =E' / E'0 (2) Comparison of the presence and absence of amorphous cross-linked structure

[1021] R E”X =E” Z / E” Z0 (3) Comparison before and after battery installation

[1022] R E”mix=E” / E”0 (4) Comparison of the presence and absence of cross-linked structure in the amorphous part

[1023] An example of a graph for explaining the relationship between temperature and storage modulus is shown in Figure 9 .like Figure 9 As shown in the figure, the storage modulus of the standard film (separator for storage device without amorphous cross-linked structure) and the cross-linked film in the temperature range of -50℃ to 310℃ can be compared. Figure 9 The transition temperature between the rubbery flat region and the crystalline melt flow region is determined in the figure. The transition temperature is the temperature at the intersection of a straight line extending the high temperature side baseline toward the low temperature side and a tangent line drawn at the inflection point of the curve of the crystalline melt change portion.

[1024] An example of a graph for explaining the relationship between temperature and loss modulus is shown in Figure 10 .exist Figure 10 The loss modulus of the standard film (separator for storage device without silane-modified polyolefin) and the cross-linked film in the temperature range of -50℃ to 310℃ is compared. Figure 9 The same method is used to determine the transition temperature. In this technical field, the storage modulus and loss modulus can be interchanged according to the following formula:

[1025] tanδ=E” / E'

[1026] {wherein, tanδ represents the loss tangent, E' represents the storage modulus, and E" represents the loss modulus.}

[1027] It should be noted that the mixed storage modulus ratio (R E’mix ) or mixed loss modulus ratio (R E”mix ) in the measurement, a polyolefin microporous membrane having a gelation degree of approximately 0% was used as a separator for a storage device having no amorphous crosslinked structure. In addition, regarding E', E'0, E" and E"0, when no fracture of the sample was observed at 160°C to 300°C (a sharp decrease in the elastic modulus), the values ​​were calculated based on the average value of the temperature at 160°C to 300°C. When fracture of the sample occurred at 160°C to 300°C, the values ​​were calculated based on the average value of the temperature from 160°C to the fracture point. For example, Tables 11 and 12 and Figure 9 and Figure 10 The standard film shown breaks at 210°C.

[1028] In this specification, a separator for a power storage device that does not have an amorphous crosslinked structure may be a separator made of any one selected from the group consisting of polyethylene: X (viscosity average molecular weight 100,000 to 400,000), PE: Y (viscosity average molecular weight 400,000 to 800,000), and PE: Z (viscosity average molecular weight 800,000 to 9,000,000), or a mixture of two or three selected from the group consisting of X, Y, and Z in any proportion. It should be noted that polyolefins composed solely of a hydrocarbon backbone, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and olefin-based thermoplastic elastomers, may be added to the mixed composition. More specifically, a separator for a power storage device that does not have an amorphous crosslinked structure may be a polyolefin microporous membrane having a solid content change rate (hereinafter referred to as "gelation degree") of 10% or less before and after heating in a decalin solution at 160°C. It should be noted that when measuring the gelation degree, the solid content refers only to the resin and does not include other materials such as inorganic substances.

[1029] On the other hand, the degree of gelation of the polyolefin microporous membrane having an amorphous portion crosslinked structure such as a silane crosslinked structure is preferably 30% or more, more preferably 70% or more.

[1030] <Storage modulus, loss modulus, film softening transition temperature, and film rupture temperature (version 3)>

[1031] The solid viscoelasticity of the separator is measured using a dynamic viscoelasticity measuring apparatus to calculate the storage modulus (E'), loss modulus (E"), and film softening transition temperature. The solid viscoelasticity measurement conditions are as follows (i) to (iv).

[1032] (i) Dynamic viscoelasticity measurements were performed under the following conditions:

[1033] · Measurement device used: RSA-G2 (manufactured by TA Instruments)

[1034] Sample thickness: 200 μm to 400 μm (If the thickness of a single sample is less than 200 μm, multiple samples are stacked to a total thickness within the range of 200 μm to 400 μm for dynamic viscoelasticity measurement.)

[1035] ·Measurement temperature range: -50℃~250℃

[1036] Heating rate: 10℃ / min

[1037] Measuring frequency: 1Hz

[1038] Deformation mode: Sine wave stretching mode (Linear tension)

[1039] Initial value of static tensile load: 0.2N

[1040] Initial gap distance (at 25°C): 10mm

[1041] Automatic strain adjustment: Disabled.

[1042] (ii) static tensile load refers to the midpoint between the maximum stress and the minimum stress under each period of motion, and sinusoidal load refers to the oscillating stress centered on the static tensile load;

[1043] (iii) Sine wave tensile mode refers to measuring vibration stress while performing periodic motion with a fixed amplitude of 0.1%. In the sine wave tensile mode, the vibration stress is measured by changing the gap distance and the static tensile load so that the difference between the static tensile load and the sine wave load is within 5%. When the sine wave load is less than 0.1N, the static tensile load is fixed at 0.1N to measure the vibration stress.

[1044] (iv) Calculate the storage modulus (E') and loss modulus (E") based on the relationship between the obtained sinusoidal wave load and amplitude value and the following formula:

[1045] σ * =σ0·Exp[i(ωt+δ)],

[1046] ε * =ε0·Exp(iωt),

[1047] σ * =E * ·ε *

[1048] E * =E'+iE"

[1049] {where, σ * :Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : complex modulus, E': storage modulus, E': loss modulus

[1050] Vibration stress: Sine wave load / initial cross-sectional area

[1051] Static tensile load: The load at the minimum point of vibration stress in each cycle (the minimum point of gap distance in each cycle)

[1052] Sine wave load: The difference between the measured vibration stress and the static tensile load.

[1053] In addition, the average of the maximum value and the minimum value of E’ is calculated and denoted as average E’ (E’ ave ), and the average of the maximum value and the minimum value of E” is calculated and denoted as average E” (E” ave ).

[1054] It should be noted that E’ and E” calculate the maximum value and the minimum value of each storage modulus or each loss modulus at -50°C to 250°C in the dynamic viscoelasticity measurement data. More specifically, when no fracture (sharp decrease in elastic modulus) of the sample is observed at -50°C to 250°C, the maximum value and the minimum value at -50°C to 250°C are calculated, and the value at the temperature where the fracture of the sample occurs at -50°C to 250°C is taken as the minimum value. In addition, in the technical field, the storage modulus and the loss modulus can be interchanged according to the following formula:

[1055] tanδ = E” / E’

[1056] {In the formula, tanδ represents the loss tangent, E’ represents the storage modulus, and E” represents the loss modulus.}.

[1057] The film softening transition point temperature is the temperature of the minimum value obtained by taking the first derivative of the curve of the sample gap distance in the dynamic viscoelasticity measurement data. In addition, the film fracture temperature is the temperature at which the fracture (sharp decrease in elastic modulus) of the sample is observed in the dynamic viscoelasticity measurement data. From the perspective of the thermal decomposition reaction of the polyolefin resin, the measurement limit temperature is sometimes set at 250°C. However, the phenomenon can also be understood in the same way through measurement at a high temperature above 250°C. Therefore, in this embodiment, a separator for a power storage device with a film fracture temperature of 180°C or higher can be implemented.

[1058] <Film rupture temperature of layer A>

[1059] Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, the environmental temperature is changed between 25 and 250°C, and the temperature at the moment when the load is completely released is determined as the TMA film rupture temperature (the film rupture temperature of layer A measured by TMA).

[1060] Specifically, TD3mm and MD14mm are taken from layer A and used as specimen pieces (specimen pieces with MD as the long side). The two ends of the MD of the specimen piece are installed on a special probe with a clamp distance of 10mm, and a load of 1.0g is applied to the specimen piece. The furnace carrying the test piece is heated, and the temperature at which the load display is 0g is taken as the film rupture temperature (°C).

[1061] It should be noted that when measuring the TD of a sample piece with TD as the long side, take TD14mm and MD3mm from layer A and use them as sample pieces. Use special probes to clamp both ends of TD, set the distance between the clamps to 10mm, initially apply a load of 1.0g, and perform the same operation as above.

[1062] <Heat shrinkage at 150°C>

[1063] From the laminate (including layer A and layer B) before forming a crosslinked structure, take a sample piece with a TD of 100 mm and a MD of 100 mm. Place the sample piece in a 150°C oven for 1 hour. During this time, sandwich the sample piece between two sheets of paper to prevent the hot air from directly blowing onto the sample piece. Remove the sample piece from the oven, cool it, measure the area of ​​the sample piece, and calculate the thermal shrinkage (T1) at 150°C before forming a crosslinked structure using the following formula.

[1064] Thermal shrinkage at 150°C (%) = (10,000 (mm 2 )-area of ​​the heated specimen (mm 2 ))×100 / 10,000

[1065] Furthermore, a sample piece having a TD of 100 mm and a MD of 100 mm was taken from the laminate after forming the crosslinked structure, and the same operation as above was performed to calculate the heat shrinkage (T2) at 150° C. after forming the crosslinked structure.

[1066] Then, the ratio (T2 / T1) is obtained by dividing the thermal shrinkage rate (T2) by the thermal shrinkage rate (T1). The value of this ratio (T2 / T1) corresponds to the change ratio of the thermal shrinkage rate (T2) at 150°C after the cross-linked structure is formed relative to the thermal shrinkage rate (T1) at 150°C before the cross-linked structure is formed.

[1067] <Battery destruction safety test 1>

[1068] Battery Destruction Safety Test 1 involves driving an iron nail through a battery charged to 4.5V at a speed of 20mm / sec, inducing an internal short circuit. This test measures the temporal behavior of the battery voltage drop and the resulting temperature rise in the battery surface caused by the internal short circuit, clarifying the phenomena occurring during an internal short circuit. Furthermore, due to insufficient separator shutdown function or membrane rupture at low temperatures during an internal short circuit, the battery may experience rapid heating, which can lead to electrolyte ignition, smoke generation, and / or explosion.

[1069] (Preparation of Batteries Used in Battery Destruction Safety Test 1)

[1070] 1a. Preparation of positive electrode

[1071] Take 92.2% by mass of lithium cobalt composite oxide LiCoO2 as the positive electrode active material, 2.3% by mass of flaky graphite and acetylene black as the conductive material, and 3.2% by mass of polyvinylidene fluoride (PVDF) as the resin binder, and disperse them in N-methylpyrrolidone (NMP) to prepare a slurry. The slurry is applied to one side of a 20 μm thick aluminum foil constituting the positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roller press. At this time, the coating amount of the positive electrode active material is adjusted to 250 g / m 2 , the active material volume density is adjusted to 3.00 g / cm 3 .

[1072] 1b. Preparation of negative electrode

[1073] 96.9% by mass of artificial graphite as the negative electrode active material, 1.4% by mass of carboxymethyl cellulose ammonium salt as the resin binder, and 1.7% by mass of styrene-butadiene copolymer latex as the resin binder were dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12μm thick copper foil constituting the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press. At this time, the amount of negative electrode active material applied was adjusted to 106 g / m 2 , the active material volume density is adjusted to 1.35 g / cm 3 .

[1074] 1c. Preparation of non-aqueous electrolyte

[1075] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[1076] 1d.Battery Assembly

[1077] Cut the separator into 60 mm in the width (TD) direction and 1000 mm in the length (MD) direction, fold the separator repeatedly, and alternately overlap the positive and negative electrodes between the separators (12 positive electrodes and 13 negative electrodes). It should be noted that the positive electrode uses an area of ​​30 mm × 50 mm and the negative electrode uses an area of ​​32 mm × 52 mm. After the repeatedly folded stack is placed in a laminated bag, the non-aqueous electrolyte obtained in the above c. is injected and sealed. After being placed at room temperature for 1 day, the battery voltage is charged to 4.2 V at a current value of 3 mA (0.5 C) in an atmosphere of 25°C. After reaching 4.2 V, the current value is reduced from 3 mA, and the initial charge after the battery is made is performed in this way for a total of 6 hours. Then, the battery voltage is discharged to 3.0 V at a current value of 3 mA (0.5 C).

[1078] (Maximum heating speed)

[1079] After an iron nail was passed through the obtained battery, the battery surface temperature was measured for 300 seconds using a thermocouple based on a temperature change graph. The rate at which the temperature rise per 1 second was the largest was determined as the maximum heat generation rate.

[1080] (Voltage drop time)

[1081] After an iron nail was passed through the obtained battery, the time required for the voltage to decrease from 4.5 V to 3 V was determined as the voltage drop time (time until the voltage dropped to 3 V).

[1082] <Evaluation of Cycle Characteristics and Method for Making a Battery>

[1083] Batteries for cycle characteristics evaluation were prepared in the same manner as in 1a. to 1c. of the battery preparation method used in the above item <Battery destruction safety test 1>, except that the assembly was performed according to 1d-2. below.

[1084] 1d-2. Battery assembly

[1085] Cut the separator into a circular shape with an 18mm diameter, and the positive and negative electrodes into circular shapes with a 16mm diameter. The positive electrode, separator, and negative electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other. The cells were then placed in a stainless steel container with a lid. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode and the lid in contact with the aluminum foil of the positive electrode. The non-aqueous electrolyte solution obtained in 1c. of the above-mentioned "Battery Destruction Safety Test 1" was injected into the container and sealed. After standing at room temperature for one day, the cells were charged at 3mA (0.5C) in a 25°C atmosphere until the battery voltage reached 4.2V. After reaching 4.2V, the current was gradually reduced from 3mA to maintain the voltage. This method was used for the initial charge after battery fabrication for a total of 6 hours. Subsequently, the cells were discharged at 3mA (0.5C) until the battery voltage reached 3.0V.

[1086] The resulting battery was charged and discharged for 100 cycles in an atmosphere of 60°C. Charging was performed at a current of 6.0 mA (1.0 C) until the battery voltage reached 4.2 V. After reaching 4.2 V, the current was decreased from 6.0 mA to maintain the voltage at 4.2 V. This method of charging was continued for a total of 3 hours. Discharging was performed at a current of 6.0 mA (1.0 C) until the battery voltage reached 3.0 V.

[1087] (Cycle Characteristics Evaluation 1)

[1088] The capacity retention rate was calculated from the discharge capacity at the 100th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[1089] (Cycle Characteristics Evaluation 2)

[1090] The capacity retention rate (%) was calculated based on the following formula from the discharge capacity at the 300th cycle and the discharge capacity at the 1st cycle: A high capacity retention rate was evaluated as having good cycle characteristics.

[1091] Evaluation result (%) = (100 × retention capacity after 300 cycles / discharge capacity at the first cycle)

[1092] <Fusing / Melt Fracture (F / MD) Characteristics>

[1093] (i) 0.5 MPa pressure and 2°C / min heating rate

[1094] The positive electrode, separator and negative electrode are cut into a circular shape with a diameter of 200mm and overlapped, and a non-aqueous electrolyte is added to the resulting laminate to penetrate the entire body. The laminate is clamped at the center of a circular aluminum heater with a diameter of 600mm, and the aluminum heater is pressurized to 0.5MPa from the top and bottom with a hydraulic jack to complete the preparation for the measurement. While heating the aforementioned laminate with an aluminum heater at a heating rate of 2°C / min, the resistance (Ω) between the electrodes is measured. The temperature at which the separator melts and the resistance between the electrodes rises and the resistance exceeds 1000Ω for the first time is taken as the melting temperature (shutdown temperature). In addition, heating is continued, and the temperature at which the resistance is reduced to below 1000Ω is taken as the melting rupture temperature (film rupture temperature).

[1095] (ii) 10 MPa maximum pressure and 15°C / min heating rate

[1096] The positive electrode, separator and negative electrode are cut into circular shapes with a diameter of 200 mm, and a non-aqueous electrolyte is added to the stacked body to penetrate the whole body. The stack is clamped at the center of a circular aluminum heater with a diameter of 600 mm, and a hydraulic jack is used to apply pressure to the aluminum heater from the top and bottom to 10 MPa to complete the preparation for the measurement. While heating the stack with an aluminum heater at a heating rate of 15°C / min, the resistance (Ω) between the electrodes is measured. The temperature at which the resistance between the electrodes rises and the resistance exceeds 1000Ω for the first time is taken as the shutdown temperature (°C). In addition, the temperature at which the resistance is reduced to below 1000Ω by further heating is taken as the melt fracture temperature (°C).

[1097] For both evaluations (i) and (ii), a resistance measuring wire was bonded to the back surface of the aluminum foil of the positive electrode produced in "1a. Preparation of Positive Electrode" in the above-mentioned section <Battery Destruction Safety Test 1> using a conductive silver paste. Furthermore, a resistance measuring wire was bonded to the back surface of the copper foil of the negative electrode produced in "1b. Preparation of Negative Electrode" in the above-mentioned section <Battery Destruction Safety Test 1> using a conductive silver paste. Furthermore, the electrolyte-containing solution prepared in "1c. Preparation of Non-aqueous Electrolyte Solution" in the above-mentioned section <Battery Destruction Safety Test 1> was also used in the F / MD characteristics test.

[1098] <Safety Test (Nail Penetration Test) 2>

[1099] 2a. Preparation of positive electrode

[1100] The positive electrode active material is nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70g / cm 3 ) 90.4 mass%, graphite powder (KS6) as a conductive additive (density 2.26 g / cm 3 , number average particle size 6.5 μm) 1.6 mass% and acetylene black powder (AB) (density 1.95 g / cm 3 , number average particle size 48nm) 3.8% by mass, and PVDF (density 1.75g / cm 3 ) at a ratio of 4.2 mass % and dispersed in NMP to prepare a slurry. The slurry was applied to one side of a 20 μm thick aluminum foil constituting the positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to produce a positive electrode. At this time, the amount of positive electrode active material applied was 109 g / m 2 .

[1101] 2b. Preparation of negative electrode

[1102] Graphite powder A (density 2.23 g / cm 3 , number average particle size 12.7 μm) 87.6 mass% and graphite powder B (density 2.27 g / cm 3, number average particle size 6.5μm) 9.7% by mass, and 1.4% by mass (solid content conversion) of ammonium salt of carboxymethyl cellulose as a resin binder (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass (solid content conversion) of diene rubber latex (solid content concentration 40% by mass aqueous solution) are dispersed in purified water to prepare a slurry. The slurry is applied to one side of a copper foil with a thickness of 12μm constituting the negative electrode collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roller press to produce a negative electrode. At this time, the amount of negative electrode active material applied is 52g / m 2 .

[1103] 2c. Preparation of non-aqueous electrolyte

[1104] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[1105] 2d. Battery production

[1106] Using the positive electrode, negative electrode, non-aqueous electrolyte, and separator (separator of the embodiment or separator of the comparative example) obtained in the above 2a to 2c, a laminated secondary battery with a size of 100 mm × 60 mm and a capacity of 3 Ah was prepared, which was charged by constant current constant voltage (CCCV) for 3 hours at a current value of 1 A (0.3 C) and a final battery voltage of 4.2 V.

[1107] 2e. Nail evaluation

[1108] The prepared laminated secondary battery was placed on an iron plate in a temperature-controlled explosion-proof chamber. The temperature in the chamber was set to 40°C. A 3.0mm diameter iron nail was driven through the center of the laminated secondary battery at a speed of 2mm / second, with the nail maintained. The temperature of a thermocouple installed inside the nail, designed to measure the internal temperature of the laminated secondary battery after penetration, was measured to assess the presence of ignition.

[1109] The evaluation was repeated using a laminated secondary battery newly produced by the same method, and the number of samples that did not ignite (non-ignition) was calculated as a % value according to the following formula.

[1110] Evaluation result (%) = (100 × number of samples without ignition / total number of samples)

[1111] The pass rate of the nail penetration evaluation is preferably 50% or more at 200 cycles and 5% or more at 1000 cycles, for example.

[1112] <Experimental Group I>

[1113] [Method for producing silane-grafted polyolefin]

[1114] The raw material polyolefin used in silane-grafted polyolefin modification can have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be an alpha-olefin copolymerized with propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the alpha-olefin polymer chain. Trimethoxyalkoxide-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the alpha-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, to control the free radical concentration in the system, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to suppress chain reactions (gelation) within the alpha-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then dried by heating at 80°C for two days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 10 to 1500 ppm.

[1115] The silane-grafted modified polyethylene obtained by the above-mentioned production method was used as "silane-modified polyolefin (B)" in Table 8.

[1116] [Example I-1]

[1117] To 79.2% by mass of polyethylene (A) which is a homopolymer with a weight average molecular weight of 500,000, 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity average molecular weight of 20,000 by replacing vinylsilane with trimethoxyalkoxide (according to which the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) are injected into the extruder roller.

[1118] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1119] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[1120] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1121] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[1122] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Then, a relaxation operation of 0.5 times in the TD direction (i.e., a HS relaxation ratio of 0.5 times) was performed to obtain a microporous membrane.

[1123] Then, the end portion of the obtained microporous membrane was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[1124] During the above evaluation, the microporous film unwound from the mother roll was slit as needed and used as separators for evaluation.

[1125] [Examples I-2 to I-6]

[1126] As shown in Table 8, the same operations as in Example I-1 were carried out except that the quantitative ratio of components A and B and the cross-linking method and conditions were changed to obtain the microporous membrane shown in Table 8.

[1127] [Comparative Examples I-1, I-2]

[1128] To 79.2% by mass of polyethylene (A) which is a homopolymer with a weight average molecular weight of 500,000, 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity average molecular weight of 20,000 by replacing vinylsilane with trimethoxyalkoxide (according to which the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5m2 / s) is injected into the extruder drum.

[1129] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1130] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[1131] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1132] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[1133] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Thereafter, a relaxation operation of 0.5 times in the TD direction was performed (i.e., a HS relaxation ratio of 0.5 times).

[1134] Furthermore, the porous body was introduced into an ethanol bath (affinity treatment tank), immersed and allowed to remain there for 60 seconds, and affinity treatment of the heat-treated porous body was performed to obtain an affinity-treated porous body.

[1135] Furthermore, in Comparative Example I-1, the affinity-treated porous body was introduced into a 25% caustic soda aqueous solution (temperature 80°C, pH 8.5-14), and in Comparative Example I-2, the affinity-treated porous body was introduced into a 10% hydrochloric acid aqueous solution (temperature 60°C, pH 1-6.5), and the immersion was allowed to stand for 60 seconds to perform cross-linking treatment on the affinity-treated porous body, thereby obtaining a cross-linked porous body.

[1136] The crosslinked porous body was then introduced into water (water washing tank) and immersed therein for 60 seconds to wash the crosslinked porous body. The crosslinked porous body was then introduced into a conveyor dryer and dried at 120° C. for 60 seconds to obtain a microporous membrane.

[1137] Then, the end portion of the obtained microporous membrane was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[1138] During the above evaluation, the microporous film unwound from the mother roll was slit as needed and used as separators for evaluation.

[1139] [Evaluation results]

[1140] The microporous membranes and batteries obtained in Examples I-1 to I-6 and Comparative Examples I-1 to I-2 were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 8. In addition, the relationship between temperature and resistance of the battery having the microporous membrane obtained in Example I-1 as a separator is shown in Table 8. Figure 3 .Depend on Figure 3 As shown in Table 8, the separator obtained in Example I-1 has a shutdown temperature of 143°C and a film rupture temperature of 200°C or higher. 1 H and 13 C-NMR spectrum (b) is shown in Figure 13 .

[1141] [Table 8]

[1142]

[1143] It should be noted that the “silane-modified polyethylene (B)” in Table 8 is obtained by a modification reaction based on trimethoxyalkoxide-substituted vinylsilane using a polyolefin with a viscosity average molecular weight of 20,000 as a raw material, and has a density of 0.95 g / cm 3 A silane-modified polyethylene having a melt flow rate (MFR) at 190° C. of 0.4 g / min.

[1144] <Experimental Group IIa>

[1145] [Method for producing silane-grafted polyolefin]

[1146] The raw material polyolefin used in silane-grafted polyolefin modification can have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be an ethylene homopolymer or an alpha-olefin copolymer of ethylene and propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the alpha-olefin polymer chain. Trimethoxyalkoxide-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the alpha-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to adjust the free radical concentration in the reaction system and inhibit chain reactions (gelation) within the alpha-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then dried by heating at 80°C for two days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1500 ppm or less.

[1147] The silane-grafted polyethylene obtained by the above-mentioned production method was used as "silane-modified polyethylene (B)" in Table 9.

[1148] [Example II-1]

[1149] To 80% by mass of polyethylene (polyethylene (A)) which is a homopolymer with a weight average molecular weight of 700,000, 20% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity average molecular weight of 10,000 by replacing vinylsilane with trimethoxyalkoxide (thereby, the resin compositions of (A) and (B) are 80% and 20%, respectively), and 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) are injected into the extruder roller.

[1150] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1151] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1100 μm.

[1152] The sheet-like molded product was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times the MD ratio, 6.2 times the TD ratio, and a biaxial stretching temperature of 120°C.

[1153] Next, the stretched gel sheet was introduced into a dichloromethane tank, fully immersed in dichloromethane to extract and remove the liquid paraffin, and then dried to remove the dichloromethane, thereby obtaining a porous body.

[1154] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 133° C. and a stretching ratio of 2.1 times. Thereafter, a relaxation operation was performed to 2.0 times in the TD direction.

[1155] Then, the end portion of the obtained microporous membrane was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[1156] During the above evaluation, the microporous film unwound from the mother roll was slit as needed and used as separators for evaluation.

[1157] [Examples II-2 to II-8, Comparative Examples II-1 to II-3]

[1158] As shown in Table 9, the same operation as in Example II-1 was carried out except that the quantitative ratio of components A and B, the presence or absence of the additional component (C) other resin, the membrane properties, and the crosslinking method / conditions were changed to obtain the microporous membrane shown in Table 9. It should be noted that as the component "PP" in Table 9, a microporous membrane having an MFR of 2.5 g / 10 min or less measured at a temperature of 230°C and a mass of 2.16 kg and a density of 0.89 g / cm 3 The above silane-unmodified polypropylene. In the crosslinking method "alkali treatment crosslinking" in Table 9, the sample was treated with a 25% caustic soda aqueous solution (temperature 80°C, pH 8.5-14).

[1159] [Evaluation results]

[1160] The microporous membranes and batteries obtained in Examples II-1 to II-8 and Comparative Examples II-1 to II-3 were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 9. In addition, regarding the viscoelasticity measurement when the obtained microporous membranes were used as separators for power storage devices, the relationship between the temperature, gap distance, storage modulus and loss modulus of Example II-1 is shown in Table 9. Figure 4(a), the comparative example II-1 is shown in Figure 4 (b), and further, the film softening transition temperature determined based on the first derivative of temperature, gap distance and gap displacement of Example II-1 is shown in Figure 5 (a), the comparative example II-1 is shown in Figure 5 (b). In Examples II-1 to II-8 and Comparative Example II-3, no film rupture was observed at the measurement limit temperature of 250°C. It should be noted that in Example II-1 and Comparative Example II-1, 26 films with a thickness of 8 μm were overlapped, and the storage modulus, loss modulus, film softening transition temperature, and film rupture temperature were measured under the condition that the total film thickness of the sample was 208 μm.

[1161] [Table 9A]

[1162]

[1163] [Table 9B]

[1164]

[1165] <Experimental Series IIb>

[1166] [Standard film]

[1167] As a separator for a power storage device that does not contain silane-modified polyolefin (hereinafter referred to as the "standard membrane"), a silane-grafted, unmodified polyolefin microporous membrane was used. The change in solid content (hereinafter referred to as the "gelation degree") before and after heating at 160°C in a decalin solution was approximately 0%. When measuring the gelation degree, the solid content refers only to the resin and does not include other materials such as inorganic substances.

[1168] In this specification, a separator for a power storage device that does not contain a silane-grafted modified polyolefin can be produced using any one selected from the group consisting of polyethylene (PE): X (viscosity average molecular weight 100,000 to 400,000), PE: Y (viscosity average molecular weight 400,000 to 800,000), and PE: Z (viscosity average molecular weight 800,000 to 9,000,000), or a composition comprising a mixture of two or three selected from the group consisting of X, Y, and Z in any proportion. Furthermore, a polyolefin composed solely of a hydrocarbon backbone, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), or an olefin-based thermoplastic elastomer, can be added to the mixed composition.

[1169] [Cross-linked film]

[1170] The polyolefin microporous membrane of Example II-1 described above after contact with the electrolyte, or the polyolefin microporous membrane of Example II-1 removed from the battery after initial charge and discharge, was dried and used as a separator for a power storage device after a silane crosslinking reaction (hereinafter referred to as a "crosslinked membrane"). The crosslinked membrane had a gelation degree of 30% or greater, or 70% or greater.

[1171] [Viscoelastic behavior]

[1172] The standard film and the cross-linked film were measured for the above-mentioned items <Storage modulus, loss modulus, film softening transition temperature, and film rupture temperature (version 3)>. The measurement results are shown in Table 10.

[1173] [Table 10]

[1174]

[1175] <Experimental Group III>

[1176] [Method for producing silane-grafted polyolefin]

[1177] The raw material polyolefin used in silane-grafted polyolefin modification can have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can also be an α-olefin copolymerized with propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the α-olefin polymer chain. Trimethoxyalkoxide-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, to control the free radical concentration in the system, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit chain reactions (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then heat-dried at 80°C for two days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1000 to 1500 ppm.

[1178] The silane-grafted modified polyolefin obtained by the above-mentioned production method is represented as "silane-modified polyethylene" in Tables 11 and 12.

[1179] [Method for producing modified PE and copolymers having various functional groups other than silane-modified PE]

[1180] Modified PE and copolymers having various functional groups other than silane-modified PE were produced by the following methods.

[1181] For any raw material, the molecular weight of the raw material used is used to adjust the MI so that it is within the range of 0.5 to 10. Modified PE with hydroxyl groups is produced by saponifying and neutralizing EVA copolymers. Modified resins such as amine-modified and oxazoline-modified resins are obtained by allowing a tungsten-based catalyst to act on the terminal vinyl group of PE obtained by polymerization using a chromium catalyst under hydrogen peroxide conditions, converting the vinyl group into an epoxy group. Afterwards, a well-known functional group conversion organic reaction is used to convert the target reaction site into a target functional group to obtain various modified PEs. For example, in the case of amine-modified PE, while the modified PE with epoxy groups is melt-kneaded at 200°C in an extruder, primary amines or secondary amines are injected in a liquid state to react. Then, the unreacted amines are removed through a pressure reducing valve, and the resulting amine-modified resin is extruded into a strand shape and cut into pellets.

[1182] The modified PE obtained by the above-mentioned production method is shown as one type of "modified PE or copolymer (B)" in Tables 11 and 12.

[1183] [Example III-1]

[1184] To 79.2% by mass of polyethylene (A) having a homopolymer weight average molecular weight of 500,000, 19.8% by mass of silane-grafted polyethylene (PE (B)) having an MFR of 0.4 g / min, obtained by modifying a polyolefin having a viscosity average molecular weight of 20,000 by replacing vinylsilane with trimethoxyalkoxide (according to which the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) is injected into the extruder roller.

[1185] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1186] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[1187] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1188] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[1189] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Then, a relaxation operation of 0.5 times in the TD direction (i.e., a HS relaxation ratio of 0.5 times) was performed to obtain a microporous membrane.

[1190] Then, the end portion of the obtained microporous membrane was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[1191] During the above evaluation, the microporous film unwound from the mother roll was slit as needed and used as separators for evaluation.

[1192] The separators and batteries for evaluation were subjected to various evaluations according to the above-mentioned evaluation methods. The evaluation results are shown in Table 11.

[1193] [Examples III-2 to III-18]

[1194] The same procedures as in Example III-1 were followed, except that the types and quantitative ratios of resins A and B, as well as the crosslinking method and conditions, were changed as described in Table 11 or Table 12, to produce the microporous membranes and batteries shown in Table 11 or Table 12. The resulting microporous membranes and batteries were subjected to various evaluations according to the above-described evaluation methods, and the evaluation results are also shown in Table 11 or Table 12. It should be noted that in Examples III-8 to III-10, and III-15 to III-18, an electrolyte containing appropriate amounts of the additives listed in Table 11 or Table 12 was used prior to the injection of the electrolyte.

[1195] [Comparative Examples III-1, III-2]

[1196] As shown in Table 12, the same procedures as in Example III-1 were performed, except that the types and quantitative ratios of resins A and B, as well as the crosslinking method and conditions, were changed to obtain the microporous membranes shown in Table 12. The obtained microporous membranes were irradiated with a predetermined dose for electron beam crosslinking. The obtained electron beam crosslinked microporous membranes and batteries were subjected to various evaluations according to the above-described evaluation methods, and the evaluation results are also shown in Table 12.

[1197] Regarding Comparative Example III-2 and Example III-1, the strain amount-crystal fraction ratio is shown in FIG. Figure 8 , observe the changes in X-ray crystal structure during tensile fracture test. Figure 8 In the figure, the microporous membrane of Comparative Example III-2 is represented by a dotted line "EB crosslinked", and the microporous membrane of Example III-1 is represented by a solid line "before chemical crosslinking" and a dashed line "after chemical crosslinking".

[1198] [Table 11A]

[1199]

[1200] [Table 11B]

[1201]

[1202] [Table 12A]

[1203]

[1204] [Table 12B]

[1205]

[1206] Explanation of Abbreviations in Tables 11 and 12

[1207] * "Silane-modified polyethylene" is obtained by using a polyolefin with a viscosity average molecular weight of 20,000 as a raw material through a modification reaction based on trimethoxyalkoxide-substituted vinylsilane. It has a density of 0.95 g / cm 3 A silane-modified polyethylene having a melt flow rate (MFR) at 190° C. of 0.4 g / min.

[1208] "-COOH modified PE", "-oxazoline modified PE", "-oxazoline, -OH modified PE", "-OH modified PE", "-OH, -NH- modified PE" and "-OH, amine modified PE" are all modified PE obtained by the above-mentioned [method for producing modified PE and copolymers having various functional groups other than silane modified PE].

[1209] ** (I) Condensation reaction of multiple identical functional groups

[1210] (II) Reactions between multiple functional groups

[1211] (III) Chain condensation reaction between functional groups and electrolyte

[1212] (IV) Reaction of functional groups with additives

[1213] (V) Reaction in which multiple identical functional groups are crosslinked by coordination bonds with dissolved metal ions

[1214] *** EC: Ethylene carbonate

[1215] **** BS(PEG)5: Bis-succinimide at both ends, EO unit repetition number 5

[1216] Diisocyanate: A compound in which bis-isocyanate at both ends is connected to a hexane unit by a urethane bond

[1217] Bicyclic epoxide: A compound in which epoxy groups at both ends are connected to a butane unit

[1218] <Experimental Group IV>

[1219] [Example IV-1]

[1220] <Production of A layer>

[1221] (Production of silane-grafted modified polyolefin)

[1222] Using polyethylene with a viscosity-average molecular weight of 120,000 as the raw material polyethylene, while melt-kneading the raw material polyethylene with an extruder, adding an organic peroxide (di-tert-butyl peroxide), generating free radicals in the polymer chain of the α-olefin, injecting trimethoxyalkoxide-substituted vinyl silane, and introducing an alkoxysilyl group into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, at the same time, in order to adjust the free radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) was added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin was cooled in water, pelletized, and then heated and dried at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 1500 ppm or less.

[1223] As described above, through the modification reaction using trimethoxyalkoxide-substituted vinyl silane, silane-modified polyethylene with an MFR (190°C) of 0.4 g / minute was obtained.

[1224] (Production of A layer)

[1225] Mix 35% by mass of the above-obtained silane-modified polyethylene with 65% by mass of a homopolymer polyethylene having a weight-average molecular weight of 800,000 to form a resin blend. Add 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant to the blend and perform dry mixing using a drum mixer to obtain a mixture. Feed the obtained mixture from a feeder to a twin-screw extruder under a nitrogen atmosphere. In addition, inject liquid paraffin (kinematic viscosity at 37.78 °C: 7.59×10 -5 m 2 / s) into the extruder barrel through a plunger pump.

[1226] Melt and knead the mixture and the liquid paraffin in the extruder, and adjust the feeder and the pump so that the amount ratio of the liquid paraffin in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-kneading conditions are a set temperature of 220 °C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / hour. Then, pass the melt-kneaded material through a T-die and extrude it onto a cooling roll with a surface temperature controlled at 25 °C and cast it to obtain a gel sheet (sheet-shaped molded body) with a blank film thickness of 1400 μm.

[1227] Next, guide the sheet-shaped molded body to a simultaneous biaxial tentering machine and perform biaxial stretching to obtain a stretched product. Set the stretching conditions to an MD magnification of 7.0 times, a TD magnification of 6.3 times (i.e., 7×6.3 times), and a biaxial stretching temperature of 122 °C.

[1228] Next, guide the stretched gel sheet to a dichloromethane bath, fully immerse it in dichloromethane to extract and remove the liquid paraffin, and then dry it to remove dichloromethane to obtain a porous body.

[1229] Next, in order to perform heat setting (HS), guide the porous body to a TD tenter, perform HS at a heat setting temperature of 133 °C and a stretching ratio of 1.8 times, and then perform a relaxation operation to a TD of 1.7 times to obtain a microporous membrane.

[1230] Then, for the obtained microporous membrane, cut off the ends and wind it into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1231] During the above evaluation, slit the microporous membrane unwound from the master roll as needed and use it as the evaluation A layer.

[1232] For the obtained evaluation A layer, measure the film thickness, air permeability, porosity, etc., as shown in Table 13.

[1233] <Manufacture of B layer>

[1234] A dispersion was prepared by uniformly dispersing 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solids content conversion) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by SAN NOPCO LIMITED, solids concentration 40%) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was crushed using a bead mill (200 cc tank volume, 0.1 mm diameter zirconia microbeads, 80% filling weight) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, thereby preparing a slurry containing inorganic particles.

[1235] Next, the microporous membrane is continuously unwound from the above-mentioned microporous membrane mother roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coater. Then, the membrane is dried in a drier at 60°C to remove water, and wound up to obtain a separator mother roll.

[1236] During the evaluation, the separators unwound from the mother roll were cut as needed and used as separators for evaluation.

[1237] [Examples IV-2 to IV-5, and Comparative Examples IV-1 to IV-2]

[1238] The weight average molecular weight of the polyethylene homopolymer, the stretching conditions, the heat setting conditions, and the relaxation conditions were changed with the physical property values ​​listed in Table 13 as the target. In addition, the structure of the B layer was changed to that shown in Table 13.

[1239] Except for these changes, a separator was produced by the same method as in Example IV-1, and the above-mentioned evaluation was performed using the obtained separator. The evaluation results are shown in Table 13.

[1240] [Table 13]

[1241]

[1242] <Experimental Group V>

[1243] [Method for producing silane-grafted polyolefin]

[1244] The raw material polyolefin used in silane-grafted polyolefin modification can have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can also be an α-olefin copolymerized with propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the α-olefin polymer chain. Trimethoxyalkoxide-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to control the free radical concentration in the reaction system and inhibit chain reactions (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then dried by heating at 80°C for two days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 10 to 1500 ppm.

[1245] The silane-grafted modified polyolefin obtained by the above-mentioned production method was used as "silane-modified polyethylene (B)" in Tables 14 to 16. The density of the silane-grafted modified polyolefin used this time was 0.94 g / cm 3 And the MFR is 0.65 g / min.

[1246] [Example V-1]

[1247] (Formation of Microporous Membrane)

[1248] To 79.2% by weight of polyethylene (A), a homopolymer having a weight-average molecular weight of 500,000, 19.8% by weight of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin having a viscosity-average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinylsilane reaction (according to which the resin compositions of (A) and (B) are 80% and 20%), and 1% by weight of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The resulting mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) are injected into the extruder roller.

[1249] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by weight of the extruded polyolefin composition (i.e., a polymer concentration of 30% by weight). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1250] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[1251] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1252] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[1253] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Then, a relaxation operation of 0.5 times in the TD direction (i.e., a HS relaxation ratio of 0.5 times) was performed to obtain a microporous membrane.

[1254] Then, the end portion of the obtained microporous membrane was cut and wound into a microporous membrane mother roll having a width of 1,100 mm and a length of 5,000 m.

[1255] (Method for producing acrylic latex)

[1256] The acrylic latex used as the resin binder can be produced as follows.

[1257] To a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer were added 70.4 parts by mass of ion-exchanged water, along with 0.5 parts by mass of "Aquaron KH1025" (registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., a 25% aqueous solution) and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., a 25% aqueous solution) as emulsifiers. The temperature inside the reaction vessel was then raised to 80°C, and while maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to form an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

[1258] The emulsion was prepared by mixing the following for 5 minutes using a homomixer: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aquaron KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "ADEKA REASOAPSR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water.

[1259] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex having a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

[1260] (Formation of Inorganic Porous Layer)

[1261] 95 parts by weight of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by weight (based on solids content) of an aqueous polycarboxylate ammonium solution (SN Dispersant 5468 manufactured by SAN NOPCO LIMITED, solids concentration 40%) as an ionic dispersant were uniformly dispersed in 100 parts by weight of water to prepare a dispersion. The resulting dispersion was crushed using a bead mill (200 cc tank volume, 0.1 mm diameter zirconium oxide microbeads, 80% filler) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To this dispersion with adjusted particle size distribution, 4.6 parts by weight (based on solids content) of an acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, monomers: butyl acrylate, methyl methacrylate, methacrylic acid) as a resin binder were added to prepare a slurry containing the inorganic particles.

[1262] Next, the microporous membrane is continuously unwound from the above-mentioned microporous membrane mother roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coater. Then, the membrane is dried in a drier at 60°C to remove water, and wound up to obtain a separator mother roll.

[1263] During the evaluation, the separators unwound from the mother roll were cut as needed and used as separators for evaluation.

[1264] [Examples V-2 to V-12, Comparative Example V-2]

[1265] As shown in Tables 14 to 16, the same operations as in Example V-1 were performed except that the quantitative ratio of components A and B, the presence or composition of the inorganic layer, and the crosslinking method and conditions were changed to obtain the microporous membranes shown in Tables 14 to 16.

[1266] [Comparative Example V-1]

[1267] To 79.2% by weight of polyethylene (A), a homopolymer having a weight-average molecular weight of 500,000, 19.8% by weight of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin having a viscosity-average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinylsilane reaction (according to which the resin compositions of (A) and (B) are 80% and 20%, respectively), and 1% by weight of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 - 5m2 / s) is injected into the extruder drum.

[1268] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by weight of the extruded polyolefin composition (i.e., a polymer concentration of 30% by weight). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1269] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[1270] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1271] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[1272] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Thereafter, a relaxation operation of 0.5 times in the TD direction was performed (i.e., a HS relaxation ratio of 0.5 times).

[1273] In Comparative Example V-1, in order to use the heat-treated porous body as a separator, the end portion of the obtained porous body was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[1274] Regarding Comparative Example V-1, during the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as separators for evaluation.

[1275] [Evaluation results]

[1276] The microporous membranes and batteries obtained in Examples V-1 to V-12 and Comparative Examples V-1 and V-2 were subjected to various evaluations according to the above-mentioned evaluation methods. The evaluation results are also shown in Tables 14 to 16.

[1277] [Table 14]

[1278]

[1279] [Table 15]

[1280]

[1281] [Table 16]

[1282]

[1283] <Experimental Group VI>

[1284] Porous membranes were formed in the same manner as in Examples 1 to 3 and Comparative Examples 2 to 3 given in Patent Document 5 (Japanese Patent Application Laid-Open No. 2001-176484), and are designated as Porous Membranes V-1 to V-5, respectively. The gel fraction (%), heat-resistant temperature (°C), and needle penetration strength (gf / 25 μm) of the porous membranes V-1 to V-5 were evaluated according to the method described in Patent Document 5. Furthermore, the change ratio R of the storage modulus and loss modulus of the porous membrane V-4 before and after contact with the electrolyte was measured according to the above-mentioned item <Storage modulus, loss modulus, and transition temperature (version 1)> of this specification. △E’ and R △E” The results are shown in Table 17.

[1285] [Table 17]

[1286]

[1287] The following points can be clarified from Table 17.

[1288] (a) Even for the porous membrane V-4 with the lowest gel fraction (Comparative Example 2 of Patent Document 5, gel fraction 36%), the elastic modulus change ratio remains unchanged at 1, thus confirming that the porous membranes V-1 to V-5 have all undergone thorough cross-linking reactions, and the porous membranes described in Patent Document 5 do not have self-cross-linking properties (uncross-linked parts).

[1289] (b) Comparative Example 1 of Patent Document 5 is a silane-unmodified product.

[1290] (c) The value of the separator of the seventh embodiment of the present invention described above lies in the selective chemical crosslinking of the amorphous region between the crystals and the crystalline portion. When the unsilane-modified polyolefin and the silane-modified polyolefin form a mixed crystal, the modified units are repelled by the amorphous portion and become irregularly dispersed. In this state, the connected crosslinked units come into contact, allowing the crosslinking reaction to proceed.

[1291] On the other hand, if multiple crosslinking units are located far apart, even if they exist, they cannot contribute to the crosslinking reaction. In particular, the crosslinking reaction from silanol to siloxane in the porous membrane proceeds immediately once all its reaction conditions are met, and the units that can participate in crosslinking are fully crosslinked, making further crosslinking of residual units impossible in a battery containing the porous membrane.

[1292] Therefore, even if residual silanol groups remain in the porous membranes such as porous membranes V-1 to V-5, as long as cross-linking treatment is performed during the manufacturing process of these membranes, the cross-linking reaction in the battery containing the membrane will not proceed (that is, the residual silanol groups cannot contribute to the cross-linked structure).

[1293] (d) Regarding the separator of the seventh embodiment of the present invention, by adjusting the molecular weight of the raw resin, copolymer concentration, and blending ratio, and further combining it with a stretching film-forming process, experiments have revealed a crystal structure with a high probability of crosslinking the crosslinking units and a dispersed distribution of the crosslinking units. This has successfully improved the battery's damage resistance and heat safety, and successfully suppressed the degradation of the battery's cycling performance caused by residual heterofunctional groups.

Claims

1. A separator for an electrical storage device, characterized in that: The separator for the storage device comprises a microporous membrane, wherein the microporous membrane comprises a silane-modified polyolefin, and no cross-linking reaction occurs during the manufacturing process of the separator. When the separator for the storage device comes into contact with a non-aqueous electrolyte containing water and / or hydrogen fluoride during the manufacturing process of the storage device, a silane cross-linking reaction of the silane-modified polyolefin is initiated; wherein the separator for the storage device further comprises polyethylene on the basis of the silane-modified polyolefin, and the mass ratio of the silane-modified polyolefin to the polyethylene, i.e., the mass of the silane-modified polyolefin / the mass of the polyethylene, is 0.06 / 0.94 to 0.38 / 0.62; the silane-modified polyolefin is a silane-grafted modified polyolefin, and the density of the silane-grafted modified polyolefin is 0.90 to 0.96 g / cm 3 , and the melt mass flow rate MFR at 190° C. and 2.16 kg load is 0.2 to 5 g / min; the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst for cross-linking the silane-modified polyolefin. 2 . An electricity storage device comprising an electrode, the separator for an electricity storage device according to claim 1 , and a non-aqueous electrolyte.

3. A method for producing a separator for an electrical storage device, the method for producing a separator for an electrical storage device according to claim 1, comprising the following steps: (1) a sheet forming step of extruding a mixture of silane-modified polyolefin, polyethylene, and a plasticizer, cooling and solidifying the mixture, and forming the mixture into a sheet to obtain a sheet; (2) a stretching step of stretching the sheet in at least one uniaxial direction to obtain a stretched product; (3) a porous body forming step of extracting the plasticizer from the stretched product in the presence of an extraction solvent to make the stretched product porous to form a porous body; and (4) A heat treatment step of subjecting the porous body to heat treatment.

4. An electrical storage device assembly kit comprising the following two elements: Element 1: an outer casing accommodating a laminate or a wound body of electrodes and the separator for a power storage device according to claim 1; and Element 2: A container containing a non-aqueous electrolyte.

5. The power storage device assembly kit according to claim 4, wherein: The non-aqueous electrolyte contains a lithium salt containing fluorine (F).

6. The power storage device assembly kit according to claim 4, wherein: The non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6).

7. The power storage device assembly kit according to claim 4, wherein: The non-aqueous electrolyte is an acid solution and / or an alkaline solution.

8. A method for manufacturing an electricity storage device, comprising the following steps: a step of preparing the power storage device assembly kit according to any one of claims 4 to 7, and The step of initiating a silane cross-linking reaction of the silane-modified polyolefin is performed by bringing the separator for the electricity storage device in element 1 into contact with the non-aqueous electrolyte in element 2 of the electricity storage device assembly kit.

9. The method for manufacturing an electric storage device according to claim 8, further comprising the following step: a step of connecting a lead terminal to the electrode of the element 1, and A step of performing at least one cycle of charge and discharge.

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