Lithium ion battery using crosslinked separator

Abstract

The present invention relates to a lithium ion battery using a crosslinked separator, and provides a separator for an electrical storage device, and a manufacturing method thereof, the separator for an electrical storage device being characterized by comprising a silane-modified polyolefin, and a silane crosslinking reaction of the silane-modified polyolefin being initiated when the separator is brought into contact with an electrolyte.

Description

[0001] This application is a divisional application of the application filed on October 11, 2019, with application number 201980007742.8 and invention title "Lithium-ion Battery Using Crosslinking Separators". Technical Field

[0002] This invention relates to separators for energy storage devices and their crosslinking methods, energy storage device assembly kits, and methods for manufacturing energy storage devices. Background Technology

[0003] Microporous membranes are widely used as separation or selective permeation membranes and separation materials for various substances. 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 energy storage devices. Among these, polyolefin microporous membranes are suitable for use as separators in lithium-ion batteries, which are widely used in laptops, mobile phones, and digital cameras.

[0004] To ensure battery safety, the separator must balance the activation of the shut-off function with the increase in membrane rupture temperature. For example, Patent Document 1 describes adjusting the high-order physical properties of polyolefin resin, an essential component of separators for lithium-ion batteries. Furthermore, as shown in Patent Document 2, it is known that within specific crystallinity and gelation rate regions, the separator can suppress heat generation caused by short circuits within the battery while maintaining its shut-off function, and on the other hand, it can prevent membrane rupture (breakdown above 170°C) even when high temperatures are locally generated within the battery cell, thereby ensuring battery safety. More specifically regarding Patent Documents 1 and 2, it has been experimentally discovered that by constructing silane crosslinking portions (gelation structures) within polyolefin separators, high-temperature membrane rupture resistance can be achieved.

[0005] For example, Patent Documents 1-6 describe silane crosslinking structures formed by contacting a silane-modified polyolefin separator with water. Patent Document 8 describes a crosslinking structure formed by ring-opening of norbornene using irradiation with ultraviolet light, electron beams, etc. Patent Document 9 describes a separator whose insulating layer comprises a crosslinked structure, such as a (meth)acrylic acid copolymer or a styrene-butadiene rubber adhesive. Furthermore, for example, a separator has been proposed in which the thickness ratio of an A layer with blocking properties to a B layer containing aramid resin and inorganic materials is adjusted to a specified range (see Patent Document 11).

[0006] With respect to the members for lithium-ion batteries, positive electrode, negative electrode material, electrolyte, and separator are used. Among these members, with respect to the separator, based on the characteristics thereof as an insulating material, it is required to be inactive to electrochemical reaction or surrounding members. On the other hand, the negative electrode material of the lithium-ion battery has established a technology of suppressing decomposition of electrolyte on the surface of the negative electrode by forming a solid electrolyte interface (SEI) by utilizing chemical reaction at the time of initial charging from the beginning of development thereof (non-patent document 1). In addition, there are also reported cases in which even if a polyolefin resin is used for the separator, oxidation reaction is induced on the surface of the positive electrode at high voltage, the separator is blackened, surface deterioration, and the like occur.

[0007] Based on the above idea, with respect to the material of the separator for the power storage device, a chemical structure that is inactive to electrochemical reaction or other chemical reaction is adopted, and thus development and practical use of polyolefin-made micro-porous membranes have been widely carried out. However, as long as polyolefin is adopted as the resin, even if the mechanical micro-porous structure of the separator is improved, the performance improvement is limited. For example, due to the heat resistance stability of the separator above the melting point of the polyolefin or the electronegativity possessed by the olefin unit, affinity or liquid retention with respect to the electrolyte is insufficient, and thus permeability of Li ions or ion clusters solvated therewith in the separator cannot be satisfied.

[0008] Thus, due to the above limitations, when the present situation is dealt with, it is not expected to satisfy the high-speed charge and discharge or heat resistance stability required by modern battery development.

[0009] Prior Art Documents

[0010] Patent Documents

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

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

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

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

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

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

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

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

[0019] Patent Literature 9: Japanese Patent Application Laid-Open (JP A) No. 2014-056843

[0020] Patent Literature 10: Japanese Patent Application Laid-Open (JP A) No. 10-261435

[0021] Patent Literature 11: Japanese Patent Application Laid-Open (JP A) No. 2007-299612

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

[0023] Patent Literature 13: Japanese Patent Application Laid-Open (JP A) No. 2016-072150

[0024] Non-Patent Literature

[0025] Non-Patent Literature 1: Lithium Ion Secondary Battery (2nd Edition) published by Nikkan Kogyo Shimbun, Ltd.

[0026] Non-Patent Literature 2: Fundamentals of Polymer Chemistry published by Tokyo Kagaku Dojin SUMMARY

[0027] Problem to be solved by the invention

[0028] In recent years, high output and high energy density of lithium ion secondary batteries for mobile device mounting applications or vehicle mounting applications are being pursued, on the other hand, miniaturization of battery cells and stable cycle charge-discharge performance during long-term use are required. Therefore, as the separator used, a material that is a thin film (e.g., 15 μm or less) and has high quality (e.g., has uniformity of physical properties and is free of resin agglomerates) is required. Furthermore, with respect to the level of battery safety, it is more stringent than before, as described in Patent Literatures 1 and 2, it is required to have a shutdown function and high temperature film breaking property, and development of a separator resin composition and a production method that can be stably produced is expected. In connection therewith, as the level of shutdown temperature, it is more ideal that it is lower than 150°C, furthermore, as the level of film breaking temperature, it is more ideal that it is higher temperature.

[0029] For example, the method described in Patent Literature 3 performs crosslinking reaction of the silane-modified polyethylene in the extruder by using a crosslinking catalyst master batch at the extrusion step, but there is a problem that the generation of resin agglomerates occurs, which reduces the uniformity of the properties of the separator. In response to this, the methods described in Patent Literatures 4, 5, and 6 cope with it by providing a plasticizer extraction step or a silane gel crosslinking step, or controlling the gel fraction of the resin film, or passing the uncrosslinked resin through hot water to be formed and then dehydrated. Further, Patent Literature 7 proposes to provide a heat-resistant resin microporous film which has excellent low heat shrinkability, low flowability, and melt fracture resistance by adjusting the gel fraction of a polyolefin microporous film, the storage modulus at a temperature of 40°C to 250°C in dynamic viscoelasticity (DMA) measurement, the maximum shrinkage based on thermal mechanical analysis (TMA), and the amount of free radicals measured by electron spin resonance method (ESR).

[0030] Further, regarding the separator for power storage devices, from the viewpoint of dimensional stability, maintenance of the closing function, and improvement of the film breakage temperature, dimensional stability, and the like, it is proposed to provide an inorganic porous layer containing inorganic particles such as calcined kaolin and boehmite and a resin binder on at least one surface of a polyolefin microporous film (Patent Literatures 12 and 13).

[0031] However, the method shown in Patent Literature 4 cannot sufficiently perform the silane crosslinking reaction, and it is difficult to obtain high-temperature film breakage resistance. The plasticizer extraction step described in Patent Literatures 3 and 4 can perform the crosslinking reaction because a tin (II) crosslinking catalyst is used, but there is a risk that the crosslinking catalyst remains thereafter.

[0032] The heat-resistant resin microporous film described in Patent Literature 7 is obtained only by coating a film which has been porousized by a dry method with a photopolymerizable coating solution. Further, Example 5 of Patent Literature 7 adds a low-molecular-weight silane coupling agent such as γ-methacryloyloxypropyltrimethoxysilane to the porous film, but if a low-molecular-weight silane coupling agent is used for a wet-type porousization method, it is expected that the low-molecular-weight silane coupling agent easily reacts or binds with the plasticizer used for the porousization, rather than binding with the resin of the porous film. Further, a battery having the heat-resistant resin microporous film described in Patent Literature 7 as a separator has poor cycle characteristics, and further, when used for a long period of time, an unpredictable side reaction can occur in the battery, and there is a risk that the safety of the battery is reduced.

[0033] Further, the coating layer described in Patent Literature 7 is formed by cross-linking reaction by external stimulus after a compound having a polymerizable functional group is applied to a resin-made porous film, and thus it is expected that a liquid will intrude into a part of the resin-made porous film at the time of applying the coating layer, and that a mixed region of the coating layer and the resin-made porous film will be formed near the interface between them after the cross-linking reaction. Thus, good TMA heat shrinkage properties can be obtained, but a decrease in battery cycle characteristics due to clogging of the resin-made porous film or a decrease in the melting (shutdown) properties accompanied by a melting phenomenon of the resin-made porous film is expected. Furthermore, in the composite microporous film obtained by the method described in Patent Literature 7, a small amount of a free radical species compound is detected by ESR, and since it remains, a chain reaction of decomposition of the electrolyte solution is expected to occur when the composite microporous film is assembled into a battery, and it is considered that the battery performance will be significantly deteriorated.

[0034] Further, the microporous films and separators described in Patent Literatures 1, 2, and 7 lack studies on the arrangement of an inorganic porous layer containing inorganic particles and a resin binder on their surfaces. The existing separators having an inorganic porous layer on a microporous film show an increase in the membrane breaking temperature on the temperature-resistance curve of the power storage device. However, in reality, the resin sometimes dissolves out from the microporous film into the inorganic porous layer, and thus a decrease in the membrane amount of the separator as a whole and a decrease in the stress resistance resulting therefrom are expected. Thus, the multilayer porous films described in Patent Literatures 12 and 13, although having a polyolefin-made microporous film and an inorganic porous layer, leave room for studies on the balance between the low-temperature shutdown function and the high-temperature membrane breaking property as a separator for a power storage device, or the improvement in the cycle characteristics and the battery nail safety of the power storage device.

[0035] Further, the cycle characteristics of a battery using the separators described in Patent Literatures 3 to 7 are poor, and in addition, unpredictable side reactions are expected to occur in the battery during long-term use, and there is a risk of a decrease in the battery safety.

[0036] A conventional molded article such as a hot water pipe has a tin (Sn)-based catalyst put into an extruder at the time of extrusion. On the other hand, the wet-type manufacturing process of a separator for a power storage device generally includes the processes of extrusion · sheet molding, stretching, plasticizer extraction (porous formation), heat treatment, winding, and the like, and thus if the silane cross-linking is promoted in the extruder in the sheet molding process, the gelled portion will be defective, and the stretching of the silane cross-linked polyolefin will be difficult in the stretching process as a subsequent process. Thus, there is room for studies on a new separator for a power storage device suitable for the manufacturing process.

[0037] Further, the cross-linking methods described in Patent Documents 1 to 6, 8, and 9 are all performed in a batch manner in the process of forming the separator film or immediately after the separator is manufactured. Therefore, after the cross-linked structure described in Patent Documents 1 to 6, 8, and 9 is formed, the separator has to be subjected to coating processing and slitting, and the internal stress increases in the subsequent lamination / winding process with the electrode, and thus the battery produced sometimes deforms. For example, if the cross-linked structure is formed by heating, the internal stress of the separator having the cross-linked structure sometimes increases at normal temperature or room temperature.

[0038] Further, if the cross-linked structure is formed by light irradiation of ultraviolet rays, electron rays, or the like, the light irradiation sometimes becomes non-uniform, and the cross-linked structure becomes non-homogeneous. It is considered that this is because the periphery of the crystal portion of the resin constituting the separator is easily cross-linked by electron rays.

[0039] Note that Patent Document 10 describes a technology for improving the cycle characteristics of a lithium-ion secondary battery by adding a succinimide or the like to an electrolyte. However, the technology described in Patent Document 10 is not a technology for improving the cycle characteristics by specifying the structure of the separator.

[0040] In addition, the separator for a power storage device described in Patent Documents 1, 2, and 11 has room for improvement in achieving performance improvement of the power storage device thereof.

[0041] The present application was made in view of the above-described problems, and aims to provide a separator for a power storage device that can balance the closing function and the high-temperature film breakage resistance, and that can ensure the safety, the output, and / or the cycle stability of the power storage device, and a new cross-linking method or a power storage device assembly kit or a manufacturing method that is suitable for the manufacturing process thereof.

[0042] Solution for solving the problem

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

[0045] A separator for a power storage device, characterized by comprising a silane-modified polyolefin, and starting a silane cross-linking reaction of the silane-modified polyolefin when the separator for a power storage device 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 master batch resin containing a dehydration condensation catalyst that cross-links the silane-modified polyolefin. [3]

[0049] The separator for a power storage device according to item 1 or 2, wherein the separator for a power storage device further comprises polyethylene in addition to the silane-modified polyolefin. [4]

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

[0053] A separator for power storage device containing 5 to 40 mass% of a silane-modified polyolefin and 60 to 95 mass% of a polyolefin other than the silane-modified polyolefin, has a storage modulus change ratio (R ΔE’ ) defined by the following formula (1) of 1.5 times to 20 times:

[0054] R ΔE’ = E' S / E' j (1)

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

[0056] (i) Dynamic viscoelasticity measurement is performed under the following conditions:

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

[0058] • Sample film thickness: in the range of 5 to 50 μm

[0059] • Measurement temperature range: -50 to 225°C

[0060] • Temperature increase rate: 10°C / min

[0061] • Measurement frequency: 1 Hz

[0062] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0063] • Initial value of static tension load: 0.5 N

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

[0065] • Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sinusoidal load 0.02 to 5 N).

[0066] (ii) The aforementioned static tensile load refers to the intermediate value of the maximum stress and the minimum stress under periodic motion, and the aforementioned sinusoidal load refers to a vibrational stress centered on the aforementioned static tensile load.

[0067] (iii) The aforementioned sinusoidal tensile mode refers to a mode in which the aforementioned vibrational stress is measured while performing periodic motion at a fixed amplitude of 0.2%, and in the aforementioned sinusoidal tensile mode, the aforementioned vibrational stress is measured by changing the gap distance and the aforementioned static tensile load in such a way that the difference between the aforementioned static tensile load and the aforementioned sinusoidal load is within 20%, and in the case where the aforementioned sinusoidal load is 0.02 N or less, the aforementioned amplitude value is increased in such a way that the aforementioned sinusoidal load is within 5 N and the increase in the aforementioned amplitude value is within 25%.

[0068] (iv) The storage modulus E' is calculated from the obtained sinusoidal load and amplitude value, and the following equation:

[0069] σ * = σ0· Exp[i(ωt + δ)],

[0070] ε * = ε0· Exp(iωt),

[0071] σ * = E * · ε *

[0072] E * = E' + iE"

[0073] (In the equation, σ * : vibrational stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E * : complex modulus, E' : storage modulus, E" : loss modulus

[0074] Vibrational stress: sinusoidal load / initial cross-sectional area

[0075] Static tensile load: load at the minimum point of the vibrational stress within each cycle (minimum point of the gap distance within each cycle)

[0076] Sinusoidal load: difference between the measured vibrational stress and the static tensile load). [6]

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

[0079] R ΔE” = E" S / E" j (3)

[0080] {in the formula, E" j is the loss modulus of the aforementioned separator for an electrical storage device before cross-linking reaction of the aforementioned silane-modified polyolefin, measured at 160°C to 220°C, and E" S is the loss modulus of the aforementioned separator for an electrical storage device after cross-linking reaction of the aforementioned silane-modified polyolefin, 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 (i) to (iv).

[0081] (i) Dynamic viscoelasticity measurement is performed under the following conditions:

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

[0083] • Sample film thickness: in the range of 5 to 50 pm

[0084] • Measurement temperature range: -50 to 225°C

[0085] • Temperature increase rate: 10°C / min

[0086] • Measurement frequency: 1 Hz

[0087] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0088] • Initial value of static tension load: 0.5 N

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

[0090] • Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sinusoidal wave load 0.02 to 5 N).

[0091] (ii) The aforementioned static tension load refers to the intermediate value of the maximum stress and the minimum stress under each periodic motion, and the aforementioned sinusoidal wave load refers to the oscillation stress centered on the aforementioned static tension load.

[0092] (iii) The aforementioned sinusoidal wave tension mode refers to a mode in which the aforementioned vibration stress is measured while performing periodic motion at a fixed amplitude of 0.2%. In the aforementioned sinusoidal wave tension mode, the gap distance and the aforementioned static tension load are changed in such a manner that the difference between the aforementioned static tension load and the aforementioned sinusoidal wave load is within 20% to measure the aforementioned vibration stress. In the case where the aforementioned sinusoidal wave load is 0.02 N or less, the amplitude value is increased in such a manner that the aforementioned sinusoidal wave load is within 5 N and the increase in the amplitude value is within 25% to measure the aforementioned vibration stress.

[0093] (iv) The loss modulus E" is calculated from the obtained sinusoidal wave load and amplitude value, and the following equation:

[0094] σ * = σ0· Exp[i(ωt + δ)],

[0095] ε * = ε0· Exp(iωt),

[0096] σ * = E * · ε *

[0097] E * = E' + iE"

[0098] (In the equation, 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: sinusoidal wave load / initial cross-sectional area

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

[0101] Sinusoidal wave load: difference between measured vibration stress and static tension load). [7]

[0103] A separator for an electrical storage device, wherein when the separator for an electrical storage device is in contact with an electrolyte, a silane cross-linking reaction of a silane-modified polyolefin occurs. [8]

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

[0106] R E’mix = E' a / E'0 (2)

[0107] {in the formula, E' a is the storage modulus of the separator for electrical storage devices described above measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for electrical storage devices not containing the silane-modified polyolefin described above measured at 160°C to 220°C, and is E' a The measurement conditions of the storage modulus E' of E' or E'0 are specified by the following (i) to (iv).

[0108] (i) Dynamic viscoelasticity measurement is performed under the following conditions:

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

[0110] • Sample film thickness: in the range of 5 μm to 50 μm

[0111] • Measurement temperature range: -50 to 225°C

[0112] • Temperature increase rate: 10°C / min

[0113] • Measurement frequency: 1 Hz

[0114] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0115] • Initial value of static tension load: 0.5 N

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

[0117] • Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sinusoidal wave load 0.02 to 5 N).

[0118] (ii) The static tension load described above refers to the intermediate value of the maximum stress and the minimum stress under each periodic motion, and the sinusoidal wave load refers to the oscillation stress centered on the static tension load described above.

[0119] (iii) The aforementioned sinusoidal wave tension mode refers to a mode in which the aforementioned vibration stress is measured while performing periodic motion at a fixed amplitude of 0.2%. In the aforementioned sinusoidal wave tension mode, the gap distance and the aforementioned static tension load are changed in such a manner that the difference between the aforementioned static tension load and the aforementioned sinusoidal wave load is within 20% to measure the aforementioned vibration stress. In the case where the aforementioned sinusoidal wave load is 0.02 N or less, the amplitude value is increased in such a manner that the aforementioned sinusoidal wave load is within 5 N and the increase in the aforementioned amplitude value is within 25% to measure the aforementioned vibration stress.

[0120] (iv) The storage modulus E' is calculated from the obtained sinusoidal wave load and amplitude value, and the following equation:

[0121] σ * = σ0 · Exp[i(ωt + δ)],

[0122] ε * = ε0 · Exp(iωt),

[0123] σ * = E * · ε *

[0124] E * = E' + iE"

[0125] (In the equation, 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: sinusoidal wave load / initial cross-sectional area

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

[0128] Sinusoidal wave load: difference between measured vibration stress and static tension load). [9]

[0130] A separator for an electrical storage device, which contains 5 to 40 mass% of a silane-modified polyolefin and 60 to 95 mass% of a polyolefin other than the aforementioned silane-modified polyolefin, has a mixed loss modulus ratio (R E”mix ) defined by the following equation (4) of 1.5 times to 20.0 times:

[0131] R E”mix = E" a / E"0 (4)

[0132] {in the formula, E" a is a loss modulus measured at 160°C to 220°C of the separator for electrical storage devices described above, and E"0is a loss modulus measured at 160°C to 220°C of the separator for electrical storage devices not containing the silane-modified polyolefin described above, and is E" a The measurement conditions of the loss modulus E" of E" or E"0are specified by the following (i) to (iv).

[0133] (i) Dynamic viscoelasticity measurement is performed under the following conditions:

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

[0135] • Sample film thickness: in the range of 5 to 50 μm

[0136] • Measurement temperature range: -50 to 225°C

[0137] • Temperature increase rate: 10°C / min

[0138] • Measurement frequency: 1 Hz

[0139] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0140] • Initial value of static tension load: 0.5 N

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

[0142] • Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sinusoidal wave load 0.02 to 5 N).

[0143] (ii) The static tension load described above refers to the intermediate value of the maximum stress and the minimum stress under each periodic motion, and the sinusoidal wave load described above refers to the oscillation stress centered on the static tension load described above.

[0144] (iii) The sinusoidal wave tension mode described above refers to measurement of the oscillation stress while performing periodic motion at a fixed amplitude of 0.2%, and under the sinusoidal wave tension mode, the gap distance and the static tension load described above are changed in such a manner that the difference between the static tension load and the sinusoidal wave load described above is within 20%, and the oscillation stress is measured, and in the case where the sinusoidal wave load described above is 0.02 N or less, the amplitude value is increased in such a manner that the sinusoidal wave load described above is within 5 N and the increase in the amplitude value is within 25%, and the oscillation stress is measured.

[0145] (iv) The loss modulus E" is calculated from the relationship between the obtained sinusoidal wave load and the 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] (In the formula, σ * : oscillatory stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between oscillatory stress and strain, E * : complex modulus, E': storage modulus, E": loss modulus

[0151] Oscillatory stress: sinusoidal wave load / initial cross-sectional area

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

[0153] Sinusoidal wave load: difference between measured oscillatory stress and static tensile load).

[10]

[0155] The separator for power storage devices according to item 8 or 9, wherein the separator for power storage devices not containing the aforementioned silane-modified polyolefin is a micro-porous film of a silane-unmodified polyolefin having a gelation degree of 0% or more and 10% or less.

[11]

[0157] A separator for power storage devices containing 5 to 40 mass% of a silane-modified polyolefin and 60 to 95 mass% of a polyolefin other than the aforementioned silane-modified polyolefin, wherein the transition temperature of a rubbery flat region and a crystalline melting flow region in the temperature change of the storage modulus of the aforementioned separator for power storage devices is 135°C to 150°C.

[12]

[0159] A separator for power storage devices containing a polyolefin micro-porous film,

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

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

[0162] the minimum value of the loss modulus is 0.1 MPa to 10 MPa, and the maximum value of the loss modulus is 10 MPa to 10,000 MPa,

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

[0164] (i) The dynamic viscoelasticity measurement is performed under the following conditions:

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

[0166] • Sample film thickness: 200 μm to 400 μm (in the case where the film thickness of a single sample is less than 200 μm, the dynamic viscoelasticity measurement is performed in such a manner that a plurality of samples are laminated so that the total thickness is in the range of 200 μm to 400 μm.)

[0167] • Measurement temperature range: -50°C to 250°C

[0168] • Temperature increase rate: 10°C / min

[0169] • Measurement frequency: 1 Hz

[0170] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0171] • Initial value of static tension load: 0.2 N

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

[0173] • Automatic strain adjustment (automatic strain adjustment): disabled (Disabled);

[0174] (ii) The aforementioned static tension load refers to the intermediate value of the maximum stress and the minimum stress under each periodic motion, and the aforementioned sinusoidal wave load refers to the oscillation stress centered on the aforementioned static tension load;

[0175] (iii) The aforementioned sinusoidal wave tension mode refers to the measurement of the aforementioned oscillation stress while performing periodic motion at a fixed amplitude of 0.1%, and under the aforementioned sinusoidal wave tension mode, the gap distance and the aforementioned static tension load are changed so that the difference between the aforementioned static tension load and the aforementioned sinusoidal wave load is within 5%, and the aforementioned oscillation stress is measured, and in the case where the aforementioned sinusoidal wave load is 0.1 N or less, the aforementioned static tension load is fixed to 0.1 N, and the aforementioned oscillation stress is measured;

[0176] (iv) The aforementioned storage modulus and the aforementioned loss modulus are calculated from 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] {in the formula, σ * : oscillatory stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between oscillatory stress and strain, E * : complex modulus, E': storage modulus, E": loss modulus

[0182] Oscillatory stress: sinusoidal wave load / initial cross-sectional area

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

[0184] Sinusoidal wave load: difference between measured oscillatory stress and static tensile load}.

[13]

[0186] A separator for power storage devices, comprising a polyolefin microporous membrane, wherein, in a solid viscoelasticity measurement of the aforementioned separator for power storage devices from a film softening transition temperature to a film breakage temperature, an average storage modulus is 1.0 MPa to 12 MPa, and an average loss modulus is 0.5 MPa to 10 MPa.

[14]

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

[15]

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

[16]

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

[17]

[0194] A separator for an electrical storage device, characterized by comprising a polyolefin, the aforementioned polyolefin having one or two or more functional groups, and

[0195] After being housed in an electrical storage device, (1) condensation reactions occur between the aforementioned functional groups, or (2) the aforementioned functional groups react with chemical substances inside the aforementioned electrical storage device, or (3) the aforementioned functional groups react with other types of functional groups, thereby forming crosslinked structures.

[18]

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

[19]

[0199] A separator for an electrical storage device, which comprises a polyolefin, and has an amorphous portion crosslinked structure obtained by crosslinking an amorphous portion of the aforementioned polyolefin.

[20]

[0201] The separator for an electrical storage device according to item 19, wherein the aforementioned separator for an electrical storage device has a hybrid storage modulus ratio (R E’X ) defined by the following formula (1) of 1.5 times to 20 times:

[0202] R E’X = E' Z / E' Z0 (1)

[0203] {wherein E' Z is a storage modulus measured in a temperature range of 160°C to 300°C after crosslinking reactions of the aforementioned separator for an electrical storage device are performed inside an electrical storage device, and

[0204] E' Z0 is a storage modulus measured in a temperature range of 160°C to 300°C before the aforementioned separator for an electrical storage device is assembled into the aforementioned electrical storage device.}.

[21]

[0206] The separator for an electrical storage device according to item 19 or 20, wherein the aforementioned separator for an electrical storage device has a hybrid loss modulus ratio (R E”X ) defined by the following formula (3) of 1.5 times to 20 times:

[0207] R E”X = E" Z / E" Z0 (3)

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

[0209] E" Z0 is a loss modulus measured in a temperature range of 160°C to 300°C before the separator for power storage device is assembled in the power storage device.

[22]

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

[23]

[0213] The separator for power storage device according to any one of items 17 to 22, wherein the separator for power storage device has a hybrid storage modulus ratio (R E’mix ) of 1.5 times to 20 times as defined by the following formula (2):

[0214] R E’mix = E' / E'0 (2)

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

[0216] E'0 is a storage modulus measured at 160°C to 300°C of the separator for power storage device which does not have an amorphous portion cross-linked structure.}

[24]

[0218] The separator for power storage device according to any one of items 17 to 23, wherein the separator for power storage device has a hybrid loss modulus ratio (R E”mix ) of 1.5 times to 20 times as defined by the following formula (4):

[0219] R E”mix = E" / E"0 (4)

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

[0221] E"0 is a loss modulus measured at 160°C to 300°C of the separator for power storage device which does not have an amorphous portion cross-linked structure.}

[25]

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

[26]

[0225] The separator for power storage devices 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 power storage devices according to any one of items 17 to 26, wherein the crosslinking structure is formed by a reaction via any of a covalent bond, a hydrogen bond, or a coordination bond.

[28]

[0229] The separator for power storage devices 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 a plurality of identical functional groups;

[0231] (II) reaction between a plurality of different functional groups;

[0232] (III) chain condensation reaction of a functional group and an electrolyte; and

[0233] (IV) reaction of a functional group and an additive.

[29]

[0235] The separator for power storage devices according to item 27, wherein,

[0236] The reaction via a coordination bond is the following reaction (V):

[0237] (V) reaction of a plurality of identical functional groups crosslinking via a coordination bond with a metal ion.

[30]

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

[31]

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

[32]

[0243] The separator for power storage devices according to item 28, wherein the reaction (IV) is a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction of a compound Rx constituting the separator for power storage devices and a 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 power storage devices according to the above 32, wherein

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

[0247] The functional group x of the above 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 above compound Ry is at least two selected from the group consisting of CH3SO2-, CF3SO2-, ArSO2-, CH3SO3-, CF3SO3-, ArSO3-, and monovalent radicals represented by the following formulae (y1-1) to (y1-6):

[0249]

[0250] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0251]

[0252] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0253]

[0254] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0255]

[0256] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0257]

[0258] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0259]

[0260] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[34]

[0262] The separator for power storage devices according to the above 32 or 33, wherein

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

[0264] The above compound Ry has a chain unit y2 in addition to the above linking reaction unit y1, and

[0265] The aforementioned 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] {in the formula, m is an integer of 0 to 20, and n is an integer of 1 to 20.}

[0268]

[0269] {in the formula, n is an integer of 1 to 20.}

[0270]

[0271] {in the formula, n is an integer of 1 to 20.}

[0272]

[0273] {in the formula, n is an integer of 1 to 20.}

[0274]

[0275] {in the formula, X is an alkylene group having 1 to 20 carbons, or an arylene group, and n is an integer of 1 to 20.}

[0276]

[0277] {in the formula, X is an alkylene group having 1 to 20 carbons, or an arylene group,

[0278] and n is an integer of 1 to 20.}.

[35]

[0280] The separator for power storage devices according to item 32, wherein

[0281] The aforementioned reaction (IV) is a nucleophilic addition reaction,

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

[0283] The aforementioned 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] {in the formula, R is a hydrogen atom or a monovalent organic group.}

[0286]

[36]

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

[0289] The aforementioned reaction (IV) is a ring-opening reaction,

[0290] The functional group x of the aforementioned compound Rx is at least 1 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 2 groups represented by the following formula (ROy1-1):

[0292]

[0293] {In the formula, each of the plurality of X is independently a hydrogen atom or a monovalent substituent.}.

[37]

[0295] The separator for power storage device according to item 29, wherein in the aforementioned reaction (V), the aforementioned metal ion is at least 1 selected from the group consisting of Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ , and Li + .

[38]

[0297] A separator for power storage device including a silane-modified polyolefin, provided with a first porous layer (A layer) capable of forming a crosslinked structure and a second porous layer (B layer) including inorganic particles, a thermal shrinkage at 150°C after the aforementioned crosslinked structure is formed is 0.02 times or more and 0.91 times or less of a thermal shrinkage at 150°C before the aforementioned crosslinked structure is formed.

[39]

[0299] The separator for power storage device according to item 38, wherein the aforementioned crosslinked structure in the aforementioned A layer is formed by an acid, a base, swelling, or a compound generated in the power storage device.

[40]

[0301] A separator for power storage device including:

[0302] A microporous membrane including a silane-modified polyolefin, and

[0303] An inorganic porous layer including inorganic particles and a resin binder arranged on at least one surface of the aforementioned microporous membrane.

[41]

[0305] The separator for power storage devices according to the above 40, wherein the content of the inorganic particles in the inorganic porous layer is 5 to 99% by mass.

[42]

[0307] The separator for power storage devices according to the above 40 or 41, wherein the content of the silane-modified polyolefin in the microporous film is 0.5 to 40% by mass.

[43]

[0309] The separator for power storage devices according to any one of the above 40 to 42, wherein the inorganic particles are at least one selected from the group consisting of alumina (Al203), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide (AIO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, phlogopite, montmorillonite, sericite, mica, antigorite, bentonite, asbestos, zeolite, diatomite, quartz sand, and glass fiber.

[44]

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

[45]

[0313] The separator for power storage devices according to any one of the above 40 to 44, wherein the silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator for power storage devices is in contact with an electrolyte.

[46]

[0315] The separator for power storage devices according to any one of the above 40 to 45, wherein,

[0316] The storage modulus change ratio (R △E’ ) defined by the following formula (1A) is 1.5 to 20 when the separator for power storage devices is measured by removing the inorganic porous layer:

[0317] R △E’ = E' S / E' j (1A)

[0318] {wherein E' j is the storage modulus of the separator for power storage devices measured at 160 to 220°C before the silane-modified polyolefin is crosslinked, and E' SThe storage modulus of the aforementioned separator for power storage devices after the cross-linking reaction of the aforementioned 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] {in the formula, E" j is the loss modulus of the aforementioned separator for power storage devices measured at 160°C to 220°C before the cross-linking reaction of the aforementioned silane-modified polyolefin, and E" S is the loss modulus of the aforementioned separator for power storage devices measured at 160°C to 220°C after the cross-linking reaction of the aforementioned silane-modified polyolefin.}

[47]

[0323] The separator for power storage devices according to any one of items 40 to 46, wherein

[0324] The aforementioned separator for power storage devices, when measured by removing the aforementioned inorganic porous layer, has a hybrid storage modulus ratio (R E’mix ) of 1.5 to 20 times, defined by the following formula (2A):

[0325] R E’mix = E' / E'0 (2A)

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

[0327] and / or a hybrid loss modulus ratio (R E”mix ) of 1.5 to 20 times, defined by the following formula (2B):

[0328] R E”mix = E" / E"0 (2B)

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

[48]

[0331] The separator for power storage device according to any one of items 40 to 47, in a temperature change of the storage modulus of the aforementioned separator for power storage device, the transition temperature of the rubber-like flat region and the crystal melting flow region is 135°C to 150°C.

[49]

[0333] A power storage device including an electrode, the separator for power storage device according to any one of items 1 to 48, and a nonaqueous electrolyte.

[50]

[0335] A power storage device including a separator including polyethylene, and including an electrolyte or an additive, a functional group-modified polyethylene or a functional group-grafted copolymer polyethylene reacts with a chemical substance included in the aforementioned electrolyte or the aforementioned additive, thereby forming a crosslinked structure.

[51]

[0337] A manufacturing method of a separator for power storage device according to any one of items 1 to 50, including the following steps:

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

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

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

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

[52]

[0343] A manufacturing method of a separator for power storage device, including the following steps:

[0344] (1) A sheet forming step of extruding a silane-modified polyolefin, polyethylene, and a plasticizer into a sheet shape with an extruder, cooling and solidifying, and processing into a sheet-shaped formed body;

[0345] (2) A stretching step of biaxially stretching the aforementioned sheet-shaped formed body at a surface ratio of 20 times or more and 250 times or less, to form a stretched product;

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

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

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

[0349] (9) an assembly step of housing an electrode, a laminate or a wound body of the silane crosslinking precursor, and a nonaqueous electrolyte solution in an outer housing, and bringing the silane crosslinking precursor into contact with the nonaqueous electrolyous solution.

[53]

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

[0352] (1) an outer housing housing a laminate or a wound body of an electrode and a separator for a power storage device described in any one of items 1 to 48; and

[0353] (2) a container housing a nonaqueous electrolyte solution.

[54]

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

[55]

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

[56]

[0359] The power storage device assembly kit according to any one of items 53 to 55, wherein the nonaqueous electrolyte solution is an acid solution and / or an alkali solution.

[57]

[0361] A method for manufacturing a power storage device, comprising the following steps:

[0362] a step of preparing a power storage device assembly kit described in any one of items 53 to 56, and

[0363] a step of starting a silane crosslinking reaction of a silane-modified polyolefin by bringing the separator for a power storage device in the element (1) of the power storage device assembly kit into contact with the nonaqueous electrolyte solution in the element (2).

[58]

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

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

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

[59]

[0369] A method for manufacturing an electrical storage device, which is a method for manufacturing an electrical storage device using a separator containing a polyolefin,

[0370] The aforementioned polyolefin contains one or two or more functional groups, and the method includes a cross-linking step of:

[0371] (1) allowing condensation reactions between the aforementioned functional groups, or (2) allowing the aforementioned functional groups to react with chemical substances inside the aforementioned electrical storage device, or (3) allowing the aforementioned functional groups to react with other types of functional groups, thereby forming a cross-linking structure.

[60]

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

[0374] Effects of the invention

[0375] According to the present application, it is possible to provide an electrical storage device and an assembly kit thereof, which can take into account both a low-temperature closing function and a high-temperature film rupture resistance of a separator for an electrical storage device, further suppress the generation of unmelted resin agglomerates in the manufacturing process thereof, contribute to productivity and economy, and further have good cycle characteristics and high safety.

[0376] Further, according to the present application, it is possible to form a cross-linking structure without using a high energy such as light irradiation or heating in or immediately after a film formation process, and thus it is possible to suppress an increase in internal stress of the separator and deformation after the electrical storage device is manufactured, and / or it is possible to impart a cross-linking structure to the separator without using a high energy such as light irradiation or heating, and reduce cross-linking unevenness. Further, according to the present application, a cross-linking structure is formed not only inside the separator but also between the separator and an electrode or between the separator and a solid electrolyte interface (SEI), it is possible to improve the strength between the plurality of members of the electrical storage device, suppress a gap generated between the separator and the electrode due to expansion and contraction of the electrode at the time of charge and discharge of the electrical storage device, and significantly improve cycle stability during long-term use. BRIEF DESCRIPTION OF DRAWINGS

[0377] Figure 1 is one example of a graph for explaining the relationship between temperature and storage modulus, and shows the transition temperature of a rubber-like flat region and a crystal melting flow region by comparing the storage modulus of a standard film and a film after cross-linking in the temperature range of -50°C to 225°C.

[0378] Figure 2 is one example of a graph for explaining the relationship between temperature and loss modulus, and shows the transition temperature of a rubber-like flat region and a crystal melting flow region by comparing the loss modulus of a standard film and a film after cross-linking in the temperature range of -50°C to 225°C.

[0379] Figure 3 is a graph showing the relationship between the temperature and the resistance of the power storage device provided with the separator obtained in Example I-1.

[0380] Figure 4 is a graph for explaining the relationship between the temperature, the gap distance, the storage modulus, and the loss modulus in the viscoelasticity measurement of the separator for power storage, and illustrates graph (a) of Example II-1 and graph (b) of Comparative Example II-1.

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

[0382] Figure 6 is a schematic diagram for explaining a crystalline polymer having a high-order structure of a lamella (crystal portion) having a crystal structure, an amorphous portion, and an intermediate layer portion between them.

[0383] Figure 7 is a schematic diagram for explaining the crystal growth of a polyolefin molecule.

[0384] Figure 8 is a strain amount-crystal fraction graph for showing the X-ray crystal structure change at the time of tensile fracture failure test for the film of one embodiment of the present application.

[0385] Figure 9 is one example of a graph for explaining the relationship between the temperature and the storage modulus, and compares the storage modulus of a standard film with that of a film after crosslinking in the temperature range of -50°C to 310°C, and shows the transition temperature of a rubbery flat region and a crystal melting flow region.

[0386] Figure 10 is one example of a graph for explaining the relationship between the temperature and the loss modulus, and compares the loss modulus of a standard film with that of a film after crosslinking in the temperature range of -50°C to 310°C, and shows the transition temperature of a rubbery flat region and a crystal melting flow region.

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

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

[0389] Figure 13 is a crosslinked state of the separator obtained in Example I-1 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b). DETAILED DESCRIPTION

[0390] Hereinafter, a specific embodiment of the present application (hereinafter, simply referred to as "embodiment") will be explained in detail. It should be noted that the present application is not limited to the following embodiment, and can be implemented by various modifications within the scope of the gist thereof.

[0391] In the present specification, "~" means that the numerical value including both ends thereof is included as the upper limit value and the lower limit value. Further, in the present specification, the upper limit value and the lower limit value of the numerical range can be combined arbitrarily. For example, the upper limit value of the preferable numerical range can be combined with the lower limit value of the more preferable numerical range, and vice versa, the upper limit value of the more preferable numerical range can be combined with the lower limit value of the preferable numerical range.

[0392] It should be noted that in the present specification, "on" and "formed on the surface of" do not mean that the positional relationship of the members is limited to "directly above". For example, the description of "a layer B formed on a layer A" and "a layer B formed on the surface of a layer A" does not exclude a manner including any layer other than any one of the layer A and the layer B therebetween.

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

[0394] <Separator for power storage device>

[0395] One aspect of the present application is a separator for power storage device (hereinafter, also simply referred to as "separator"). The separator needs to have insulation and ion permeability, and thus generally includes paper, polyolefin nonwoven fabric, or a resin microporous membrane, or the like, which are insulating materials having a porous structure. In particular, in a lithium ion battery, a polyolefin microporous membrane that can construct a porous structure that is resistant to oxidation-reduction deterioration and is dense and uniform is preferable.

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

[0397] In the case where the power storage device includes the separator, the separator can be taken out 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 other polyolefins may also be included, depending on preference. When the separator of the first embodiment comes into contact with the electrolyte, a silane crosslinking reaction of the silane-modified polyolefin contained in the separator begins. Since the separator of the first embodiment can undergo crosslinking of the silane-modified polyolefin when in contact with the electrolyte, the timing of the crosslinking can be controlled. Therefore, the crosslinking reaction can be carried out in the manufacturing process of the energy storage device without it occurring in the manufacturing process of the separator.

[0400] The separator of the second embodiment is characterized in that a silane crosslinking reaction of the silane-modified polyolefin occurs upon contact with the electrolyte. In the second embodiment, regardless of whether the separator contains silane-modified polyolefin, the location of the residual silane-modified polyolefin, or whether the silane crosslinking reaction occurs initially, sequentially, or continuously upon contact with the electrolyte, it is acceptable as long as the silane crosslinking reaction is observed upon contact with the electrolyte. Through the silane crosslinking reaction of the silane-modified polyolefin that occurs upon contact with the electrolyte by the separator of the second embodiment, the crosslinking time point can be controlled regardless of the manufacturing or usage process of the separator.

[0401] The separators of the first and second embodiments can promote cross-linking reactions when electrolyte is injected into the outer casing containing the separator, thus avoiding manufacturing defects in their manufacturing process and achieving safety and high output of the energy storage device in the manufacturing process of the energy storage device. From the perspective of the components contained in the separator and the timing of the cross-linking reaction, it is preferable to start the silane cross-linking reaction of the silane-modified polyolefin when the separator is mixed or in contact with the electrolyte.

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

[0403] R ΔE’ =E' S / E' j (1)

[0404] In the formula, E' j The energy storage modulus of the separator for an energy storage device measured at 160℃~220℃ before crosslinking reaction of silane-modified polyolefin, and E' S The energy storage modulus of a separator for an energy storage device after crosslinking a silane-modified polyolefin was measured at 160℃~220℃.

[0405] and / or the loss modulus change ratio (R) defined by the following equation (3) ΔE”) is 1.5 times to 20 times:

[0406] R ΔE” = E" S / E" j (3)

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

[0408] The third embodiment can achieve a balance of the closing function and the high-temperature film breakage resistance by making the storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE” ) be in the range of 1.5 times to 20 times. The storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE” ) is preferably 2 times to 18 times. Note that E' j and E' S and E" j and E" S are average values of the storage modulus or the loss modulus measured in the set temperature range of the measuring device when 160 to 220°C is set as the widest temperature range. Further, in the case where the separator is in the form of a laminate film, the storage modulus E' j and E' S and the loss modulus E" j and E" S are measured from the porous film containing the silane-modified polyolefin only out of the laminate film.

[0409] The separator of the fourth embodiment contains 5 to 40 mass% of the silane-modified polyolefin and 60 to 95 mass% of the polyolefin other than the aforementioned silane-modified polyolefin, and the mixed storage modulus ratio (R E’mix ) defined by the following formula (2) is 1.5 times to 20 times with respect to the viscoelasticity measurement (version 1) described in the examples:

[0410] R E’mix = E' a / E'0 (2)

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

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

[0413] R E”mix = E" a / E"0 (4)

[0414] {In the formula, E" a is the loss modulus of the separator for power storage described above measured at 160°C to 220°C, and E"0 is the loss modulus of the separator for power storage not containing the silane-modified polyolefin measured at 160°C to 220°C.}.

[0415] In the fourth embodiment, by making the hybrid storage modulus ratio (R E’mix ) and / or the hybrid loss modulus ratio (R E”mix ) be in the range of 1.5 to 20.0, the simultaneous achievement of the closing function and the high-temperature film breakage resistance can be achieved. The hybrid storage modulus ratio (R E’mix ) and / or the hybrid loss modulus ratio (R E”mix ) is preferably 2 to 18. Note that E' a and E'0 and E" a and E"0 are the average values of the storage modulus or the loss modulus measured in the set temperature range of the measuring device when 160 to 220°C is set as the widest temperature range. Further, in the case where the separator is in the form of a laminated film, the storage modulus E' a and E'0 and the loss modulus E" a and E"0 are measured from the porous film containing the silane-modified polyolefin only out of the laminated film.

[0416] The separator of the fifth embodiment contains 5 to 40 mass% of the silane-modified polyolefin and 60 to 95 mass% of the polyolefin other than the silane-modified polyolefin, and, in the temperature change in the storage modulus or the loss modulus thereof, the transition temperature of the rubbery flat region and the crystalline melting flow region is 135°C to 150°C with respect to the viscoelasticity measurement (version 1) described in the examples. The fifth embodiment, by making the transition temperature of the rubbery flat region and the crystalline melting flow region be in the range of 135°C to 150°C, can achieve the simultaneous achievement of the closing function and the high-temperature film breakage resistance. The transition temperature of the rubbery flat region and the crystalline melting flow region is preferably 137°C to 147°C, more preferably 140°C to 145°C, and further preferably 140°C to 143°C. Note that, in the case where the separator is in the form of a laminated film, the transition temperature of the rubbery flat region and the crystalline melting flow region is measured from the porous film containing the silane-modified polyolefin only out of the laminated body.

[0417] <Sixth and Seventh Embodiments>

[0418] The separator of the sixth embodiment contains a polyolefin having one or two or more functional groups, and after being housed in the power storage device, (1) condensation reactions occur between the functional groups of the polyolefin, or (2) reactions occur between the functional groups of the polyolefin and chemical substances inside the power storage device, or (3) reactions occur between the functional groups of the polyolefin and other types of functional groups, thereby forming a crosslinked structure. It is thought that the functional groups contained in the polyolefin constituting the separator do not enter the crystal portion of the polyolefin, but rather crosslink in the amorphous portion, and thus the separator of the sixth embodiment forms a crosslinked structure using the surrounding environment or chemical substances inside the power storage device after being housed in the power storage device, thereby being able to suppress an increase in internal stress or deformation of the manufactured power storage device.

[0419] On the other hand, in the case where the crosslinking reaction is performed before being housed in the power storage device, and processes such as winding and slitting are performed, the effects of stress such as tension generated at the time of the processes remain. At this time, in the case where the stress is released after assembly of the power storage device, it is thought that this will cause deformation of the electrode winding or the like, or breakage due to stress concentration, and thus is not preferable.

[0420] In the sixth embodiment, (1) the condensation reactions between the functional groups of the polyolefin can be, for example, reactions between two or more functional groups A contained in the polyolefin via covalent bonds. (3) The reactions between the functional groups of the polyolefin and other types of functional groups can be, for example, reactions between a functional group A and a functional group B contained in the polyolefin via covalent bonds.

[0421] Further, in (2) the reactions between the functional groups of the polyolefin and chemical substances inside the power storage device, for example, the functional group A contained in the polyolefin can form a covalent bond or a coordination bond with any of an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof contained in the power storage device. Further, according to reaction (2), a crosslinked 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), and the strength between the various members of the power storage device can be improved.

[0422] The separator of the seventh embodiment contains a polyolefin, and has an amorphous portion crosslinked structure in which the amorphous portion of the polyolefin is crosslinked. It is thought that the functional groups contained in the polyolefin constituting the separator do not enter the crystal portion of the polyolefin, but rather crosslink in the amorphous portion, and thus the separator of the seventh embodiment, compared to the existing crosslinked separators in which the crystal portion and the periphery thereof easily crosslink, is able to suppress an increase in internal stress or deformation of the manufactured power storage device while giving consideration to the closing function and high-temperature puncture resistance, and furthermore is able to ensure 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 crystal portion.

[0423] The crosslinking reaction mechanism and crosslinking structure of the seventh embodiment described above are not yet clear, but the inventors have made the following considerations.

[0424] (1) Crystal structure in microporous membranes made of high-density polyethylene

[0425] Polyolefin resins, such as high-density polyethylene, etc. Figure 6 As shown, these are generally crystalline polymers with a higher-order structure consisting of crystalline lamellar (crystalline) portions, amorphous portions, and intermediate layers between them. In the crystalline portions and the intermediate layers between the crystalline and amorphous portions, the polymer chains have low mobility and are difficult to cut; however, relaxation phenomena can be observed in solid viscoelasticity measurements in the 0–120°C region. On the other hand, the polymer chains in the amorphous portions have very high mobility, and this has been observed in solid viscoelasticity measurements in the -150–-100°C region. This is closely related to free radical relaxation, free radical transfer reactions, cross-linking reactions, etc., which will be discussed later.

[0426] Furthermore, the polyolefin molecules that make up the crystal are not singular, such as... Figure 7 As an example, multiple polymer chains form small lamellae, which then aggregate to form crystals. This phenomenon is difficult to observe directly. In recent years, simulations have been used to advance research and clarify this phenomenon. It should be noted that, here, "crystal" refers to the smallest crystalline unit measured through X-ray structural analysis, a unit whose size can be calculated as a microcrystal. Thus, although it refers to the crystalline part (the interior of the lamellae), it is predicted that there exists a portion within the crystal that is unconstrained and has slightly higher mobility.

[0427] (2) Crosslinking reaction mechanism based on electron beams

[0428] Next, the reaction mechanism of electron beam crosslinking (hereinafter, abbreviated as EB crosslinking) of the polymer is as follows. (i) Irradiation of electron beam of several tens to several hundreds of kGy, (ii) penetration of the electron beam into the reaction target (the polymer) and generation of secondary electrons, (iii) hydrogen abstraction reaction in the polymer chain based on the secondary electrons and generation of radicals, (iv) abstraction of adjacent hydrogen based on the radicals and movement of active sites, (v) crosslinking reaction based on recombination between radicals or formation of polyene. Here, regarding the radicals generated in the crystal portion, since the movement is poor, the radicals exist for a long time, and impurities and the like cannot enter the crystal, so the probability of reaction and quenching is low. Such a radical species is called a stable radical, and remains for several months, and the lifetime is clarified by ESR measurement. As a result, it is considered that the crosslinking reaction in the crystal is poor. However, the radicals generated in the slightly present molecular chain or the peripheral crystal-amorphous intermediate layer portion have a slightly long lifetime. Such a radical species is called a persistent radical, and it is considered that the crosslinking reaction between the molecular chains proceeds with a high probability in an environment having mobility. On the other hand, since the amorphous portion has very high mobility, the lifetime of the radical species generated is short, and it is considered that not only the crosslinking reaction between the molecular chains but also the polyene reaction within one molecular chain proceeds with a high probability.

[0429] As described above, it can be inferred that the crosslinking reaction based on EB crosslinking locally exists in the crystal or the periphery thereof in the microscopic view at the crystal level.

[0430] (3) Crosslinking reaction mechanism based on chemical reaction

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

[0432] As described above, the crystal portion and the amorphous portion exist in the polyolefin resin. However, the aforementioned functional group locally exists in the amorphous portion due to steric hindrance, and does not exist in the crystal. This is widely known that a unit such as a methyl group slightly contained in a polyethylene chain sometimes enters the crystal, but a graft having a larger volume than an ethyl group does not enter (non-patent literature 2). Therefore, the crosslinking point based on a reaction different from electron beam crosslinking locally exists in the amorphous portion.

[0433] (4) Relationship between difference in crosslinking structure and effect

[0434] As described above, in the cross-linking reaction based on the chemical reaction inside the battery in the seventh embodiment of the present application, the morphology of the reaction product is different. In the research until the present application was completed, in order to clarify the cross-linking structure and to clarify the change in the physical properties of the microporous membrane accompanying the structural change, the phenomenon was clarified by the following experiments.

[0435] First, the mechanical properties of the membrane based on the tensile fracture test were investigated. In addition, while the tensile fracture test was performed, the change in the crystal structure was analyzed by in-situ X-ray structure analysis using a radioactive light. As a result, as shown in Figure 8 , compared with the membrane on which no EB cross-linking or chemical cross-linking (before) was performed, the EB cross-linked membrane was inhibited from being subdivided in the crystal portion as the strain amount increased. This is because the cross-linking was selectively performed in or around the crystal portion. As a result, the Young's modulus and the breaking strength were significantly improved, and a high mechanical strength could be exhibited. On the other hand, the chemical cross-linked membrane did not show a difference in the subdivision of the crystal before and after the cross-linking reaction, and thus it was suggested that the cross-linking was selectively performed in the amorphous portion. In addition, there was no change in the mechanical strength before and after the cross-linking reaction.

[0436] Next, the behavior at the time of melting of the crystal was investigated by the fusing / melt fracture property test. As a result, the fusing temperature of the EB cross-linked membrane was significantly increased, and the melt fracture temperature was increased to 200°C or more. On the other hand, it was confirmed that the fusing temperature of the chemical cross-linked membrane did not show a change before and after the cross-linking treatment, and the melt fracture temperature was increased to 200°C or more. From this, it was considered that in the fusing (closing) property generated by the melting of the crystal, the EB cross-linked membrane was cross-linked around the crystal portion, and thus the increase in the melting temperature and the decrease in the melting speed were the causes. On the other hand, it was judged that the chemical cross-linked membrane did not have a cross-linking structure in the crystal portion, and thus did not change the closing property. In addition, in the high temperature region of 200°C or more, since both of them had a cross-linking structure after the melting of the crystal, the entire resin material could be stabilized in a gel state, and a good melt fracture property could be obtained.

[0437] The above knowledge is summarized in the following table.

[0438] [Table 1]

[0439]

[0440] The separator of the seventh embodiment is defined by the following equation (1) with respect to the viscoelasticity measurement (version 2) described in the examples, in terms of forming an amorphous portion cross-linking structure, taking into account the closing function and the high temperature breakage resistance, and the like, the mixed storage modulus ratio (R E’X ) of the following equation (1):

[0441] R E’X = E' Z / E'Z0 (1)

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

[0443] E' Z0 is a storage modulus measured in a temperature range of 160°C to 300°C before the separator for power storage device is assembled in the power storage device.}

[0444] and / or a loss modulus ratio (R E”X ) defined by the following formula (3):

[0445] R E”X = E'0 / E' Z Z0 (3)

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

[0447] E' Z0 is a loss modulus measured in a temperature range of 160°C to 300°C before the separator for power storage device is assembled in the power storage device.}

[0448] is preferably 1.5 times to 20 times, and more preferably 3 times to 18 times. Note that E' Z and E' Z0 and E' Z and E' Z0 are each an average value of the storage modulus or the loss modulus measured in the set temperature range of the measuring device when 160°C to 300°C is set as the widest temperature range. Further, in the case where the separator is in the form of a layered film, the storage modulus E' Z and E' Z0 and the loss modulus E' Z and E' Z0 are measured from only the polyolefin porous film of the layered film.

[0449] The separators of the sixth and seventh embodiments, from the viewpoint of forming an amorphous portion cross-linked structure, taking into account the closing function and high-temperature breakage resistance, etc., with respect to the viscoelasticity measurement (version 2) described in the examples, a mixed storage modulus ratio (R E’mix ) defined by the following formula (2):

[0450] R E’mix = E' / E'0 (2) ​

[0451] {wherein E' is a storage modulus of the separator for electrical storage devices having a crosslinked structure in an amorphous portion measured at 160°C to 300°C, and

[0452] E'0is a storage modulus of the separator for electrical storage devices not having a crosslinked structure in an amorphous portion measured at 160°C to 300°C.}

[0453] and / or a loss modulus ratio (R E”mix ) defined by the following formula (4):

[0454] R E”mix = E" / E"0 (4)

[0455] {wherein E" is a loss modulus measured at 160°C to 300°C when the aforementioned separator for electrical storage devices has a crosslinked structure in an amorphous portion, and

[0456] E"0is a loss modulus of the aforementioned separator for electrical storage devices not having a crosslinked structure in an amorphous portion measured at 160°C to 300°C.}

[0457] is preferably 1.5 times to 20 times, more preferably 3 times to 19 times, and further preferably 5 times to 18 times. Note that E' and E'0and E" and E"0are each an average value of the storage modulus or the loss modulus measured in a set temperature range of the measuring device when 160°C to 300°C is the widest temperature range. Further, in the case where the separator is in the form of a laminate film, the storage modulus E' and E'0and the loss modulus E" and E"0are measured from only the polyolefin microporous film of the laminate film.

[0458] <Eighth Embodiment>

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

[0460] The separator of the eighth embodiment contains a polyolefin microporous film, and with respect to the viscoelasticity measurement (version 3) described in the examples, in the solid viscoelasticity measurement at temperatures of -50°C to 250°C, the minimum value (E' min ) of the storage modulus (E') is 1.0 MPa to 10 MPa, the maximum value (E' max ) of E' is 100 MPa to 10,000 MPa, and / or the minimum value (E" min ) of the loss modulus (E") is 0.1 MPa to 10 MPa, and the maximum value (E" max ) of E" is 10 MPa to 10,000 MPa. If 1.0 MPa ≤ E' min ≤ 10 MPa and 100 MPa ≤ E' max≤10,000MPa, and / or 0.1MPa≤E” min ≤10MPa and 10MPa≤E” max Within the range of ≤10,000 MPa, there is a tendency to balance the closing function of the separator and its resistance to high-temperature membrane rupture, and manufacturing defects can be avoided in the manufacturing process of the separator or the energy storage device, thus achieving the stability and safety of the energy storage device. From these perspectives, 1.1 MPa ≤ E' is preferred. 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. Furthermore, 0.2MPa≤E” is preferred. 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 determination (version 3), the average E'(E') is measured from the membrane softening transition temperature of the separator containing the polyolefin microporous membrane to the membrane rupture temperature. ave Preferably, the pressure is 1.0 MPa to 12 MPa, more preferably 1.2 MPa to 10 MPa, and even more preferably 1.8 MPa to 8.2 MPa, and / or the average pressure E (E) is... ave The pressure 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-mentioned ranges at the temperatures from the membrane softening transition temperature to the membrane rupture temperature, there is a tendency for the cycle stability and safety of the energy storage device equipped with the separator to be improved.

[0462] In the solid viscoelasticity test (version 3), considering both the shut-off function and high-temperature membrane rupture resistance, the membrane softening transition temperature of the separator containing the polyolefin microporous membrane is preferably 140°C to 150°C, more preferably 141°C to 149°C or 146°C to 149°C, and / or the membrane rupture temperature is preferably 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; in this technical field, it should be understood 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. In the case where the separator is in the form of a laminate film, only the polyolefin microporous film is taken out from the laminate film, and E' and E" of the taken-out polyolefin microporous film are measured. Furthermore, in the case where the film thickness of the single polyolefin microporous film is less than 200 μm, the dynamic viscoelasticity measurement (version 3) is performed by laminating a plurality of polyolefin microporous films or folding the single polyolefin microporous film so that the total thickness is in the range of 200 μm to 400 μm.

[0464] The separator of the first to eighth embodiments can include, from the viewpoint of balancing the closing function at a lower temperature and the film breaking property at a higher temperature and improving the cycle characteristics and safety of the power storage device, a microporous film, and an inorganic porous layer containing inorganic particles and a resin binder disposed on at least one surface of the microporous film. The separator can be in a state in which the microporous film is used as a base material, and the base material is complexed with an inorganic coating layer.

[0465] <The ninth embodiment>

[0466] The separator of the ninth embodiment includes:

[0467] a microporous film containing a silane-modified polyolefin; and

[0468] an inorganic porous layer containing inorganic particles and a resin binder disposed on at least one surface of the microporous film.

[0469] The separator of the ninth embodiment can include, as desired, a layer other than the microporous film and the inorganic porous layer.

[0470] In the ninth embodiment, the combination of the microporous film containing a silane-modified polyolefin and the inorganic porous layer has a tendency to balance the closing function at a temperature lower than 150°C and the film breaking property at a higher temperature and improve the cycle characteristics and the battery nail penetration safety of the power storage device. It is presumed that since the silane-modified polyolefin in the microporous film is silane-crosslinkable, once silane crosslinking occurs, the viscosity of the resin in the microporous film is sometimes increased, and thus, in the event of an abnormal high temperature of the power storage device including the separator of the ninth embodiment, if a compressive force is applied between a plurality of electrodes, the high-viscosity resin that has been crosslinked does not easily flow into the inorganic layer (i.e., does not easily integrate), the gap between the electrodes can be sufficiently ensured, and the battery short circuit can be suppressed.

[0471] The separator of the ninth embodiment preferably starts the silane cross-linking reaction of the silane-modified polyolefin upon contact with the electrolyte solution. More preferably, the silane cross-linking reaction occurs upon contact of the separator with the electrolyte solution, whether initially, sequentially, or continuously. By the silane cross-linking reaction of the silane-modified polyolefin occurring upon contact of the separator with the electrolyte solution, not only can the timing of cross-linking of the separator be controlled, and production failures in the separator manufacturing process be avoided, but also safety and high output in the manufacturing process of the power storage device can be achieved. Furthermore, by contacting the separator with the electrolyte solution, a cross-linking reaction other than the silane cross-linking reaction can be induced.

[0472] The separator of the ninth embodiment, when measured after removal of the inorganic porous layer from the separator, preferably has a storage modulus change ratio (R △E’ ) of 1.5 to 20, as defined by the following equation (1A) with respect to the viscoelasticity measurement (version 1) described in the examples:

[0473] R △E’ = E' S / E' j (1A)

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

[0475] and / or a loss modulus change ratio (R △E ") of 1.5 to 20, as defined by the following equation (1B):

[0476] R △E” = E" S / E" j (1B)

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

[0478] By having the storage modulus change ratio (R △E’ ) and / or the loss modulus change ratio (R △E” ) in the range of 1.5 to 20, it is easy to balance the shutdown function and the high-temperature film breakage resistance. The storage modulus change ratio (RΔE’ ) and / or a loss modulus change ratio (R ΔE” ) is more preferably 2 to 18 times. Note that E' j and E' S and E" j and E" S are average values of the storage modulus or the loss modulus measured in the set temperature range of the measuring device when the widest temperature range is set to 160 to 220°C. Further, in the case where the separator is in the form of a laminate film or the form of a composite film of a microporous film and an inorganic porous layer, the storage modulus E' j and E' S and the loss modulus E" j and E" S of the microporous film of the silane-modified polyolefin are measured from the microporous film of the silane-modified polyolefin alone.

[0479] The separator of the ninth embodiment is preferably such that, when measured after removing the inorganic porous layer from the separator, the mixed storage modulus ratio (R E’mix ) defined by the following formula (2A) is 1.5 to 20:

[0480] R E’mix = E' / E'0 (2A)

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

[0482] and / or the mixed loss modulus ratio (R E”mix ) defined by the following formula (2B) is 1.5 to 20:

[0483] R E”mix = E" / E"0 (2B)

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

[0485] By setting the mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix ) in the range of 1.5 to 20, it is easy to achieve both the closing function and the high-temperature film breakage resistance. The mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix)more preferably 2 to 18 times. Note that E' and E'0and E" and E"0are the average values of the storage modulus or the loss modulus measured in the set temperature range of the measuring device when the temperature range of 160 to 220°C is set as the widest temperature range. Further, in the case where the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, the storage modulus E' and E'0and the loss modulus E" and E"0of the microporous film of the silane-modified polyolefin are measured by taking out only the microporous film of the silane-modified polyolefin from the laminated film or the composite film. Note that the separator for power storage devices not containing the silane-modified polyolefin is described in detail in the example section.

[0486] The separator of the ninth embodiment is preferably such that the transition temperature of the rubbery flat region and the crystalline melting flow region is 135 to 150°C in the temperature change of the storage modulus thereof from the viewpoint of balancing the closing function and the high-temperature breakage resistance. The transition temperature of the rubbery flat region and the crystalline melting flow region is preferably 137 to 147°C, more preferably 140 to 145°C, and further preferably 140 to 143°C. Note that in the case where the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, the transition temperature of the microporous film of the silane-modified polyolefin is measured by taking out only the microporous film of the silane-modified polyolefin from the laminated body or the composite film.

[0487] <Tenth Embodiment>

[0488] The separator for power storage devices (hereinafter also referred to simply as "separator") of the tenth embodiment is provided with a first porous layer (A layer) containing a silane-modified polyolefin and capable of forming a crosslinked structure, and a second porous layer (B layer) containing inorganic particles. Each of the A layer and the B layer is a single layer or a plurality of layers. The B layer is formed on one side of the A layer or on both sides.

[0489] In a LIB, which is a representative example of a power storage device, lithium (Li) ions move back and forth between the positive and negative electrodes. Therefore, by disposing the separator including the A layer and the B layer between the positive and negative electrodes, the Li ions can be moved at a high speed between the positive and negative electrodes, and at the same time, contact between the positive and negative electrodes can be avoided.

[0490] (Ratio of thicknesses)

[0491] The A layer functions as a microporous film having crosslinkability, and the B layer functions as an inorganic porous layer formed on the microporous film.

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

[0493] By making the A layer and the B layer each have a specific structure, and further, by setting the ratio (TA / TB) thereof to the above range, a separator that can achieve an improvement in the cycle characteristics and safety of the power storage device can be provided. Such a separator can be suitably used, for example, as a constituent material of an LIB for mobile device mounting use or vehicle mounting use.

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

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

[0496] The total thickness (TA+TB) of the A layer and the B layer is preferably 3.0 μm or more and 22 μm or less. If the total thickness (TA+TB) is 3.0 μm or more, there is a tendency for the film strength of the separator to increase. On the other hand, if the total thickness (TA+TB) is 22 μm or less, there is a tendency for the ion permeability of the separator to increase.

[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 less than 11 μm, 10 μm or less, or 8 μm or less, for example. Even with such a thin separator, as long as it is within the scope of the present application, an improvement in the cycle characteristics and safety of the power storage device can be achieved.

[0499] The ratio (TA / TB) and the total thickness (TA+TB) can each be measured by the method described in the Examples column, and in addition, can be controlled by adjusting the thickness (TA) and / or the thickness (TB). Regarding the A layer and the B layer, this is described later.

[0500] (closing temperature and melting rupture temperature)

[0501] As for the A layer, the closing temperature (sometimes referred to as the fusing temperature) measured based on the electric resistance under pressurization of 0.1 MPa or more and 10.0 MPa or less (preferably, 10 MPa) is 130°C to 160°C, and the melting rupture temperature (sometimes referred to as the film rupture temperature) is preferably 200°C or more.

[0502] If the above closing temperature is 130°C or more, it is possible to avoid exerting the closing function unnecessarily at the time of normal reaction of the power storage device, and it is possible to ensure sufficient output characteristics of the power storage device. On the other hand, if the above closing temperature is 160°C or less, it is possible to appropriately exert the closing function at the time of abnormal reaction of the power storage device.

[0503] Further, if the above closing temperature is 200°C or more, it is possible to stop the abnormal reaction of the power storage device before reaching an ultrahigh temperature region at the time of abnormal reaction of the power storage device, and it is also possible to prevent melting film rupture of the separator at the time of abnormal reaction of the power storage device.

[0504] That is, by causing the closing temperature and the melting rupture temperature to satisfy the above conditions, it is possible to realize a separator of a power storage device that provides excellent heat resistance, closed cell characteristics (closing function), and melting film rupture characteristics (melting rupture function), and it is also possible to ensure mechanical characteristics, ion permeability, and the like for the separator itself. Therefore, by providing a separator in which the closing temperature and the melting rupture temperature satisfy the above conditions, it is possible to realize an improvement in cycle characteristics and safety of the power storage device.

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

[0506] Similarly, from the viewpoint of the above effects, the melting rupture temperature is preferably 175°C or more, more preferably 178°C or more, and further preferably 180°C or more. On the other hand, the melting rupture temperature is preferably 230°C or less, more preferably 225°C or less, and further preferably 220°C or less.

[0507] Note that, as for the melting rupture temperature, even in a case where it cannot be accurately measured in a range exceeding 200°C, as long as it is 200°C or more, the above condition of "the melting rupture temperature is 200°C or more" is satisfied.

[0508] The "shut-down temperature" and "melt fracture temperature" in the present specification refer to values obtained based on resistance measurement under the above-described pressurization. That is, while applying the above-described pressure to a laminate including a positive electrode, a separator, and a negative electrode, the temperature of the laminate is increased, and the shut-down temperature and the melt fracture temperature are derived based on the AC resistance (AC resistance between electrodes) that rises therewith. In the tenth embodiment, the temperature at which the AC resistance first exceeds a prescribed reference value (for example, 1000 Ω) is set as the shut-down temperature, and the temperature at which, after further continuing heating, the AC resistance that exceeds the above-described reference value decreases to below the above-described reference value (for example, 1000 Ω) is set as the melt fracture temperature.

[0509] The pressurization of the laminate can use a hydraulic jack, but is not limited thereto, and a known pressurization means other than a hydraulic jack can be used. Furthermore, the heating of the laminate can use an aluminum heater, but is not limited thereto, and a known heating means other than an aluminum heater can be used.

[0510] The above-described shut-down temperature and melt fracture temperature can be measured by the method described in the Examples column, and furthermore, can be controlled by adjusting the composition or manufacturing method of the A layer.

[0511] (Thermal shrinkage at 150°C)

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

[0513] Since the A layer can form a crosslinked structure based on a silane-modified polyolefin, the change in thermal shrinkage before and after crosslinking thereof can be focused on.

[0514] If the ratio (T2 / T1) is 0.02 or more, the generation of short circuits can be effectively suppressed, and thus, the temperature rise of the entire power storage device and the smoke generation and further the ignition that can occur therewith can be reliably prevented. On the other hand, if the ratio (T2 / T1) is 0.91 or less, it can be judged that the crosslinking reaction in the A layer has been successfully and sufficiently performed. That is, if the ratio (T2 / T1) is within the above-described range, a separator for a power storage device that can achieve the improvement of the cycle characteristics and the safety of the power storage device can be provided.

[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 further 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 further preferably 0.4 or less.

[0516] Note that the heat shrinkage at 150°C before formation of the crosslinked structure (T1) is preferably 70% or less, and more preferably 60% or less.

[0517] Further, the heat shrinkage at 150°C after formation of the crosslinked structure (T2) is preferably 60% or less, and more preferably 50% or less. However, by forming the crosslinked structure, there is a tendency that the above-mentioned heat shrinkage decreases compared to before formation of the crosslinked structure, and therefore the heat shrinkage (T2) is generally a value smaller than the heat shrinkage (T1).

[0518] The heat shrinkage at 150°C can be measured by the method described in the Examples column, and in addition, can be controlled by adjusting the constitution or manufacturing method of the A layer.

[0519] The separators of the above-mentioned embodiments can be interchanged, or can be combined with each other. The separators of the above-mentioned ninth or tenth embodiments can include a layer other than the microporous membrane and the inorganic porous layer, as desired. The constitution elements of the separators of the first to tenth embodiments are described below.

[0520] [microporous membrane]

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

[0522] The microporous membrane contains a silane-modified polyolefin, and can also contain other polyolefins, as desired. The microporous membrane can undergo a crosslinking reaction in the manufacturing process of the separator, due to the silane crosslinkability of the silane-modified polyolefin.

[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 of at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene, and the like can be exemplified. Among these, from the viewpoint that heat setting (sometimes abbreviated as "HS") at a higher temperature can be performed without clogging the pores, high-density polyethylene (homopolymer) or low-density polyethylene is preferable, and high-density polyethylene (homopolymer) is more preferable. Note that the polyolefin can be used alone as one kind, or two or more kinds can be used in combination.

[0524] From the viewpoint of resistance to redox deterioration and a dense and uniform porous structure, it is preferable to use both of a silane-modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) as raw materials for the production of the microporous membrane. Generally, it is known that the weight average molecular weight of the ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more. More preferably, in the production of the microporous membrane or the separator, the weight ratio of the silane-modified polyolefin to the 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, and preferably 80% by weight or more and 100% by weight or less. Furthermore, the microporous membrane preferably contains a polyolefin having a weight average molecular weight of 100,000 or more and less than 1,000,000 (preferably contained at a ratio of 40% by weight or more, more preferably 80% by weight or more, with respect to the entire polyolefin). 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 a heating safety test, in particular, in that shrinkage of the polymer at an early stage occurs in a heating test or the like of the power storage device. By adjusting the weight average molecular weight of the microporous membrane to be less than 1,000,000, it is possible to suppress a molding defect (film texture) at the time of extrusion, which is called melt fracture. On the other hand, by adjusting the weight average molecular weight of the microporous membrane to be 100,000 or more, it is possible to suppress the transfer of a depression when the microporous membrane is wound around a core (winding core).

[0526] With respect to the viscosity average molecular weight of the microporous membrane at the time of removal of the inorganic porous layer and without crosslinking treatment, it is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less, from the viewpoint of not generating polymer powder due to frictional shear in the winding transport of the separator.

[0527] The film 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 film thickness of the microporous membrane 1.0 μm or more, there is a tendency for the film strength to further increase. In addition, the film 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 film thickness of the microporous membrane 500 μm or less, there is a tendency for the ion permeability to further increase. The film 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 of high capacity in recent years, the film thickness of the microporous membrane is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, and further preferably 18 μm or less, and particularly preferably 16 μm or less. In this case, by making the film thickness of the microporous membrane 25 μm or less, there is a tendency for the permeability to further increase. In this case, the lower limit of the film thickness of the microporous membrane can 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 viewpoint of the high-temperature film breakage resistance of the separator for power storage devices and the safety of the power storage device, the microporous membrane as a separator is preferably such that, at the time of thermomechanical analysis (TMA) measurement thereof, the melting film breakage temperature is preferably 180°C to 220°C, and more preferably 180°C to 200°C. Generally, in the case where a power storage device is heated due to an unintended runaway reaction, a polyolefin-made separator for power storage devices is fused at a low temperature (for example, 150°C or lower), the movement of Li ions is stopped at an early stage, and also the discharge inside or outside the power storage device accompanying this is stopped. Then, in the natural cooling of the power storage device using external air or a refrigerant, the entire power storage device is cooled, ignition of the electrolyte or decomposition reaction of the electrolyte can be prevented, and it is expected that the safety can be ensured. However, the runaway reaction occurring in the aforementioned power storage device does not stop due to the fusion of the separator, continues to heat, the separator is melted and broken, and it is not possible to ensure the safety of the device. Therefore, it is important that the separator does not be melted and broken until the entire power storage device is sufficiently cooled. In addition, in the case where the temperature is accidentally increased to a super-high temperature region of 220°C or higher, the decomposition reaction of the electrolyte or the electrolyte is sharply progressed, the corrosion reaction of the counter electrode is initiated by the decomposition product, further heating is caused, and explosion is caused. In this case, the separator coats the active material by being melted and broken, and penetrated into both electrodes, and it is possible to prevent the corrosion reaction.

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

[0531] The A layer contains a silane-modified polyolefin, and a crosslinked structure can be formed. The A layer preferably also contains polyethylene as a polyolefin different from the silane-modified polyolefin from the viewpoint of ensuring resistance to deterioration against oxidation reduction, and also ensuring a dense and uniform porous body structure. Note that the A layer can contain components other than the silane-modified polyolefin and the polyethylene.

[0532] As the polyolefin constituting the silane-modified polyolefin in the A layer, a homopolymer of ethylene or propylene; a copolymer formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-l-pentene, 1-hexene, 1-octene, and norbornene, and the like can be exemplified. Among these, as the polyolefin, a homopolymer of ethylene (polyethylene) is preferable from the viewpoint that heat setting can be performed at a higher temperature while avoiding clogging of the pores, a high-density polyethylene and / or a low-density polyethylene is more preferable, and a high-density polyethylene is further preferable. The polyolefin can be used alone or in combination with two or more kinds.

[0533] The A layer can contain a polymer (other polymer) that does not belong to either of the silane-modified polyolefin and the polyethylene, within a range that does not excessively hinder the effects brought about by the present application.

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

[0535] (Thickness of the A layer)

[0536] The thickness (TA) of the A layer is preferably 1 μm or greater, more preferably 2 μm or greater, and further preferably 3 μm or greater. If the thickness (TA) is 1 μm or greater, there is a tendency for the film strength to further improve. 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 further improve. Note that the thickness (TA) can be set to, for example, 1.00 μm or greater, 2.00 μm or greater, or 3.00 μm or greater.

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

[0538] The thickness (TA) can be measured by the method described in the Examples column, and in addition, can be controlled by changing the draw ratio of the A layer, or the like.

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

[0540] (Breaking film temperature of the A layer)

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

[0542] Even if the power storage device abnormally generates heat due to an unexpected runaway reaction, it is expected that the movement of Li ions, and also the discharge inside or outside the power storage device, is stopped by the closing function of the separator. Then, it is expected that the entire power storage device is cooled using the refrigerant, and the safety is ensured. On the other hand, by making the breaking film temperature in the above range, even in the case where the entire power storage device is not sufficiently cooled, or in the case where the super-high temperature region is reached by chance, the separator can coat the active material by melting and breaking the film, and permeating into both electrodes, and thus it is easy to suppress further heat generation.

[0543] The breaking film temperature can be measured by the method described in the Examples column, and in addition, can be controlled by changing the draw temperature and / or draw ratio, or the like, in the manufacturing process.

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

[0545] The porosity of the microporous membrane or A layer is preferably 20% or more, more preferably 25% or more, and even more preferably 28%, 30%, 32%, or 35% or more. If the porosity is 20% or more, there is a tendency to further improve the ability to follow the rapid movement 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. If the porosity is 90% or less, there is a tendency to further improve the membrane strength and further suppress self-discharge.

[0546] Porosity can be determined by the methods described in the Examples section, and can also be controlled during the manufacturing process by changing the stretching temperature and / or stretching ratio.

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

[0548] The preferred air permeability for the microporous membrane or A layer is 1 second / 100cm. 3 The above is preferred to be 50 seconds per 100cm. 3 The above is further optimized to 55 seconds per 100cm. 3 The above, and even more preferably 70 seconds or more, 90 seconds or more, or 110 seconds or more. If the air permeability is 1 second / 100cm... 3 The above suggests a tendency to further improve the balance between membrane thickness, porosity, and average pore size. On the other hand, the preferred air permeability is 400 seconds / 100 cm². 3 Below, more preferably 300 seconds or less / 100cm 3 Further optimized to 270 seconds per 100cm 3 Below. If the air permeability is 400 seconds / 100cm. 3 The following shows a tendency for further increases in ion permeability.

[0549] Air permeability can be measured by the methods described in the Examples section. In addition, it can be controlled during the manufacturing process by changing the stretching temperature and / or stretch ratio.

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

[0551] The puncture strength of the microporous membrane or A layer is preferably 200 gf / 20 μm or more, and more preferably 300 gf / 20 μm or more. If the puncture strength is 200 gf / 20 μm or more, even if active material or the like detaches during the winding of the separator and electrode laminate, membrane rupture caused by the detached active material or the like is easily suppressed. Furthermore, the possibility of short circuits due to the expansion and contraction of the electrodes accompanying charging and discharging is easily reduced. On the other hand, the puncture strength is preferably 4000 gf / 20 μm or less, and more preferably 3800 gf / 20 μm or less. If the puncture strength is 3500 gf / 20 μm or less, thermal shrinkage during heating is easily reduced.

[0552] Puncture strength can be determined by the method described in the Examples section. In addition, it can be controlled in the manufacturing process by changing the stretching temperature and / or stretching ratio.

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

[0554] The tensile strength of the microporous membrane or A layer is preferably 1000 kgf / cm² in both the MD (length direction, mechanical direction, or processing direction of the membrane or A layer) and TD (width direction orthogonal to MD, the direction of the membrane or A layer). 2 The above, more preferably 1050 kgf / cm 2 The above is further optimized to 1100 kgf / cm². 2 The above. By achieving a tensile strength of 1000 kgf / cm. 2 The above features a tendency to further suppress breakage during slitting or winding of the energy storage device, and to further suppress short circuits caused by foreign objects within the energy storage device. On the other hand, the tensile strength is preferably 5000 kgf / cm². 2 The following is more preferably 4500 kgf / cm² 2 The following is a further preferred value: 4000 kgf / cm² 2 The following is an example of achieving a tensile strength of 5000 kgf / cm. 2 The following results in the microporous membrane or A layer relaxing early and reducing contractile force during heating tests, which tends to improve safety.

[0555] [Tensive modulus of elasticity of microporous membrane or layer A]

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

[0557] <polyolefin>

[0558] As the polyolefin, there is no particular limitation, and for example, 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, and the like can be cited. Among these, from the perspective of being able to perform heat setting (sometimes abbreviated as "HS") at a higher temperature without clogging the pores, high-density polyethylene or low-density polyethylene is preferable, and high-density polyethylene is more preferable. Note that the polyolefin can be used alone or in combination with two or more.

[0559] Further, the separator preferably includes a polyolefin having a weight average molecular weight (Mw) of less than 2,000,000, and more preferably includes the polyolefin having an Mw of less than 2,000,000 at a ratio of 40% by mass or more, and further preferably at a ratio of 80% by mass or more, relative to the entire polyolefin. By using a polyolefin having an Mw of less than 2,000,000, there is a tendency for relaxation of the shrinkage of the polymer to occur early in a heating test or the like of the power storage device, and in particular, for safety to be easily maintained in a heating safety test. Note that in the case of using a polyolefin having an Mw of less than 2,000,000, compared to the case of using a polyolefin having an Mw of 1,000,000 or more, there is a tendency for the elastic modulus in the thickness direction of the resulting microporous membrane to be small, and thus a microporous membrane that is more easily transferred to the unevenness of the core can be obtained. The weight average molecular weight of the polyolefin microporous membrane as a whole that constitutes 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] (polyolefin having one or two or more functional groups)

[0561] The separator is preferably a polyolefin having one or more functional groups from the viewpoint of formation of a crosslinked structure, resistance to redox deterioration, and a dense and uniform porous structure. The polyolefin having one or more functional groups is preferably a functional group-modified polyolefin or a polyolefin obtained by copolymerization of a monomer having a functional group. Note that the functional group-modified polyolefin herein refers to a substance obtained by attaching a functional group to a polyolefin after the polyolefin is produced. The functional group is attached to the polyolefin skeleton or can be introduced into a comonomer, and preferably participates in selective crosslinking of the amorphous portion of the polyolefin. The functional group can be, for example, at least one selected from the group consisting 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 azide group, a chain or cyclic heteroatom-containing hydrocarbon group, an amino group, a mercapto group, a metal chelate group, and a halogen-containing group.

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

[0563] (Crosslinked structure)

[0564] The crosslinked structure of the separator contributes to the balance between the closing function and the high-temperature film rupture resistance of the separator and the safety of the power storage device, and 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 via any of a covalent bond, a hydrogen bond, or a coordination bond. Among these, the reaction via the covalent bond is preferably at least one selected from the group consisting of the following reactions (I) to (IV):

[0565] (I) Condensation reaction of a plurality of the same functional groups

[0566] (II) Reaction between a plurality of different functional groups

[0567] (III) Chain condensation reaction of a functional group with an electrolyte

[0568] (IV) Chain condensation reaction of a functional group with an additive.

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

[0570] (V) a plurality of identical functional groups are crosslinked by means of a reaction of coordination with a metal ion that dissolves.

[0571] Reaction (I)

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

[0573]

[0574] In the case where the functional group A used for performing Reaction (I) is a silanol group, the polyolefin contained in the separator is preferably silane-graft-modified. The silane-graft-modified polyolefin is composed of a polyolefin as a main chain, and an alkoxysilyl group as a graft on the main chain. Note that the alkoxide that is replaced with the aforementioned alkoxysilyl group can be exemplified by a methoxide, an ethoxide, a butoxide, and the like. For example, in the above formula, R can be a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a sec-butyl group, an i-butyl group, a t-butyl group, and the like. Further, the main chain and the graft are connected by a covalent bond, and a structure such as an alkyl group, an ether, a diol, or an ester, and the like can be exemplified. In view of the manufacturing process of the separator of the present embodiment, the silane-graft-modified polyolefin has a silicon-to-carbon ratio (Si / C) of preferably 0.2 to 1.8%, and more preferably 0.5 to 1.7% at a stage before the crosslinking treatment process.

[0575] The density of the preferred silane-graft-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. The silane-graft-modified polyolefin is preferably not a master batch resin containing a dehydration condensation catalyst from the viewpoint of inhibiting the generation of resin agglomerates in the manufacturing process of the separator, and maintaining the silane crosslinkability until contact with the electrolyte solution. The dehydration condensation catalyst is known to also function as a catalyst for the formation of siloxane bonds of a resin containing an alkoxysilyl group. In the present specification, a substance obtained by adding a dehydration condensation catalyst (for example, containing an organometallic catalyst) to a resin containing an alkoxysilyl group or another kneaded resin and mixing in advance in a continuous process of resin kneading using an extruder is referred to as a master batch resin.

[0576] Reaction (II)

[0577] The first functional group of the separator is denoted as A, and the second functional group is denoted as B, and the principle schematic diagram and specific examples of Reaction (II) are shown below.

[0578] Scheme of the reaction (II)

[0579]

[0580] Examples of combinations of functional groups A and B:

[0581] hydroxyl and carboxyl (esterification);

[0582] carbonyl and alkyl (aldol condensation);

[0583] halogen and carboxyl (intramolecular condensation);

[0584] alkoxy and alkyl (Claisen reaction);

[0585] carbonyl and acid anhydride group (Perkin reaction);

[0586] amino and halogen;

[0587] isocyanate group and hydroxyl group (formation of urethane bond); and

[0588]

[0589] (oxazoline) and hydroxyl group, etc.

[0590]

[0591] Reactions (I) and (II) can be catalyzed, for example, by a chemical substance inside the power storage device assembled by the separator. The chemical substance can be, for example, any of an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof contained in the power storage device.

[0592] Reaction (III)

[0593] Let the first functional group of the separator be A, and let the electrolytic solution be Sol. The principle schematic diagram and specific examples of Reaction (III) are shown below.

[0594] Scheme of the reaction (III)

[0595]

[0596] Examples of functional groups A:

[0597] hydroxyl group, carboxyl group, amino group, carbonyl group, ether group, isocyanate group, etc.

[0598] Examples of electrolytes:

[0599] Electrolyte: LiPF6, LiBF4, LiN(SO2CF3)2, LiSO3CF3, LiBC4O8(LiBOB), etc.

[0600] Non-aqueous solvent: ethylene carbonate, methyl ethyl carbonate, or a mixture thereof, etc.

[0601]

[0602]

[0603] Reaction (IV)

[0604] The first functional group of the separator is denoted as A, the second functional group to be introduced as desired is denoted as B, and the additive is denoted as Add. The principle diagram of Reaction (IV) is shown below.

[0605]

[0606] Reaction (IV) is preferably a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction of a compound Rx constituting the separator and a compound Ry constituting the additive (Add) from the viewpoint of forming a covalent bond indicated by a broken line in the above principle diagram. The compound Rx can be a polyolefin, such as polyethylene or polypropylene, or the like, included in the separator, and the polyolefin is preferably modified by a functional group x, such as at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH.

[0607] Since a plurality of compounds Rx are crosslinked via a compound Ry as an additive, the compound Ry preferably has 2 or more linking reaction units y1. The plurality of 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 the compound Rx, can be substituted or unsubstituted, can include a heteroatom or an inorganic substance, and can be the same as or different from each other. Furthermore, when the compound Ry has a chain structure, the plurality of linking reaction units y1 can each independently be a terminal group, or introduced to a main chain, or be a side chain or a side group.

[0608] In the case where Reaction (IV) is a nucleophilic substitution reaction, the functional group x of the compound Rx is described below as a nucleophilic group, and the linking reaction unit y1 of the compound Ry is described as a leaving group, merely as one example, but in the present embodiment, both the functional group x and the linking reaction unit y1 can form a leaving group depending on the nucleophilicity.

[0609] From the viewpoint of the nucleophilic reagent, 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. As the oxygen-based nucleophilic group, a hydroxyl group, an alkoxy group, an ether group, a carboxyl group, and the like can be exemplified, and among them, -OH and -COOH are preferable. As the nitrogen-based nucleophilic group, an ammonium group, a primary amino group, a secondary amino group, and the like can be exemplified, and among them, -NH2 and -NH- are preferable. As the sulfur-based nucleophilic group, for example, -SH, a thioether group, and the like can be exemplified, and -SH is preferable.

[0610] In the case where the reaction (IV) is a nucleophilic substitution reaction, from the viewpoint of leaving group, as the linking reaction unit y1 of the compound Ry, alkylsulfonyl groups such as CH3SO2-, CH3CH2SO2-, and the like; arylsulfonyl groups (-ArSO2-); halogenated alkylsulfonyl groups such as CF3SO2-, CCl3SO2-, and the like; alkylsulfonate groups such as CH3SO3-, CH3CH2SO3-, and the like; arylsulfonate groups (ArSO3-); halogenated alkylsulfonate groups such as CF3SO3-, CCl3SO3-, and the like; and heterocyclic groups can be used alone or in a combination of a plurality of kinds. As the heteroatom contained in the heterocyclic ring, nitrogen atoms, oxygen atoms, sulfur atoms, and the like can be exemplified, among which, from the viewpoint of leaving group, nitrogen atoms are preferred. As the leaving group containing a nitrogen atom in the heterocyclic ring, monovalent groups represented by the following formulae (y1-1) to (y1-6) are preferred:

[0611]

[0612] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0613]

[0614] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0615]

[0616] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0617]

[0618] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0619]

[0620] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0621]

[0622] {in the formula, X is a hydrogen atom or a monovalent substituent.}

[0623] In the formulae (y1-1) to (y1-6), X is a hydrogen atom or a monovalent substituent. As the monovalent substituent, for example, alkyl groups, halogenated alkyl groups, alkoxy groups, halogen atoms, and the like can be exemplified.

[0624] In the case where the reaction (IV) is a nucleophilic substitution reaction and the compound Ry has a chain structure, the compound Ry preferably has at least one chain unit y2 selected from the group consisting of divalent groups represented by the following formulae (y2-1) to (y2-6) in addition to the group y1 that links the reaction units:

[0625]

[0626] {in the formula, m is an integer of 0 to 20, and n is an integer of 1 to 20.}

[0627]

[0628] {in the formula, n is an integer of 1 to 20.}

[0629]

[0630] {in the formula, n is an integer of 1 to 20.}

[0631]

[0632] {in the formula, n is an integer of 1 to 20.}

[0633]

[0634] {in the formula, X is an alkylene group or an arylene group having 1 to 20 carbons, and n is an integer of 1 to 20.}

[0635]

[0636] {in the formula, X is an alkylene group or an arylene group having 1 to 20 carbons, and n is an integer of 1 to 20.}

[0637] Further, in the case where the compound Ry includes a plurality of chain units y2, they can be the same as or different from each other, and their arrangement can be block or random.

[0638] In the formula (y2-1), m is an integer of 0 to 20, and is preferably 1 to 18 from the viewpoint of crosslinking network. In the formulae (y2-1) to (y2-6), n is an integer of 1 to 20, and is preferably 2 to 19 or 3 to 16 from the viewpoint of crosslinking network. In the formulae (y2-5) to (y2-6), X is an alkylene group or an arylene group having 1 to 20 carbons, and is preferably a methylene group, an ethylene group, a n-propylene group, a n-butylene group, a n-hexylene group, a n-heptylene group, a n-octylene group, a n-dodecylene group, an o-phenylene group, an m-phenylene group or a p-phenylene group from the viewpoint of stability of chain structure.

[0639] In the case where the reaction (IV) is a nucleophilic substitution reaction, preferred combinations of the functional group x of the compound Rx and the linking reactive unit yl and the chain unit y2 of the compound Ry are shown in Tables 2 to 4 below.

[0640] [Table 2]

[0641]

[0642] [Table 3]

[0643]

[0644] [Table 4]

[0645]

[0646] As a specific example 1 of the nucleophilic substitution reaction, a reaction scheme is shown below when the functional group x of the polyolefin is -NH2, the linking reactive unit yl of the additive (compound Ry) is a skeleton derived from a succinimide, and the chain unit y2 is -(0-C2H5)- n

[0647]

[0648] As a specific example 2 of the nucleophilic substitution reaction, a reaction scheme is shown below when the functional group x of the polyolefin is -SH and -NH2, the linking reactive unit yl of the additive (compound Ry) is a nitrogen-containing cyclic skeleton, and the chain unit y2 is an ortho-phenylene group.

[0649]

[0650] In the case where the reaction (IV) is a nucleophilic addition reaction, the functional group x of the compound Rx and the linking reactive unit yl of the compound Ry can undergo an addition reaction. In the nucleophilic addition reaction, 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. As the oxygen-based nucleophilic group, a hydroxyl group, an alkoxy group, an ether group, a carboxyl group, and the like can be exemplified, of which -OH and -COOH are preferred. As the nitrogen-based nucleophilic group, an ammonium group, a primary amino group, a secondary amino group, and the like can be exemplified, of which -NH2 and -NH- are preferred. As the sulfur-based nucleophilic group, for example, -SH, a thioether group, and the like can be exemplified, with -SH being preferred.

[0651] In the nucleophilic addition reaction, the linking reactive unit yl of the compound Ry is preferably at least one selected from the group consisting of the groups represented by the following formulae (Ay1-1) to (Ay1-6) from the viewpoint of reactivity in the addition reaction or ease of availability of the starting material:

[0652]

[0653] ​{in the formula, R is a hydrogen atom or a monovalent organic group.}

[0654]

[0655]

[0656] In formula (Ay1-4), R is a hydrogen atom or a monovalent organic group, preferably a hydrogen atom, a C 1～20 an alkyl group, an alicyclic group, or an aromatic group, more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group.

[0657] In the case where reaction (IV) is a nucleophilic addition reaction, preferred combinations of the functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry are shown in Tables 5 and 6 below.

[0658] [Table 5]

[0659]

[0660] [Table 6]

[0661]

[0662] As a specific example of the nucleophilic addition reaction, the reaction scheme 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.

[0663]

[0664] In the case where reaction (IV) is a ring-opening reaction, the functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry can undergo a ring-opening reaction, and from the viewpoint of ease of availability of starting materials, it is preferable that the cyclic structure on the linking reaction unit y1 side be opened. From the same viewpoint, the linking reaction unit y1 is more preferably an epoxy group, and the compound Ry is further preferably has at least two epoxy groups, and is still further preferably a bis-epoxy compound.

[0665] In the case where 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):

[0666]

[0667] {in the formula, each of the plurality of X is independently a hydrogen atom or a monovalent substituent.}.

[0668] In formula (ROy1-1), each of the plurality of X is independently a hydrogen atom or a monovalent substituent, preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group, more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group. Preferred combinations of the functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry for the ring-opening reaction of the epoxy group are shown in Table 7 below. 1～20 alkyl, alicyclic, or aromatic group, more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group. Preferred combinations of the functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry for the ring-opening reaction of the epoxy group are shown in Table 7 below.

[0669] [Table 7]

[0670]

[0671] Reaction (V)

[0672] The first functional group of the separator is denoted as A, and the metal ion is denoted as M n+ The principle diagram of reaction (V) and examples of the functional group A are shown below.

[0673]

[0674] In the above principle diagram, the metal ion M n+ is preferably a metal ion dissolved from the power storage device (hereinafter also referred to as a dissolved metal ion), and for example, can be at least one selected from the group consisting of Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ , and Li + . The following illustrates the coordination bond when the functional group A is -COO - .

[0675]

[0676] The following illustrates a specific principle diagram of reaction (V) when the functional group A is -COOH and the dissolved metal ion is Zn 2+ .

[0677]

[0678] In the above principle diagram, hydrofluoric acid (HF) can be derived from any of the electrolyte, the electrolytic solution, the electrode active material, the additive, or their decomposition products or water-absorbing substances contained in the power storage device, for example, according to the charge and discharge cycle of the power storage device.

[0679] Silane-modified polyolefin

[0680] The silane-modified polyolefin is composed of a structure in which the main chain is a polyolefin and an alkoxy silyl group is grafted to the main chain. The silane-modified polyolefin can be obtained by grafting an alkoxy silyl group to the main chain of a silane-unmodified polyolefin.

[0681] The alkoxysilyl group is presumed to be converted into a silanol group by a water-based hydrolysis reaction, a cross-linking reaction occurs, and a siloxane bond is formed (see the following formula; the proportions of the T1 structure, the T2 structure, and the T3 structure are arbitrary). As the alkoxysilyl group-substituted alkoxide, there can be mentioned a methanolate, an ethanolate, a butanolate, and the like. In the following formula, as R, there can be mentioned 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 t-butyl group, and the like.

[0682]

[0683] The covalent bond is connected between the main chain and the graft. As a structure forming the covalent bond, there can be mentioned an alkyl group, an ether, a diol, an ester, and the like. The silane-modified polyolefin is in a stage before the cross-linking reaction is performed, and the modification amount of the silanol unit with respect to the main chain ethylene unit is 2% or less.

[0684] The density of the preferable silane-graft-modified polyolefin is 0.90 to 0.96 g / cm3. 3 and the melt mass flow rate (MFR) at 190°C is 0.2 to 5 g / minute.

[0685] 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, with respect to the total amount of the microporous membrane or the A layer, from the viewpoint of good exertion of the effects brought about by the present application. The amount of the silane-modified polyolefin is preferably 40% by mass or less, and more preferably 38% by mass or less, with respect to the total amount of the microporous membrane, from the viewpoint of the cycle characteristics and the safety of the power storage device. Furthermore, the amount of the silane-modified polyolefin can be set to 30% by mass or more or 50% by mass or more, and further can be set to 100% by mass, with respect to the total amount of the A layer.

[0686] The cross-linking structure in the microporous membrane or the A layer is preferably formed by a compound generated in the power storage device.

[0687] That is, the cross-linking structure formed by the swelling of the microporous membrane or the A layer and / or a compound generated in the power storage device is also preferably the cross-linking structure in the microporous membrane or the A layer when the separator is brought into contact with the nonaqueous electrolyte solution in the manufacturing process of the power storage device. The cross-linking structure at this time is a cross-linking structure obtained by not actively promoting the cross-linking reaction in the manufacturing process of the separator and actively promoting the cross-linking reaction in the manufacturing process of the power storage device, and thus the self-cross-linking property of the separator can be maintained until the power storage device is housed.

[0688] From the viewpoint of inhibiting the generation of resin agglomerates in the manufacturing process of the separator and maintaining the silane crosslinkability until contact with the electrolyte solution, the silane-modified polyolefin is preferably not a master batch resin containing a dehydration condensation catalyst. The dehydration condensation catalyst is known to also function as a catalyst for the formation of siloxane bonds of an alkoxysilyl group-containing resin. In the present specification, a substance obtained by previously adding a dehydration condensation catalyst (for example, containing an organometallic catalyst) to an alkoxysilyl group-containing resin or another kneaded resin and mixing in a continuous process having a resin kneading step using an extruder is referred to as a master batch resin.

[0689] (polyethylene)

[0690] In the present specification, the polyethylene that can be further contained on the basis of the silane-modified polyolefin (polyethylene further contained as a polyolefin different from the silane-modified polyolefin in the microporous membrane or the A layer) refers to a polyethylene that is a homopolymerization high polymer of a homopolymer of ethylene having a weight average molecular weight of 100,000 or more and 10,000,000 or less, or a copolymerization high polymer of a copolymer containing an alkane unit.

[0691] In the case where the microporous membrane or the A layer 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 further preferably 50% by mass or more, based on the total amount of the silane-modified polyolefin and the polyethylene. If the content of the polyethylene is 20% by mass or more, there is a tendency to easily ensure the resistance to deterioration against oxidation and reduction and also to ensure a dense and uniform porous structure.

[0692] On the other hand, the content of the polyethylene is preferably 97% by mass or less, more preferably 96% by mass or less, and further preferably 95% by mass or less. If the content of the polyethylene is 97% by mass or less, the content of the silane-modified polyolefin in the microporous membrane or the A layer can be ensured.

[0693] (detection method of the silane-modified polyolefin contained in the separator)

[0694] In the case where the silane-modified polyolefin contained in the separator is in a state where crosslinking has occurred, the solubility in an organic solvent is insufficient or zero, and thus it is sometimes difficult to directly measure the content of the silane-modified polyolefin from the separator. In this case, as a pretreatment of the sample, the siloxane bond is decomposed into a methoxysilanol by using methyl orthoformate that does not cause a side reaction, and then solution NMR measurement is performed, whereby the silane-modified polyolefin contained in the separator can be detected. The experiment of the pretreatment can be performed with reference to Japanese Patent No. 3529854 and Japanese Patent No. 3529858.

[0695] Specifically, the detection method of the silane-modified polyolefin contained in the separator can effectively utilize the silane-modified polyolefin used as a raw material in the manufacture of the separator 1 H or 13 C NMR identification. One example of the measurement method of the NMR of 1 H and 13 C is described below.

[0696] ( 1 H NMR measurement)

[0697] The sample was dissolved in o-dichlorobenzene-d4 at 140°C to obtain a 1 H-NMR spectrum with a proton resonance frequency of 600 MHz. 1 The measurement conditions of the H-NMR are described below.

[0698] Apparatus: AVANCE NEO 600 manufactured by Bruker Inc.

[0699] Sample tube diameter: 5 mmφ

[0700] Solvent: o-dichlorobenzene-d4

[0701] Measurement temperature: 130°C

[0702] Pulse angle: 30°

[0703] Pulse waiting time: 1 sec

[0704] Number of accumulations: 1000 times or more

[0705] Sample concentration: 1 wt / vol%

[0706] ( 13 C NMR measurement)

[0707] The sample was dissolved in o-dichlorobenzene-d4 at 140°C to obtain a 13 C-NMR spectrum. 13 The measurement conditions of the C-NMR are described below.

[0708] Apparatus: AVANCE NEO 600 manufactured by Bruker Inc.

[0709] Sample tube diameter: 5 mmφ

[0710] Solvent: o-dichlorobenzene-d4

[0711] Measurement temperature: 130°C

[0712] Pulse angle: 30°

[0713] Pulse waiting time: 5 sec

[0714] Total number of times: 10,000 or more

[0715] Sample concentration: 10 wt / vol%

[0716] Figure 11 and 12 It uses two types of polyolefins, silane-modified polyolefin raw materials 1 and 2. 1 H and 13 The C-NMR spectra of raw materials 1 and 2 are different, and their respective melt index (MI), C3 grafting amount, C4 grafting amount and / or silanol modification amount are different.

[0717] Figure 11 of 1 H and 13 The C-NMR measurement conditions are as follows.

[0718] ( 1 (H-NMR measurement conditions)

[0719] Device: Bruker Avance NEO 600

[0720] Observation kernel: 1 H

[0721] Observation frequency: 600MHz

[0722] Pulse program: zg30

[0723] Pulse wait time: 1 sec

[0724] Total number of times: 1024

[0725] Measurement temperature: 130℃

[0726] Chemical shift reference: 7.219 ppm (o-DCBz)

[0727] Solvent: o-dichlorobenzene-d4

[0728] Sample concentration: 1 wt / vol%

[0729] Sample tube: 5mmφ

[0730] ( 13 C-NMR measurement conditions)

[0731] Device: Bruker Avance NEO 600

[0732] Observation kernel: 13 C

[0733] Observation frequency: 150.91MHz

[0734] Pulse program: zgpg30

[0735] Pulse length: 5 sec

[0736] Number of accumulations: 24000 or 12800

[0737] Measurement temperature: 130 °C

[0738] Chemical shift reference: 132.39 ppm (o-DCBz)

[0739] Solvent: o-dichlorobenzene-d4

[0740] Sample concentration: 10 wt / vol %

[0741] Sample tube: 5 mm φ

[0742] Figure 12 of 1 H and 13 C-NMR measurement conditions are as follows.

[0743] ( 1 H-NMR measurement conditions)

[0744] Apparatus: Bruker Avance NEO 600

[0745] Observed nucleus: 1 H

[0746] Observed frequency: 600 MHz

[0747] Pulse program: zg30

[0748] Pulse length: 1 sec

[0749] Number of accumulations: 1024

[0750] Measurement temperature: 130 °C

[0751] Chemical shift reference: 7.219 ppm (o-DCBz)

[0752] Solvent: o-dichlorobenzene-d4

[0753] Sample concentration: 1 wt / vol %

[0754] Sample tube: 5 mm φ

[0755] ( 13 C-NMR measurement conditions)

[0756] Apparatus: Bruker Avance NEO 600

[0757] Observed nucleus: 13 C

[0758] Observation frequency: 150.91 MHz

[0759] Pulse program: zgpg30

[0760] Pulse delay: 5 sec

[0761] Number of accumulations: 12800

[0762] Measurement temperature: 130°C

[0763] Chemical shift reference: 132.39 ppm (o-DCBz)

[0764] Solvent: o-dichlorobenzene-d4

[0765] Sample concentration: 10 wt / vol%

[0766] Sample tube: 5 mm φ

[0767] Figure 13 is a crosslinked state of a separator made of a silane-modified polyolefin raw material 1 shown in Figure 11 Example I-1 described later. 1 H and 13 C-NMR spectra. Figure 13 of 1 H and 13 C-NMR measurement conditions are as follows.

[0768] ( 1 H-NMR measurement conditions)

[0769] Apparatus: Bruker Avance NEO 600

[0770] Observation nucleus: 1 H

[0771] Observation frequency: 600 MHz

[0772] Pulse program: zg30

[0773] Pulse delay: 1 sec

[0774] Number of accumulations: 1024

[0775] Measurement temperature: 130°C

[0776] Chemical shift reference: 7.219 ppm (o-DCBz)

[0777] Solvent: o-dichlorobenzene-d4

[0778] Sample concentration: 1 wt / vol%

[0779] Sample tube: 5 mm φ

[0780] ( 13 C-NMR measurement conditions)

[0781] Device: Bruker Avance NEO 600

[0782] Observation kernel: 13 C

[0783] Observation frequency: 150.91MHz

[0784] Pulse program: zgpg30

[0785] Pulse wait time: 5 seconds

[0786] Total number of times: 24,000 or 12,800

[0787] Measurement temperature: 130℃

[0788] Chemical shift reference: 132.39 ppm (o-DCBz)

[0789] Solvent: o-dichlorobenzene-d4

[0790] Sample concentration: 10 wt / vol%

[0791] Sample tube: 5mmφ

[0792] Furthermore, for cross-linked separators, after the pretreatment described above, they can be separated by... Figure 13 The same NMR measurements were performed (not shown).

[0793] like Figures 11 to 13 As shown, through 1 H and / or 13 NMR determination of C can confirm the amount of silane unit modification and alkyl modification in silane-modified polyolefins in polyolefin raw materials. Furthermore, in separators, the presence of (-CH) groups in silane-modified polyolefins can be identified. 2 -Si: 1 H, 0.69ppm,t; 13 C, 6.11 ppm, s).

[0794] [Combination of microporous membranes and inorganic porous layers]

[0795] The combination of the microporous film containing the silane-modified polyolefin and the inorganic porous layer has a tendency to improve the cycle characteristics and the nail penetration safety of the power storage device while giving consideration to the closing function at a temperature lower than 150°C and the film breaking property at a high temperature. It is presumed that since the silane-modified polyolefin in the microporous film is silane-crosslinkable, if silane-crosslinking occurs, the viscosity of the resin in the microporous film is sometimes increased, and thus if a compression force is applied between the plurality of electrodes at an abnormally high temperature of the power storage device including the separator, the high-viscosity resin that has undergone crosslinking is difficult to flow into the inorganic layer (i.e., difficult to integrate), the gap between the electrodes can be sufficiently ensured, and the battery short circuit can be suppressed.

[0796] [Inorganic porous layer]

[0797] The inorganic porous layer is a layer containing inorganic particles and a resin binder, and depending on the case, can further contain a dispersant that disperses the inorganic particles in the binder resin.

[0798] 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 viewpoint of the ion permeability of the separator and the 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.

[0799] [Second porous layer (B layer)]

[0800] The B layer contains inorganic particles. The B layer can further contain a resin binder. In the case where the B layer contains inorganic particles and a resin binder, the B layer can be the inorganic porous layer described above. Note that the B layer can contain components other than inorganic particles and a resin binder.

[0801] (Thickness of B layer)

[0802] The thickness (TB) of the B layer is preferably 0.2 μm or more, and 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 further increase. On the other hand, the thickness (TB) is preferably less than 22 μm, and more preferably 20 μm or less, and further preferably 15 μm or less. If the thickness (TB) is 30 μm or less, the occupied volume of the separator in the power storage device decreases, and thus there is a tendency to be advantageous in terms of high capacity of the power storage device. Furthermore, this is also preferable from the viewpoint of preventing excessive increase in the air permeability of the separator. Note 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 furthermore, can be set to less than 22.00 μm, 20.00 μm or less, or 15.00 μm or less.

[0803] The thickness (TB) can be measured by the method described in the Examples column, and in addition, can be controlled by changing the coating amount of the coating liquid (slurry) used to form the B layer, or the like.

[0804] In the case where the B layer is a single layer, the thickness of this B layer is regarded as the above-mentioned "thickness (TB)". In the case where the B layer is a multilayer, the total thickness of the B layers of this multilayer is regarded as the above-mentioned "thickness (TB)".

[0805] In addition, in the case where the B layer is disposed on both one face and the other face of the A layer, the total thickness of the B layer disposed on the one face and the B layer disposed on the other face is regarded as the above-mentioned "thickness (TB)".

[0806] (Inorganic particles)

[0807] As the inorganic particles, for example, inorganic oxides (oxide-based ceramics) such as alumina (AI2O3), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride-based ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxyhydroxide (AIO(OH)), potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, phlogopite, sericite, muscovite, chrysotile, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomite, and quartz sand; and glass fibers can be listed. These can be used alone or in combination with two or more kinds.

[0808] The amount of the inorganic particles, based on the total amount of the inorganic porous layer or the B layer, is preferably 5% by mass or more or 20% by mass or more, more preferably 30% by mass or more, from the viewpoint of ensuring heat resistance. The amount of the inorganic particles, based on the total amount of the inorganic porous layer or the B layer, can be set to 50% by mass or more, more than 80% by mass, or 85% by mass or more. On the other hand, the amount of the inorganic particles is preferably 99.9% by mass or less, more preferably 99.5% by mass or less or 99% by mass or less.

[0809] Note that the amount of the inorganic particles can be set to 20.00% by mass or more, 30.00% by mass or more, 50.00% by mass or more, more than 80.00% by mass, or 85.00% by mass or more, and on the other hand, can be set to 99.90% by mass or less or 99.50% by mass or less, for example.

[0810] As the shape of the inorganic particles, flaky, scaly, needle-like, columnar, spherical, polyhedral, spindle-like, and block shapes can be listed. A plurality of inorganic particles having these shapes can be used in combination.

[0811] The number-average particle size of the inorganic particles is, for example, 0.01 μm or more, 0.1 μm or more, or 0.3 μm or more, preferably 0.5 μm or more. On the other hand, the number-average particle size is, for example, 10.0 μm or less, 9.0 μm or less, or 6.0 μm or less, preferably 2.5 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less. From the perspective of improving safety during short circuits, it is preferable to adjust the number-average particle size of the inorganic particles to the above-mentioned range. As a method for adjusting the number-average particle size of the inorganic particles, methods such as pulverizing the inorganic particles using a suitable pulverizing device such as a ball mill, bead mill, or jet mill can be listed.

[0812] Regarding the particle size distribution of inorganic particles, the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. Furthermore, the ratio of the maximum particle size to the average particle size is preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less. From the perspective of suppressing thermal shrinkage at high temperatures, it is preferable to adjust the particle size distribution of inorganic particles to the above-mentioned range. In addition, multiple particle size peaks may exist between the maximum and minimum particle sizes. It should be noted that, as methods for adjusting the particle size distribution of inorganic particles, examples include: methods of pulverizing and adjusting inorganic fillers to the desired particle size distribution using a ball mill, bead mill, jet mill, etc., and methods of mixing multiple fillers having multiple particle size distributions after preparation.

[0813] (Resin adhesive)

[0814] The resin binder contains a resin that binds 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 inorganic particles and stability of the inorganic porous layer or B layer in the manufacturing process of the separator, the manufacturing process of the energy storage device, or the charge-discharge process.

[0815] The glass transition temperature is determined from a DSC curve obtained in differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of a straight line obtained by extending the baseline on the low temperature side of the DSC curve to the high temperature side and a tangent at the inflection point of the stepped change portion of the glass transition can be used as the glass transition temperature. More specifically, the glass transition temperature can be determined according to the method described in the examples. Further, the "glass transition" refers to a heat change in the DSC that occurs on the endothermic side accompanying a change in the state of the polymer as a test piece. This heat change is observed as a stepped change in the DSC curve. The "stepped change" indicates a portion in the DSC curve in which the curve departs from the baseline on the low temperature side to the baseline on the new high temperature side. Note that a combination of a stepped change and a peak is also included in the stepped change. Furthermore, the "inflection point" indicates a point at which the slope of the DSC curve in the stepped change portion reaches a maximum. Further, at the stepped change portion, in the case where the upper side is the heat generation side, it can also be expressed as a point at which the convex upward curve changes to a convex downward curve. The "peak" indicates a portion in the DSC curve in which the curve departs from the baseline on the low temperature side to return to the same baseline again. The "baseline" indicates the DSC curve of a temperature region in which no transition and reaction occur in the test piece.

[0816] As the resin binder, for example, the following 1) to 7) can be listed. These can be used alone or in combination with two or more.

[0817] 1) Polyolefin: for example, polyethylene, polypropylene, ethylene-propylene rubber, and modified products thereof;

[0818] 2) Conjugated diene-based polymer: for example, styrene-butadiene copolymer and hydrogenated products thereof, acrylonitrile-butadiene copolymer and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymer and hydrogenated products thereof;

[0819] 3) Acrylic polymer: for example, methacrylate-acrylate copolymer, styrene-acrylate copolymer, and acrylonitrile-acrylate copolymer;

[0820] 4) Polyvinyl alcohol-based resin: for example, polyvinyl alcohol and polyvinyl acetate;

[0821] 5) Fluorine-containing resin: for example, PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer;

[0822] 6) Cellulose derivative: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and

[0823] 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.

[0824] These kinds of resin binders can be obtained by a publicly known emulsion polymerization or solution polymerization or the like using a desired monomer as a raw material. In the polymerization, the polymerization temperature, the pressure at the time of polymerization, the method of adding the monomer, and the additives (polymerization initiator, molecular weight modifier, and pH modifier, etc.) used are not limited.

[0825] The amount of the resin binder is, for example, 0.5% by mass or more or 1.0% by mass or more, and on the other hand, for example, 50% by mass or less or 30% by mass or less, based on the total amount of the inorganic porous layer or the B layer. Further, as described above, the resin binder is an optional component with respect to the B layer, and thus the amount of the resin binder contained in the B layer can be set to less than 20% by mass, 15% by mass or less, or 0% by mass, based on the total amount of the B layer. If the amount of the resin binder contained in the B layer is reduced, the leeway for containing the above-mentioned inorganic particles in the B layer can be increased accordingly.

[0826] (Dispersant)

[0827] The dispersant is a substance that adsorbs on the surface of the inorganic particles in the slurry used for forming the inorganic porous layer or the B layer, and stabilizes the inorganic particles by electrostatic repulsion or the like, and for example, can be a polycarboxylate, a sulfonate, a polyoxyether, a surfactant, or the like. In the inorganic porous layer or the B layer, in addition to the above-mentioned components, other components that are usually added and compounded in water-based paints and the like can further be contained within the range of their effects. As such other components, there is no particular limitation, and for example, thickening agents, film-forming aids, plasticizers, crosslinking agents, antifreezes, defoaming agents, dyes, preservatives, ultraviolet absorbers, light stabilizers, and the like can be listed. These other components can be used alone as one kind, or two or more kinds in combination.

[0828] (Additive)

[0829] The microporous membrane, the inorganic porous layer, the A layer, and / or the B layer can contain a known additive as needed. As the additive, for example, organometallic catalysts (dehydration condensation catalysts), plasticizers, antioxidants of phenol, phosphorus, and sulfur, and the like, metal soaps of calcium stearate, zinc stearate, and the like, tackifiers, film-forming aids, crosslinking agents, antifreezes, defoaming agents, preservatives, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, dyes, and coloring pigments can be listed.

[0830] Further, the B layer can contain a crosslinking agent. The crosslinking agent can contain a functional group that has reactivity with the above-mentioned inorganic particles.

[0831] <Properties of the separator>

[0832] In the case where the separator is used for a lithium ion secondary battery of a higher capacity, the film thickness of the entire 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 film thickness of the separator 25 μm or less, there is a tendency that the ion permeability is further improved. The lower limit value of the film thickness of the entire separator 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.

[0833] The air permeability of the separator is preferably 50 seconds / 100 cm 3 ~ 400 seconds / 100 cm 3 , more preferably 75 seconds / 100 cm 3 ~ 275 seconds / 100 cm 3 , further preferably 100 seconds / 100 cm 3 ~ 200 seconds / 100 cm 3 . If the air permeability of the separator is 50 seconds / 100 cm 3 or more, the mechanical strength is moderate, and if the air permeability is 400 seconds / 100 cm 3 or less, the battery characteristics are improved from the viewpoint of permeability, and thus it is preferable.

[0834] [Assembly kit for power storage device]

[0835] Another aspect of the present application provides an assembly kit for a power storage device including the separator for a power storage device described above. The assembly kit for a power storage device has the following two elements:

[0836] (A) a housing body that accommodates a laminate or a wound body of an electrode and the separator for a power storage device of each of the embodiments described above; and

[0837] (B) a container that accommodates a nonaqueous electrolytic solution.

[0838] In the use of the assembly kit for a power storage device, by bringing the separator in element (A) into contact with the nonaqueous electrolytic solution in element (B), bringing the electrolytic solution into contact with the laminate or the wound body in the housing body, and / or by continuously performing charge and discharge cycles of the assembled power storage device, a crosslinked structure is formed in the separator, and a power storage device that balances safety and output can be formed.

[0839] While not wishing to be bound by theory, it is believed that a substance that catalyzes the cross-linking reaction or a substance having a functional group that forms a part of the cross-linking structure exists in the electrolyte, the inner surface of the housing, or the electrode surface when the electrolyte or the electrolytic solution is in contact with the electrode, and / or when the charge and discharge of the power storage device is performed, and it dissolves in the electrolyte, uniformly swells and diffuses into the amorphous portion of the polyolefin, thereby uniformly promoting the cross-linking reaction of the layered body or the wound body containing the separator. The substance that catalyzes the cross-linking reaction can be in the form of an acid solution or a film, and 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 a part of the cross-linking structure can be, for example, a compound having the functional groups A and / or B described above, the electrolyte itself, various additives, and the like.

[0840] The non-aqueous electrolyte contained in the element (2) can be, from the viewpoint of promoting the cross-linking reaction of the separator, a lithium salt containing fluorine (F) such as LiPF6that generates HF, an electrolyte having a lone pair of electrons such as LiN(SO2CF3)2, LiSO3CF3, and the like, or LiBF4, LiBC4O8(LiBOB), and the like.

[0841] The power storage device assembly kit can be provided with, as an accessory (or an element (C)), another container that contains a catalyst for promoting the cross-linking reaction, such as a mixture containing an organometallic catalyst and water, an acid solution, an alkali solution, and the like.

[0842] [Power Storage Device]

[0843] The separator described above can be used in a power storage device. The power storage device is provided with a positive electrode, a negative electrode, the separator of the present embodiment disposed between the positive and negative electrodes, an electrolyte, and an additive as desired. Once the separator is contained in the device housing, the functional group-modified polyethylene or the functional group-grafted copolymerized polyethylene reacts with chemical substances contained in the electrolyte or the additive, thereby forming a cross-linking structure, and thus the cross-linking structure is present in the manufactured power storage device. The functional group-modified polyethylene or the functional group-grafted copolymerized polyethylene is not limited, and can be derived from a polyolefin raw material of a microporous film or a polyolefin modified in a manufacturing process of a microporous film.

[0844] As the power storage device, specifically, there can be mentioned 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, and the like. Among these, from the viewpoint of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-hydrogen batteries, or lithium ion capacitors are preferable, and lithium batteries or lithium ion secondary batteries are more preferable.

[0845] The additive can be, for example, a dehydration condensation catalyst, a metal soap such as calcium stearate or zinc stearate, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifog agent, a coloring pigment, or the like.

[0846] [lithium ion secondary battery]

[0847] The lithium ion secondary battery is a secondary battery in which a lithium transition metal oxide such as lithium cobaltate or lithium cobalt complex oxide is used as a positive electrode, a carbon material such as graphite or black lead is used as a negative electrode, and an organic solvent containing a lithium salt such as LiPF6 is used as an electrolyte. With respect to the power storage device assembly kit, the electrolyte described above can also be used for a lithium ion secondary battery.

[0848] During charging / discharging of the lithium ion secondary battery, ionized lithium reciprocates between electrodes. In addition, it is necessary to move the aforementioned ionized lithium between electrodes at a high speed while suppressing contact between the electrodes, and therefore a separator is disposed between the electrodes.

[0849] [Manufacturing method of separator for power storage device]

[0850] Another aspect of the present application is a manufacturing method of a separator for a power storage device. The manufacturing method of the separator can include, for example, a manufacturing step of a microporous membrane or an A layer, and a manufacturing step of an inorganic porous layer on the microporous membrane or a manufacturing step of a B layer on the A layer, as desired. The material used in the manufacturing method of the separator can be the material described in the first to tenth embodiments, in the absence of a specific description.

[0851] [eleventh embodiment]

[0852] As the manufacturing method of the separator of the eleventh embodiment, the case of a microporous membrane (flat membrane) will be described below, but it is not intended to exclude forms other than flat membranes. The manufacturing method of the microporous membrane of the eleventh embodiment includes the following steps:

[0853] (1) a sheet forming step;

[0854] (2) a stretching step;

[0855] (3) a porous body forming step; and

[0856] (4) a heat treatment step.

[0857] By performing the steps (1) to (4), the A layer described above can also be formed.

[0858] The manufacturing method of the separator of the eleventh embodiment can further include the following steps on the basis of the steps (1) to (4) as desired:

[0859] (8B) a coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the aforementioned heat-treated porous body, forming a silane crosslinking precursor;

[0860] (9) an assembly step of housing an electrode and a laminate of the aforementioned silane crosslinking precursor or a roll body thereof, and a nonaqueous electrolyte solution in an outer case, and bringing the aforementioned silane crosslinking precursor into contact with the aforementioned nonaqueous electrolyte solution.

[0861] In the eleventh embodiment, after the coating of the inorganic porous layer on the microporous membrane that maintains the silane crosslinking property in the step (8B), the separator in the power storage device is brought into contact with the electrolyte solution in the step (9), and thus the stress resistance of the power storage device and the separator therein is improved, and further the cycle stability and the safety of the power storage device can be achieved.

[0862] The manufacturing method of the microporous membrane of the eleventh embodiment can include a kneading step before the sheet forming step (1) and / or a winding / slitting step after the heat treatment step (3) as desired, and it is preferable not to include a silane crosslinking treatment step from the viewpoint of maintaining the silane crosslinking property until the contact with the electrolyte solution. The silane crosslinking treatment step is generally a step of bringing a treated object containing a silane-modified polyolefin into contact with a mixture containing an organometallic catalyst and water, or immersing it in an alkali solution or an acid solution to perform a silane dehydration condensation reaction to form an oligosiloxane bond.

[0863] The metal of the organometallic catalyst can be at least one selected from the group consisting of scandium, titanium, vanadium, copper, zinc, aluminum, zirconium, palladium, gallium, tin, and lead, for example. As the organometallic catalyst, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, and the like can be cited, and it is known that these substances can overwhelmingly promote the reaction rate based on the reaction mechanism proposed by Weij et al. (F. W. van der Weij: Macromol. Chem., 181, 2541, 1980.). Furthermore, in recent years, in order to avoid the environmental and health hazards to the human body caused by organotin, it is known that by utilizing the Lewis function of a chelate complex of copper and / or titanium, by combining with an organic base, the reaction of forming a siloxane bond between alkoxysilyl groups can be promoted as in the organotin complex.

[0864] The pH of the alkaline solution exceeds 7, and for example, can include alkali metal hydroxides, alkaline earth metal hydroxides, carbonates of alkali metals, phosphates of alkali metals, ammonia, amine compounds, and the like. Among these, from the viewpoint of safety of the power storage device and silane crosslinkability, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is further preferred.

[0865] The pH of the acid solution is less than 7, and for example, can include inorganic acids, organic acids, and the like. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0866] The kneading step uses a kneader, and in the present embodiment, the silane-modified polyolefin, the plasticizer or inorganic material as desired, and the other polyolefin can be kneaded. From the viewpoint of suppressing the generation of resin agglomerates in the manufacturing process and maintaining silane crosslinkability until contact with the electrolyte solution, it is preferred that a master batch resin containing a dehydration condensation catalyst not be added to the kneaded product.

[0867] As the plasticizer, there is no particular limitation, and for example, an organic compound that can form a uniform solution with the polyolefin at a temperature below the boiling point can be cited. More specifically, decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil, and the like can be cited. Among these, paraffin oil and dioctyl phthalate are preferred. The plasticizer can be used alone as one kind, or two or more kinds can be used in combination. The proportion of the plasticizer is not particularly limited, and from the viewpoint of the porosity of the resulting microporous membrane, the polyolefin and the silane-modified polyolefin are preferably 20% by mass or more and 90% by mass or less, as needed, relative to the total mass, from the viewpoint of the viscosity at the time of melt kneading.

[0868] The sheet-forming step is a step of extruding, cooling and solidifying, and molding the resulting kneaded product or the mixture of the silane-grafted modified polyolefin and the polyethylene with the plasticizer into a sheet shape to obtain a sheet. As the method of sheet forming, there is no particular limitation, and for example, a method of solidifying a melt extruded by compression cooling can be cited. As the cooling method, a method of contacting a roll and / or a press machine cooled with a refrigerant, and the like can be cited, and the method of contacting a roll and / or a press machine cooled with a refrigerant is preferred in that the film thickness controllability is excellent.

[0869] From the viewpoint of resin agglomerates in the separator or the internal maximum heat generation rate, the mass ratio of the silane-modified polyolefin to the polyethylene (mass of the silane-modified polyolefin / mass of the polyethylene) in the sheet-forming step is preferably 0.05 / 0.95 to 0.4 / 0.6, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0870] From the viewpoint of suppressing thermal runaway at the time of destruction of the power storage device while having low-temperature shutdown properties of 150°C or lower and high-temperature resistance to film breakage at 180 to 220°C, and improving safety, it is preferable in the sheet forming step that the silane-modified polyolefin does not contain a master batch resin containing a dehydration condensation catalyst for crosslinking the silane-modified polyolefin before the sheet forming step.

[0871] The stretching step is a step of extracting the plasticizer and / or the inorganic material from the obtained sheet as needed and further stretching the sheet in one or more directions. As the stretching method of the sheet, there can be cited MD uniaxial stretching based on a roll stretching machine, TD uniaxial stretching based on a tenter, sequential biaxial stretching based on a combination of a roll stretching machine and a tenter or a tenter and a tenter, simultaneous biaxial stretching based on a simultaneous biaxial tenter or blow molding, and the like. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferable. The total area stretch ratio is preferably 8 times or more, more preferably 15 times or more, and further preferably 20 times or more or 30 times or more, from the viewpoint of the uniformity of the film thickness, the balance between the stretching elongation and the porosity and the average pore diameter. By making the total area stretch ratio 8 times or more, there is a tendency that a sheet having high strength and good thickness distribution is easily obtained. In addition, the area stretch ratio can be 250 times or less from the viewpoint of preventing breakage and the like.

[0872] The porous body forming step is a step of extracting the plasticizer from the stretched product after the stretching step and making the stretched product porous. The method of extracting the plasticizer is not particularly limited, and there can be cited, for example, a method of immersing the stretched product in an extraction solvent, a method of spraying the stretched product with an extraction solvent, and the like. The extraction solvent is not particularly limited, and there are preferably solvents that are poor solvents for polyolefins and good solvents for the plasticizer and / or the inorganic material, and the boiling point of which is lower than the melting point of the polyolefin. As such an extraction solvent, there can be cited, for example, hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropyl alcohol; ketones such as acetone and 2-butanone; and the like. The extraction solvent can be used alone or in combination with two or more.

[0873] The heat treatment step is a step of further extracting the plasticizer from the sheet as needed after the stretching step, further performing heat treatment, and obtaining a microporous membrane. As the method of heat treatment, there is no particular limitation, and for example, a heat setting method using stretching and relaxation operation by a tenter and / or a roll stretching machine, and the like can be cited. The relaxation operation refers to a reduction operation at a prescribed temperature and relaxation rate in the machine direction (MD) and / or the width direction (TD) of the membrane. The relaxation rate refers to a value obtained by dividing the MD size of the membrane after the relaxation operation by the MD size of the membrane before the operation, or a value obtained by dividing the TD size after the relaxation operation by the TD size of the membrane before the operation, or in the case of relaxation in both the MD and TD, a value obtained by multiplying the relaxation rate in the MD by the relaxation rate in the TD.

[0874] [Coating step of inorganic porous layer]

[0875] The coating step (8B) of the inorganic porous layer 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.

[0876] The B layer described above can also be formed by performing the coating step (8B). As the method of forming the B layer, a known manufacturing method can be employed. As the method of producing a laminate including the A layer and the B layer, for example, a method of applying a slurry containing inorganic particles to the A layer, a method of layering and extruding a raw material of the B layer and a raw material of the A layer by a co-extrusion method, a method of adhering the A layer and the B layer after producing them separately, and the like can be cited.

[0877] The inorganic porous layer can be formed, for example, by applying a slurry containing inorganic particles, a resin binder, water or a water-based solvent (for example, a mixture of water and alcohol, and the like), and a dispersant as desired to at least one surface of the microporous membrane. The inorganic particles, the resin binder, and the dispersant can be as described in the first to tenth embodiments.

[0878] As the solvent contained in the slurry, a solvent that can uniformly and stably disperse or dissolve the inorganic particles is preferred. As the solvent, for example, N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, dichloromethane, and hexane can be cited.

[0879] As the method of producing the slurry containing inorganic particles, for example, a mechanical stirring method based on a ball mill, a bead mill, a planetary ball mill, a vibration ball mill, a sand mill, a colloid mill, a mortar mill, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, a stirring blade, and the like can be cited.

[0880] As a coating method of the slurry containing inorganic particles, for example, there can be mentioned a gravure coater method, a small-diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air knife coater method, a blade coater method, a bar coater method, a squeeze coater method, a curtain coater method, a die coater method, a screen printing method, a spray coating method, and the like.

[0881] As a method for removing the solvent from the coated film, there can be mentioned a method of drying at a temperature lower than the melting point of the material constituting the microporous film, a method of drying under reduced pressure at a low temperature, and the like. Furthermore, a part of the solvent can be left if it does not significantly affect the device characteristics.

[0882] [Rolling / slit process]

[0883] The rolling process is a process of slitting, as necessary, the obtained microporous film or microporous film to which the inorganic porous layer is coated, and rolling onto a prescribed core.

[0884] [Power storage device assembly process]

[0885] The power storage device assembly process is a process of laminating a separator precursor that maintains silane crosslinkability (hereinafter also referred to as a silane crosslinking precursor) and an electrode to form a laminate, further rolling the laminate as desired to form a roll, housing the laminate or the roll and a nonaqueous electrolyte in an outer case, and bringing the silane crosslinking precursor into contact with the nonaqueous electrolyte. By the power storage device assembly process, the film reduction of the microporous film can be suppressed, the morphology can be maintained, the penetration of the polyolefin resin from the microporous film into the inorganic porous layer can be suppressed, and further the stress resistance of the power storage device or the separator can be improved.

[0886] In the power storage device assembly process (9) or after the process (9), the silane-modified polyolefin is crosslinked, and thus it is possible to initiate the silane crosslinking reaction of the separator after the power storage device is manufactured while fitting into the existing manufacturing process of the power storage device, thereby improving the safety of the power storage device.

[0887] In the power storage device assembly process, from the viewpoint of the handling properties of the electrolyte, it is preferable to inject the nonaqueous electrolyte into the outer case after housing the laminate or the roll in the outer case, or to house the laminate or the roll in the outer case after injecting the electrolyte into the outer case.

[0888] The electrolyte of the nonaqueous electrolyte can be a lithium salt containing fluorine (F) such as LiPF6 that generates hydrogen fluoride (HF), LiN(SO2CF3)2, LiSO3CF3, and the like having a lone pair of electrons, or LiBF4, LiBC4O8 (LiBOB), and the like from the viewpoint of promoting the crosslinking reaction of the separator.

[0889] While not wishing to be bound by theory, it is presumed that the methoxysilane grafted portion is converted to silanol by the trace amount of moisture contained in the power storage device (moisture contained in the members such as the electrode, separator, and electrolyte solution), and undergoes cross-linking reaction to change to siloxane bond. Further, it is considered that once the electrolyte or electrolyte solution comes into contact with the electrode, a substance that catalyzes the silane cross-linking reaction is generated in the electrolyte solution or on the surface of the electrode, they dissolve in the electrolyte solution, and uniformly swell and diffuse into the amorphous portion of the polyolefin in which the silane-modified grafted portion is present, thereby uniformly promoting the cross-linking reaction of the layered body 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 film, and in the case where the electrolyte contains lithium hexafluorophosphate (LiPF6), it can be HF generated by the reaction of LiPF6 with moisture, or a fluorine-containing organic substance derived from HF.

[0890] From the viewpoint of the efficiency of the silane cross-linking reaction, it is preferable to connect the lead terminals to the electrodes after the layered body or wound body and the non-aqueous electrolyte solution are housed in the outer case of the power storage device, and to perform at least one cycle of charge and discharge. It is considered that by the cycle of charge and discharge, a substance that catalyzes the silane cross-linking reaction is generated in the electrolyte solution or on the surface of the electrode, and thereby the silane cross-linking reaction is achieved. The cycle of charge and discharge can be performed by a known method and device, and specifically can be the method described in the examples.

[0891] [Method for manufacturing power storage device]

[0892] Another aspect of the present application is a method for manufacturing a power storage device.

[0893] [Eleventh embodiment]

[0894] The method for manufacturing a power storage device of the eleventh embodiment includes the following steps;

[0895] (I) a step of preparing the power storage device assembly kit described above;

[0896] (II) a step of starting the silane cross-linking reaction of the silane-modified polyolefin by bringing the separator in element (1) of the power storage device assembly kit into contact with the non-aqueous electrolyte in element (2);

[0897] (III) a step of connecting the lead terminals to the electrodes of element (1) as desired; and

[0898] (IV) a step of performing at least one cycle of charge and discharge as desired.

[0899] The steps (I) to (IV) can be performed by a method known in the technical field, except that the separator for power storage device of the present embodiment is used, and further, in the steps (I) to (IV), a positive electrode, a negative electrode, an electrolyte solution, an outer case, and a charge and discharge device known in the technical field can be used.

[0900] For the process (I), a separator having an elongated shape 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. Subsequently, in the process (I), the separators can be stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, and wound into a circular or flat spiral shape to obtain a wound body. In the processes (II) and (III), by housing the wound body in a device can (for example, a battery can), and further injecting a nonaqueous electrolyte solution, an electrical storage device can be manufactured. In addition, an electrical storage device can also be manufactured by a method in which a wound body prepared by folding an electrode and a separator is housed in a device container (for example, an aluminum-made film), and a nonaqueous electrolyte solution is injected.

[0901] At this time, the wound body can be pressed. Specifically, the separator, and the electrode having a current collector and an active material layer formed on at least one surface of the current collector can be overlapped and pressed.

[0902] Regarding the pressing temperature, as a temperature at which adhesiveness can be effectively exhibited, for example, 20°C or higher is preferable. In addition, from the viewpoint of suppressing clogging of pores in the separator or thermal shrinkage caused by heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the microporous film, and more preferably 120°C or lower. The pressing pressure is preferably 20 MPa or lower from the viewpoint of suppressing clogging of pores in the separator. Regarding the pressing time, when using roll pressing, it can be 1 second or less, or it can be surface pressure for several hours, and from the viewpoint of productivity, 2 hours or less is preferable.

[0903] By the above manufacturing process, press back when the wound body composed of the electrode and the separator is pressed into a shape can be suppressed. Therefore, reduction in yield in the device assembly process can be suppressed, the production process time can be shortened, and this is preferable.

[0904] From the viewpoint of reliably performing the silane crosslinking reaction of the separator after the process (II), the processes (III) and (IV) are preferably performed. It is considered that by the charge and discharge cycle, a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte solution or on the electrode surface, and thus the silane crosslinking reaction is achieved.

[0905] For example, in the manufacturing method of the separator, in the case where the manufacturing method of the A layer described above does not include the silane crosslinking treatment step, the crosslinking reaction can be actively promoted by bringing the separator into contact with the nonaqueous electrolyte solution. Although not wishing to be bound by theory, it is presumed that the silane-modified grafted portion is converted into silanol by the trace amount of moisture contained in the power storage device (the moisture slightly contained in the electrode, the separator, the nonaqueous electrolyte solution, and the like), undergoes the crosslinking reaction, and changes into a siloxane bond. In addition, it is considered that once the nonaqueous electrolyte solution comes into contact with the electrode, a substance that catalyzes the silane crosslinking reaction is generated in the nonaqueous electrolyte solution or on the surface of the electrode. It is considered that this substance that catalyzes the silane crosslinking reaction dissolves in the nonaqueous electrolyte solution, uniformly swells and diffuses into the amorphous portion of the polyolefin in which the silane-modified grafted portion is present, and thus uniformly promotes the crosslinking reaction of the laminate or the wound body including the separator.

[0906] The substance that catalyzes the silane crosslinking reaction can be in the form of an acid solution or a film. In the case where the electrolyte contains lithium hexafluorophosphate (LiPF6), LiPF6 reacts with moisture, and hydrogen fluoride (HF) or a fluorine-containing organic compound derived from hydrogen fluoride (HF) generated thereby is considered to be the substance that catalyzes the silane crosslinking reaction (a compound generated in the power storage device).

[0907] <Thirteenth Embodiment>

[0908] The thirteenth embodiment is a method of manufacturing a power storage device using a separator including a polyolefin having one or two or more functional groups, and includes the following step:

[0909] (1) a condensation reaction between the functional groups, or (2) a reaction of the functional groups with a chemical substance inside the power storage device, or (3) a reaction of the functional groups of the polyolefin with other kinds of functional groups, thereby forming a crosslinked structure.

[0910] The crosslinking step can be performed in the same manner as the reaction for forming the crosslinked structure of the separator described above. In addition, since the crosslinking step can be performed using a compound in the power storage device, the environment around the device, and the like, it is not necessary to use an excessive condition such as an electron beam, a high temperature of 100°C or higher, and thus a mild condition such as a temperature of 5°C to 90°C and / or an isothermal condition in the ambient atmosphere can be used.

[0911] By performing the crosslinking step in the manufacturing process of the power storage device, it is possible to omit the formation of the crosslinked structure in the film formation process of the separator or immediately after the process, to relax or eliminate the stress and strain after the power storage device is manufactured, and / or to impart the crosslinked structure to the separator even without using a higher energy such as light irradiation or heating, to reduce the occurrence of crosslinking unevenness, unmelted resin agglomerates, and the burden on the environment, and the like.

[0912] In the cross-linking step, by (2) causing the functional group to react with a chemical substance inside the power storage device, or (3) causing the functional group of the polyolefin to react with another kind of functional group, 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), and the strength between the plurality of members of the power storage device can be improved.

[0913] The separator described above can improve the safety of the power storage device because the silane-modified polyolefin is cross-linked when in contact with the electrolyte solution, and thus the silane cross-linking reaction can be induced after the power storage device is manufactured, while fitting into the manufacturing process of the existing power storage device.

[0914] Examples

[0915] The present application is more specifically described by giving examples and comparative examples, but the present application is not limited to the following examples as long as it does not deviate from the gist thereof. Note that the physical properties in the examples are measured by the following methods.

[0916] <Weight average molecular weight>

[0917] A standard polystyrene was measured under the following conditions using an ALC / GPC 150C (trademark) manufactured by Waters Corporation to prepare a calibration curve. Furthermore, for each of the following polymers, a chromatogram was also measured under the same conditions, and the weight average molecular weight of each polymer was calculated based on the calibration curve according to the following method.

[0918] Chromatography column: GMH6-HT (trademark) 2 pieces + GMH6-HTL (trademark) 2 pieces manufactured by Showa Denko K.K.

[0919] Mobile phase: o-dichlorobenzene

[0920] Detector: differential refractometer

[0921] Flow rate: 1.0 ml / min

[0922] Column temperature: 140°C

[0923] Sample concentration: 0.1 wt%

[0924] <Weight average molecular weight of polyethylene>

[0925] The weight average molecular weight was calculated by multiplying each molecular weight component in the resulting calibration curve by 0.43 (Q factor of polyethylene / Q factor of polystyrene = 17.7 / 41.3) to obtain a molecular weight distribution curve converted to polyethylene.

[0926] <Weight average molecular weight of resin composition>

[0927] 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.

[0928] <Viscosity average molecular weight (Mv)>

[0929] The intrinsic viscosity [η] at 135°C in decalin solvent was determined based on ASTM-D4020. The Mv of the polyethylene was calculated according to the following equation.

[0930] [η] = 6.77 x 10 -4 Mv 0.67

[0931] <Melt mass flow rate (MFR) (g / 10 min)>

[0932] The weight of the resin material extruded for 10 minutes at 190°C under a load of 2.16 kg was determined as the MFR value using a melt mass flow rate tester (MELT INDEXER F-F01) manufactured by Toyo Seiki Co., Ltd.

[0933] <Measurement of glass transition temperature>

[0934] An appropriate amount of an aqueous dispersion containing a resin sample (solid content = 38 to 42% by weight, pH = 9.0) was taken into an aluminum dish, and dried with a hot air drier at 130°C for 30 minutes to obtain a dried coating film. About 17 mg of the dried coating film was filled into an aluminum container for measurement, and a DSC curve and a DSC curve under a nitrogen atmosphere were obtained using a DSC measurement device (manufactured by Shimadzu Corporation, model "DSC6220"). The measurement conditions were as described below.

[0935] First temperature rising program: temperature was raised at a rate of 15°C per minute from 70°C. After reaching 110°C, it was maintained for 5 minutes.

[0936] Second temperature lowering program: temperature was lowered at a rate of 40°C per minute from 110°C. After reaching -50°C, it was maintained for 5 minutes.

[0937] Third temperature rising program: temperature was raised at a rate of 15°C per minute from -50°C to 130°C. The data of DSC and DDSC were obtained at this third temperature rising.

[0938] The intersection of the baseline (a straight line obtained by extending the baseline in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (point at which the convex curve changes to the concave curve) was taken as the glass transition temperature (Tg).

[0939] <Film thickness (μm)>

[0940] 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 room temperature of 23 ± 2°C and 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.

[0941] <The thickness of layer A (TA), and the thickness of layer B (TB)>

[0942] Using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, Ltd., the thickness of layer A (TA) is measured at room temperature of 23 ± 2°C and 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, by subtracting the thickness of layer A (TA) from the thickness of the obtained laminate, the thickness of layer B (TB) is obtained.

[0943] 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.

[0944] <Porosity (%)>

[0945] (i) Calculated based on the density of the mixed composition

[0946] 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. It should be noted 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.

[0947] Porosity (%) = (Volume - Mass / Density of the mixed composition) / Volume × 100 >

[0948] (ii) Calculated based on the film density

[0949] Alternatively, the porosity of the microporous membrane is calculated from the volume, mass, and film density (g / cm 3 ) using the following formula.

[0950] Porosity (%) = (Volume - Mass / Film density) / Volume × hundred

[0951] It should be noted that in the present invention, the film density refers to the value measured by the D) density gradient tube method described in JIS K7112 (1999).

[0952] (iii) porosity of layer A

[0953] A 10 cm x 10 cm square sample was cut from layer A, and its volume (cm 3 ) and mass (g) were determined, and from these and the density (g / cm 3 ) of the mixed composition, the porosity was calculated using the following formula. The density of the mixed composition was calculated using the respective densities of the raw materials used and the mixing ratio.

[0954] Porosity (%) = (volume - mass / density of mixed composition) / volume x 100

[0955] <Air permeability (sec / 100 cm 3 )>

[0956] The air permeability of the sample or layer A was measured according to JIS P-8117 (2009) using a GURLEY type air permeability meter, G-B2 (trademark), manufactured by Toyo Seiki Co., Ltd.

[0957] <Puncture strength of layer A>

[0958] A layer A was fixed using a hand-held compression tester, KES-G5 (model), manufactured by KATO TECH Co., Ltd., with a sample holder having an opening diameter of 11.3 mm. Next, a needle having a tip with a radius of curvature of 0.5 mm was used to perform a puncture test at a puncture speed of 2 mm / sec in an atmosphere at 25°C on the central portion of the fixed layer A, whereby the maximum puncture load was measured. This maximum puncture load was converted to a value corresponding to a thickness of 20 μm, and this value was taken as the puncture strength (gf / 20 μm). In the case where the thermoplastic polymer is present only on one side of the base material, the puncture by the needle can be performed from the side where the thermoplastic polymer is present.

[0959] <Quantification of resin agglomerates in the separator>

[0960] The resin agglomerates in the separator were defined as regions having an area of 100 μm x 100 μm or more and being non-transparent when the separator obtained by the film formation process of the Examples and Comparative Examples described below was observed using a transmission optical microscope. In the observation based on the transmission optical microscope, the number of resin agglomerates per 1000 m 2 of the area of the separator was measured.

[0961] <Storage modulus, loss modulus, and transition temperature (version 1)>

[0962] The dynamic viscoelasticity measurement of the separators was performed using a dynamic viscoelasticity measuring device, and the storage modulus (E'), the loss modulus (E"), and the transition temperature between the rubbery plateau region and the crystalline melting flow region were calculated. The storage modulus change ratio (R ΔE’ ) was calculated according to the following equation (1), the mixing storage modulus change ratio (R E’mix ) was calculated according to the following equation (2), the loss modulus change ratio (R ΔE” ) was calculated according to the following equation (3), and the mixing loss modulus change ratio (R E”mix ) was calculated according to the following equation (4). Note that the measurement conditions were as follows (i) to (iv).

[0963] (i) The dynamic viscoelasticity measurement was performed under the following conditions.

[0964] • Atmosphere: nitrogen

[0965] • Measuring device used: RSA-G2 (manufactured by TA Instruments)

[0966] • Sample film thickness: in the range of 5 to 50 μm

[0967] • Measurement temperature range: -50 to 225°C

[0968] • Temperature increase rate: 10°C / min

[0969] • Measurement frequency: 1 Hz

[0970] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[0971] • Initial value of static tension load: 0.5 N

[0972] • Initial (at 25°C) gap distance: 25 mm

[0973] • Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sinusoidal wave load 0.02 to 5 N).

[0974] (ii) The static tension load refers to the intermediate value of the maximum stress and the minimum stress under each periodic motion, and the sinusoidal wave load refers to the oscillation stress centered on the static tension load.

[0975] (iii) The sinusoidal wave stretching mode is a mode in which the vibration stress is measured while one side is subjected to periodic motion at a fixed amplitude of 0.2%, and in this case, the gap distance and the static tensile load are changed in such a manner that the difference between the static tensile load and the sinusoidal wave load is within 20% to measure the vibration stress. Note that in the case where the sinusoidal wave load is 0.02 N or less, the amplitude value is increased in such a manner that the sinusoidal wave load is within 5 N and the increase in the amplitude value is within 25% to measure the vibration stress.

[0976] (iv) The storage modulus and the loss modulus are calculated from the obtained sinusoidal wave load and the amplitude value, and the following equation:

[0977] σ * = σ0• Exp[i(ωt + δ)],

[0978] ε * = ε0• Exp(iωt),

[0979] σ * = E * • ε *

[0980] E * = E' + iE"

[0981] {in the equation, σ * : vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between the vibration stress and the strain, E * : complex modulus, E': storage modulus, E": loss modulus

[0982] Vibration stress: sinusoidal wave load / initial cross-sectional area

[0983] Static tensile load: load at the minimum point of the vibration stress in each cycle (minimum point of the gap distance in each cycle)

[0984] Sinusoidal wave load: difference between the measured vibration stress and the static tensile load

[0985] E' S and E' j and E" S and E" j The average of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelasticity measurement data is used for E' a and E'0and E" a and E"0.

[0986] R ΔE’ = E'S / E' j (1) Before and after the battery into the contrast

[0987] R E’mix = E' a / E'0 (2) With or without silane cross-linked contrast

[0988] R ΔE” = E" S / E" j (3) Before and after the battery into the contrast

[0989] R E”mix = E" a / E"0 (4) With or without silane cross-linked contrast

[0990] An example of a graph for illustrating the relationship between temperature and storage modulus is shown in Figure 1 . As shown in Figure 1 , the storage modulus of the standard film (a separator for an electrical storage device not containing a silane-modified polyolefin) and the cross-linked film in the temperature range of -50°C to 225°C are compared, and the transition temperature of the rubbery flat region and the crystal melting flow region can be confirmed in Figure 1 . Note that the transition temperature is the temperature at which the intersection of the straight line obtained by extending the baseline on the high temperature side to the low temperature side and the tangent line made at the inflection point of the curve in the crystal melting change portion.

[0991] An example of a graph for illustrating the relationship between temperature and loss modulus is shown in Figure 2 . Figure 2 The loss modulus of the standard film (a separator for an electrical storage device not containing a silane-modified polyolefin) and the cross-linked film in the temperature range of -50°C to 220°C are compared, and the transition temperature determined by the same method as in Figure 1 is shown. In this technical field, the storage modulus and the loss modulus can be converted according to the following equation:

[0992] tan δ = E" / E'

[0993] {In the equation, tan δ represents the loss tangent, E' represents the storage modulus, and E" represents the loss modulus.}.

[0994] Note that in the measurement of the mixed storage modulus ratio (R E’mix ) or the mixed loss modulus ratio (R E”mix ), a micro-porous film of a silane-unmodified polyolefin having a gelation degree of about 0% is used as a separator for an electrical storage device not containing a silane-modified polyolefin. Furthermore, regarding E' a , E'0, E" aand E"0, the average value of each storage modulus or each loss modulus in the range of 160°C to 300°C in the dynamic viscoelasticity measurement data was used. E' and E'0 and E" and E"0, the average value of each storage modulus or each loss modulus in the range of 160°C to 300°C in the dynamic viscoelasticity measurement data was used. Figure 1 and 2 The standard film shown in Table 1 exhibited a break at 207°C.

[0995] <Storage modulus, loss modulus, and transition temperature (version 2)>

[0996] The dynamic viscoelasticity measurement of the separators was performed using a dynamic viscoelasticity measuring device, and the storage modulus (E'), the loss modulus (E"), and the transition temperature of the rubbery flat region and the crystal melting flow region were calculated. The storage modulus change ratio (R ΔE’X ) was calculated according to the following formula (1), the mixed storage modulus ratio (R E’mix ) was calculated according to the following formula (2), the mixed loss modulus ratio (R E”X ) was calculated according to the following formula (3), and the mixed loss modulus ratio (R E”mix ) was calculated according to the following formula (4). Note that, regarding the measurement conditions, a dynamic viscoelasticity measuring device, RSA-G2 manufactured by TA Instruments, was used, the measurement frequency was 1 Hz, the strain was 0.2%, and the temperature region was -50°C to 310°C under a nitrogen atmosphere, and regarding other conditions, the storage modulus and the loss modulus were measured according to the above version 1. E' Z and E' Z0 and E" Z and E" Z0 The average value of each storage modulus or each loss modulus in the range of 160°C to 300°C in the dynamic viscoelasticity measurement data was used. E' and E'0 and E" and E"0, the average value of each storage modulus or each loss modulus in the range of 160°C to 300°C in the dynamic viscoelasticity measurement data was used.

[0997] R ΔE’X = E' Z / E' Z0 (1) Comparison before and after being put into a battery

[0998] R E’mix = E' / E'0 (2) Comparison of the presence or absence of an amorphous portion crosslinked structure

[0999] R E”X = E" Z / E" Z0 (3) Comparison before and after being put into a battery

[1000] R E”mix=E” / E”0 (4) Comparison of the presence and absence of amorphous cross-linked structures

[1001] An example of a graph used to illustrate the relationship between temperature and energy storage modulus is shown below. Figure 9 .like Figure 9 As shown, by comparing the energy storage modulus of a standard membrane (a separator for energy storage devices without amorphous cross-linked structures) and a cross-linked membrane within a temperature range of -50℃ to 310℃, it can be seen that... Figure 9 The transition temperature between the rubbery flat region and the crystalline melting and flow region was confirmed. It should be noted that the transition temperature is the temperature at the intersection of the straight line obtained by extending the baseline from the high-temperature side to the low-temperature side and the tangent line drawn at the inflection point of the curve in the crystalline melting and change region.

[1002] An example of a graph illustrating the relationship between temperature and loss modulus is shown below. Figure 10 .exist Figure 10 In the comparison of the loss modulus of a standard membrane (a separator for an energy storage device without silane-modified polyolefin) and a cross-linked membrane within a temperature range of -50℃ to 310℃, it is shown that by comparing with Figure 9 The transition temperature was determined using the same method. In this technical field, the storage modulus and loss modulus can be interchanged according to the following formula:

[1003] tanδ=E” / E'

[1004] {In the formula, tanδ represents the loss tangent, E' represents the energy storage modulus, and E” represents the loss modulus.}

[1005] It should be noted that the hybrid energy storage modulus ratio (R) E’mix ) or mixed loss modulus ratio (R E”mix In the determination of E', a microporous membrane made of polyolefin with a gelation degree of approximately 0% was used as a separator for an energy storage device without amorphous cross-linked structure. Furthermore, regarding E', E'0, E”, and E”0, in cases where no fracture of the sample was observed at 160℃ to 300℃ (elastic modulus decreased sharply), the values ​​were calculated based on the average values ​​from 160℃ to 300℃; in cases where fracture occurred at 160℃ to 300℃, the values ​​were calculated based on the average values ​​from 160℃ to the fracture point. For example, Tables 11 and 12, and... Figure 9 and Figure 10 The standard membrane shown broke at 210°C.

[1006] In the present specification, the separator for power storage devices having no amorphous portion crosslinked structure can be one made of a composition using 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 two or three selected from the group consisting of X, Y, and Z, mixed in any ratio. Note that low-density polyethylene: LDPE, linear low-density polyethylene: LLDPE, polypropylene: PP, olefin-based thermoplastic elastomer, and the like, which are composed only of a hydrocarbon skeleton, can be added to the mixed composition. In more detail, the separator for power storage devices having no amorphous portion crosslinked structure can be a polyolefin microporous membrane in which the change rate of the solid content before and after heating at 160°C in decalin solution (hereinafter referred to as "degree of gelation") is 10% or less. Note that in the measurement of the degree of gelation, the solid content refers only to the resin, and does not include other materials such as inorganic substances.

[1007] 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, and more preferably 70% or more.

[1008] <Storage modulus, loss modulus, film softening transition temperature, and film breakage temperature (version 3)>

[1009] The solid viscoelasticity measurement of the separator was performed using a dynamic viscoelasticity measuring device, and the storage modulus (E'), the loss modulus (E"), and the film softening transition temperature were calculated. Note that the conditions for the solid viscoelasticity measurement were as follows (i) to (iv).

[1010] (i) The dynamic viscoelasticity measurement was performed under the following conditions.

[1011] • Measuring device used: RSA-G2 (manufactured by TA Instruments)

[1012] • Sample film thickness: 200 to 400 μm (in the case where the film thickness of a single sample is less than 200 μm, a plurality of samples were laminated so as to have a total thickness in the range of 200 to 400 μm, and the dynamic viscoelasticity measurement was performed.)

[1013] • Measurement temperature range: -50 to 250°C

[1014] • Temperature increase rate: 10°C / min

[1015] • Measurement frequency: 1 Hz

[1016] • Deformation mode: sinusoidal wave tension mode (Linear tension)

[1017] • Initial value of static tensile load: 0.2 N

[1018] • Initial (at 25°C) gap distance: 10 mm

[1019] • Auto-strain adjustment (Auto-strain adjustment): Disabled.

[1020] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress under each periodic motion, and the sinusoidal wave load refers to the vibrating stress centered on the static tensile load;

[1021] (iii) The sinusoidal wave tensile mode refers to a mode in which the vibrating stress is measured while performing periodic motion at a fixed amplitude of 0.1%, and in the sinusoidal wave tensile mode, the vibrating 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 5%, and in the case where the sinusoidal wave load is 0.1 N or less, the static tensile load is fixed to 0.1 N to measure the vibrating stress.

[1022] (iv) The storage modulus (E') and the loss modulus (E") are calculated from the obtained sinusoidal wave load and the amplitude value, and the following equation:

[1023] σ * = σ0• Exp[i(ωt + δ)],

[1024] ε * = ε0• Exp(iωt),

[1025] σ * = E * • ε *

[1026] E * = E' + iE"

[1027] {wherein σ * : vibrating stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between the vibrating stress and the strain, E * : complex modulus, E': storage modulus, E": loss modulus

[1028] Vibrating stress: Sinusoidal wave load / initial cross-sectional area

[1029] Static tensile load: Load at the minimum point of the vibrating stress within each cycle (minimum point of the gap distance within each cycle)

[1030] Sinusoidal wave load: Difference between the measured vibrating stress and the static tensile load

[1031] Further, the average of the maximum value and the minimum value of E' is calculated, and is denoted as average E' (E'ave). ave Further, the average of the maximum value and the minimum value of E" is calculated, and is denoted as average E" (E"ave). ave

[1032] Note that E' and E" are calculated from 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, in a case where no breakage (sharp decrease in the 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 at which the breakage of the sample occurs is taken as the minimum value. Further, in this technical field, the storage modulus and the loss modulus can be converted from each other according to the following equation:

[1033] tan δ = E" / E'

[1034] {In the equation, tan δ represents the loss tangent, E' represents the storage modulus, and E" represents the loss modulus.}.

[1035] The film softening transition point temperature is the temperature of the minimum value obtained by first-order derivation of the curve of the gap distance of the sample in the dynamic viscoelasticity measurement data. Further, the film breakage temperature is the temperature at which the breakage (sharp decrease in the elastic modulus) of the sample is observed in the dynamic viscoelasticity measurement data, and the measurement limit temperature is sometimes set to 250°C from the viewpoint of performing the thermal decomposition reaction of the polyolefin resin. However, the phenomenon can also be understood in the same manner by measurement at a high temperature higher than 250°C, and thus the present embodiment can implement the separator for power storage devices having a film breakage temperature of 180°C or higher.

[1036] <Breakage temperature of the A layer>

[1037] A constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation was used, the environmental temperature was changed between 25°C and 250°C, and the temperature at the instant when the load was completely released was determined as the TMA breakage temperature (breakage temperature of the A layer measured by TMA).

[1038] Specifically, TD 3 mm and MD 14 mm were taken from the A layer, and were used as the test piece (test piece with the MD as the long side). The both ends of the MD of the test piece were installed in the special probe with a jig distance of 10 mm, and a load of 1.0 g was applied to the test piece. The oven on which the test piece was mounted was warmed up, and the temperature at which the load was displayed as 0 g was taken as the breakage temperature (°C).

[1039] ​Note that, when the sample piece TD for which TD is long side is measured, TD 14 mm, MD 3 mm are taken from the A layer, and used as a sample piece. The distance between the two ends of the sample piece is set to 10 mm using a special probe, and the initial load of 1.0 g is applied, and the same operation as described above is performed.

[1040] Thermal shrinkage at 150°C

[1041] TD 100 mm, MD 100 mm are taken from the laminate before the crosslinked structure is formed (the laminate including the A layer and the B layer), and used as a sample piece. Also, the sample piece is left in an oven at 150°C for 1 hour. At this time, the sample piece is sandwiched with two sheets of paper so that hot air does not directly blow on the sample piece. After the sample piece is taken out of the oven and cooled, the area of the sample piece is measured, and the thermal shrinkage at 150°C before the crosslinked structure is formed (Tl) is calculated according to the following equation.

[1042] Thermal shrinkage at 150°C (%) = (10,000 (mm 2 ) - area of the sample piece after heating (mm 2 )) x 100 / 10,000

[1043] Also, for the laminate after the crosslinked structure is formed, TD 100 mm, MD 100 mm are taken, and used as a sample piece, and the same operation as described above is performed, whereby the thermal shrinkage at 150°C after the crosslinked structure is formed (T2) is calculated.

[1044] Then, by dividing the thermal shrinkage (T2) by the thermal shrinkage (Tl), the ratio (T2 / Tl) is obtained. The value of the ratio (T2 / Tl) corresponds to the change rate of the thermal shrinkage at 150°C after the crosslinked structure is formed (T2) with respect to the thermal shrinkage at 150°C before the crosslinked structure is formed (Tl).

[1045] <Battery destruction safety test 1>

[1046] Battery destruction safety test 1 is a test in which a battery charged to 4.5 V is struck with a nail at a speed of 20 mm / sec and the nail is made to penetrate, thereby causing internal short circuit. This test makes it possible to understand the phenomenon at the time of internal short circuit by measuring the time-dependent behavior of the voltage decrease of the battery due to internal short circuit and the behavior of the temperature increase on the surface of the battery due to internal short circuit. Also, due to the insufficient closing function of the separator at the time of internal short circuit or the breakage of the film at low temperature, the battery sometimes sharply heats up, and in conjunction therewith, the electrolyte sometimes catches fire, and the battery sometimes emits smoke and / or explodes.

[1047] (Production of the battery used in battery destruction safety test 1)

[1048] 1a. Production of the positive electrode

[1049] A slurry was prepared by dispersing 92.2% by mass of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 2.3% by mass each of flake graphite and acetylene black as conductive materials, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a resin binder in N-methylpyrrolidone (NMP). The slurry was then coated onto one side of a 20 μm thick aluminum foil constituting the positive electrode current collector using a die coater. After drying at 130°C for 3 minutes, the foil was compressed and shaped using a roller press. At this point, the coating weight of the positive electrode active material was adjusted to 250 g / m². 2 The bulk density of the active substance was adjusted to 3.00 g / cm³. 3 .

[1050] 1b. Production of the negative electrode

[1051] A slurry was prepared by dispersing 96.9% by mass of artificial graphite (as the negative electrode active material), 1.4% by mass of ammonium salt of carboxymethyl cellulose (as a resin binder), and 1.7% by mass of styrene-butadiene copolymer latex in purified water. The slurry was coated onto one side of a 12 μm thick copper foil constituting the negative electrode current collector using a die coater. After drying at 120°C for 3 minutes, it was compressed and shaped using a roller press. At this point, the coating amount of the active material for the negative electrode was adjusted to 106 g / m². 2 The bulk density of the active substance was adjusted to 1.35 g / cm³. 3 .

[1052] 1c. Preparation of non-aqueous electrolytes

[1053] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1:2 to achieve a concentration of 1.0 mol / L.

[1054] 1d. Battery assembly

[1055] Cut separators to a width (TD) of 60 mm and a length (MD) of 1000 mm. Fold the separators repeatedly, alternating layers of positive and negative electrodes between the separators (12 positive electrodes and 13 negative electrodes). Note that the positive electrode uses a material with an area of ​​30 mm × 50 mm, and the negative electrode uses a material with an area of ​​32 mm × 52 mm. Place the repeatedly folded stack into a laminated bag, inject the non-aqueous electrolyte obtained in step c above, and seal it. After standing at room temperature for one day, charge the battery at 3 mA (0.5C) to a battery voltage of 4.2V at 25°C. Once reached, maintain the voltage at 4.2V while gradually decreasing the current from 3 mA. Perform this initial charge for 6 hours after battery fabrication. Then, discharge the battery at 3 mA (0.5C) to a battery voltage of 3.0V.

[1056] (Maximum heat generation rate)

[1057] After the iron nail was made to penetrate the resulting battery, the temperature change chart obtained by measuring the surface temperature of the battery for 300 seconds using a thermocouple, the rate at which the temperature changed most in every 1 sec was determined as the maximum heat generation rate.

[1058] (Voltage reduction time)

[1059] After the iron nail was made to penetrate the resulting battery, the time required for the voltage to be reduced from 4.5 V to 3 V was determined as the voltage reduction time (time to 3 V).

[1060] <Cycle characteristic evaluation and method for producing the battery therefor>

[1061] The cycle characteristic evaluation battery was produced according to the same method as la. to lc. of the method for producing the battery used in the above item <Battery destruction safety test 1>, but assembled according to the following Id-2.

[1062] Id-2. Battery assembly

[1063] The separator was cut into a circle of 18 mm in diameter, and the positive electrode and the negative electrode were cut into a circle of 16 mm in diameter, and the positive electrode, the separator, and the negative electrode were sequentially overlapped with the active material surface of the positive electrode facing the active material surface of the negative electrode, and accommodated in a stainless steel container with a lid. The container was insulated from the lid, the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. The nonaqueous electrolytic solution obtained in lc. of the above item <Battery destruction safety test 1> was injected into the container and sealed. After being left at room temperature for 1 day, the initial charging after battery production was performed for a total of 6 hours by charging to a battery voltage of 4.2 V at a current value of 3 mA (0.5 C) in a 25°C atmosphere, and after reaching, reducing the current value from 3 mA while maintaining 4.2 V, and then discharging to a battery voltage of 3.0 V at a current value of 3 mA (0.5 C).

[1064] The charge and discharge of the resulting battery was performed for 100 cycles in a 60°C atmosphere. The charging was performed for a total of 3 hours by charging to a battery voltage of 4.2 V at a current value of 6.0 mA (1.0 C), and after reaching, reducing the current value from 6.0 mA while maintaining 4.2 V, and the discharging was performed by discharging to a battery voltage of 3.0 V at a current value of 6.0 mA (1.0 C).

[1065] (Cycle characteristic evaluation 1)

[1066] The capacity retention rate was calculated from the discharge capacity of the 100th cycle and the discharge capacity of the 1st cycle. The case where the capacity retention rate was high was evaluated as having good cycle characteristics.

[1067] (Cycle characteristic evaluation 2)

[1068] From the discharge capacity of the 300th cycle and the discharge capacity of the 1st cycle, the capacity retention rate (%) was calculated based on the following formula. The case where the capacity retention rate was high was evaluated as having good cycle characteristics.

[1069] Evaluation result (%) = (100 x the capacity after 300 cycles / the discharge capacity of the 1st cycle)

[1070] <Fuse / Melt-Disconnection (F / MD) characteristics>

[1071] (i) 0.5 MPa of pressure and 2°C / min of temperature increase rate

[1072] The positive electrode, the separator, and the negative electrode were cut into a circular shape of 200 mm in diameter and overlapped, and a non-aqueous electrolytic solution was added to the obtained laminate and permeated throughout. The laminate was sandwiched in the center portion of a circular aluminum heater of 600 mm in diameter, and the aluminum heater was pressurized to 0.5 MPa from the upper and lower directions using a hydraulic jack, and the preparation for the measurement was completed. While the aforementioned laminate was heated with the aluminum heater at a temperature increase rate of 2°C / min, the resistance (Ω) between the electrodes was measured. The temperature at which the separator was fused and the resistance between the electrodes rose and the resistance first exceeded 1000 Ω was taken as the fuse temperature (shut-down temperature). Further, the heating was continued, and the temperature at which the resistance decreased to 1000 Ω or less was taken as the melt-disconnection temperature (film-breaking temperature).

[1073] (ii) 10 MPa maximum pressure and 15°C / min of temperature increase rate

[1074] The positive electrode, the separator, and the negative electrode were cut into a circular shape of 200 mm in diameter, and a non-aqueous electrolytic solution was added to the obtained laminate and permeated throughout. The laminate was sandwiched in the center portion of a circular aluminum heater of 600 mm in diameter, and a pressure was applied to the aluminum heater to 10 MPa from the upper and lower directions using a hydraulic jack, and the preparation for the measurement was completed. While the laminate was heated with the aluminum heater at a temperature increase rate of 15°C / min, the resistance (Ω) between the electrodes was measured. The temperature at which the resistance between the electrodes rose and the resistance first exceeded 1000 Ω was taken as the shut-down temperature (°C). Further, the heating was continued, and the temperature at which the resistance decreased to 1000 Ω or less was taken as the melt-disconnection temperature (°C).

[1075] Note that, for evaluation of either (i) or (ii), an electric resistance measuring wire was attached to the back surface of the aluminum foil of the positive electrode made through "1a. Production of positive electrode" of the above item <Battery destruction safety test 1> with a conductive silver paste. In addition, an electric resistance measuring wire was attached to the back surface of the copper foil of the negative electrode made through "1b. Production of negative electrode" of the above item <Battery destruction safety test 1> with a conductive silver paste. Furthermore, the electrolyte-containing electrolyte prepared through "1c. Preparation of nonaqueous electrolyte" of the above item <Battery destruction safety test 1> was also used for the F / MD characteristic test.

[1076] <Safety test (nail penetration test) 2>

[1077] 2a. Production of positive electrode

[1078] A nickel-manganese-cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) 90.4 mass%, graphite powder (KS6) (density 2.26 g / cm 3 , number average particle diameter 6.5 μm) 1.6 mass% as a conductive aid, and acetylene black powder (AB) (density 1.95 g / cm 3 , number average particle diameter 48 nm) 3.8 mass% as a conductive aid, and PVDF (density 1.75 g / cm 3 ) 4.2 mass% as a resin binder were mixed at a ratio, and they were dispersed in NMP to prepare a slurry. The slurry was coated on one surface of an aluminum foil having a thickness of 20 μm constituting a positive electrode current collector using a die coater, and after drying at 130°C for 3 minutes, compression molding was performed using a roll press, whereby a positive electrode was produced. At this time, the positive electrode active material coating amount was 109 g / m 2 .

[1079] 2b. Production of negative electrode

[1080] Graphite powder A (density 2.23 g / cm 3 , number average particle diameter 12.7 μm) 87.6 mass% and graphite powder B (density 2.27 g / cm 3A slurry was prepared by dispersing 9.7 mass% of a styrene-butadiene copolymer latex (number average particle size 6.5 μm), 1.4 mass% (solid content conversion) of an ammonium salt of carboxymethylcellulose (solid content concentration 1.83 mass% aqueous solution) and 1.7 mass% (solid content conversion) of a diene rubber-based latex (solid content concentration 40 mass% aqueous solution) as a resin binder in purified water, as a solute, in a mixed solvent of ethylene carbonate:methyl ethyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol / L. This slurry was coated on one side of a copper foil having a thickness of 12 μm constituting the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and compression-molded using a roll press, whereby a negative electrode was produced. At this time, the negative electrode active material coating amount was 52 g / m 2 .

[1081] 2c. Preparation of non-aqueous electrolyte

[1082] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:methyl ethyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol / L.

[1083] 2d. Production of battery

[1084] A laminated secondary battery having a size of 100 mm x 60 mm and a capacity of 3 Ah, which was subjected to constant current constant voltage (CCCV) charging under conditions of a current value of 1 A (0.3 C) and a terminal cell voltage of 4.2 V for 3 hours, was produced using the positive electrode, negative electrode and non-aqueous electrolyte obtained in 2a to 2c above, and a separator (the separator of the example or the separator of the comparative example).

[1085] 2e. Nail penetration evaluation

[1086] The laminated secondary battery produced was left on an iron plate in a temperature-adjustable explosion-proof chamber. The temperature in the explosion-proof chamber was set to 40°C, and an iron nail having a diameter of 3.0 mm was penetrated through the center of the laminated secondary battery at a speed of 2 mm / sec, and the nail was maintained in the penetrated state. The temperature of a thermocouple provided inside the nail in such a manner that the temperature inside the laminated battery could be measured after penetration of the nail was measured, and the presence or absence of ignition was evaluated.

[1087] The evaluation was repeatedly performed using a newly produced laminated secondary battery by the same method, and the number of samples in which ignition did not occur (no ignition) was calculated as a % value according to the following equation.

[1088] Evaluation result (%) = (100 x number of samples in which ignition did not occur / total number of samples)

[1089] The pass rate with respect to the nail penetration evaluation is, for example, preferably 50% or more at 200 cycles, and 5% or more at 1000 cycles.

[1090] <Experiment Group I>

[1091] [Method for producing silane-graft-modified polyolefin]

[1092] The raw polyolefin used in the silane graft modification of the polyolefin can have a viscosity average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight of 10,000 or more and 150,000 or less, and can be a propylene or butene copolymer α-olefin. While melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate radicals within the polymer chain of the α-olefin, and a trimethoxyalkoxide-substituted vinyl silane is injected to introduce an alkoxysilyl group into the α-olefin polymer by an addition reaction, thereby forming a silane graft structure. In addition, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to adjust the radical concentration in the system and to suppress chain linking reactions (gelling) within the α-olefin. The resulting silane-grafted polyolefin melt resin is cooled in water, pelletized, and then heated at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. Note that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 10 to 1,500 ppm.

[1093] The silane-grafted polyethylene obtained by the above production method was used as "Silane-modified polyolefin (B)" in Table 8.

[1094] [Example I-1]

[1095] To 79.2 mass% of a homopolymer polyethylene (A) having a weight average molecular weight of 500,000, 19.8 mass% of a silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, which was obtained by modifying a polyolefin having a viscosity average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinyl silane, 1 mass% of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added, and dry mixing was performed using a drum mixer, thereby obtaining 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 x 10 -5 m 2 / s) was injected into the extruder cylinder by means of a plunger pump.

[1096] The mixture and the liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the amount of the liquid paraffin in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1097] Next, the molten mixture 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-shaped molded article) having a thickness of 1400 μm.

[1098] Next, the sheet-shaped molded article was introduced into a simultaneous biaxial stenter, and biaxial stretching was performed, thereby obtaining a stretched product. The stretching conditions were set to MD draw ratio 7.0, TD draw ratio 6.0 (i.e., 7 x 6), and biaxial stretching temperature 125°C.

[1099] Next, the gel sheet after stretching was introduced into a methylethyl ketone tank, and sufficiently immersed in methylethyl ketone to extract and remove liquid paraffin, and then dried to remove methylethyl ketone, thereby obtaining a porous body.

[1100] Next, the porous body was introduced into a TD stenter for heat setting (HS) at a heat setting temperature of 125°C and a draw ratio of 1.8, and then a relaxation operation in the TD direction of 0.5 was performed (i.e., the HS relaxation ratio was 0.5), thereby obtaining a microporous membrane.

[1101] Then, the obtained microporous membrane was cut at the end portions and wound into a parent roll having a width of 1,100 mm and a length of 5,000 m.

[1102] In the above evaluation, the microporous membrane was slit as needed from the parent roll and used as a partition for evaluation.

[1103] [Examples I-2 to I-6]

[1104] The same operation as in Example I-1 was performed except that the amount ratio of Components A and B and the crosslinking method / conditions were changed as described in Table 8, thereby obtaining the microporous membranes shown in Table 8.

[1105] [Comparative Examples I-1 and I-2]

[1106] To 79.2 mass% of a homopolymer polyethylene (A) having a weight average molecular weight of 500,000, 19.8 mass% of a silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / minute, which was obtained by modifying reaction of a polyolefin having a viscosity average molecular weight of 20,000 with a vinyl silane substituted with trimethoxyalkoxide (hereby, the resin composition of (A) and (B) was 0.8 and 0.2, respectively), and 1 mass% of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added, and dry mixing was performed using a drum mixer, thereby obtaining a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10 -5 m2 / s) into the extruder barrel.

[1107] The mixture and the liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the amount of the liquid paraffin in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1108] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C and was cast, thereby obtaining a gel sheet (sheet-shaped molded product) having a film thickness of 1400 μm.

[1109] Next, the sheet-shaped molded product was introduced into a simultaneous biaxial stenter, and biaxial stretching was performed, thereby obtaining a stretched product. The stretching conditions were set to an MD draw ratio of 7.0 times, a TD draw ratio of 6.0 times (i.e., 7 x 6 times), and a biaxial stretching temperature of 125°C.

[1110] Next, the gel sheet after stretching was introduced into a methylethyl ketone tank, was sufficiently dipped in methylethyl ketone to extract and remove the liquid paraffin, and then was dried to remove the methylethyl ketone, thereby obtaining a porous body.

[1111] Next, the porous body was introduced into a TD stenter for heat setting (HS) at a heat setting temperature of 125°C and a draw ratio of 1.8 times, and then a relaxation operation in the TD direction of 0.5 times was performed (i.e., the HS relaxation ratio was 0.5 times).

[1112] Further, the porous body was introduced into an ethanol bath (affinity treatment tank), was dipped and left for 60 seconds, and was subjected to affinity treatment for heat-treated porous body, thereby obtaining an affinity-treated porous body.

[1113] Further, the affinity-treated porous body was introduced into a 25% aqueous caustic solution (temperature 80°C, pH 8.5 to 14) in Comparative Example I-1 and a 10% aqueous hydrochloric acid solution (temperature 60°C, pH 1 to 6.5) in Comparative Example I-2, was dipped and left for 60 seconds, and was subjected to cross-linking treatment for the affinity-treated porous body, thereby obtaining a cross-linked porous body.

[1114] Further, the cross-linked porous body was introduced into water (water washing treatment tank), was dipped and left for 60 seconds, and was subjected to water washing for the cross-linked porous body. It was introduced into a conveyer-type dryer, was dried at 120°C for 60 seconds, and thereby obtained a microporous membrane.

[1115] Then, the obtained microporous membrane was cut at the end portions and was wound into a parent roll having a width of 1,100 mm and a length of 5,000 m.

[1116] At the time of the above evaluation, the microporous film released from the parent roll was slitted as needed and used as the evaluation separator.

[1117] [Results of Evaluation]

[1118] The microporous films and batteries obtained in Examples I-1 to I-6 and Comparative Examples I-1 to I-2 were subjected to various evaluations in accordance with the above evaluation methods, and the results of the evaluations are also shown in Table 8. Further, the relationship between the temperature and the resistance of the battery equipped with the microporous film obtained in Example I-1 as the separator is shown in Figure 3 . From Figure 3 and Table 8, it was found that the closing temperature of the separator obtained in Example I-1 was 143°C, and the film rupture temperature was 200°C or higher. Furthermore, the 1 H and 13 C-NMR spectrum (b) of the separator obtained in Example I-1 in the uncrosslinked state is shown in Figure 13 .

[1119] [Table 8]

[1120]

[1121] Note that the "silane-modified polyethylene (B)" in Table 8 is a silane-modified polyethylene obtained by a modification reaction based on substitution of a vinyl silane with trimethoxyalkoxide using a polyolefin having a viscosity average molecular weight of 20,000 as a raw material, having a density of 0.95 g / cm 3 and a melt mass flow rate (MFR) at 190°C of 0.4 g / minute.

[1122] <Experimental Group Ha>

[1123] [Method for producing silane-graft-modified polyolefin]

[1124] The raw polyolefin used in the silane graft modification of the polyolefin can have a viscosity average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight of 10,000 or more and 150,000 or less, and can be an ethylene homopolymer or a copolymer of ethylene and propylene or butene. While the raw polyethylene is melt-kneaded with an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals in the polymer chain of the α-olefin, and a trimethoxyalkoxide-substituted vinyl silane is injected to introduce an alkoxysilyl group into the α-olefin polymer by an addition reaction to form a silane graft structure. In addition, an antioxidant (pentaerythritol tetra[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to adjust the radical concentration in the reaction system and to suppress the chain-like polymerization (gelling) in the α-olefin. The resulting silane-grafted polyolefin melt resin is cooled in water, pelletized, and then dried at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. Note that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 1,500 ppm or less.

[1125] The silane-grafted polyethylene obtained by the above production method was used as "Silane-modified polyethylene (B)" in Table 9.

[1126] [Example II-1]

[1127] To 80 mass% of a homopolymer polyethylene (polyethylene (A)) having a weight average molecular weight of 700,000, 20 mass% of a silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, which was obtained by modifying a polyolefin having a viscosity average molecular weight of 10,000 with a trimethoxyalkoxide-substituted vinyl silane, 1 mass% of pentaerythritol-tetra-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added, and dry mixing was performed using a drum mixer, thereby obtaining 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 x 10 -5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

[1128] The mixture and the liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the amount of the liquid paraffin in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1129] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with a blank film thickness of 1100 μm.

[1130] Next, the sheet-shaped molded body is guided to a biaxial stretching machine for biaxial stretching to obtain the stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 6.2, and biaxial stretching temperature 120°C.

[1131] Next, the stretched gel sheet is guided into a dichloromethane bath and fully impregnated in dichloromethane to extract and remove liquid paraffin. Then, it is dried to remove the dichloromethane and obtain a porous body.

[1132] Next, the porous body is guided to the TD stretcher for heat setting (HS) at a heat setting temperature of 133°C and a stretch ratio of 2.1 times. Then, a relaxation operation is performed to TD 2.0 times.

[1133] Then, the ends of the obtained microporous membrane are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1134] During the above evaluation, the microporous membrane released from the master roll is cut as needed and used as evaluation separators.

[1135] [Examples II-2 to II-8, Comparative Examples II-1 to II-3]

[1136] As shown in Table 9, the same procedures as in Example II-1 were performed by changing the ratio of components A to B, the presence or absence of other resins (C) as additional components, the membrane properties, and the crosslinking method / conditions, to obtain the microporous membrane shown in Table 9. It should be noted that the component "PP" in Table 9 was selected based on an MFR of 2.5 g / 10 min or less and a density of 0.89 g / cm³, measured at 230°C and 2.16 kg. 3 The above refers to unmodified polypropylene with silane. Furthermore, in the crosslinking method "alkali-treated crosslinking" in Table 9, the samples were treated with a 25% sodium hydroxide aqueous solution (temperature 80°C, pH 8.5–14).

[1137] [Evaluation Results]

[1138] For the microporous membranes and batteries obtained in Examples II-1 to II-8 and Comparative Examples II-1 to II-3, various evaluations were performed according to the evaluation methods described above, and the evaluation results are shown in Table 9. Furthermore, regarding the viscoelasticity measurement of the obtained microporous membranes as separators for energy storage devices, the relationships between temperature, gap distance, energy storage modulus, and loss modulus in Example II-1 are shown in Table 9. Figure 4(a) of FIG. 9A, and Figure 4 (b) of FIG. 9A, and further, the film softening transition temperatures determined based on the first derivatives of temperature, gap distance, and gap displacement of Example II-1 are shown in Figure 5 (a) of FIG. 9A, and Figure 5 (b) of FIG. 9A. No film breakage was observed at the limit temperature of 250°C for Examples II-1 to II-8 and Comparative Example II-3. Note that, in Example II-1 and Comparative Example II-1, the determination of the storage modulus, loss modulus, film softening transition temperature, and film breakage temperature was performed under the condition that the film having a thickness of 8 μm was overlapped by 26 sheets, and the total film thickness of the sample was 208 μm.

[1139] [Table 9A]

[1140]

[1141] [Table 9B]

[1142]

[1143] [Experiment Series IIb]

[1144] [Standard Film]

[1145] As a separator for electrical storage devices not containing a silane-modified polyolefin (hereinafter referred to as "standard film"), a silane-grafted non-modified polyolefin microporous film having a change rate of solid content (hereinafter referred to as "gelation degree") of about 0% before and after heating at 160°C in decalin solution was used. In the determination of the gelation degree, the solid content refers only to the resin, and does not include other materials such as inorganic substances.

[1146] Note that, in the present specification, the separator for electrical storage devices not containing a silane-grafted modified polyolefin can be manufactured 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 manufactured from a mixture of two or three selected from the group consisting of X, Y, and Z, in any ratio. Note that, a polyolefin composed only of a hydrocarbon skeleton, such as low-density polyethylene: LDPE, linear low-density polyethylene: LLDPE, polypropylene: PP, olefin-based thermoplastic elastomer, and the like, can be added to the mixture composition.

[1147] [Crosslinked Film]

[1148] As a separator for an electrical storage device after silane crosslinking reaction (hereinafter referred to as "crosslinked film"), the polyolefin microporous membrane of Example II-1 after contact with electrolyte described above, or the polyolefin microporous membrane of Example II-1 taken out from the battery after initial charge and discharge was dried and used. The degree of gelation of the crosslinked film was 30% or more or 70% or more.

[1149] [Viscoelastic behavior]

[1150] The standard film and the crosslinked film were subjected to the measurement of the above item <Storage modulus, loss modulus, film softening transition temperature, and film breakage temperature (version 3)>. The measurement results are shown in Table 10.

[1151] [Table 10]

[1152]

[1153] <Experiment Group III>

[1154] [Method for producing silane graft-modified polyolefin]

[1155] The raw polyolefin used in the silane graft-modified polyolefin can have a viscosity average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight of 10,000 or more and 150,000 or less, and can be a propylene or butene copolymer α-olefin. While melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate radicals within the α-olefin polymer chain, and a trimethoxyalkoxide-substituted vinyl silane is injected to introduce an alkoxysilyl group into the α-olefin polymer by addition reaction, thereby forming a silane graft structure. In addition, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to adjust the radical concentration in the system and suppress chain-like chain reactions (gelation) within the α-olefin. The obtained silane graft polyolefin melt resin is cooled in water, subjected to pellet processing, and then dried by heating at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. Note that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 1,000 to 1,500 ppm.

[1156] The silane graft-modified polyolefin obtained by the above production method is indicated as "silane-modified polyethylene" in Tables 11 and 12.

[1157] [Production method of modified PE and copolymer having various functional groups other than silane-modified PE]

[1158] The modified PE and copolymer having various functional groups other than silane-modified PE were produced by the following method.

[1159] For any of the raw materials, the molecular weight of the raw material used is adjusted so that the MI is in the range of 0.5 to 10. The modified PE having a hydroxyl group is manufactured by saponifying and neutralizing an EVA copolymer. The modified resin of amine modification, oxazoline modification, etc. is subjected to a tungsten-based catalyst under hydrogen peroxide conditions to convert a vinyl group at the end of PE polymerized using a chromium catalyst into an epoxy group. Thereafter, a known functional group conversion organic reaction is used to convert the target reaction site into a target functional group, obtaining various modified PEs. For example, in the case of an amine-modified PE, a primary amine or a secondary amine is injected in a liquid state while melt-kneading the modified PE having an epoxy group at 200°C in an extruder, and a reaction is performed. Then, the unreacted amine is removed by a pressure-reducing valve, and the obtained amine-modified resin is extruded into a strand shape and cut into a pellet shape.

[1160] The modified PE obtained by the above manufacturing method is one of "modified PEs or copolymers (B)" in Tables 11 and 12.

[1161] [Example III-1]

[1162] To 79.2 mass% of a homopolymer polyethylene (A) having a weight average molecular weight of 500,000, 19.8 mass% of a silane-grafted polyethylene (PE(B)) having an MFR of 0.4 g / minute, which was obtained by a modification reaction of a polyolefin having a viscosity average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinyl silane (hereby, the resin composition of (A) and (B) is 0.8 and 0.2, respectively), 1 mass% of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, dry mixing was performed using a drum mixer, thereby obtaining a mixture. The obtained mixture was supplied from a feeder to a twin-screw extruder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10 -5 m 2 / s) was injected to the extruder cylinder by a plunger pump.

[1163] The mixture and the liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the amount of the liquid paraffin in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30 mass%). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1164] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll having a surface temperature controlled to 25°C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) having a raw film thickness of 1400 μm.

[1165] Next, the sheet-shaped molded body was guided to a simultaneous biaxial stenter stretching machine, and biaxial stretching was performed to obtain a stretched product. The stretching conditions were set to MD draw ratio 7.0 times, TD draw ratio 6.0 times (i.e., 7 x 6 times), and biaxial stretching temperature 125°C.

[1166] Next, the stretched gel sheet was guided to a methyl ethyl ketone tank, and sufficiently immersed in methyl ethyl ketone to extract the liquid paraffin, and then dried to remove the methyl ethyl ketone, to obtain a porous body.

[1167] Next, the porous body was guided to a TD stenter for heat setting (HS) at a heat setting temperature of 125°C and a draw ratio of 1.8 times, and 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.

[1168] Then, the obtained microporous membrane was cut at the end portions and wound into a parent roll having a width of 1,100 mm and a length of 5,000 m.

[1169] In the above evaluation, the microporous membrane was slit as needed from the parent roll and used as an evaluation separator.

[1170] For the evaluation separator and the battery, various evaluations were performed in accordance with the above evaluation method, and the evaluation results are shown in Table 11.

[1171] [Examples III-2 to III-18]

[1172] As shown in Table 11 or Table 12, the types, amount ratios, and crosslinking methods / conditions of the resins A and B were changed, and the same operations as in Example III-1 were performed, to obtain the microporous membranes and batteries shown in Table 11 or Table 12. For the obtained microporous membranes and batteries, various evaluations were performed in accordance with the above evaluation method, and the evaluation results are also shown in Table 11 or Table 12. Note that in Examples III-8 to III-10 and III-15 to III-18, an electrolyte solution in which an appropriate amount of the additive shown in Table 11 or Table 12 was previously dissolved was used when the electrolyte solution was injected.

[1173] [Comparative Examples III-1 and III-2]

[1174] As shown in Table 12, the types, amount ratios, and crosslinking methods / conditions of the resins A and B were changed, and the same operations as in Example III-1 were performed, to obtain the microporous membranes shown in Table 12. Using the obtained microporous membranes, electron beam crosslinking was performed by irradiation with a prescribed dose. For the obtained electron beam crosslinked microporous membranes and batteries, various evaluations were performed in accordance with the above evaluation method, and the evaluation results are also shown in Table 12.

[1175] Regarding Comparative Example III-2 and Example III-1, the strain- crystal fraction is plotted in Figure 8 , and the X-ray crystal structure change at the time of tensile fracture failure test is observed. Figure 8 In the figure, the microporous membrane of Comparative Example III-2 is indicated by a dotted line "EB crosslinking", and the microporous membrane of Example III-1 is indicated by a solid line "before chemical crosslinking" and by a broken line "after chemical crosslinking".

[1176] [Table 11A]

[1177]

[1178] [Table 11B]

[1179]

[1180] [Table 12A]

[1181]

[1182] [Table 12B]

[1183]

[1184] Explanation of abbreviations in Tables 11 and 12

[1185] * "Silane-modified polyethylene" is a silane-modified polyethylene obtained by a modification reaction based on substitution of a vinyl silane with trimethoxyalkoxide using a polyolefin having a viscosity average molecular weight of 20,000 as a raw material, having a density of 0.95 g / cm 3 and a melt mass flow rate (MFR) at 190°C of 0.4 g / min.

[1186] " -COOH-modified PE", " -oxazoline-modified PE", " -oxazoline, -OH-modified PE", " -OH-modified PE", " -OH, -NH- modified PE", and " -OH, amine-modified PE" are each a modified PE obtained by the above [manufacturing method of modified PE and copolymer having various functional groups other than silane-modified PE].

[1187] ** (I) Condensation reaction of multiple identical functional groups

[1188] (II) Reaction between multiple different functional groups

[1189] (III) Chain condensation reaction of functional groups with electrolyte

[1190] (IV) Reaction of functional groups with additives

[1191] (V) a reaction in which a plurality of identical functional groups are crosslinked by coordination bonds with metal ions eluted

[1192] *** EC: ethylene carbonate

[1193] **** BS(PEG)5: both ends succinimide, EO unit repeat number 5

[1194] Diisocyanate: a compound in which both ends isocyanate are connected to a hexane unit by a urethane bond

[1195] Bisepoxide: a compound in which both ends epoxy group are connected to a butane unit

[1196] <Experiment Group IV>

[1197] [Example IV-1]

[1198] <Manufacture of A Layer>

[1199] <Manufacture of Silane Graft Modified Polyolefin>

[1200] Using polyethylene having a viscosity average molecular weight of 120,000 as a raw polyethylene, while melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals in the polymer chain of the α-olefin, and a trimethoxyalkoxide-substituted vinylsilane is injected to introduce an alkoxysilyl group into the α-olefin polymer by an addition reaction, thereby forming a silane graft structure. In addition, in order to adjust the radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to suppress the chain-like chain reaction (gelling) in the α-olefin. The obtained silane graft polyolefin melt resin is cooled in water, pelletized, and then dried at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinylsilane. Note that the residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is about 1500 ppm or less.

[1201] As described above, by using the modification reaction of the trimethoxyalkoxide-substituted vinylsilane, a silane-modified polyethylene having an MFR (190°C) of 0.4 g / minute is obtained.

[1202] <Manufacture of A Layer>

[1203] Mix 35% by mass of the above-obtained silane-modified polyethylene with 65% by mass of a homopolymer of 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. Supply the obtained mixture from a feeder to a twin-screw extruder under a nitrogen atmosphere. Further, inject liquid paraffin (kinematic viscosity at 37.78 °C: 7.59×10 -5 m 2 / s) into the extruder barrel through a plunger pump.

[1204] Melt-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 amount of 18 kg / hour. Next, 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.

[1205] 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.

[1206] Next, guide the stretched gel sheet to a methylene chloride bath, fully immerse it in methylene chloride to extract and remove the liquid paraffin, and then dry it to remove the methylene chloride to obtain a porous body.

[1207] Next, guide the porous body to a TD tenter for heat setting (HS), 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.

[1208] 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.

[1209] At the above evaluation, slit the microporous membrane unwound from the master roll as needed and use it as evaluation layer A.

[1210] For the obtained evaluation layer A, measure the film thickness, air permeability, porosity, etc., as shown in Table 13.

[1211] <Production of layer B>

[1212] A dispersion liquid was prepared by uniformly dispersing 95 parts by mass of aluminum oxide hydroxide (average particle diameter 1.4 μm) as inorganic particles, and 0.4 parts by mass (solid content conversion) of an aqueous ammonium polycarboxylate solution (manufactured by SAN NOPCO LIMITED, SN Dispersant 5468, solid content concentration 40%) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion liquid was subjected to a crushing treatment with a bead mill (tank volume 200 cc, zirconium oxide microbeads 0.1 mm in diameter, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm, to produce a slurry containing inorganic particles.

[1213] Next, the microporous film was continuously discharged from the above microporous film parent roll, and the slurry containing inorganic particles was applied to one side of the microporous film using a photogravure reverse coater, and then dried to remove water using a dryer at 60°C, and wound up, to obtain a parent roll of separators.

[1214] At the time of evaluation, the separators discharged from the parent roll were slitted as needed, and used as evaluation separators.

[1215] [Examples IV-2 to IV-5, and Comparative Examples IV-1 to IV-2]

[1216] With the physical property values described in Table 13 as targets, at least any one of the weight average molecular weight of the polyethylene of the homopolymer, the stretching conditions, the heat setting conditions, and the relaxation operation conditions was changed. In addition, the constitution of the B layer was changed as shown in the description of Table 13.

[1217] In addition to these changes, separators were produced by the same method as in Example IV-1, and the resulting separators were used to perform the above evaluation. The evaluation results are shown in Table 13.

[1218] [Table 13]

[1219]

[1220] [Experiment Group V]

[1221] [Method for producing silane-graft-modified polyolefin]

[1222] The raw polyolefin used in the silane graft modification of the polyolefin can have a viscosity average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight of 10,000 or more and 150,000 or less, and can be a propylene or butene copolymer α-olefin. While the raw polyethylene is melt-kneaded using an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate radicals in the polymer chain of the α-olefin, and a trimethoxyalkoxide-substituted vinyl silane is injected to introduce an alkoxysilyl group into the α-olefin polymer by an addition reaction, thereby forming a silane graft structure. In addition, in order to adjust the radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to suppress the chain-like polymerization reaction (gelling) in the α-olefin. The resulting silane grafted polyolefin melt resin is cooled in water, pelletized, and then heated at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. Note that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 10 to 1,500 ppm.

[1223] The silane graft modified polyolefin obtained by the above production method was used as "silane modified polyethylene (B)" in Tables 14 to 16. Note that the density of the silane graft modified polyolefin used this time was 0.94 g / cm 3 and the MFR was 0.65 g / min.

[1224] [Example V-1]

[1225] (Formation of microporous membrane)

[1226] To 79.2 wt% of a homopolymer polyethylene (A) having a weight average molecular weight of 500,000, 19.8 wt% of a silane grafted polyethylene (silane modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, which was obtained by modifying a polyolefin having a viscosity average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinyl silane, 1 wt% of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, were added, and dry mixing was performed using a drum mixer, thereby obtaining 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 x 10 -5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

[1227] The mixture and the liquid paraffin were melt-kneaded in an extruder, and the feeders and the pump were adjusted so that the amount of the liquid paraffin in the extruded polyolefin composition was 70% by weight (i.e., the polymer concentration was 30% by weight). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1228] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C and was cast, thereby obtaining a gel sheet (sheet-shaped molded body) having a raw film thickness of 1400 μm.

[1229] Next, the sheet-shaped molded body was introduced into a simultaneous biaxial stenter, and biaxial stretching was performed, thereby obtaining a stretched product. The stretching conditions were set to an MD draw ratio of 7.0 times, a TD draw ratio of 6.0 times (i.e., 7 x 6 times), and a biaxial stretching temperature of 125°C.

[1230] Next, the gel sheet after stretching was introduced into a methylethyl ketone tank, was sufficiently immersed in methylethyl ketone to extract and remove the liquid paraffin, and then was dried to remove the methylethyl ketone, thereby obtaining a porous body.

[1231] Next, the porous body was introduced into a TD stenter for heat setting (HS) at a heat setting temperature of 125°C and a draw ratio of 1.8 times, and then a relaxation operation in the TD direction of 0.5 times (i.e., a HS relaxation ratio of 0.5 times) was performed, thereby obtaining a microporous membrane.

[1232] Then, the obtained microporous membrane was cut at the ends and was wound into a microporous membrane parent roll having a width of 1,100 mm and a length of 5,000 m.

[1233] Method for producing acrylic latex

[1234] The acrylic latex used as the resin binder can be produced by the following method.

[1235] Into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, 70.4 parts by mass of ion exchange water, and 0.5 parts by mass each of "Aquaron KH1025" (registered trademark, manufactured by the First Industrial Co., Ltd., 25% aqueous solution) and "ADEKA REASOAP SR1025" (registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution) as emulsifiers were added. Next, the temperature inside the reaction vessel was raised to 80°C, and 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added while the temperature was maintained at 80°C, thereby obtaining an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, an emulsion was dropped from the dropping tank into the reaction vessel over a period of 150 minutes.

[1236] Note that the above emulsion was prepared by mixing the following materials 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, manufactured by the First Industrial Co., Ltd., 25% aqueous solution) and 3 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion exchange water.

[1237] After the completion of the dropwise addition of the emulsion, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH = 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex having a solid content of 40%. The number average particle diameter of the resulting acrylic latex was 145 nm, and the glass transition temperature was -23°C.

[1238] (Formation of inorganic porous layer)

[1239] A dispersion liquid was prepared by uniformly dispersing 95 parts by weight of aluminum oxide hydroxide (average particle diameter 1.4 μm) as inorganic particles, and 0.4 parts by weight (solid content conversion) of an aqueous ammonium polycarboxylate solution (SN Dispersant 5468, manufactured by SAN NOPCO LIMITED, solid content concentration 40%) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion liquid was subjected to a crushing treatment using a bead mill (tank volume 200 cc, zirconia-made microbeads diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. To the dispersion liquid having the adjusted particle size distribution, 4.6 parts by weight (solid content conversion) of an acrylic latex (solid content concentration 40%, average particle diameter 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) as a resin binder was added, thereby producing a slurry containing inorganic particles.

[1240] Next, the microporous film was continuously discharged from the above microporous film parent roll, and the slurry containing inorganic particles was applied to one side of the microporous film using a photogravure reverse coater, and then dried to remove water using a dryer at 60°C, and wound up to obtain a parent roll of the separator.

[1241] At the time of evaluation, the separator discharged from the parent roll was slit as needed, and used as an evaluation separator.

[1242] [Examples V-2 to V-12, Comparative Example V-2]

[1243] The same operation as in Example V-1 was performed except for changing the amount ratio of components A and B, the presence or absence of the inorganic layer, or the composition of the inorganic layer, and the crosslinking method / conditions, to obtain the microporous membranes shown in Tables 14 to 16.

[1244] [Comparative Example V-1]

[1245] To 79.2% by weight of a homopolymer of polyethylene (A) having a weight average molecular weight of 500,000, 19.8% by weight of a silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min obtained by modifying reaction of polyolefin having a viscosity average molecular weight of 20,000 with a vinyl silane substituted with trimethoxy alkoxide (hereby, the resin composition of (A) and (B) is 80% and 20%, respectively), 1% by weight of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, dry mixing was performed using a drum mixer, whereby a mixture was obtained. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78°C of 7.59 x 10 - 5m2 / s) was injected into the extruder cylinder by a plunger pump.

[1246] The mixture and the liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the amount ratio of the liquid paraffin in the extruded polyolefin composition was 70% by weight (i.e., the polymer concentration was 30% by weight). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg / h.

[1247] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll having a surface temperature controlled to 25°C and was cast, whereby a gel sheet (sheet-shaped molded product) having a raw film thickness of 1400 μm was obtained.

[1248] Next, the sheet-shaped molded product was guided to a simultaneous biaxial stenter, and biaxial stretching was performed, whereby a stretched product was obtained. The stretching conditions were set to an MD draw ratio of 7.0 times, a TD draw ratio of 6.0 times (i.e., 7 x 6 times), and a biaxial stretching temperature of 125°C.

[1249] Next, the gel sheet after stretching was guided to a methylethyl ketone tank, was sufficiently immersed in methylethyl ketone to extract and remove the liquid paraffin, and was dried to remove the methylethyl ketone, whereby a porous product was obtained.

[1250] Next, the porous product was guided to a TD stenter for heat setting (HS) at a heat setting temperature of 125°C and a draw ratio of 1.8 times, and then, a relaxation operation in the TD direction of 0.5 times was performed (i.e., the HS relaxation ratio was 0.5 times).

[1251] 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.

[1252] In Comparative Example V-1, the micro-porous membrane was slit from the mother roll as needed and used as an evaluation separator in the above evaluation.

[1253] [Results of Evaluation]

[1254] The micro-porous membranes and batteries obtained in Examples V-1 to V-12 and Comparative Examples V-1 to V-2 were subjected to various evaluations in accordance with the above evaluation methods, and the results of the evaluations are also shown in Tables 14 to 16.

[1255] [Table 14]

[1256]

[1257] [Table 15]

[1258]

[1259] [Table 16]

[1260]

[1261] [Experimental Group VI]

[1262] The porous membranes were formed in the same manner as in Examples 1 to 3 and Comparative Examples 2 to 3 of Patent Document 5 (Japanese Patent Application Publication No. 2001-176484), and are denoted as porous membranes V-1 to V-5, respectively. The gel fraction (%), heat resistance temperature (°C), and needle penetration strength (gf / 25 μm) of the porous membranes V-1 to V-5 were evaluated in accordance with the methods described in Patent Document 5, and further, the change ratio R of the storage modulus and the loss modulus of porous membrane V-4 before and after contact with electrolyte solution was measured in accordance with the above item <Storage modulus, loss modulus, and transition temperature (version 1)> of the present specification. △E’ and R △E” The results are shown in Table 17.

[1263] [Table 17]

[1264]

[1265] From Table 17, the following points can be understood.

[1266] (a) Even the porous membrane V-4 (Comparative Example 2 of Patent Document 5, gel ratio 36%) having the lowest gel ratio, the modulus of elasticity change ratio remained 1, and thus it was confirmed that the porous membranes V-1 to V-5 had all undergone the cross-linking reaction completely, and the porous membrane described in Patent Document 5 did not have self-cross-linking property (un-cross-linked portion).

[1267] (b) In addition, Comparative Example 1 of Patent Document 5 is a silane-unmodified product.

[1268] (c) The spacer of the seventh embodiment of the present application described above is valuable in that the amorphous region between the crystals is selectively chemically cross-linked. When the silane-unmodified polyolefin and the silane-modified polyolefin form a mixed crystal, the modified units are repelled by the amorphous region and dispersed irregularly, and in this state, the cross-linked units connected to each other are in contact and undergo cross-linking reaction.

[1269] On the other hand, if the plurality of cross-linking units are distanced from each other, even if the cross-linking units exist, they cannot contribute to the cross-linking reaction. In particular, the cross-linking reaction from silanol to siloxane in the porous membrane proceeds immediately once the reaction conditions thereof (all) are satisfied, and the units that can participate in the cross-linking are sufficiently cross-linked, and thus it is impossible to perform further cross-linking of the residual units in the battery including the porous membrane.

[1270] Therefore, even if there are residual silanol groups in the porous membranes as in the porous membranes V-1 to V-5, as long as the cross-linking treatment is performed in the manufacturing process of these membranes, the cross-linking reaction in the battery including the membrane does not proceed (i.e., the residual silanol groups cannot contribute to the cross-linking structure).

[1271] (d) With regard to the spacer of the seventh embodiment of the present application, by adjusting the molecular weight, copolymer concentration, compounding rate, etc. of the raw material resin, further in combinatio...

Claims

1. A separator for an energy storage device, comprising 5-40% by mass of a silane-modified polyolefin and 60-95% by mass of a polyolefin other than the silane-modified polyolefin, wherein, The energy storage modulus change ratio R is defined by the following equation (1). ΔE’ 2 to 18 times: R ΔE’ =It's S / AND' j (1) In the formula, E' j The energy storage modulus of the separator for the energy storage device measured at 160°C to 220°C before the crosslinking reaction of the silane-modified polyolefin, and E' S The energy storage modulus of the separator of the energy storage device after crosslinking reaction of the silane-modified polyolefin is measured at 160°C to 220°C, and is E'. j or E' S The conditions for determining the storage modulus E' are specified by the following components (i) to (iv): (i) Dynamic viscoelasticity was measured under the following conditions: • Measuring apparatus used: RSA-G2, manufactured by TA Instruments • Sample film thickness: 5 μm to 50 μm • Measurement temperature range: -50~225℃ • Heating rate: 10℃ / min • Measurement frequency: 1Hz • Deformation mode: Linear tension mode Initial static tensile load: 0.5 N • Initial gap distance at 25℃: 25mm • Automatic strain adjustment: Enabled, range: amplitude 0.05~25%, sinusoidal load 0.02~5N; (ii) The static tensile load refers to the midpoint between the maximum and minimum stress under each periodic motion, and the sinusoidal load refers to the vibration stress centered on the static tensile load. (iii) The sinusoidal stretching mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the sinusoidal stretching mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a way that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a way that the sinusoidal load is within 5N and the increase in the amplitude value is within 25%. (iv) Calculate the storage modulus E' based on the relationship between the obtained sinusoidal load and amplitude value and the following formula: s * =σ0·Exp[i(ωt+δ)], e * =ε0·Exp(iωt)、 s * =E * ·e * E * =E'+iE” In the formula, 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 Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: The load at the point of minimum vibration stress within each cycle, i.e., the point of minimum distance between gaps within each cycle. Sine wave load: the difference between the measured vibration stress and the static tensile load; In the manufacturing process of the separator, the silane crosslinking reaction of the silane-modified polyolefin is not carried out, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

2. A separator for an energy storage device, comprising 5-40% by mass of a silane-modified polyolefin and 60-95% by mass of a polyolefin other than the silane-modified polyolefin, wherein, The loss modulus change ratio, i.e., R, is defined by the following equation (3). ΔE” 2 to 18 times: R ΔE” =And” S / AND" j (3) In the formula, E” j The loss modulus of the separator for the energy storage device measured at 160°C to 220°C before the crosslinking reaction of the silane-modified polyolefin, and E”. S The loss modulus of the separator for the energy storage device after crosslinking the silane-modified polyolefin is measured at 160°C to 220°C, and is E”. j or E” S The conditions for determining the loss modulus E are defined by the following (i) to (iv): (i) Dynamic viscoelasticity was measured under the following conditions: • Measuring apparatus used: RSA-G2, manufactured by TA Instruments • Sample film thickness: 5 μm to 50 μm • Measurement temperature range: -50~225℃ • Heating rate: 10℃ / min • Measurement frequency: 1Hz • Deformation mode: Linear tension mode Initial static tensile load: 0.5 N • Initial gap distance at 25℃: 25mm • Automatic strain adjustment: Enabled, range: amplitude 0.05~25%, sinusoidal load 0.02~5N; (ii) The static tensile load refers to the midpoint between the maximum and minimum stress under each periodic motion, and the sinusoidal load refers to the vibration stress centered on the static tensile load. (iii) The sinusoidal stretching mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the sinusoidal stretching mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a way that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a way that the sinusoidal load is within 5N and the increase in the amplitude value is within 25%. (iv) Calculate the loss modulus E” based on the obtained sinusoidal load and amplitude values ​​and the following formula: s * =σ0·Exp[i(ωt+δ)], e * =ε0·Exp(iωt)、 s * =E * ·e * E * =E'+iE” In the formula, 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 Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: The load at the point of minimum vibration stress within each cycle, i.e., the point of minimum distance between gaps within each cycle. Sine wave load: the difference between the measured vibration stress and the static tensile load; In the manufacturing process of the separator, the silane crosslinking reaction of the silane-modified polyolefin is not carried out, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

3. A separator for an energy storage device, comprising 5-40% by mass of a silane-modified polyolefin and 60-95% by mass of a polyolefin other than the silane-modified polyolefin, wherein, The hybrid energy storage modulus ratio R is defined by the following equation (2). E’mix 2 to 18 times: R E’mix =It's a / E'0(2) In the formula, E' a E'0 is the energy storage modulus of the separator for the energy storage device measured at 160°C to 220°C, and E'0 is the energy storage modulus of the separator for the energy storage device without the silane-modified polyolefin measured at 160°C to 220°C, and E'0 is... a The conditions for determining the storage modulus E' of E'0 are specified by the following components (i) to (iv): (i) Dynamic viscoelasticity was measured under the following conditions: • Measuring apparatus used: RSA-G2, manufactured by TA Instruments • Sample film thickness: 5 μm to 50 μm • Measurement temperature range: -50~225℃ • Heating rate: 10℃ / min • Measurement frequency: 1Hz • Deformation mode: Linear tension mode Initial static tensile load: 0.5 N • Initial gap distance at 25℃: 25mm • Automatic strain adjustment: Enabled, range: amplitude 0.05~25%, sinusoidal load 0.02~5N; (ii) The static tensile load refers to the midpoint between the maximum and minimum stress under each periodic motion, and the sinusoidal load refers to the vibration stress centered on the static tensile load. (iii) The sinusoidal stretching mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the sinusoidal stretching mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a way that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a way that the sinusoidal load is within 5N and the increase in the amplitude value is within 25%. (iv) Calculate the storage modulus E' based on the relationship between the obtained sinusoidal load and amplitude value and the following formula: s * =σ0·Exp[i(ωt+δ)], e * =ε0·Exp(iωt)、 s * =E * ·e * E * =E'+iE” In the formula, 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 Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: The load at the point of minimum vibration stress within each cycle, i.e., the point of minimum distance between gaps within each cycle. Sine wave load: the difference between the measured vibration stress and the static tensile load; In the manufacturing process of the separator, the silane crosslinking reaction of the silane-modified polyolefin is not carried out, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

4. A separator for an energy storage device, comprising 5-40% by mass of a silane-modified polyolefin and 60-95% by mass of a polyolefin other than the silane-modified polyolefin, wherein, The hybrid loss modulus ratio R is defined by the following equation (4). E”mix 2 to 18 times: R E”mix =And” a / E”0 (4) In the formula, E” a E”0 is the loss modulus of the separator for the energy storage device measured at 160°C to 220°C, and E”0 is the loss modulus of the separator for the energy storage device without the silane-modified polyolefin measured at 160°C to 220°C, and E”0 is... a The conditions for determining the loss modulus E" of E"0 are specified by the following (i) to (iv): (i) Dynamic viscoelasticity was measured under the following conditions: • Measuring apparatus used: RSA-G2, manufactured by TA Instruments • Sample film thickness: 5 μm to 50 μm • Measurement temperature range: -50~225℃ • Heating rate: 10℃ / min • Measurement frequency: 1Hz • Deformation mode: Linear tension mode Initial static tensile load: 0.5 N • Initial gap distance at 25℃: 25mm • Automatic strain adjustment: Enabled, range: amplitude 0.05~25%, sinusoidal load 0.02~5N; (ii) The static tensile load refers to the midpoint between the maximum and minimum stress under each periodic motion, and the sinusoidal load refers to the vibration stress centered on the static tensile load. (iii) The sinusoidal stretching mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the sinusoidal stretching mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a way that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load is less than 0.02N, the vibration stress is measured by increasing the amplitude value in such a way that the sinusoidal load is within 5N and the increase in the amplitude value is within 25%. (iv) Calculate the loss modulus E” based on the obtained sinusoidal load and amplitude values ​​and the following formula: s * =σ0·Exp[i(ωt+δ)], e * =ε0·Exp(iωt)、 s * =E * ·e * E * =E'+iE” In the formula, 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 Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: The load at the point of minimum vibration stress within each cycle, i.e., the point of minimum distance between gaps within each cycle. Sine wave load: the difference between the measured vibration stress and the static tensile load; In the manufacturing process of the separator, the silane crosslinking reaction of the silane-modified polyolefin is not carried out, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

5. The separator for an energy storage device according to claim 3 or 4, wherein, The separator for an energy storage device that does not contain the silane-modified polyolefin is a microporous membrane made of unmodified silane polyolefin with a gelation degree of 0% or more and 10% or less.

6. A separator for an energy storage device, comprising 5-40% by mass of a silane-modified polyolefin and 60-95% by mass of a polyolefin other than the silane-modified polyolefin, wherein, In the temperature change of the energy storage modulus of the separator in the energy storage device, the transition temperature between the rubbery flat region and the crystalline melting flow region is 140℃~145℃. In the manufacturing process of the separator, the silane crosslinking reaction of the silane-modified polyolefin is not carried out, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

7. A separator for an energy storage device, comprising a polyolefin microporous membrane, wherein, In the solid viscoelasticity test of the separator for the energy storage device at temperatures ranging from -50°C to 250°C, The minimum energy storage modulus ranges from 1.1 MPa to 9.0 MPa, and the maximum ranges from 150 MPa to 9,500 MPa. The minimum loss modulus ranges from 0.2 MPa to 9 MPa, and the maximum loss modulus ranges from 56 MPa to 9,000 MPa. The conditions for determining the viscoelasticity of the solid used to determine the storage modulus and the loss modulus are specified by the following components (i) to (iv): (i) Dynamic viscoelasticity was measured under the following conditions: • Measuring apparatus used: RSA-G2, manufactured by TA Instruments • Sample film thickness: 200 μm to 400 μm. Where the film thickness of a single sample is less than 200 μm, dynamic viscoelasticity is measured by stacking multiple samples to achieve a total thickness within the range of 200 μm to 400 μm. • Measurement temperature range: -50℃~250℃ • Heating rate: 10℃ / min • Measurement frequency: 1Hz • Deformation mode: Linear tension mode Initial value of static tensile load: 0.2N • Initial gap distance at 25℃: 10mm • Automatic strain adjustment: Disabled; (ii) The static tensile load refers to the midpoint between the maximum and minimum stress under each periodic motion, and the sinusoidal load refers to the vibration stress centered on the static tensile load. (iii) The sinusoidal stretching mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.1%. In the sinusoidal stretching mode, the vibration stress is measured by changing the gap distance and the static tensile load in such a way that the difference between the static tensile load and the sinusoidal load is within 5%. When the sinusoidal load is less than 0.1N, the static tensile load is fixed at 0.1N to measure the vibration stress. (iv) Calculate the energy storage modulus and the loss modulus based on the relationship between the obtained sinusoidal load and the amplitude value, and the following formula: s * =σ0·Exp[i(ωt+δ)], e * =ε0·Exp(iωt)、 s * =E * ·e * E * =E'+iE” In the formula, 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 Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: The load at the point of minimum vibration stress within each cycle, i.e., the point of minimum distance between gaps within each cycle. Sine wave load: the difference between the measured vibration stress and the static tensile load; The separator comprises 5% to 40% by mass of silane-modified polyolefin and 60% to 95% by mass of polyolefin other than the silane-modified polyolefin. The silane crosslinking reaction of the silane-modified polyolefin is not carried out in the manufacturing process of the separator, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

8. A separator for an energy storage device, comprising a polyolefin microporous membrane, wherein, In the solid viscoelasticity test of the separator for the energy storage device from the membrane softening transition temperature to the membrane rupture temperature, the average storage modulus was 1.2 MPa to 12 MPa, and the average loss modulus was 0.8 MPa to 10 MPa. The separator comprises 5% to 40% by mass of silane-modified polyolefin and 60% to 95% by mass of polyolefin other than the silane-modified polyolefin. The silane crosslinking reaction of the silane-modified polyolefin is not carried out in the manufacturing process of the separator, but the silane crosslinking reaction of the silane-modified polyolefin is carried out in the manufacturing process of the energy storage device.

9. The separator for an energy storage device according to claim 8, wherein, In the solid viscoelasticity test, the film softening transition temperature is 140℃~150℃, and the film rupture temperature is above 180℃.

10. An energy storage device comprising electrodes, a separator for an energy storage device according to any one of claims 1 to 9, and a non-aqueous electrolyte.

11. A method for manufacturing a separator for an energy storage device, comprising the method for manufacturing a separator for an energy storage device as described in any one of claims 1 to 9, comprising the following steps: (1) Sheet forming process: The mixture of silane-modified polyolefin, polyethylene and plasticizer is extruded, cooled and solidified to form a sheet, thus obtaining a sheet; (2) Stretching process: stretching the sheet along at least one uniaxial direction to obtain a stretched material; (3) A porous body forming process, wherein the plasticizer is extracted from the stretched material in the presence of an extraction solvent, thereby porousening the stretched material to form a porous body; and (4) Heat treatment process, wherein the porous body is subjected to heat treatment.

12. An energy storage device assembly kit, comprising the following two elements: Element 1: A housing containing a laminated or wound body of electrodes and a separator for an energy storage device as described in any one of claims 1 to 9; and Element 2: A container that holds a non-aqueous electrolyte.

13. The energy storage device assembly kit according to claim 12, wherein, The non-aqueous electrolyte contains a fluorine (F)-containing lithium salt.

14. The energy storage device assembly kit according to claim 12, wherein, The non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6).

15. The energy storage device assembly kit according to claim 12, wherein, The non-aqueous electrolyte is an acid solution and / or an alkaline solution.

16. A method for manufacturing an energy storage device, comprising the following steps; The process of preparing the energy storage device assembly kit according to any one of claims 12 to 15, and The process of initiating the silane crosslinking reaction of the silane-modified polyolefin is to bring the separator of the energy storage device in element 1 of the energy storage device assembly kit into contact with the non-aqueous electrolyte in element 2.

17. The method for manufacturing an energy storage device according to claim 16, further comprising the following steps: The process of connecting lead terminals to the electrode of element 1, and The process involves performing at least one charge-discharge cycle.

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