Lithium-ion battery using a crosslinked separator

Abstract

The present invention relates to a lithium-ion battery using a crosslinked separator, and provides a separator for an electricity storage device and a method for manufacturing the same. The separator for the electricity storage device is characterized by including a silane-modified polyolefin, and when it comes into contact with an electrolyte, a silane crosslinking reaction of the silane-modified polyolefin starts.

Description

[0001] This application is a divisional application of an application with an application date of October 11, 2019, an application number of 201980007742.8, and an invention title of "Lithium-ion battery using a crosslinked separator". Technical Field

[0002] The present invention relates to a separator for a power storage device, a crosslinking method thereof, a power storage device assembly kit, a method for manufacturing a power storage device, and the like. Background Art

[0003] Microporous membranes are widely used as separation or selective permeation separation membranes for various substances and as insulating materials, etc. Examples of their uses include microfiltration membranes, separators for fuel cells and capacitors, or substrates for functional membranes in which a functional material is filled into pores to exhibit a new function, and separators for power storage devices. Among them, polyolefin microporous membranes are suitable as separators for lithium-ion batteries widely used in notebook personal computers, mobile phones, digital cameras, etc.

[0004] In order to ensure battery safety, it is required that the separator balance the activation of the shut-off function and the increase in the membrane breakage temperature. For example, Patent Document 1 describes adjusting the higher-order physical properties of a polyolefin resin, which is an essential component of a separator for a lithium-ion battery. In addition, as shown in Patent Document 2, it is known to have a performance of suppressing heat generation caused by a short circuit inside the battery with a shut-off function in a specific crystallinity and gel fraction region, and on the other hand, not breaking the membrane (breakdown at 170°C or higher) even when a local high-temperature site is generated inside the battery cell, thereby ensuring battery safety. Regarding Patent Documents 1 and 2, more specifically, it has been gradually found experimentally that by constructing a silane crosslinked portion (gel structure) in a polyolefin separator, high-temperature membrane breakage properties can be exhibited.

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

[0006] Regarding components for lithium-ion batteries, a positive electrode, negative electrode material, electrolyte, and separator are used. Among these components, regarding the separator, based on its properties as an insulating material, it is required to be inactive to the electrochemical reaction or surrounding components. On the other hand, in the development of the negative electrode material of lithium-ion batteries, a technology has been established since the beginning to suppress the decomposition of the electrolyte on the negative electrode surface by forming a solid electrolyte interface (SEI) through a chemical reaction during the first charge (Non-Patent Document 1). In addition, cases have been reported where even when a polyolefin resin is used as the separator, an oxidation reaction occurs on the positive electrode surface at high voltage, and the separator blackens and the surface deteriorates, etc.

[0007] Based on the above idea, regarding the material of the separator for the power storage device, a chemical structure that is inactive to the electrochemical reaction or other chemical reactions is adopted, so the development and practical application of polyolefin-based microporous membranes have been widely carried out. However, as long as polyolefin is used as the resin, even if the mechanical microporous 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 polyolefin or the electronegativity of the olefin unit, the affinity or liquid retention with the electrolyte is insufficient, so the permeability of Li ions or their solvated ion clusters in the separator cannot be satisfied.

[0008] Thus, due to the above limitations, when dealing with the current situation, it is impossible to expect to meet the high-speed charge and discharge or heat resistance stability required for modern battery development.

[0009] Prior Art Documents

[0010] Patent Documents

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

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

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

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

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

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

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

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

[0019] Patent Document 9: Japanese Unexamined Patent Application Publication No. 2014-056843

[0020] Patent Document 10: Japanese Unexamined Patent Application Publication No. 10-261435

[0021] Patent Document 11: Japanese Unexamined Patent Application Publication No. 2007-299612

[0022] Patent Document 12: WO 2010 / 134585

[0023] Patent Document 13: Japanese Unexamined Patent Application Publication No. 2016-072150

[0024] Non-Patent Document

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

[0026] Non-Patent Document 2: Basic Polymer Chemistry, published by Tokyo Kagaku Dojin Summary of the Invention

[0027] Problems to be Solved by the Invention

[0028] In recent years, efforts have been made to increase the output and energy density of lithium-ion secondary batteries for use in mobile devices or vehicles. On the other hand, there is a need for miniaturization of battery cells and stable cycle charge-discharge performance during long-term use. 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 uniform physical properties and no resin aggregates) is required. Furthermore, regarding the level of battery safety, it has become more stringent than before. As described in Patent Documents 1 and 2, a shut-off function and high-temperature film-breaking property are required, and it is expected to develop a resin composition for separators and a manufacturing method that can be stably produced. In this regard, the lower the shut-off temperature level, the more ideal it is. In addition, the higher the film-breaking temperature level, the more ideal it is.

[0029] For example, the method described in Patent Document 3 uses a crosslinking catalyst masterbatch during the extrusion process to carry out the crosslinking reaction of silane-modified polyethylene in an extruder, but resin condensates are still generated, reducing the physical property uniformity of the separator. For this method, the methods described in Patent Documents 4, 5, and 6 respond by setting a plasticizer extraction process or a silane rubber crosslinking process, or controlling the gel fraction of the resin film, or forming the uncrosslinked resin through hot water and then dehydrating it. In addition, Patent Document 7 proposes to provide a heat-resistant resin microporous membrane, which has excellent low heat shrinkage, low fluidity, and melt fracture resistance by adjusting the gel fraction of the polyolefin microporous membrane, the storage modulus at a temperature of 40°C to 250°C in dynamic viscoelasticity (DMA) measurement, the maximum shrinkage rate based on thermomechanical analysis (TMA), and the amount of free radicals measured by electron spin resonance method (ESR).

[0030] Furthermore, regarding the separator for an electric storage device, from the perspectives of dimensional stability, balancing the maintenance of the closing function and the increase in the membrane breakage temperature, dimensional stability, etc., it has been proposed to dispose an inorganic porous layer containing inorganic particles such as calcined kaolin and boehmite and a resin binder on the surface of at least one side of the polyolefin microporous membrane (Patent Documents 12 and 13).

[0031] However, the method shown in Patent Document 4 cannot fully carry out the silane crosslinking reaction, and it is difficult to obtain high-temperature membrane breakage resistance. Since the plasticizer extraction process described in Patent Documents 3 and 4 uses a tin(II)-based crosslinking catalyst, the crosslinking reaction can be carried out, but there is a risk of residual crosslinking catalyst afterwards.

[0032] The heat-resistant resin microporous membrane described in Patent Document 7 is merely obtained by coating a photocurable coating liquid on a membrane porousized by a dry method. In addition, in Example 5 of Patent Document 7, a low-molecular-weight silane coupling agent such as γ-methacryloxypropyltrimethoxysilane is added to the porous membrane. However, assuming that the low-molecular-weight silane coupling agent is used in a wet porousization method, it is expected that the low-molecular-weight silane coupling agent easily reacts or binds with the plasticizer used for porousization and does not bind to the resin of the porous membrane. Furthermore, the cycle characteristics of a battery having the heat-resistant resin microporous membrane described in Patent Document 7 as a separator are poor. In addition, during long-term use, unpredictable side reactions will be induced in the battery, and there is a risk of reducing the battery safety.

[0033] In addition, since the coating layer described in Patent Document 7 is formed by coating a compound having a polymerizable functional group on a resin porous membrane and then subjecting it to a crosslinking reaction by an external stimulus, it is expected that liquid will penetrate into a part of the resin porous membrane while the coating layer is being coated. After the crosslinking reaction, it is expected that a mixed region of them will also be formed near the interface between the coating layer and the resin porous membrane. As a result, good TMA heat shrinkage performance can be obtained, but a decrease in battery cycle characteristics due to clogging of the resin porous membrane or a decrease in fuse (shut-off) performance accompanied by melting of the resin porous membrane can be expected. Furthermore, in the composite microporous membrane obtained by the method described in Patent Document 7, a small amount of free radical species compounds are detected by ESR. Due to the residue, when the composite microporous membrane is assembled into a battery, a radical reaction occurs with other components, especially with the electrolyte, and a chain reaction of decomposing the electrolyte can be expected, which is considered to significantly deteriorate the battery performance.

[0034] Furthermore, the microporous membranes and separators described in Patent Documents 1, 2, and 7 lack research on the configuration of an inorganic porous layer containing inorganic particles and a resin binder on their surfaces. Existing separators with an inorganic porous layer on the microporous membrane seem to have an increased breakdown temperature on the temperature-resistance curve of the power storage device. However, in practice, resin may sometimes dissolve from the microporous membrane into the inorganic porous layer, so a decrease in the overall membrane weight of the separator and a resulting decrease in stress tolerance can be anticipated. Therefore, although the multilayer porous membranes described in Patent Documents 12 and 13 have a polyolefin microporous membrane and an inorganic porous layer, there is room for research on achieving both the low-temperature shut-off function and high-temperature breakdown property as a separator for a power storage device, or improving the cycle characteristics and battery nail penetration safety of the power storage device.

[0035] Furthermore, the cycle characteristics of batteries using separators described in Patent Documents 3 to 7 are poor. In addition, during long-term use, unpredictable side reactions will be induced inside the battery, posing a risk of reduced battery safety.

[0036] For conventional molded products such as hot water pipes, a tin (Sn)-based catalyst is introduced into the extruder during the extrusion process. On the other hand, the wet manufacturing process of separators for power storage devices generally includes processes such as extrusion - sheet forming, stretching, plasticizer extraction (porous formation), heat treatment, and winding. Therefore, if silane crosslinking is promoted in the extruder during the sheet forming process, the gelled part will cause defects, and it is difficult to stretch the silane-crosslinked polyolefin in the subsequent stretching process. Therefore, there is still room for research on new separators for power storage devices that are suitable for the manufacturing process.

[0037] Furthermore, the crosslinking methods described in Patent Documents 1 to 6, 8, and 9 are all carried out in an intermittent manner during the process of forming the separator film or immediately after the separator is manufactured. Therefore, after the formation of the crosslinked structure described in Patent Documents 1 to 6, 8, and 9, it is necessary to perform coating and slitting of the separator. In the subsequent lamination / winding process with the electrode, the internal stress will increase, and thus the manufactured battery may sometimes be deformed. For example, if the crosslinked structure is formed by heating, the internal stress of the separator having the crosslinked structure may sometimes increase at normal temperature or room temperature.

[0038] Furthermore, if the crosslinked structure is formed by light irradiation such as ultraviolet rays or electron beams, the irradiation of light may sometimes be uneven and the crosslinked structure may be inhomogeneous. It is considered that this is because the periphery of the crystal part of the resin constituting the separator is easily crosslinked by electron beams.

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

[0040] In addition, there is still room for improvement in the separators for power storage devices described in Patent Documents 1, 2, and 11 in terms of achieving the improvement of the performance of their power storage devices.

[0041] In view of the above problems, an object of the present invention is to provide a separator for a power storage device that can balance the shut-off function and high-temperature burst resistance, ensure the safety, output, and / or cycle stability of the power storage device, a new crosslinking method suitable for its manufacturing process, an assembly kit for a power storage device, or a manufacturing method.

[0042] Solutions for Solving the Problems

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

[0044] A separator for a power storage device, characterized in that the separator for a power storage device contains a silane-modified polyolefin, and when the separator for a power storage device comes into contact with an electrolyte, the silane crosslinking reaction of the silane-modified polyolefin is started.

[0045] The separator for a power storage device according to item 1, wherein the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst for crosslinking the silane-modified polyolefin.

[0046] The separator for a power storage device according to item 1 or 2, wherein the separator for a power storage device further contains polyethylene on the basis of the silane-modified polyolefin.

[0047] The separator for a 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.

[0048] A separator for a power storage device, the separator for a power storage device containing 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the silane-modified polyolefin, and the storage modulus change ratio (R ΔE’ ) defined by the following formula (1) is 1.5 times to 20 times:

[0049] R ΔE’ = E’ S / E’ j (1)

[0050] {In the formula, E’ j is the storage modulus of the separator for a power storage device before the crosslinking reaction of the silane-modified polyolefin measured at 160°C to 220°C, and E’ S is the storage modulus of the separator for a power storage device after the crosslinking reaction of the silane-modified polyolefin measured at 160°C to 220°C, and the measurement conditions of the storage modulus E’ of E’ j or E’ S are specified by the following (i) to (iv).

[0051] (i) Dynamic viscoelasticity measurement is carried out under the following conditions:

[0052] · Use of measurement device: RSA-G2 (manufactured by TA Instruments)

[0053] · Sample film thickness: in the range of 5 μm to 50 μm

[0054] · Measurement temperature range: -50 to 225°C

[0055] · Heating rate: 10°C / min

[0056] · Measurement frequency: 1 Hz

[0057] · Deformation mode: sine wave tensile mode (Linear tension)

[0058] · Initial value of static tensile load: 0.5 N

[0059] · Initial (at 25°C) gap distance: 25 mm

[0060] · Automatic strain adjustment: enabled (range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5 N).

[0061] (ii) The aforementioned static tensile load refers to the median value of the maximum stress and the minimum stress under each cycle of movement, and the aforementioned sine-wave load refers to the vibration stress centered on the aforementioned static tensile load.

[0062] (iii) The aforementioned sine-wave tensile mode refers to measuring the aforementioned vibration stress while performing cyclic movement with a fixed amplitude of 0.2%. Under the aforementioned sine-wave tensile mode, the distance between gaps and the aforementioned static tensile load are changed in such a way that the difference between the aforementioned static tensile load and the aforementioned sine-wave load is within 20% to measure the aforementioned vibration stress. When the aforementioned sine-wave load is 0.02 N or less, the aforementioned amplitude value is increased in such a way that the aforementioned sine-wave load is within 5 N and the increase amount of the aforementioned amplitude value is within 25% to measure the aforementioned vibration stress.

[0063] (iv) Calculate the storage modulus E’ based on the relationship between the obtained sine-wave load and amplitude value and the following formula:

[0064] σ * = σ0·Exp[i(ωt + δ)],

[0065] ε * = ε0·Exp(iωt),

[0066] σ * = E * ·ε *

[0067] E * = E’ + iE”

[0068] (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

[0069] Vibration stress: sine-wave load / initial cross-sectional area

[0070] Static tensile load: load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between gaps in each cycle)

[0071] Sine-wave load: difference between the measured vibration stress and the static tensile load).}

[0072] A separator for a power storage device, the separator for a power storage device contains 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin, and the loss modulus change ratio (R ΔE” ) defined by the following formula (3) is 1.5 times to 20 times:

[0073] R ΔE” = E” S / E” j (3)

[0074] {Wherein, E” j is the loss modulus measured at 160 °C to 220 °C for the separator for the electric storage device before the crosslinking reaction of the aforementioned silane-modified polyolefin, and E” S is the loss modulus measured at 160 °C to 220 °C for the separator for the electric storage device after the crosslinking reaction of the aforementioned silane-modified polyolefin, and for E” j or E” S the measurement conditions of the loss modulus E” are specified by the following (i) to (iv).

[0075] (i) Dynamic viscoelasticity measurement is carried out under the following conditions:

[0076] · Use a measuring device: RSA-G2 (manufactured by TA Instruments)

[0077] · Sample film thickness: in the range of 5 μm to 50 μm

[0078] · Measurement temperature range: -50 to 225 °C

[0079] · Heating rate: 10 °C / min

[0080] · Measurement frequency: 1 Hz

[0081] · Deformation mode: sine wave tensile mode (Linear tension)

[0082] · Initial value of static tensile load: 0.5 N

[0083] · Initial (at 25 °C) gap distance: 25 mm

[0084] · Automatic strain adjustment: Enabled (range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5 N).

[0085] (ii) The aforementioned static tensile load refers to the intermediate value between the maximum stress and the minimum stress under each periodic motion, and the aforementioned sine wave load refers to the vibration stress centered on the aforementioned static tensile load.

[0086] (iii) The aforementioned sine wave stretching mode means measuring the aforementioned vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the aforementioned sine wave stretching mode, the distance between the gaps and the aforementioned static tensile load are changed in such a way that the difference between the aforementioned static tensile load and the aforementioned sine wave load is within 20% to measure the aforementioned vibration stress. When the aforementioned sine wave load is 0.02 N or less, the aforementioned amplitude value is increased in such a way that the aforementioned sine wave load is within 5 N and the increase amount of the amplitude value is within 25% to measure the aforementioned vibration stress.

[0087] (iv) Calculate the loss modulus E” based on the relationship between the obtained sine wave load and the amplitude value and the following formula:

[0088] σ * = σ0·Exp[i(ωt + δ)],

[0089] ε * = ε0·Exp(iωt),

[0090] σ * = E * ·ε *

[0091] E * = E’ + iE”

[0092] (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

[0093] Vibration stress: Sine wave load / Initial cross-sectional area

[0094] Static tensile load: Load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between the gaps in each cycle)

[0095] Sine wave load: Difference between the measured vibration stress and the static tensile load).}

[0096] A separator for a power storage device, characterized in that when the separator for a power storage device comes into contact with the electrolyte, a silane cross-linking reaction of silane-modified polyolefin occurs.

[0097] A separator for a power storage device, the separator for a power storage device contains 5 to 40% by mass of silane-modified polyolefin and 60 to 95% by mass of 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:

[0098] RE’mix = E’ a / E’0 (2)

[0099] {In the formula, E’ a is the storage modulus measured for the separator for the electric storage device at 160°C to 220°C, and E’0 is the storage modulus measured for the separator for the electric storage device without the aforementioned silane-modified polyolefin at 160°C to 220°C, and the measurement conditions for the storage modulus E’ of E’ a or E’0 are defined by the following (i) to (iv).

[0100] (i) Dynamic viscoelasticity measurement is carried out under the following conditions:

[0101] · Use a measurement device: RSA-G2 (manufactured by TA Instruments)

[0102] · Sample film thickness: in the range of 5 μm to 50 μm

[0103] · Measurement temperature range: -50 to 225°C

[0104] · Heating rate: 10°C / min

[0105] · Measurement frequency: 1 Hz

[0106] · Deformation mode: sine wave tensile mode (Linear tension)

[0107] · Initial value of static tensile load: 0.5 N

[0108] · Initial (at 25°C) distance between gaps: 25 mm

[0109] · Automatic strain adjustment: Enabled (range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5 N).

[0110] (ii) The aforementioned static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each cycle of motion, and the aforementioned sine wave load refers to the vibration stress centered on the aforementioned static tensile load.

[0111] (iii) The aforementioned sine wave tensile mode means measuring the aforementioned vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the aforementioned sine wave tensile mode, the vibration stress is measured by changing the distance between gaps and the aforementioned static tensile load so that the difference between the aforementioned static tensile load and the aforementioned sine wave load is within 20%. When the aforementioned sine wave load is 0.02 N or less, the vibration stress is measured by increasing the aforementioned amplitude value so that the aforementioned sine wave load is within 5 N and the increase amount of the aforementioned amplitude value is within 25%.

[0112] (iv) Calculate the storage modulus E’ according to the relationship between the obtained sine wave load and the amplitude value and the following formula:

[0113] σ * = σ0·Exp[i(ωt + δ)],

[0114] ε * = ε0·Exp(iωt),

[0115] σ * = E * ·ε *

[0116] E * = E’ + iE”

[0117] (wherein, 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

[0118] Vibration stress: sine wave load / initial cross-sectional area

[0119] Static tensile load: load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between the gaps in each cycle)

[0120] Sine wave load: difference between the measured vibration stress and the static tensile load).}.

[0121] A separator for a power storage device, the separator for a power storage device contains 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin, and the mixed loss modulus ratio (R E”mix ) defined by the following formula (4) is 1.5 times to 20.0 times:

[0122] R E”mix = E” a / E”0 (4)

[0123] {wherein, E” a is the loss modulus measured for the aforementioned separator for a power storage device at 160°C to 220°C, and E”0 is the loss modulus measured for a separator for a power storage device that does not contain the aforementioned silane-modified polyolefin at 160°C to 220°C, and the measurement conditions for the loss modulus E” of E” a or E”0 are specified by the following (i) to (iv).

[0124] (i) Perform dynamic viscoelasticity measurement under the following conditions:

[0125] · Use the measuring device: RSA-G2 (manufactured by TA Instruments)

[0126] · Sample film thickness: in the range of 5 μm to 50 μm

[0127] · Measuring temperature range: -50 to 225 °C

[0128] · Heating rate: 10 °C / min

[0129] · Measuring frequency: 1 Hz

[0130] · Deformation mode: sine wave tensile mode (Linear tension)

[0131] · Initial value of static tensile load: 0.5 N

[0132] · Initial (at 25 °C) distance between gaps: 25 mm

[0133] · Automatic strain adjustment: Enabled (range: amplitude value 0.05 - 25%, sine wave load 0.02 - 5 N).

[0134] (ii) The aforementioned static tensile load refers to the intermediate value between the maximum stress and the minimum stress under each periodic motion, and the aforementioned sine wave load refers to the vibration stress centered on the aforementioned static tensile load.

[0135] (iii) The aforementioned sine wave tensile mode refers to measuring the aforementioned vibration stress while performing periodic motion with a fixed amplitude of 0.2%. In the aforementioned sine wave tensile mode, the distance between gaps and the aforementioned static tensile load are changed in such a way that the difference between the aforementioned static tensile load and the aforementioned sine wave load is within 20% to measure the aforementioned vibration stress. When the aforementioned sine wave load is 0.02 N or less, the aforementioned amplitude value is increased in such a way that the aforementioned sine wave load is within 5 N and the increase amount of the amplitude value is within 25% to measure the aforementioned vibration stress.

[0136] (iv) Calculate the loss modulus E” based on the relationship between the obtained sine wave load and the amplitude value and the following formula:

[0137] σ * = σ0·Exp[i(ωt + δ)],

[0138] ε * = ε0·Exp(iωt),

[0139] σ * = E * · ε *

[0140] E * = E’ + iE”

[0141] (wherein, 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

[0142] Vibration stress: sine-wave load / initial cross-sectional area

[0143] Static tensile load: load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between the gaps in each cycle)

[0144] Sine-wave load: difference between the measured vibration stress and the static tensile load).}.

[0145] The separator for an electric storage device according to item 8 or 9, wherein the separator for an electric storage device that does not contain the aforementioned silane-modified polyolefin is a microporous membrane made of a silane-unmodified polyolefin having a gelation degree of 0% or more and 10% or less.

[0146] A separator for an electric storage device, the separator for an electric storage device containing 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin, and the transition temperature between the rubbery plateau region and the crystal melting flow region in the temperature change of the storage modulus of the aforementioned separator for an electric storage device is 135°C to 150°C.

[0147] A separator for an electric storage device, the separator for an electric storage device comprising a polyolefin microporous membrane

[0148] In the measurement of the solid viscoelasticity of the aforementioned separator for an electric storage device at a temperature of -50°C to 250°C

[0149] 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

[0150] The minimum value of the loss modulus is 0.1 MPa to 10 MPa, the maximum value of the loss modulus is 10 MPa to 10,000 MPa,

[0151] 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):

[0152] (i) Perform dynamic viscoelasticity measurement under the following conditions:

[0153] · Use a measurement device: RSA-G2 (manufactured by TA Instruments)

[0154] · Sample film thickness: 200 μm to 400 μm (wherein, when the film thickness of a single sample is less than 200 μm, dynamic viscoelasticity measurement is performed by laminating multiple samples so that the total thickness is within the range of 200 μm to 400 μm.)

[0155] · Measurement temperature range: -50 °C to 250 °C

[0156] · Heating rate: 10 °C / min

[0157] · Measurement frequency: 1 Hz

[0158] · Deformation mode: Sinusoidal wave tensile mode (Linear tension)

[0159] · Initial value of static tensile load: 0.2 N

[0160] · Initial (at 25 °C) distance between gaps: 10 mm

[0161] · Automatic strain adjustment (Automatic strain adjustment): Disabled;

[0162] (ii) The aforementioned static tensile load refers to the intermediate value between the maximum stress and the minimum stress under each periodic motion, and the aforementioned sinusoidal wave load refers to the vibration stress centered on the aforementioned static tensile load;

[0163] (iii) The aforementioned sinusoidal wave tensile mode refers to measuring the aforementioned vibration stress while performing periodic motion with a fixed amplitude of 0.1%. In the aforementioned sinusoidal wave tensile mode, the distance between gaps and the aforementioned static tensile load are changed so that the difference between the aforementioned static tensile load and the aforementioned sinusoidal wave load is within 5% to measure the aforementioned vibration stress. When the aforementioned sinusoidal wave load is 0.1 N or less, the aforementioned static tensile load is fixed at 0.1 N to measure the aforementioned vibration stress;

[0164] (iv) Calculate the aforementioned storage modulus and the aforementioned loss modulus based on the relationship between the obtained sinusoidal wave load and amplitude value and the following formula:

[0165] σ * = σ0·Exp[i(ωt + δ)],

[0166] ε * = ε0·Exp(iωt),

[0167] σ * = E * · ε *

[0168] E * = E’ + iE”

[0169] {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

[0170] Vibration stress: Sine wave load / Initial cross-sectional area

[0171] Static tensile load: Load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between the gaps in each cycle)

[0172] Sine wave load: Difference between the measured vibration stress and the static tensile load}.

[0173] A separator for a storage device, the separator for the storage device includes a polyolefin microporous membrane, and in the measurement of the solid viscoelasticity of the separator for the storage device from the film softening transition temperature to the film fracture temperature, the average storage modulus is 1.0 MPa to 12 MPa, and the average loss modulus is 0.5 MPa to 10 MPa.

[0174] The separator for a storage device according to item 13, wherein in the measurement of the solid viscoelasticity, the film softening transition temperature is 140 °C to 150 °C, and the film fracture temperature is 180 °C or higher.

[0175] The separator for a storage device according to any one of items 12 to 14, which includes a silane-modified polyolefin and a polyolefin other than the silane-modified polyolefin.

[0176] The separator for a storage device according to item 15, which includes 5% to 40% by mass of a silane-modified polyolefin and 60% to 95% by mass of a polyolefin other than the silane-modified polyolefin.

[0177] A separator for a storage device, characterized in that the separator for the storage device includes a polyolefin, the polyolefin has one or more than two kinds of functional groups, and

[0178] After being accommodated in the storage device, (1) a condensation reaction occurs between the functional groups, or (2) the functional groups react with the chemical substances inside the storage device, or (3) the functional groups react with other kinds of functional groups to form a crosslinked structure.

[0179] The separator for a storage device according to item 17, wherein the chemical substance is any one of the electrolyte, electrolytic solution, electrode active material, additive or their decomposition products contained in the storage device.

[0180] A separator for a power storage device, the separator for a power storage device containing polyolefin and having an amorphous crosslinked structure obtained by crosslinking an amorphous part of the polyolefin.

[0181] The separator for a power storage device according to item 19, wherein the separator for a power storage device has a hybrid storage modulus ratio (R E’X ) defined by the following formula (1) of 1.5 to 20 times:

[0182] R E’X = E’ Z / E’ Z0 (1)

[0183] {In the formula, E’ Z is the storage modulus measured in the temperature range of 160°C to 300°C after the crosslinking reaction of the separator for a power storage device in the power storage device, and

[0184] E’ Z0 is the storage modulus measured in the temperature range of 160°C to 300°C before the separator for a power storage device is assembled into the power storage device.}.

[0185] The separator for a power storage device according to item 19 or 20, wherein the separator for a power storage device has a hybrid loss modulus ratio (R E”X ) defined by the following formula (3) of 1.5 to 20 times:

[0186] R E”X = E” Z / E” Z0 (3)

[0187] {In the formula, E” Z is the loss modulus measured in the temperature range of 160°C to 300°C after the crosslinking reaction of the separator for a power storage device in the power storage device, and

[0188] E” Z0 is the loss modulus measured in the temperature range of 160°C to 300°C before the separator for a power storage device is assembled into the power storage device.}.

[0189] The separator for a power storage device according to any one of items 19 to 21, wherein the amorphous part is selectively crosslinked.

[0190] The separator for a power storage device according to any one of items 17 to 22, wherein the separator for a power storage device has a hybrid storage modulus ratio (R E’mix ) defined by the following formula (2) of 1.5 to 20 times:

[0191] R E’mix= E’ / E’0 (2)

[0192] {In the formula, E’ is the storage modulus measured at 160°C to 300°C when the separator for the electric storage device has an amorphous part crosslinked structure, and

[0193] E’0 is the storage modulus measured at 160°C to 300°C for the separator for the electric storage device that does not have an amorphous part crosslinked structure.}.

[0194] The separator for the electric storage device according to any one of items 17 to 23, wherein the separator for the electric storage device has a loss modulus ratio (R E”mix ) defined by the following formula (4) of 1.5 times to 20 times:

[0195] R E”mix = E” / E”0 (4)

[0196] {In the formula, E” is the loss modulus measured at 160°C to 300°C when the separator for the electric storage device has an amorphous part crosslinked structure, and

[0197] E”0 is the loss modulus measured at 160°C to 300°C for the separator for the electric storage device that does not have an amorphous part crosslinked structure.}.

[0198] The separator for the electric storage device according to any one of items 17 to 24, wherein the polyolefin is polyethylene.

[0199] The separator for the electric storage device according to any one of items 17 to 25, wherein the polyolefin is a functional group-modified polyolefin or a polyolefin obtained by copolymerizing a monomer having a functional group.

[0200] The separator for the electric storage device according to any one of items 17 to 26, wherein the crosslinked structure is formed by a reaction using any one of covalent bonds, hydrogen bonds, or coordination bonds.

[0201] The separator for the electric storage device according to item 27, wherein the reaction using a covalent bond is at least one selected from the group consisting of the following reactions (I) to (IV):

[0202] (I) Condensation reaction of multiple identical functional groups;

[0203] (II) Reaction between multiple different functional groups;

[0204] (III) Chain condensation reaction of a functional group and an electrolyte; and

[0205] (IV) Reaction of a functional group and an additive.

[0206] The separator for an electricity storage device according to Item 27, wherein,

[0207] The reaction by means of a coordination bond is the following reaction (V):

[0208] (V) A reaction in which multiple identical functional groups are crosslinked by means of a coordination bond with a metal ion.

[0209] The separator for an electricity storage device according to Item 28, wherein the aforementioned reaction (I) and / or (II) is catalytically promoted by a chemical substance inside the electricity storage device.

[0210] The separator for an electricity storage device according to Item 28, wherein the aforementioned reaction (I) is a condensation reaction of multiple silanol groups.

[0211] The separator for an electricity storage device according to Item 28, wherein the aforementioned reaction (IV) is a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between a compound Rx constituting the aforementioned separator for an electricity storage device and a compound Ry constituting the aforementioned additive, the aforementioned compound Rx has a functional group x, and the aforementioned compound Ry has a linking reaction unit y1.

[0212] The separator for an electricity storage device according to Item 32, wherein,

[0213] The aforementioned reaction (IV) is a nucleophilic substitution reaction,

[0214] The functional group x of the aforementioned compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH, and

[0215] The linking reaction unit y1 of the aforementioned compound Ry is at least two selected from the group consisting of CH3SO2-, CF3SO2-, ArSO2-, CH3SO3-, CF3SO3-, ArSO3-, and monovalent groups represented by the following formulas (y1-1) to (y1-6):

[0216]

[0217] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0218]

[0219] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0220]

[0221] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0222]

[0223] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0224]

[0225] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0226]

[0227] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0228] The separator for an electric storage device according to item 32 or 33, wherein,

[0229] The aforementioned reaction (IV) is a nucleophilic substitution reaction,

[0230] The aforementioned compound Ry further has a chain unit y2 based on the aforementioned linking reaction unit y1, and

[0231] The aforementioned chain unit y2 is at least one selected from the group consisting of divalent groups represented by the following formulas (y2-1) to (y2-6):

[0232]

[0233] {In the formula, m is an integer from 0 to 20, and n is an integer from 1 to 20.}

[0234]

[0235] {In the formula, n is an integer from 1 to 20.}

[0236]

[0237] {In the formula, n is an integer from 1 to 20.}

[0238]

[0239] {In the formula, n is an integer from 1 to 20.}

[0240]

[0241] {In the formula, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer from 1 to 20.}

[0242]

[0243] {In the formula, X is an alkylene group having 1 to 20 carbon atoms or an arylene group,

[0244] and n is an integer from 1 to 20.}

[0245] The separator for a power storage device according to item 32, wherein,

[0246] The aforementioned reaction (IV) is a nucleophilic addition reaction,

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

[0248] The linking reaction unit y1 of the aforementioned compound Ry is at least one selected from the group consisting of the groups represented by the following formulas (Ay1-1) to (Ay1-6):

[0249]

[0250] {In the formula, R is a hydrogen atom or a monovalent organic group.}

[0251]

[0252] The separator for a power storage device according to item 32, wherein,

[0253] The aforementioned reaction (IV) is a ring-opening reaction,

[0254] The functional group x of the aforementioned compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH, and

[0255] The linking reaction unit y1 of the aforementioned compound Ry is at least two groups represented by the following formula (ROy1-1):

[0256]

[0257] {In the formula, each of the plurality of Xs is independently a hydrogen atom or a monovalent substituent.}.

[0258] In the following reaction (V), for the separator for a power storage device according to item 29, the aforementioned metal ion is at least one selected from the group consisting of Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ , and Li + and forming a group.

[0259] A separator for a power storage device, the separator for a power storage device includes a silane-modified polyolefin, has a first porous layer (layer A) capable of forming a crosslinked structure and a second porous layer (layer B) containing inorganic particles, and the thermal shrinkage rate at 150 °C after forming the aforementioned crosslinked structure is 0.02 times or more and 0.91 times or less of the thermal shrinkage rate at 150 °C before forming the aforementioned crosslinked structure.

[0260] The separator for a power storage device according to Item 38, wherein the crosslinked structure in the A layer is formed by an acid, a base, swelling, or a compound generated in the power storage device.

[0261] A separator for a power storage device, comprising:

[0262] A microporous membrane containing a silane-modified polyolefin, and

[0263] An inorganic porous layer disposed on at least one surface of the microporous membrane and containing inorganic particles and a resin binder.

[0264] The separator for a power storage device according to Item 40, wherein the content of the inorganic particles in the inorganic porous layer is 5% by weight to 99% by weight.

[0265] The separator for a power storage device according to Item 40 or 41, wherein the content of the silane-modified polyolefin in the microporous membrane is 0.5% by weight to 40% by weight.

[0266] The separator for a power storage device according to any one of Items 40 to 42, wherein the inorganic particles are selected from the group consisting of alumina (Al2O3), silica, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxyhydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand, and glass fiber.

[0267] The separator for a power storage device according to any one of Items 40 to 43, wherein the glass transition temperature (Tg) of the resin binder is -50°C to 100°C.

[0268] The separator for a power storage device according to any one of Items 40 to 44, wherein when the separator for a power storage device comes into contact with an electrolyte, a silane crosslinking reaction of the silane-modified polyolefin is started.

[0269] The separator for a power storage device according to any one of Items 40 to 45, wherein

[0270] When the inorganic porous layer of the separator for a power storage device is removed for measurement, the storage modulus change ratio (R △E’ ) defined by the following formula (1A) is 1.5 times to 20 times:

[0271] R △E’ = E’ S / E’ j (1A)

[0272] {wherein, E’ j is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device before the crosslinking reaction of the aforementioned silane-modified polyolefin, and E’ S is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device after the crosslinking reaction of the aforementioned silane-modified polyolefin.},

[0273] and / or the loss modulus change ratio (R △E ”) defined by the following formula (1B) is 1.5 to 20 times:

[0274] R △E” = E” S / E” j (1B)

[0275] {wherein, E” j is the loss modulus measured at 160°C to 220°C for the separator for the electric storage device before the crosslinking reaction of the aforementioned silane-modified polyolefin, and E” S is the loss modulus measured at 160°C to 220°C for the separator for the electric storage device after the crosslinking reaction of the aforementioned silane-modified polyolefin.}.

[0276] The separator for the electric storage device according to any one of Items 40 to 46, wherein

[0277] when the aforementioned inorganic porous layer is removed from the aforementioned separator for the electric storage device for measurement, the mixed storage modulus ratio (R E’mix ) defined by the following formula (2A) is 1.5 to 20 times:

[0278] R E’mix = E’ / E’0 (2A)

[0279] {wherein, E’ is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device, and E’0 is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device without the aforementioned silane-modified polyolefin.},

[0280] and / or the mixed loss modulus ratio (R E”mix ) defined by the following formula (2B) is 1.5 to 20 times:

[0281] R E”mix = E” / E”0 (2B)

[0282] {In the formula, E” is the loss modulus measured for the separator for the storage battery device at 160°C to 220°C, and E”0 is the loss modulus measured for the separator for the storage battery device that does not contain the aforementioned silane-modified polyolefin at 160°C to 220°C.}.

[0283] The separator for a storage battery device according to any one of items 40 to 47, wherein in the temperature change of the storage modulus of the separator for the storage battery device, the transition temperature between the rubbery flat region and the crystal melting flow region is 135°C to 150°C.

[0284] A storage battery device, comprising an electrode, a separator for a storage battery device according to any one of items 1 to 48, and a non-aqueous electrolyte.

[0285] A storage battery device, the storage battery device comprising a separator containing polyethylene and comprising an electrolyte or an additive, and a crosslinked structure is formed by reaction of the functional group-modified polyethylene or the functional group-grafted copolymerized polyethylene with a chemical substance contained in the aforementioned electrolyte or the aforementioned additive.

[0286] A method for manufacturing a separator for a storage battery device, which is a method for manufacturing a separator for a storage battery device according to any one of items 1 to 50, and includes the following steps:

[0287] (1) A sheet forming step of extruding a mixture of a silane-modified polyolefin, polyethylene, and a plasticizer, cooling and solidifying it, and forming it into a sheet to obtain a sheet;

[0288] (2) A stretching step of stretching the aforementioned sheet in at least a uniaxial direction to obtain a stretched product;

[0289] (3) A porous body forming step of extracting the aforementioned plasticizer from the aforementioned stretched product in the presence of an extraction solvent to make the aforementioned stretched product porous and form a porous body; and

[0290] (4) A heat treatment step of subjecting the aforementioned porous body to heat treatment.

[0291] A method for manufacturing a separator for a storage battery device, which includes the following steps:

[0292] (1) A sheet forming step of extruding a silane-modified polyolefin, polyethylene, and a plasticizer into a sheet shape using an extruder, cooling and solidifying it, and processing it into a sheet-shaped formed body;

[0293] (2) A stretching step of biaxially stretching the aforementioned sheet-shaped formed body at a surface magnification of 20 times or more and 250 times or less to form a stretched product;

[0294] (3) A porous body forming step of extracting the aforementioned plasticizer from the aforementioned stretched product to form a porous body;

[0295] (4) Heat treatment process: subject the aforementioned porous body to heat treatment, perform stretching and relaxation in the width direction to obtain a heat-treated porous body;

[0296] (8B) Coating process: form an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the aforementioned heat-treated porous body to form a silane crosslinking precursor;

[0297] (9) Assembly process: accommodate an electrode, a laminate or a wound body of the aforementioned silane crosslinking precursor, and a non-aqueous electrolyte in a housing, and bring the aforementioned silane crosslinking precursor into contact with the aforementioned non-aqueous electrolyte.

[0298] A battery device assembly kit, which includes the following two elements:

[0299] (1) A housing that contains a laminate or a wound body of an electrode and a separator for a battery device according to any one of Items 1 to 48; and

[0300] (2) A container that contains a non-aqueous electrolyte.

[0301] According to the battery device assembly kit described in Item 53, wherein the aforementioned non-aqueous electrolyte contains a fluorine (F)-containing lithium salt.

[0302] According to the battery device assembly kit described in Item 53 or 54, wherein the aforementioned non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6).

[0303] According to the battery device assembly kit described in any one of Items 53 to 55, wherein the aforementioned non-aqueous electrolyte is an acid solution and / or an alkali solution.

[0304] A method for manufacturing a battery device, which includes the following processes;

[0305] A process of preparing a battery device assembly kit according to any one of Items 53 to 56, and

[0306] A process of starting a silane crosslinking reaction of a silane-modified polyolefin by bringing the separator for a battery device in the element (1) of the aforementioned battery device assembly kit into contact with the aforementioned non-aqueous electrolyte in the element (2).

[0307] According to the method for manufacturing a battery device described in Item 57, it further includes the following processes:

[0308] A process of connecting a lead terminal to the aforementioned electrode in the aforementioned element (1), and

[0309] A process of performing charge and discharge for at least one cycle.

[0310] A method for manufacturing a battery device, which is a method for manufacturing a battery device using a separator containing polyolefin

[0311] The polyolefin described above contains one or more than two functional groups, and the method includes the following crosslinking step:

[0312] (1) A condensation reaction is carried out between the aforementioned functional groups, or (2) the aforementioned functional groups react with the chemical substances inside the aforementioned energy storage device, or (3) the aforementioned functional groups react with other types of functional groups, thereby forming a crosslinked structure.

[0313] The method for manufacturing an energy storage device according to item 59, wherein the aforementioned crosslinking step is carried out at a temperature of 5°C to 90°C.

[0314] Effects of the Invention

[0315] According to the present invention, it is possible to provide an energy storage device and its assembly kit that can balance the low-temperature shut-off function and high-temperature burst resistance of the separator for the energy storage device, suppress the generation of unmolten resin aggregates in its manufacturing process, contribute to productivity and economy, and further have good cycle characteristics and high safety.

[0316] In addition, according to the present invention, a crosslinked structure can be formed not during or immediately after the film-forming process, so it is possible to suppress an increase in internal stress of the separator and deformation after the energy storage device is manufactured, and / or a crosslinked structure can be imparted to the separator even without using high energy such as light irradiation or heating, reducing crosslinking unevenness. Furthermore, according to the present invention, 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), which can improve the strength between multiple components of the energy storage device, suppress the gap generated between the separator and the electrode due to the expansion and contraction of the electrode during charge and discharge of the energy storage device, and can significantly improve the cycle stability during long-term use. Description of the Drawings

[0317] Figure 1 It is an example of a chart for explaining the relationship between temperature and storage modulus. By comparing the storage modulus of the standard film and the crosslinked film in the temperature range of -50°C to 225°C, the transition temperature between the rubbery plateau region and the crystal melting flow region is shown.

[0318] Figure 2 It is an example of a chart for explaining the relationship between temperature and loss modulus. By comparing the loss modulus of the standard film and the crosslinked film in the temperature range of -50°C to 225°C, the transition temperature between the rubbery plateau region and the crystal melting flow region is shown.

[0319] Figure 3 It is a chart showing the relationship between the temperature and resistance of an energy storage device equipped with the separator obtained in Example I-1.

[0320] Figure 4 It is a graph for explaining the relationships among temperature, gap distance, storage modulus, and loss modulus in the viscoelasticity measurement of the separator for the electricity storage device, and graphs (a) of Example II-1 and graph (b) of Comparative Example II-1 are illustrated.

[0321] Figure 5 It is a graph for determining the film softening transition temperature based on the first derivatives of temperature, gap distance, and gap displacement in the viscoelasticity measurement of the separator for the electricity storage device, and graphs (a) of Example II-1 and graph (b) of Comparative Example II-1 are illustrated.

[0322] Figure 6 It is a schematic diagram for explaining a crystalline polymer having a higher-order structure including lamellae (crystalline part) with a divided crystal structure, an amorphous part, and an intermediate layer part therebetween.

[0323] Figure 7 It is a schematic diagram for explaining the crystal growth of polyolefin molecules.

[0324] Figure 8 It is a strain - crystal subdivision ratio graph showing the change in X - ray crystal structure during the tensile fracture failure test for the film of one embodiment of the present invention.

[0325] Figure 9 It is an example of a graph for explaining the relationship between temperature and storage modulus. By comparing the storage moduli of the standard film and the cross - linked film in the temperature range of - 50°C to 310°C, the transition temperatures of the rubber - like flat region and the crystal melting flow region are shown.

[0326] Figure 10 It is an example of a graph for explaining the relationship between temperature and loss modulus. By comparing the loss moduli of the standard film and the cross - linked film in the temperature range of - 50°C to 310°C, the transition temperatures of the rubber - like flat region and the crystal melting flow region are shown.

[0327] Figure 11 It is the 1 1H - NMR spectrum (a) of the silane - modified polyolefin raw material 1 obtained using polyolefin and 13 13C - NMR spectrum (b).

[0328] Figure 12 It is the 1 1H - NMR spectrum (a) of the silane - modified polyolefin raw material 2 obtained using polyolefin and 13 13C - NMR spectrum (b).

[0329] Figure 13 It is the 1 1H - NMR spectrum (a) of the separator in the pre - cross - linked state obtained in Example I - 1 and 1313C-NMR spectrum (b). Detailed implementation manners

[0330] Hereinafter, the detailed implementation manners of the present invention (hereinafter simply referred to as "implementation manners") will be described in detail. It should be noted that the present invention is not limited to the following implementation manners, and various modifications can be made within the scope of its gist.

[0331] In this specification, "~" means including the numerical values at both ends thereof as the upper limit value and the lower limit value. In addition, in this specification, the upper limit value and the lower limit value of the numerical range can be arbitrarily combined. For example, the upper limit value of the preferred numerical range can be combined with the lower limit value of the more preferred numerical range, and conversely, the upper limit value of the more preferred numerical range can be combined with the lower limit value of the preferred numerical range.

[0332] It should be noted that in this specification, "above" and "formed on..." do not mean that the positional relationship of each component is limited to "directly above". For example, the descriptions such as "layer B formed on layer A" and "layer B formed on the surface of layer A" do not exclude the manner including any layer that does not belong to either of them between layer A and layer B.

[0333] Regarding the characteristics of the micro-porous membrane only described below, they can be measured after removing the layers other than the micro-porous membrane (such as the inorganic porous layer) from the separator for the energy storage device.

[0334] <Separator for energy storage device>

[0335] One aspect of the present invention is a separator for an energy storage device (hereinafter also simply referred to as "separator"). Since the separator needs to have insulation and ion permeability, it generally includes paper, polyolefin non-woven fabric or resin micro-porous membrane, etc. as insulating materials having a porous structure. Especially in a lithium-ion battery, a polyolefin micro-porous membrane capable of constructing a redox degradation-resistant and dense and uniform porous structure of the separator is preferred.

[0336] Here, the micro-porous membrane refers to a membrane (thin film) formed of a porous body, and its average pore diameter is preferably 10 nm or more and 500 nm or less, more preferably 30 nm or more and 100 nm or less.

[0337] When the energy storage device includes a separator, the separator can be taken out from the energy storage device.

[0338] <First, second, third, fourth and fifth implementation manners>

[0339] The separator of the first embodiment contains a silane-modified polyolefin, and may also contain other polyolefins as desired. When the separator of the first embodiment comes into contact with the electrolyte, the silane crosslinking reaction of the silane-modified polyolefin contained in the separator starts. Since the separator of the first embodiment can crosslink the silane-modified polyolefin when it comes into contact with the electrolyte, the timing of crosslinking can be controlled. Thus, the crosslinking reaction can be carried out in the manufacturing process of the storage battery device instead of in the manufacturing process of the separator.

[0340] The separator of the second embodiment is characterized in that when it comes into contact with the electrolyte, the silane crosslinking reaction of the silane-modified polyolefin occurs. In the second embodiment, regardless of whether the separator contains a silane-modified polyolefin, where the residual silane-modified polyolefin is located, and whether the silane crosslinking reaction starts initially, occurs sequentially, or occurs continuously when it comes into contact with the electrolyte, as long as the silane crosslinking reaction is observed when the separator comes into contact with the electrolyte. By the silane crosslinking reaction of the silane-modified polyolefin that occurs when the separator of the second embodiment comes into contact with the electrolyte, the control of the crosslinking timing can be achieved without being affected by the manufacturing or use process of the separator.

[0341] Since the separators of the first and second embodiments can promote the crosslinking reaction when injecting the electrolyte into the outer casing that houses the separator, production defects can be avoided in their manufacturing processes, and the safety and high output of the storage battery device can be achieved in the manufacturing process of the storage battery device. From the perspective of the components contained in the separator and the timing of the crosslinking reaction, it is preferable to start the silane crosslinking reaction of the silane-modified polyolefin when the separator is mixed with or comes into contact with the electrolyte.

[0342] The separator of the third embodiment contains 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the examples, the storage modulus change ratio (R ΔE’ ) defined by the following formula (1) is 1.5 to 20 times:

[0343] R ΔE’ =E’ S / E’ j (1)

[0344] {In the formula, E’ j is the storage modulus of the separator for the storage battery device before the crosslinking reaction of the silane-modified polyolefin measured at 160°C to 220°C, and E’ S is the storage modulus of the separator for the storage battery device after the crosslinking reaction of the silane-modified polyolefin measured at 160°C to 220°C.},

[0345] and / or the loss modulus change ratio (R ΔE”) is 1.5 to 20 times:

[0346] R ΔE” = E” S / E” j (3)

[0347] {In the formula, E” j is the loss modulus measured at 160°C to 220°C for the separator for the electric storage device before the crosslinking reaction of the aforementioned silane-modified polyolefin, and E” S is the loss modulus measured at 160°C to 220°C for the separator for the electric storage device after the crosslinking reaction of the aforementioned silane-modified polyolefin.}.

[0348] The third embodiment can achieve both the shut-off function and high-temperature burst resistance by making the storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE” ) within the range of 1.5 to 20 times. The storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE” ) is preferably 2 to 18 times. It should be noted that E’ j and E’ S as well as E” j and E” S are the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160 to 220°C as the widest temperature range. In addition, in the case where the separator is in the form of a laminated film, the porous film containing the silane-modified polyolefin is taken out from the laminated film alone to measure the storage modulus E’ j and E’ S as well as the loss modulus E” j and E” S .

[0349] The separator of the fourth embodiment contains 5 to 40% by mass of the silane-modified polyolefin and 60 to 95% by mass of the polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the examples, the mixed storage modulus ratio (R E’mix ) defined by the following formula (2) is 1.5 to 20 times:

[0350] R E’mix = E’ a / E’0 (2)

[0351] {In the formula, E’ a is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device, and E’0 is the storage modulus measured at 160°C to 220°C for the separator for the electric storage device without the silane-modified polyolefin.},

[0352] and / or the mixed loss modulus ratio (R E”mix ) is 1.5 to 20.0 times:

[0353] R E”mix = E” a / E”0 (4)

[0354] {In the formula, E” a is the loss modulus measured for the separator for the storage battery device at 160°C to 220°C, and E”0 is the loss modulus measured for the separator for the storage battery device without the aforementioned silane-modified polyolefin at 160°C to 220°C.}.

[0355] In the fourth embodiment, by making the mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix ) within the range of 1.5 to 20.0 times, it is possible to achieve both the shut-off function and the high-temperature burst resistance. The mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix ) is preferably 2 to 18 times. It should be noted that E’ a and E’0, and E” a and E”0 are respectively the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160 to 220°C as the widest temperature range. In addition, in the case where the separator is in the form of a laminated film, only the porous film containing the silane-modified polyolefin is taken out from the laminated film to measure the storage modulus E’ a and E’0 and the loss modulus E” a and E”0.

[0356] The separator of the fifth embodiment contains 5 to 40% by mass of a silane-modified polyolefin and 60 to 95% by mass of a polyolefin other than the aforementioned silane-modified polyolefin. Regarding the viscoelasticity measurement (version 1) described in the examples, in the temperature change of its storage modulus or loss modulus, the transition temperature between the rubbery plateau region and the crystal melting flow region is 135°C to 150°C. The fifth embodiment can achieve both the shut-off function and the high-temperature burst resistance by making the transition temperature between the rubbery plateau region and the crystal melting flow region within the range of 135°C to 150°C. The transition temperature between the rubbery plateau region and the crystal 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. It should be noted that in the case where the separator is in the form of a laminated film, only the porous film containing the silane-modified polyolefin is taken out from the laminate to measure the transition temperature between the rubbery plateau region and the crystal melting flow region.

[0357] <Sixth and Seventh Embodiments>

[0358] The separator of the sixth embodiment contains a polyolefin having one or more than two functional groups. After being accommodated in the electrical energy storage device, (1) a condensation reaction occurs between the functional groups of the polyolefin, or (2) the functional groups of the polyolefin react with the chemical substances inside the electrical energy storage device, or (3) the functional groups of the polyolefin react with other types of functional groups, thereby forming a crosslinked structure. It is considered that the functional groups contained in the polyolefin constituting the separator do not enter the crystal part of the polyolefin, but crosslink in the amorphous part. Therefore, after the separator of the sixth embodiment is accommodated in the electrical energy storage device, a crosslinked structure is formed by using the surrounding environment or the chemical substances inside the electrical energy storage device, whereby an increase in internal stress or deformation of the manufactured electrical energy storage device can be suppressed.

[0359] On the other hand, in the case where a crosslinking reaction is carried out before being accommodated in the electrical energy storage device and processes such as winding / slitting are performed, the influence of stresses such as tension generated during this process remains. At this time, when this stress is released after the electrical energy storage device is assembled, it is considered to be the cause of deformation or breakage due to stress concentration of the electrode winding or the like, and thus it is not preferred.

[0360] In the sixth embodiment, (1) the condensation reaction between the functional groups of the polyolefin can be, for example, a reaction of two or more functional groups A contained in the polyolefin by means of a covalent bond. (3) The reaction of the functional groups of the polyolefin with other types of functional groups can be, for example, a reaction of the functional group A contained in the polyolefin with the functional group B by means of a covalent bond.

[0361] In addition, in (2) the reaction of the functional groups of the polyolefin with the chemical substances inside the electrical energy storage device, for example, the functional group A contained in the polyolefin can form a covalent bond or a coordination bond with any of the electrolyte, electrolyte solution, electrode active material, additive or their decomposition products contained in the electrical energy storage device. In addition, 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 multiple components of the electrical energy storage device can be improved.

[0362] The separator of the seventh embodiment contains a polyolefin and has an amorphous part crosslinked structure obtained by crosslinking the amorphous part of the polyolefin. It is considered that the functional groups contained in the polyolefin constituting the separator do not enter the crystal part of the polyolefin, but crosslink in the amorphous part. Therefore, compared with the existing crosslinked separators whose crystal parts and their peripheries are easily crosslinked, the separator of the seventh embodiment can suppress an increase in internal stress or deformation of the manufactured electrical energy storage device while taking into account the shut-off function and high-temperature burst resistance, and further ensure the safety of the electrical energy storage device. From the same perspective, the amorphous part of the polyolefin contained in the separator of the seventh embodiment is preferably selectively crosslinked, and more preferably significantly crosslinked compared with the crystal part.

[0363] Regarding the crosslinking reaction mechanism and crosslinked structure of the above-described seventh embodiment, they are not yet clear, but the present inventors consider as follows.

[0364] (1) Crystal structure in the high-density polyethylene microporous membrane

[0365] Polyolefin resins represented by high-density polyethylene and the like are Figure 6 as shown, generally crystalline polymers, having a higher-order structure divided into lamellar crystals (crystalline parts), amorphous parts, and intermediate layer parts therebetween. In the crystalline part and the intermediate layer part between the crystalline part and the amorphous part, the mobility of the polymer chains is low and it is difficult to cut, but a relaxation phenomenon can be observed in the 0 to 120 °C region in solid viscoelasticity measurement. On the other hand, the mobility of the polymer chains in the amorphous part is very high and is observed in the -150 to -100 °C region in solid viscoelasticity measurement. This is closely related to the relaxation of free radicals or the transfer reaction and crosslinking reaction of free radicals described later.

[0366] In addition, the polyolefin molecules constituting the crystal are not single. As Figure 7 exemplified, after multiple polymer chains form small lamellar crystals, the lamellar crystals aggregate to form crystals. This phenomenon is difficult to directly observe. In recent years, through simulation, research has been advanced academically and clarified. It should be noted that here, a crystal refers to the smallest crystal unit measured by X-ray structure analysis and is a unit that can be calculated as the microcrystalline size. Thus, although it is the crystalline part (inside the lamellar crystal), it is predicted that there is a part in the crystal that is not restricted and has slightly higher mobility.

[0367] (2) Crosslinking reaction mechanism based on electron beam

[0368] Next, the reaction mechanism of electron beam crosslinking (hereinafter abbreviated as EB crosslinking) of polymers is as follows. (i) Irradiation with electron beams from several tens of kGy to several hundreds of kGy, (ii) penetration of electron beams into the reaction object (polymer) and generation of secondary electrons, (iii) hydrogen abstraction reaction and radical generation in the polymer chain based on secondary electrons, (iv) abstraction of adjacent hydrogen and movement of active sites based on radicals, (v) crosslinking reaction or polyene formation based on recombination between radicals. Here, regarding the radicals generated in the crystal part, due to poor mobility, they exist for a long time, and impurities and the like cannot enter the crystal, so the probability of reaction and extinction is low. This type of radical species is called a stable radical and remains for several months. By ESR measurement, the lifetime was clarified. As a result, it is considered that the crosslinking reaction in the crystal is poor. However, in the slightly unconstrained molecular chains or the surrounding crystal-amorphous intermediate layer part existing inside the crystal, the generated radicals have a slightly longer lifetime. This type of radical species is called a persistent radical, and it is considered that in an environment with mobility, the crosslinking reaction between molecular chains occurs with a high probability. On the other hand, in the amorphous part, due to very high mobility, the lifetime of the generated radical species is short, and it is considered that not only the crosslinking reaction between molecular chains but also the polyene reaction within a single molecular chain occurs with a high probability.

[0369] As described above, it can be speculated that at the microscopic level of the crystal, the crosslinking reaction based on EB crosslinking locally exists inside the crystal or its periphery.

[0370] (3) Crosslinking reaction mechanism based on chemical reaction

[0371] In the seventh embodiment of the present invention, it is preferable to use a functional group in the polyolefin resin and a chemical substance contained in the power storage device, or a chemical substance contained in the power storage device as a catalyst.

[0372] As described above, there are crystal parts and amorphous parts in the polyolefin resin. However, due to steric hindrance, the aforementioned functional groups are locally present in the amorphous part and not inside the crystal. This situation is well known. Sometimes, units such as methyl slightly contained in the polyethylene chain enter the crystal, but grafts larger in volume than ethyl do not enter (Non-Patent Document 2). Therefore, crosslinking points based on reactions different from electron beam crosslinking are only locally present in the amorphous part.

[0373] (4) Relationship between differences in crosslinking structure and effects

[0374] As described above, in the crosslinking reaction based on the chemical reaction inside the battery used in the seventh embodiment of the present invention, the morphology of the reaction product is different. In the research up to the present invention, in order to clarify the crosslinked structure and the physical property changes of the microporous membrane accompanying the structural changes, the following experiments were conducted to clarify the phenomenon.

[0375] First, the mechanical properties of the membrane based on the tensile fracture test were studied. In addition, while conducting the tensile fracture test, the crystal structure changes were analyzed by in-situ X-ray structural analysis using synchrotron radiation. As a result, as Figure 8 shown, based on the membrane without EB crosslinking or chemical crosslinking (before), in the EB crosslinked membrane, as the strain increases, the subdivision of the crystal part is suppressed. This is because crosslinking occurs selectively inside or around the crystal part. Consequently, the Young's modulus and the fracture strength are significantly increased, and high mechanical strength can be exhibited. On the other hand, in the chemically crosslinked membrane, no difference was observed in the subdivision of the crystal before and after the crosslinking reaction, which implies that crosslinking occurs selectively in the amorphous part. In addition, there is no change in the mechanical strength before and after the crosslinking reaction.

[0376] Next, the behavior during the crystal melting of both was studied through the fuse / melt rupture property test. As a result, the melting temperature of the membrane treated with EB crosslinking increased significantly, and the melt rupture temperature rose above 200 °C. On the other hand, it was confirmed that for the chemically crosslinked membrane, no change was observed in the melting temperature before and after the crosslinking treatment, and the melt rupture temperature rose above 200 °C. Therefore, it is considered that in the fuse (shut-off) property generated by crystal melting, in the EB crosslinked membrane, due to crosslinking around the crystal part, the increase in the melting temperature and the decrease in the melting rate are the reasons. On the other hand, it is judged that since the chemically crosslinked membrane does not have a crosslinked structure in the crystal part, it does not change the shut-off property. In addition, in the high temperature region around 200 °C, since both have a crosslinked structure after crystal melting, the entire resin can be stabilized in a gel state, and good melt rupture properties can be obtained.

[0377] The above understandings are summarized in the following table.

[0378] [Table 1]

[0379]

[0380] Regarding the viscoelasticity measurement (version 2) described in the examples, from the perspective of forming an amorphous part crosslinked structure and achieving both shut-off function and high temperature burst resistance, the hybrid storage modulus ratio (R E’X ) defined by the following formula (1) for the separator of the seventh embodiment:

[0381] R E’X = E’ Z / E’Z0 (1)

[0382] {In the formula, E’ Z is the storage modulus measured in the temperature range of 160°C to 300°C after the crosslinking reaction of the separator for the storage battery is carried out in the storage battery, and

[0383] E’ Z0 is the storage modulus measured in the temperature range of 160°C to 300°C before the separator for the storage battery is assembled into the storage battery.}

[0384] and / or the mixed loss modulus ratio (R E”X ):

[0385] R E”X = E” Z / E” Z0 (3)

[0386] {In the formula, E” Z is the loss modulus measured in the temperature range of 160°C to 300°C after the crosslinking reaction of the separator for the storage battery is carried out in the storage battery, and

[0387] E” Z0 is the loss modulus measured in the temperature range of 160°C to 300°C before the separator for the storage battery is assembled into the storage battery.}

[0388] is preferably 1.5 to 20 times, more preferably 3 to 18 times. It should be noted that E’ Z and E’ Z0 as well as E” Z and E” Z0 are respectively the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160°C to 300°C as the widest temperature range. In addition, in the case where the separator is in the form of a laminated film, only the polyolefin porous film is taken out from the laminated film to measure the storage modulus E’ Z and E’ Z0 as well as the loss modulus E” Z and E” Z0 .

[0389] Regarding the separator of the sixth and seventh embodiments, from the perspective of forming an amorphous part crosslinked structure and taking into account the closing function and high temperature film breakage resistance, etc., for the viscoelasticity measurement (version 2) described in the examples, the mixed storage modulus ratio (R E’mix ):

[0390] R E’mix = E’ / E’0 (2)

[0391] {In the formula, E' is the storage modulus of the separator for a power storage device having an amorphous part crosslinked structure, measured at 160°C to 300°C, and

[0392] E'0 is the storage modulus of the separator for a power storage device not having an amorphous part crosslinked structure, measured at 160°C to 300°C.}

[0393] and / or the ratio of the loss modulus (R E”mix ) defined by the following formula (4):

[0394] R E”mix = E” / E”0 (4)

[0395] {In the formula, E” is the loss modulus of the separator for the power storage device having an amorphous part crosslinked structure, measured at 160°C to 300°C, and

[0396] E”0 is the loss modulus of the separator for the power storage device not having an amorphous part crosslinked structure, measured at 160°C to 300°C.}

[0397] Preferably it is 1.5 times to 20 times, more preferably 3 times to 19 times, and still more preferably 5 times to 18 times. It should be noted that E' and E'0, and E” and E”0 are respectively the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160°C to 300°C as the widest temperature range. In addition, in the case where the separator is in the form of a laminated film, only the polyolefin microporous film is taken out from the laminated film to measure the storage modulus E' and E'0 and the loss modulus E” and E”0.

[0398] <Eighth Embodiment>

[0399] [Viscoelastic behavior (viscoelastic measurement version 3 described in the examples)]

[0400] The separator of the eighth embodiment includes a polyolefin microporous film, and regarding the viscoelastic measurement (version 3) described in the examples, in the solid viscoelastic measurement at a temperature 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, 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≤10,000 MPa, and / or 0.1 MPa ≤ E” min ≤10 MPa and 10 MPa ≤ E” max Within the range of ≤10,000 MPa, there is not only a tendency to balance the closing function of the separator and the high-temperature film-breaking tolerance, but also production defects can be avoided in the manufacturing process of the separator or the energy storage device, achieving the stability and safety of the energy storage device. From these perspectives, it is preferably 1.1 MPa ≤ E’ min ≤9.0 MPa and / or 150 MPa ≤ E’ max ≤9,500 MPa, more preferably 1.2 MPa ≤ E’ min ≤8.0 MPa and / or 233 MPa ≤ E’ max ≤9,000 MPa. In addition, it is preferably 0.2 MPa ≤ E” min ≤9.0 MPa and / or 56 MPa ≤ E” max ≤9,000 MPa, more preferably 0.4 MPa ≤ E” min ≤8.0 MPa and / or 74 MPa ≤ E” max ≤8,000 MPa.

[0401] In the solid viscoelasticity measurement (version 3), at temperatures from the film softening transition temperature to the film breaking temperature of the separator containing the polyolefin microporous membrane, the average E’ (E’ ave ) is preferably 1.0 MPa to 12 MPa, more preferably 1.2 MPa to 10 MPa, further preferably 1.8 MPa to 8.2 MPa, and / or the average E” (E” ave ) is preferably 0.5 MPa to 10 MPa, more preferably 0.8 MPa to 8.2 MPa or 0.9 MPa to 3.2 MPa. If E’ and / or E” are within the above numerical ranges at temperatures from the film softening transition temperature to the film breaking temperature, there is a tendency for the cycle stability and safety of the energy storage device equipped with the separator to be improved.

[0402] In the solid viscoelasticity measurement (version 3), from the perspective of balancing the closing function and high-temperature film-breaking tolerance, the film 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 film breaking 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, further preferably 250 °C or higher. There is no upper limit for the film breaking temperature. In the technical field, it should be understood that the film breaking phenomenon will also occur at temperatures higher than 250 °C.

[0403] The conditions for measuring E’ and E” in the measurement of the solid viscoelasticity of the separator (version 3) are described in the examples. In the case where the separator is in the form of a laminated film, only the polyolefin microporous membrane is taken out from the laminated film, and E’ and E” of the taken-out polyolefin microporous membrane are measured. Further, in the case where the film thickness of a single polyolefin microporous membrane is less than 200 μm, the dynamic viscoelasticity measurement (version 3) is carried out by laminating a plurality of polyolefin microporous membranes or folding a single polyolefin microporous membrane so that the total thickness is in the range of 200 μm to 400 μm.

[0404] From the viewpoint of achieving both the shut-off function at a relatively low temperature and the film-breaking property at a relatively high temperature and improving the cycle characteristics and safety of the power storage device, the separators of the first to eighth embodiments may include: a microporous membrane; and an inorganic porous layer disposed on at least one surface of the microporous membrane and containing inorganic particles and a resin binder. The separator may be in a state where a microporous membrane is used as a base material and the base material is composited with an inorganic coating layer.

[0405] <Ninth Embodiment>

[0406] The separator of the ninth embodiment includes:

[0407] a microporous membrane containing a silane-modified polyolefin; and

[0408] an inorganic porous layer disposed on at least one surface of the microporous membrane and containing inorganic particles and a resin binder.

[0409] The separator of the ninth embodiment may include a layer other than the microporous membrane and the inorganic porous layer as desired.

[0410] In the ninth embodiment, the combination of the microporous membrane containing a silane-modified polyolefin and the inorganic porous layer has a tendency to achieve both the shut-off function at a temperature lower than 150 °C and the film-breaking property at a relatively high temperature and improve the cycle characteristics of the power storage device and the safety against nail penetration of the battery. It is speculated that since the silane-modified polyolefin in the microporous membrane is silane crosslinkable, once silane crosslinking occurs, the viscosity of the resin in the microporous membrane sometimes increases. Therefore, in the case of an abnormally 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 crosslinked high-viscosity resin does not easily flow into the inorganic layer (i.e., is not easily integrated), and the gap between the electrodes can be sufficiently ensured, and battery short-circuit can be suppressed.

[0411] When the separator of the ninth embodiment preferably comes into contact with the electrolyte, the silane crosslinking reaction of the silane-modified polyolefin starts. More preferably, when it comes into contact with the electrolyte, whether the silane crosslinking reaction starts initially, occurs successively, or occurs continuously, the silane crosslinking reaction is observed when the separator comes into contact with the electrolyte. Through the silane crosslinking reaction of the silane-modified polyolefin that occurs when the separator comes into contact with the electrolyte, not only can the crosslinking time point of the separator be controlled to avoid production defects in the separator manufacturing process, but also safety and high output can be achieved in the manufacturing process of the electrical storage device. In addition, by bringing the separator into contact with the electrolyte, a crosslinking reaction other than the silane crosslinking reaction can be initiated.

[0412] Regarding the viscoelasticity measurement (version 1) described in the examples, when measuring the separator after removing the inorganic porous layer from the separator, the storage modulus change ratio (R △E’ ) defined by the following formula (1A) is preferably 1.5 to 20 times:

[0413] R △E’ = E’ S / E’ j (1A)

[0414] {In the formula, E’ j is the storage modulus measured at 160°C to 220°C for the separator for the electrical storage device before the crosslinking reaction of the silane-modified polyolefin, and E’ S is the storage modulus measured at 160°C to 220°C for the aforementioned separator for the electrical storage device after the crosslinking reaction of the silane-modified polyolefin.},

[0415] and / or preferably the loss modulus change ratio (R △E ) defined by the following formula (1B) is 1.5 to 20 times:

[0416] R △E” = E” S / E” j (1B)

[0417] {In the formula, E” j is the loss modulus measured at 160°C to 220°C for the separator for the electrical storage device before the crosslinking reaction of the silane-modified polyolefin, and E” S is the loss modulus measured at 160°C to 220°C for the separator for the electrical storage device after the crosslinking reaction of the silane-modified polyolefin.}.

[0418] By making the storage modulus change ratio (R △E’ ) and / or the loss modulus change ratio (R △E” ) within the range of 1.5 to 20 times, it is easy to balance the shut-off function and high-temperature burst resistance. The storage modulus change ratio (RΔE’ ) and / or the change ratio of the loss modulus (R ΔE” ) is more preferably 2 to 18 times. It should be noted that E’ j and E’ S and E” j and E” S are the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160 to 220 °C as the widest temperature range, respectively. In addition, 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 microporous film containing a silane-modified polyolefin is taken out from the laminated film or the composite film to measure the storage modulus E’ j and E’ S and the loss modulus E” j and E” S .

[0419] Regarding the viscoelasticity measurement (version 1) described in the examples, when the inorganic porous layer is removed from the separator for measurement, the separator of the ninth embodiment preferably has a mixed storage modulus ratio (R E’mix ) defined by the following formula (2A) of 1.5 to 20 times:

[0420] R E’mix = E’ / E’0 (2A)

[0421] {In the formula, E’ is the storage modulus measured for the separator for the electric storage device at 160 °C to 220 °C, and E’0 is the storage modulus measured for the separator for the electric storage device without the silane-modified polyolefin at 160 °C to 220 °C.},

[0422] and / or preferably has a mixed loss modulus ratio (R E”mix ) defined by the following formula (2B) of 1.5 to 20 times:

[0423] R E”mix = E” / E”0 (2B)

[0424] {In the formula, E” is the loss modulus measured for the separator for the electric storage device at 160 °C to 220 °C, and E”0 is the loss modulus measured for the separator for the electric storage device without the silane-modified polyolefin at 160 °C to 220 °C.}.

[0425] By making the mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix ) within the range of 1.5 to 20 times, it is easy to balance the shut-off function and the high-temperature burst resistance. The mixed storage modulus ratio (R E’mix ) and / or the mixed loss modulus ratio (R E”mix)More preferably, it is 2 to 18 times. It should be noted that E’ and E’0, and E” and E”0 are the average values of the storage modulus or loss modulus measured within the set temperature range of the measuring device when setting 160 to 220 °C as the widest temperature range. In addition, 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 microporous film containing the silane-modified polyolefin is taken out from the laminated film or composite film alone to measure the storage modulus E’ and E’0 and the loss modulus E” and E”0 of the microporous film containing the silane-modified polyolefin. It should be noted that the separator for the electric storage device that does not contain the silane-modified polyolefin is described in detail in the example items.

[0426] From the perspective of balancing the closing function and high-temperature burst resistance, the separator of the ninth embodiment preferably has a transition temperature between the rubbery flat region and the crystal melting flow region of 135 °C to 150 °C in the temperature change of its storage modulus. The transition temperature between the rubbery flat region and the crystal 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. It should be noted 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 containing the silane-modified polyolefin is measured by taking out only the microporous film containing the silane-modified polyolefin from the laminate or composite film.

[0427] <Tenth Embodiment>

[0428] The separator for the electric storage device of the tenth embodiment (hereinafter also simply referred to as "separator") includes a silane-modified polyolefin, a first porous layer (layer A) capable of forming a crosslinked structure, and a second porous layer (layer B) containing inorganic particles. Each of layer A and layer B is a single layer or multiple layers. Layer B is formed only on one side surface or both side surfaces of layer A.

[0429] In LIB, which is a representative example of an electric storage device, lithium (Li) ions move back and forth between the positive and negative electrodes. Therefore, by disposing the separator including layer A and layer B between the positive and negative electrodes, Li ions can move at a relatively high speed between the positive and negative electrodes, and at the same time, contact between the positive and negative electrodes can be avoided.

[0430] (Ratio of thickness)

[0431] Layer A functions as a crosslinkable microporous film, and layer B functions as an inorganic porous layer formed on the microporous film.

[0432] Here, the ratio (TA / TB) of the thickness (TA) of layer A to the thickness (TB) of layer B is preferably 0.22 or more and 14 or less. If the ratio (TA / TB) is 0.22 or more, the proportion of layer A in the separator can be sufficiently ensured, and the functions brought by layer A can be exerted. On the other hand, if the ratio (TA / TB) is 14 or less, the proportion of layer B in the separator can be sufficiently ensured, and the functions brought by layer B can be exerted.

[0433] By making layer A and layer B have specific structures respectively, and further setting the ratio (TA / TB) within the above range, a separator capable of improving the cycle characteristics and safety of the energy storage device can be provided. Such a separator can be suitably used as a constituent material of LIBs for mobile device mounting or vehicle mounting applications, for example.

[0434] From the perspective of the above effects, the ratio (TA / TB) is preferably 0.8 or more, more preferably 1.0 or more. On the other hand, the ratio (TA / TB) is preferably 5.5 or less, more preferably 3.2 or less.

[0435] The ratio (TA / TB) can be set to be less than 2.5, 2.0 or less, or 1.0 or less, for example. In this case, the thickness (TA) of layer A is less than 2.5 times the thickness (TB) of layer B or less than the thickness (TB) of layer B, and it is easy to realize the thinning of layer A and even the thinning of the separator.

[0436] The total thickness (TA + TB) of layer A and layer B is preferably 3.0 μm or more and 22 μm or less. If the total thickness (TA + TB) is 3.0 μm or more, 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.

[0437] From the perspective of the above effects, the total thickness (TA + TB) is more preferably 3.5 μm or more, further preferably 4.0 μm or more. On the other hand, the total thickness (TA + TB) is more preferably 20 μm or less, further preferably 18 μm or less.

[0438] The total thickness (TA + TB) can be set to be less than 11 μm, 10 μm or less, or 8 μm or less, for example. Even such a thin separator can improve the cycle characteristics and safety of the energy storage device as long as it is within the scope of the present invention.

[0439] The ratio (TA / TB) and the total thickness (TA + TB) can be measured by the methods described in the Examples column, respectively. In addition, they can be controlled by adjusting the thickness (TA) and / or the thickness (TB). Layer A and layer B will be described later.

[0440] (Shutdown temperature and melting rupture temperature)

[0441] Regarding the A layer, the shutdown temperature (sometimes referred to as the fusing temperature), measured based on resistance under a pressure of 0.1 Mpa or more and 10.0 Mpa or less (preferably under a pressure of 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.

[0442] If the above shutdown temperature is 130°C or more, it is possible to avoid the unnecessary activation of the shutdown function during the normal reaction of the energy storage device, and ensure the sufficient output characteristics of the energy storage device. On the other hand, if the above shutdown temperature is 160°C or less, it is possible to appropriately activate the shutdown function during the abnormal reaction of the energy storage device.

[0443] In addition, if the above shutdown temperature is 200°C or more, it is possible to stop the abnormal reaction before reaching the ultra-high temperature region during the abnormal reaction of the energy storage device, and also prevent the melting and film rupture of the separator during the abnormal reaction of the energy storage device.

[0444] That is, by making the shutdown temperature and the melting rupture temperature satisfy the above conditions, it is possible to realize a separator for an energy storage device with excellent heat resistance, closed cell characteristics (shutdown function), and melting and film rupture characteristics (melting rupture function), and for the separator itself, mechanical characteristics, ion permeability, etc. can also be ensured. Therefore, by having a separator with a shutdown temperature and a melting rupture temperature that satisfy the above conditions, the energy storage device can achieve an improvement in cycle characteristics and safety.

[0445] From the perspective of the above effects, the shutdown 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 shutdown temperature is preferably 150°C or less, more preferably 148°C or less, and further preferably 146°C or less.

[0446] Similarly, from the perspective 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.

[0447] It should be noted that regarding the melting rupture temperature, even if it cannot be accurately measured in the range exceeding 200°C, as long as its temperature is 200°C or more, the condition of "the melting rupture temperature is 200°C or more" is satisfied.

[0448] The "closure temperature" and "melt fracture temperature" in this specification refer to the values obtained based on resistance measurement under the above-mentioned pressure. That is, while applying the above-mentioned pressure to the laminate including the positive electrode, the separator, and the negative electrode, the temperature of the laminate is increased, and the closure temperature and the melt fracture temperature are derived based on the AC resistance (AC resistance between the electrodes) that increases accordingly. In the tenth embodiment, the temperature at which the AC resistance first exceeds a specified reference value (for example, 1000 Ω) is set as the closure temperature, and the temperature at which, after further heating, the AC resistance exceeding the above-mentioned reference value is reduced to below the above-mentioned reference value (for example, 1000 Ω) is set as the melt fracture temperature.

[0449] The pressure applied to the laminate can be applied using a hydraulic jack, but is not limited thereto, and known pressure application means other than the hydraulic jack can be used. In addition, the heating of the laminate can be performed using an aluminum heater, but is not limited thereto, and known heating means other than the aluminum heater can be used.

[0450] The above-mentioned closure temperature and melt fracture temperature can be measured by the method described in the Examples column. In addition, they can be controlled by adjusting the composition or manufacturing method of the A layer.

[0451] (Thermal shrinkage rate at 150 °C)

[0452] In the A layer, the thermal shrinkage rate (T2) at 150 °C after forming its crosslinked structure is 0.02 times or more and 0.91 times or less of the thermal shrinkage rate (T1) at 150 °C before forming the crosslinked structure. In other words, the ratio (T2 / T1) of the thermal shrinkage rate (T2) at 150 °C after forming the crosslinked structure to the thermal shrinkage rate (T1) at 150 °C before forming the crosslinked structure is 0.02 or more and 0.91 or less. As the thermal shrinkage rate here, the larger value of the thermal shrinkage rate in the machine direction (MD) of the A layer and the thermal shrinkage rate in the width direction (TD) of the A layer is used.

[0453] Since the A layer can form a crosslinked structure based on a silane-modified polyolefin, the change in the thermal shrinkage rate before and after crosslinking can be focused on.

[0454] If the ratio (T2 / T1) is 0.02 or more, the generation of a short circuit can be effectively suppressed, and thus, an increase in the temperature of the entire power storage device and possible subsequent smoke generation and even ignition 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 carried out. That is, if the ratio (T2 / T1) is within the above range, a separator for a power storage device that can improve the cycle characteristics and safety of the power storage device can be provided.

[0455] Therefore, from the perspective of the above 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.

[0456] It should be noted that the thermal shrinkage rate (T1) at 150 °C before forming the crosslinked structure is preferably 70% or less, more preferably 60% or less.

[0457] In addition, the thermal shrinkage rate (T2) at 150 °C after forming the crosslinked structure is preferably 60% or less, more preferably 50% or less. However, by forming the crosslinked structure, there is a tendency for the above thermal shrinkage rate to decrease compared to before forming the crosslinked structure. Therefore, the thermal shrinkage rate (T2) is generally a value smaller than the thermal shrinkage rate (T1).

[0458] The thermal shrinkage rate at 150 °C can be measured by the method described in the Examples column. In addition, it can be controlled by adjusting the composition or manufacturing method of the A layer.

[0459] The separators of the above-described multiple embodiments can be interchanged or combined with each other. The separator of the ninth or tenth embodiment described above may include layers other than the microporous membrane and the inorganic porous layer according to the expectation. The constituent elements of the separators of the first to tenth embodiments will be described below.

[0460] [Microporous Membrane]

[0461] The microporous membrane can be formed of polyolefin or modified polyolefin.

[0462] The microporous membrane contains silane-modified polyolefin and may also contain other polyolefins according to the expectation. Due to the silane crosslinkability of the silane-modified polyolefin, a crosslinking reaction can be carried out in the manufacturing process of the separator.

[0463] The polyolefin contained in the microporous membrane is not particularly limited. 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 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 (homopolymer) or low-density polyethylene is preferred, and high-density polyethylene (homopolymer) is more preferred. It should be noted that one kind of polyolefin can be used alone, or two or more kinds can be used in combination.

[0464] From the viewpoints of resistance to redox degradation and a dense and uniform porous structure, it is preferable to use both a silane-modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) as raw materials to manufacture the microporous membrane. Generally, it is known that the weight-average molecular weight of ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more. More preferably, in the manufacture of the microporous membrane or the separator, the weight ratio of the silane-modified polyolefin to UHMWPE (weight of silane-modified polyolefin / weight of UHMWPE) is 0.05 / 0.95 to 0.40 / 0.60.

[0465] The content of the polyolefin contained in the microporous membrane is preferably 50% by weight or more and 100% by weight or less, more preferably 70% by weight or more and 100% by weight or less, and still more preferably 80% by weight or more and 100% by weight or less. In addition, 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 in a proportion of 40% by weight or more, more preferably 80% by weight or more, relative to the total polyolefin). The weight-average molecular weight of the polyolefin is more preferably 120,000 or more and less than 950,000, and still more 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 that shrinkage relaxation of the polymer occurs at an early stage in a heating test of the electric storage device, etc., and in particular, safety is easily maintained in a heating safety test. By adjusting the weight-average molecular weight of the microporous membrane to less than 1,000,000, it is possible to suppress molding defects (film streaks) during extrusion called melt fracture. On the other hand, by adjusting the weight-average molecular weight of the microporous membrane to 100,000 or more, it is possible to suppress transfer of indentations when the microporous membrane is wound around a core (winding core).

[0466] Regarding the viscosity-average molecular weight of the microporous membrane when the inorganic porous layer is removed and the microporous membrane is not crosslinked, from the viewpoint of not generating polymer powder due to frictional shear during the roll conveyance of the separator, 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.

[0467] 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 be further improved. 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 be further improved. The film thickness of the microporous membrane can be measured by the method described in the examples.

[0468] When the microporous membrane is a separator used in a lithium ion secondary battery with a relatively 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 be further improved. In this case, the lower limit value 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.

[0469] From the viewpoints of the high-temperature burst resistance of the separator for the power storage device and the safety of the power storage device, as the microporous membrane for the separator, preferably, during the thermomechanical analysis (TMA) measurement thereof, the melting burst temperature is preferably 180°C to 220°C, and more preferably 180°C to 200°C. Generally, when the power storage device generates heat due to an accidental runaway reaction, the separator for the polyolefin-based power storage device melts and breaks at a low temperature (for example, 150°C or lower), and the movement of Li ions stops at an early stage, and the discharge inside or outside the power storage device accompanies it. Then, during the natural cooling of the power storage device using external air or a refrigerant, the entire power storage device is cooled, and ignition of the electrolyte or decomposition heat generation reaction of the electrolyte can be prevented, and ensuring safety can be expected. However, the runaway reaction occurring in the power storage device does not stop due to the melting and breaking of the separator, continues to generate heat, the separator melts and breaks, and the safety of the device cannot be ensured. Therefore, it is important that the separator does not melt and break until the entire power storage device is sufficiently cooled. In addition, in the event of rising to an ultra-high temperature region of 220°C or higher, the decomposition reaction of the electrolyte or the electrolyte proceeds rapidly, and the corrosion reaction of the electrode is caused by the decomposition products, further generating heat and leading to an explosion. In this case, the separator can prevent the corrosion reaction by melting and breaking and infiltrating into the two electrodes to coat the active material.

[0470] [First porous layer (A layer)]

[0471] Layer A contains a silane-modified polyolefin and can form a crosslinked structure. From the perspectives of ensuring resistance to deterioration against oxidation-reduction and ensuring a dense and uniform porous structure, Layer A preferably further contains polyethylene as a polyolefin different from the silane-modified polyolefin. It should be noted that Layer A may contain components other than the silane-modified polyolefin and polyethylene.

[0472] Examples of the polyolefin constituting the silane-modified polyolefin in Layer A include homopolymers of ethylene or propylene; copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene, etc. Among them, as the polyolefin, from the perspective of being able to perform heat setting at a higher temperature while avoiding pore blockage, a homopolymer of ethylene (polyethylene) is preferred, and high-density polyethylene and / or low-density polyethylene are more preferred, and high-density polyethylene is further preferred. The polyolefin can be used alone or in combination of two or more.

[0473] Layer A can contain a polymer (other polymer) that does not belong to either the silane-modified polyolefin or polyethylene within a range that does not overly impede the effects brought by the present invention.

[0474] The weight-average molecular weight of Layer A as a whole is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

[0475] (Thickness of Layer A)

[0476] The thickness (TA) of Layer A is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 3 μm or more. If the thickness (TA) is 1 μm or more, there is a tendency for the film strength to be further improved. On the other hand, the thickness (TA) is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less. If the thickness (TA) is 500 μm or less, there is a tendency for the ion permeability to be further improved. It should be noted that the thickness (TA) can be set, for example, to 1.00 μm or more, 2.00 μm or more, or 3.00 μm or more.

[0477] When the separator is a separator for LIB, the thickness (TA) is preferably less than 22 μm, more preferably 21 μm or less, and still more preferably 20.5 μm or less. When the separator is a separator for 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 for the permeability to be further improved. It should be noted that the thickness (TA) can be set, for example, to less than 22.00 μm, 21.00 μm or less, 20.00 μm or less, less than 13.00 μm or 8.50 or less. The lower limit of the thickness (TA) can be the same as above.

[0478] The thickness (TA) can be measured by the method described in the Examples section. In addition, it can be controlled by changing the draw ratio of the A layer, etc.

[0479] When the A layer is a single layer, the thickness of the A layer is regarded as the thickness (TA). When the A layer is a multi-layer, the total thickness of the multi-layer A layer is regarded as the thickness (TA).

[0480] (The film-breaking temperature of the A layer)

[0481] The film-breaking temperature of the A layer measured by thermomechanical analysis (TMA) is preferably 180 °C or higher and 220 °C or lower.

[0482] Even if an accidental runaway reaction causes abnormal heating of the energy storage device, it is expected that the movement of Li ions can be stopped by the closing function of the separator, and the discharge inside or outside the energy storage device accompanying this can also be stopped. Then, it is expected to cool the entire energy storage device using a refrigerant to ensure safety. On the other hand, by setting the film-breaking temperature within the above range, even when the entire energy storage device is not sufficiently cooled, and in the case of reaching an ultra-high temperature region in the worst case, the separator can melt and break through, penetrate into the two electrodes and coat the active material, thereby easily suppressing further heating.

[0483] The film-breaking temperature can be measured by the method described in the Examples section. In addition, it can be controlled by changing the stretching temperature and / or the draw ratio during the manufacturing process, etc.

[0484] (The porosity of the microporous membrane or the A layer)

[0485] The porosity of the microporous membrane or the A layer is preferably 20% or more, more preferably 25% or more, and further preferably 28% or more, 30% or more, 32% or more, or 35% or more. If the porosity is 20% or more, there is a tendency for the followability of the rapid movement of Li ions to be further improved. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and further preferably 60% or less. If the porosity is 90% or less, there is a tendency for the film strength to be further improved and the self-discharge to be further suppressed.

[0486] The porosity can be measured by the method described in the Examples section. In addition, it can be controlled by changing the stretching temperature and / or the stretching ratio during the manufacturing process.

[0487] (Air permeability of the microporous membrane or the A layer)

[0488] As the air permeability of the microporous membrane or the A layer, it is preferably 1 second / 100 cm 3 or more, more preferably 50 seconds / 100 cm 3 or more, and further preferably 55 seconds / 100 cm 3 or more, still more preferably 70 seconds or more, 90 seconds or more, or 110 seconds or more. If the air permeability is 1 second / 100 cm 3 or more, there is a tendency for the balance of the film thickness, porosity, and average pore diameter to be further improved. On the other hand, the air permeability is preferably 400 seconds / 100 cm 3 or less, more preferably 300 seconds or less / 100 cm 3 , and further preferably 270 seconds / 100 cm 3 or less. If the air permeability is 400 seconds / 100 cm 3 or less, there is a tendency for the ion permeability to be further improved.

[0489] The air permeability can be measured by the method described in the Examples section. In addition, it can be controlled by changing the stretching temperature and / or the stretching ratio during the manufacturing process.

[0490] (Puncture strength of the microporous membrane or the A layer)

[0491] The puncture strength of the microporous membrane or layer A is preferably 200 gf / 20 μm or more, more preferably 300 gf / 20 μm or more. If the puncture strength is 200 gf / 20 μm or more, even when the active material or the like falls off during winding of the laminate of the separator and the electrode, it is easy to suppress membrane breakage caused by the fallen active material or the like. In addition, it is easy to reduce the possibility of short circuit due to the expansion and contraction of the electrode accompanying charge and discharge. On the other hand, the puncture strength is preferably 4000 gf / 20 μm or less, more preferably 3800 gf / 20 μm or less. If the puncture strength is 3500 gf / 20 μm or less, it is easy to reduce thermal shrinkage during heating.

[0492] The puncture strength can be measured by the method described in the Examples section. In addition, it can be controlled by changing the stretching temperature and / or the stretching ratio during the manufacturing process.

[0493] [Tensile strength of the microporous membrane or layer A]

[0494] The tensile strength of the microporous membrane or layer A in both the MD (length direction, machine direction, or processing direction of the membrane or layer A) and TD (direction orthogonal to the MD, width direction of the membrane or layer A) directions is preferably 1000 kgf / cm 2 or more, more preferably 1050 kgf / cm 2 or more, and even more preferably 1100 kgf / cm 2 or more. By making the tensile strength 1000 kgf / cm 2 or more, there is a tendency to further suppress breakage during slitting or winding of the energy storage device, or to further suppress short circuits caused by foreign objects or the like inside the energy storage device. On the other hand, the tensile strength is preferably 5000 kgf / cm 2 or less, more preferably 4500 kgf / cm 2 or less, and even more preferably 4000 kgf / cm 2 or less. By making the tensile strength 5000 kgf / cm 2 or less, the microporous membrane or layer A relaxes early and the contraction force weakens during the heating test, resulting in a tendency to improve safety.

[0495] [Tensile elastic modulus of the microporous membrane or layer A]

[0496] The tensile modulus of the microporous membrane or the A layer is preferably 120 N / cm or less, more preferably 100 N / cm or less, and still more preferably 90 N / cm or less in both the MD and TD directions. A tensile modulus of 120 N / cm or less indicates that the separator for a lithium-ion secondary battery is not extremely oriented. In a heating test or the like, for example, when a blocking agent such as polyethylene melts and shrinks, stress relaxation of polyethylene or the like occurs at an early stage, whereby shrinkage of the separator in the battery is suppressed, and short circuit between electrodes can be easily prevented (that is, safety during heating of the separator can be improved). Such a low tensile modulus can be easily achieved by including polyethylene having a weight-average molecular weight of 500,000 or less in the polyolefin forming the microporous membrane or the A layer. On the other hand, the lower limit value of the tensile modulus is not particularly limited, preferably 10 N / cm or more, more preferably 30 N / cm or more, and still more preferably 50 N / cm or more. The tensile modulus can be appropriately adjusted by adjusting the degree of stretching in the manufacturing process or performing relaxation after stretching as needed.

[0497] <Polyolefin>

[0498] The polyolefin is not particularly limited. 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 can be mentioned. Among these, from the viewpoint of being able to perform heat setting (sometimes abbreviated as "HS") at a higher temperature without clogging pores, high-density polyethylene or low-density polyethylene is preferred, and high-density polyethylene is more preferred. It should be noted that one type of polyolefin can be used alone, or two or more types can be used in combination.

[0499] In addition, the separator preferably contains a polyolefin having a weight-average molecular weight (Mw) of less than 2,000,000, and more preferably contains a polyolefin having an Mw of less than 2,000,000 in a proportion of 40% by mass or more, still more preferably 80% by mass or more, relative to the total polyolefin. By using a polyolefin having an Mw of less than 2,000,000, there is a tendency for shrinkage relaxation of the polymer to occur at an early stage in a heating test or the like of the power storage device, and particularly for safety to be easily maintained in a heating safety test. It should be noted that when using a polyolefin having an Mw of less than 2,000,000 compared with using a polyolefin having an Mw of 1,000,000 or more, the elastic modulus in the thickness direction of the obtained microporous membrane tends to become smaller, and thus a microporous membrane that can more easily transfer the unevenness of the core can be obtained. The weight-average molecular weight of the polyolefin-based microporous membrane constituting the separator is preferably 100,000 or more and 2,000,000 or less, more preferably 150,000 or more and 1,500,000 or less.

[0500] (Polyolefin having one or more functional groups)

[0501] From the viewpoints of the formation of a crosslinked structure, oxidation-reduction degradation resistance, and a dense and uniform porous structure, the separator preferably includes a functional group-modified polyolefin or a polyolefin obtained by copolymerizing a monomer having a functional group, as a polyolefin having one or more kinds of functional groups. It should be noted that in this specification, the functional group-modified polyolefin refers to a substance obtained by connecting a functional group after manufacturing the polyolefin. The functional group may be connected to the polyolefin backbone or introduced into a comonomer, and preferably participates in the selective crosslinking of the amorphous part of the polyolefin. For example, it may be 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-like or cyclic heteroatom-containing hydrocarbon group, an amino group, a mercapto group, a metal chelate group, and a halogen-containing group.

[0502] From the viewpoints of the strength, ion permeability, oxidation-reduction degradation resistance, and a dense and uniform porous structure of the separator, the separator preferably contains both a polyolefin having one or more kinds of functional groups and silane-unmodified polyethylene. When a polyolefin having one or more kinds of functional groups and silane-unmodified polyethylene are used in combination, the mass ratio of the polyolefin having one or more kinds of functional groups to silane-unmodified polyethylene (mass of the polyolefin having one or more kinds of functional groups / mass of silane-unmodified polyethylene) in the separator is preferably 0.05 / 0.95 to 0.80 / 0.20.

[0503] (Crosslinked structure)

[0504] The crosslinked structure of the separator contributes to the balance between the closing function and high-temperature burst film resistance of the separator and the safety of the storage battery device, and is preferably formed in the amorphous part of the polyolefin contained in the separator. The crosslinked structure can be formed, for example, by a reaction using any of a covalent bond, a hydrogen bond, or a coordination bond. Among them, the reaction using a covalent bond is preferably at least one selected from the group consisting of the following reactions (I) to (IV):

[0505] (I) Condensation reaction of multiple identical functional groups

[0506] (II) Reaction between multiple different functional groups

[0507] (III) Chain condensation reaction of a functional group with an electrolyte

[0508] (IV) Chain condensation reaction of a functional group with an additive.

[0509] In addition, the reaction using a coordination bond is preferably the following reaction (V):

[0510] (V) Reaction in which multiple identical functional groups are crosslinked by coordination bonds with dissolved metal ions.

[0511] Reaction (I)

[0512] Denote the first functional group of the spacer as A. The following shows the schematic principle diagram and specific examples of Reaction (I).

[0513] Schematic Diagram of the Principle of Reaction (I)

[0514]

[0515] Examples of Functional Group A:

[0516] Silanol groups, etc.

[0517] Specific Examples of Reaction (I)

[0518]

[0519] {In the formula, R is an optionally substituted alkyl or heteroalkyl group having 1 to 20 carbon atoms.}

[0520] When the functional group A used for carrying out Reaction (I) is a silanol group, the polyolefin contained in the spacer is preferably subjected to silane graft modification. The silane-grafted modified polyolefin is composed of a polyolefin main chain having an alkoxysilyl group grafted on the main chain. It should be noted that examples of the alcoholate replaced by the aforementioned alkoxysilyl group include methoxide, ethoxide, butoxide, etc. For example, in the above formula, R can be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc. In addition, the main chain and the graft are connected by a covalent bond, and structures such as alkyl, ether, diol or ester can be cited. Considering the manufacturing process of the spacer of the present embodiment, in the stage before the crosslinking treatment process, the ratio of silicon to carbon (Si / C) in the silane-grafted modified polyolefin is preferably 0.2 to 1.8%, more preferably 0.5 to 1.7%.

[0521] The density of the preferred silane-grafted modified polyolefin is 0.90 - 0.96 g / cm 3and has a melt mass flow rate (MFR) of 0.2 to 5 g / minute at 190°C. From the perspective of suppressing the generation of resin condensates in the manufacturing process of the separator and maintaining the silane crosslinkability until contact with the electrolyte, the silane-grafted modified polyolefin is preferably not a masterbatch resin containing a dehydration condensation catalyst. The dehydration condensation catalyst is also known to function as a catalyst for the formation of siloxane bonds in resins containing alkoxysilyl groups. In this specification, a substance obtained by adding a dehydration condensation catalyst (such as an organometallic catalyst) to a resin containing alkoxysilyl groups or other kneaded resins in advance and mixing them in a continuous process of resin kneading using an extruder is called a masterbatch resin.

[0522] Reaction (II)

[0523] Denote the first functional group of the separator as A and the second functional group as B. The following shows the schematic diagram of the principle and specific examples of Reaction (II).

[0524] Schematic Diagram of the Principle of Reaction (II)

[0525]

[0526] Examples of Combinations of Functional Groups A and B:

[0527] Hydroxyl group and carboxyl group (esterification);

[0528] Carbonyl group and alkyl group (aldol condensation);

[0529] Halogen and carboxyl group (intramolecular condensation);

[0530] Alkoxy group and alkyl group (Claisen reaction);

[0531] Carbonyl group and acid anhydride group (Perkin reaction);

[0532] Amino group and halogen;

[0533] Isocyanate group and hydroxyl group (formation of urethane bond); and

[0534]

[0535] (Oxazoline) and hydroxyl group, etc.

[0536] Specific Example 1 of Reaction (II):

[0537]

[0538] Specific Example 2 of Reaction (II):

[0539]

[0540] Reaction (I) and reaction (II) can be subject to catalysis, for example, promoted by chemical substances inside the energy storage device assembled by the separator. The chemical substances can be, for example, any of the electrolyte, electrolyte solution, electrode active material, additive or their decomposition products contained in the energy storage device.

[0541] Reaction (III)

[0542] Denote the first functional group of the separator as A and the electrolyte solution as Sol. The following shows the schematic principle diagram and specific examples of reaction (III).

[0543] Schematic Diagram of the Principle of Reaction (III)

[0544]

[0545] Examples of Functional Group A:

[0546] Hydroxyl group, carboxyl group, amino group, carbonyl group, ether group, isocyanate group, etc.

[0547] Examples of Electrolytes:

[0548] Electrolyte: LiPF6, LiBF4, LiN(SO2CF3)2, LiSO3CF3, LiBC4O8 (LiBOB), etc.

[0549] Aprotic solvent: ethylene carbonate, ethyl methyl carbonate or their mixture, etc.

[0550] Specific Example 1 of Reaction (III):

[0551]

[0552] Specific Example 2 of Reaction (III):

[0553] Reaction (IV)

[0554] Denote the first functional group of the separator as A, the second functional group introduced according to requirements as B, and the additive as Add. The following shows the schematic principle diagram of reaction (IV).

[0555]

[0556] In terms of forming the covalent bond represented by the dashed line in the above schematic diagram, reaction (IV) is preferably a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between the compound Rx constituting the separator and the compound Ry constituting the additive (Add). The compound Rx may be a polyolefin contained in the separator, such as polyethylene or polypropylene, etc. Preferably, the polyolefin is modified by a functional group x, for example, by at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH.

[0557] Since multiple compounds Rx are crosslinked via the compound Ry as an additive, the compound Ry preferably has two or more linking reaction units y1. As long as the multiple linking reaction units y1 can undergo a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction with the functional group x of the compound Rx, they can be of any structure or group, can be substituted or unsubstituted, can contain heteroatoms or inorganic substances, and can be the same or different from each other. In addition, when the compound Ry has a chain structure, the multiple linking reaction units y1 can each independently be a terminal group, or introduced into the main chain, or be a side chain or side group.

[0558] In the case where reaction (IV) is a nucleophilic substitution reaction, merely as an example, the functional group x of the compound Rx is regarded as a nucleophilic group and the linking reaction unit y1 of the compound Ry is regarded as a leaving group for the following description. However, in this embodiment, both the functional group x and the linking reaction unit y1 can form a leaving group according to their nucleophilicity.

[0559] From the perspective of the nucleophile, the functional group x of the compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of the oxygen-based nucleophilic group include a hydroxyl group, an alkoxy group, an ether group, a carboxyl group, etc. Among them, -OH and -COOH are preferred. Examples of the nitrogen-based nucleophilic group include an ammonium group, a primary amino group, a secondary amino group, etc. Among them, -NH2 and -NH- are preferred. Examples of the sulfur-based nucleophilic group include -SH, a thioether group, etc. Preferably, it is -SH.

[0560] In the case where reaction (IV) is a nucleophilic substitution reaction, from the perspective of the leaving group, as the linking reaction unit y1 of compound Ry, it is preferably an alkylsulfonyl group such as CH3SO2-, CH3CH2SO2-; an arylsulfonyl group (-ArSO2-); a haloalkylsulfonyl group such as CF3SO2-, CCl3SO2-; an alkylsulfonate group such as CH3SO3-, CH3CH2SO3-; an arylsulfonate group (ArSO3-); a haloalkylsulfonate group such as CF3SO3-, CCl3SO3-; and a heterocyclic group, which can be used alone or in combination of multiple types. As the heteroatom contained in the heterocycle, nitrogen atom, oxygen atom, sulfur atom, etc. can be cited. Among them, from the perspective of leaving property, a nitrogen atom is preferred. As the leaving group containing a nitrogen atom in the heterocycle, a monovalent group represented by the following formula (y1-1) to (y1-6) is preferred:

[0561]

[0562] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0563]

[0564] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0565]

[0566] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0567]

[0568] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0569]

[0570] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0571]

[0572] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0573] In formulas (y1-1) to (y1-6), X is a hydrogen atom or a monovalent substituent. As the monovalent substituent, for example, an alkyl group, a haloalkyl group, an alkoxy group, a halogen atom, etc. can be cited.

[0574] When the reaction (IV) is a nucleophilic substitution reaction and the compound Ry has a chain structure, the compound Ry preferably further has at least one divalent group selected from the group consisting of the following formulas (y2-1) to (y2-6) as the chain unit y2 on the basis of the linking reaction unit y1:

[0575]

[0576] {In the formula, m is an integer from 0 to 20, and n is an integer from 1 to 20.}

[0577]

[0578] {In the formula, n is an integer from 1 to 20.}

[0579]

[0580] {In the formula, n is an integer from 1 to 20.}

[0581]

[0582] {In the formula, n is an integer from 1 to 20.}

[0583]

[0584] {In the formula, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer from 1 to 20.}

[0585]

[0586] {In the formula, X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and n is an integer from 1 to 20.}

[0587] In addition, when the compound Ry contains a plurality of chain units y2, they may be the same or different from each other, and their arrangement may be block or random.

[0588] In the formula (y2-1), m is an integer from 0 to 20, and from the perspective of the crosslinked network, it is preferably 1 to 18. In the formulas (y2-1) to (y2-6), n is an integer from 1 to 20, and from the perspective of the crosslinked network, it is preferably 2 to 19 or 3 to 16. In the formulas (y2-5) to (y2-6), X is an alkylene group having 1 to 20 carbon atoms or an arylene group, and from the perspective of the stability of the chain structure, it 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, a m-phenylene group or a p-phenylene group.

[0589] In the case where reaction (IV) is a nucleophilic substitution reaction, the preferred combinations of the functional group x of compound Rx with the linking reaction unit y1 and the chain-like unit y2 of compound Ry are shown in Tables 2 to 4 below.

[0590] [Table 2]

[0591] Nucleophilic substitution reaction (preferred combination I)

[0592]

[0593] [Table 3]

[0594] Nucleophilic substitution reaction (preferred combination II)

[0595] [Table 4]

[0596] Nucleophilic substitution reaction (preferred combination III)

[0597]

[0598] As a specific example 1 of the nucleophilic substitution reaction, the reaction principle diagram is shown below when the functional group x of the polyolefin is -NH2, the linking reaction unit y1 of the additive (compound Ry) is a skeleton derived from succinimide, and the chain-like unit y2 is -(O-C2H5) n - when.

[0599] Specific Example 1:

[0600] As a specific example 2 of the nucleophilic substitution reaction, the reaction principle diagram is shown below when the functional group x of the polyolefin is -SH and -NH2, the linking reaction unit y1 of the additive (compound Ry) is a nitrogen-containing cyclic skeleton, and the chain-like unit y2 is o-phenylene.

[0601] Specific Example 2:

[0602]

[0603] In the case where reaction (IV) is a nucleophilic addition reaction, the linking reaction unit y1 of the functional group x of compound Rx and compound Ry can undergo an addition reaction. In the nucleophilic addition reaction, the functional group x of compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of the oxygen-based nucleophilic group include a hydroxyl group, an alkoxy group, an ether group, a carboxyl group, etc., and -OH and -COOH are preferred among them. Examples of the nitrogen-based nucleophilic group include an ammonium group, a primary amino group, a secondary amino group, etc., and -NH2 and -NH- are preferred among them. Examples of the sulfur-based nucleophilic group include -SH, a thioether group, etc., and -SH is preferred.

[0604] In the nucleophilic addition reaction, from the viewpoints of addition reactivity or ease of obtaining raw materials, the linking reaction unit y1 of compound Ry is preferably at least one selected from the group consisting of the groups represented by the following formulas (Ay1-1) to (Ay1-6):

[0605]

[0606] {In the formula, R is a hydrogen atom or a monovalent organic group.}

[0607]

[0608]

[0609] In formula (Ay1-4), R is a hydrogen atom or a monovalent organic group, preferably a hydrogen atom, a C 1～20 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.

[0610] Regarding the case where reaction (IV) is a nucleophilic addition reaction, the preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 of compound Ry are shown in Tables 5 and 6 below.

[0611] [Table 5]

[0612] Nucleophilic addition reaction (preferred combination I)

[0613]

[0614] [Table 6]

[0615] Nucleophilic addition reaction (preferred combination II)

[0616] As a specific example of the nucleophilic addition reaction, the reaction schematic diagram is shown below when the functional group x of the spacer is -OH and the linking reaction unit y1 of the additive (compound Ry) is -NCO.

[0617] Specific example:

[0618]

[0619] In the case where reaction (IV) is a ring-opening reaction, the functional group x of compound Rx and the linking reaction unit y1 of compound Ry can undergo a ring-opening reaction. From the viewpoint of ease of obtaining raw materials, it is preferred that the ring structure on the linking reaction unit y1 side is opened. From the same viewpoint, the linking reaction unit y1 is more preferably an epoxy group, and compound Ry is further preferably a compound having at least two epoxy groups, and more preferably a diepoxide compound.

[0620] In the case where reaction (IV) is a ring-opening reaction, the functional group x of compound Rx is preferably at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH, and / or the linking reaction unit y1 of compound Ry is preferably at least two groups represented by the following formula (ROy1-1):

[0621]

[0622] {In the formula, each of a plurality of Xs is independently a hydrogen atom or a monovalent substituent.}.

[0623] In formula (ROy1-1), each of a plurality of Xs is independently a hydrogen atom or a monovalent substituent, preferably a hydrogen atom, C 1～20 alkyl, an alicyclic group, or an aromatic group, more preferably a hydrogen atom, methyl, ethyl, cyclohexyl, or phenyl. Regarding the epoxy ring-opening reaction, the preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 of compound Ry are shown in Table 7 below.

[0624] [Table 7]

[0625] Epoxy ring-opening reaction (preferred combinations)

[0626]

[0627] Reaction (V)

[0628] Denote the first functional group of the separator as A and the metal ion as M n+ , and the schematic diagram of the principle of reaction (V) and examples of the functional group A are shown below.

[0629] Schematic Diagram of the Principle of Reaction (V)

[0630] Examples of Functional Group A: -CHO, -COOH, acid anhydride group, -COO-, etc.

[0631] In the above schematic diagram, the metal ion M n+ is preferably a metal ion eluted from the power storage device (hereinafter also referred to as an eluted metal ion.), and can be, for example, at least one selected from the group consisting of Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ , and Li + . The following shows the coordination bond when the functional group A is -COO - .

[0632]

[0633] The following shows a specific schematic diagram of reaction (V) where the functional group A is -COOH and the eluted metal ion is Zn. 2+ when

[0634]

[0635] In the above schematic diagram, hydrofluoric acid (HF) can, for example, be derived from any of the electrolyte, electrolytic solution, electrode active material, additive, or their decomposition products or water-absorbing substances contained in the energy storage device according to the charge-discharge cycle of the energy storage device.

[0636] <Silane-modified polyolefin>

[0637] The silane-modified polyolefin has a structure in which the main chain is a polyolefin and an alkoxysilyl group is grafted onto the main chain. The silane-modified polyolefin can be obtained by grafting an alkoxysilyl group onto the main chain of a silane-unmodified polyolefin.

[0638] It is presumed that the alkoxysilyl group is converted into a silanol group through a hydrolysis reaction based on water, and a crosslinking reaction occurs to form a siloxane bond (see the following formula; the ratio of the T1 structure, T2 structure, and T3 structure is arbitrary). Examples of the alcoholate substituted with an alkoxysilyl group include: methoxide, ethoxide, butoxide, etc. In the following formula, examples of R include: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.

[0639]

[0640] The main chain and the graft are connected by a covalent bond. Examples of the structure forming this covalent bond include: alkyl, ether, diol, ester, etc. At the stage before the silane-modified polyolefin undergoes a crosslinking reaction, the modification amount of the silanol unit is 2% or less relative to the main chain ethylene unit.

[0641] The density of the preferred silane-grafted modified polyolefin is 0.90 - 0.96 g / cm 3 and the melt mass flow rate (MFR) at 190 °C is 0.2 - 5 g / minute.

[0642] From the perspective of fully exerting the effects brought by the present invention, the amount of the silane-modified polyolefin is preferably 0.5% by mass or more, or 3% by mass or more, more preferably 4% by mass or more, and further preferably 5% by mass or more, or 6% by mass or more, based on the total amount of the microporous membrane or the A layer. From the perspective of the cycle performance and safety of the energy storage device, the amount of the silane-modified polyolefin is preferably 40% by mass or less, more preferably 38% by mass or less, based on the total amount of the microporous membrane. In addition, the amount of the silane-modified polyolefin can be set to 30% by mass or more, or 50% by mass or more, based on the total amount of the A layer, and further can be set to 100% by mass.

[0643] The crosslinked structure in the microporous membrane or layer A is preferably formed by a compound generated within the power storage device.

[0644] That is, in the manufacturing process of the power storage device, when the separator is brought into contact with the non-aqueous electrolyte, a crosslinked structure having a siloxane oligomer bond formed by the swelling of the microporous membrane or layer A and / or a compound generated within the power storage device is also preferably the crosslinked structure in the microporous membrane or layer A. The crosslinked structure at this time is a crosslinked structure obtained by not actively promoting the crosslinking reaction in the manufacturing process of the separator but actively promoting the crosslinking reaction in the manufacturing process of the power storage device, and thus the self-crosslinkability of the separator can be maintained until it is accommodated in the power storage device.

[0645] From the perspective of suppressing the generation of resin condensates in the manufacturing process of the separator and maintaining the silane crosslinkability until contact with the electrolyte, the silane-modified polyolefin is preferably not a masterbatch resin containing a dehydration condensation catalyst. The dehydration condensation catalyst is also known to function as a catalyst for the siloxane bond formation reaction of a resin containing an alkoxysilyl group. In this specification, a substance obtained by previously adding a dehydration condensation catalyst (such as an organometallic catalyst) to a resin containing an alkoxysilyl group or other kneaded resins and mixing them in a continuous process having a resin kneading step using an extruder is referred to as a masterbatch resin.

[0646] (Polyethylene)

[0647] In this specification, the polyethylene that can be further contained on the basis of the silane-modified polyolefin (the polyethylene further contained as a polyolefin different from the silane-modified polyolefin in the microporous membrane or layer A) refers to polyethylene as a homopolymer polyethylene polymer having a weight average molecular weight of 100,000 or more and 10,000,000 or less, or a copolymer polyethylene polymer containing alkane units.

[0648] When the microporous membrane or layer A further contains polyethylene as a polyolefin different from the silane-modified polyolefin, its content 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 polyethylene. If the content of polyethylene is 20% by mass or more, there is a tendency to easily ensure the deterioration resistance against redox and also ensure a dense and uniform porous structure.

[0649] On the other hand, the content of 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 polyethylene is 97% by mass or less, the content of the silane-modified polyolefin in the microporous membrane or layer A can be ensured.

[0650] (Method for Detecting Silane-Modified Polyolefin Contained in Separator)

[0651] When the silane-modified polyolefin contained in the separator is in a crosslinked state, it is insoluble or has insufficient solubility in organic solvents. Therefore, 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, methyl orthoformate that does not cause side reactions is used to decompose the siloxane bond into methoxysilanol, and then solution NMR measurement is performed. Thus, the silane-modified polyolefin contained in the separator can be detected. The pretreatment experiment can be carried out with reference to Japanese Patent No. 3529854 and Japanese Patent No. 3529858.

[0652] Specifically, the method for detecting the silane-modified polyolefin contained in the separator can effectively utilize the 1 H or 13 NMR identification of C of the silane-modified polyolefin used as a raw material in the manufacture of the separator. The following is an example of the measurement method of 1 H and 13 C NMR.

[0653] ( 1 H NMR Measurement)

[0654] Dissolve the sample in ortho-dichlorobenzene-d4 at 140 °C to obtain an 1 H-NMR spectrum with a proton resonance frequency of 600 MHz. 1 The measurement conditions of 1H-NMR are as follows.

[0655] Apparatus: AVANCE NEO 600 manufactured by Bruker

[0656] Sample tube diameter: 5 mmφ

[0657] Solvent: ortho-dichlorobenzene-d4

[0658] Measurement temperature: 130 °C

[0659] Pulse angle: 30°

[0660] Pulse waiting time: 1 sec

[0661] Number of accumulations: 1000 times or more

[0662] Sample concentration: 1 wt / vol%

[0663] ( 13 C NMR Measurement)

[0664] Dissolve the sample in ortho-dichlorobenzene-d4 at 140 °C to obtain an 13 C-NMR spectrum. 13The measurement conditions of ¹³C-NMR are described as follows.

[0665] Apparatus: AVANCE NEO 600 manufactured by Bruker

[0666] Sample tube diameter: 5 mm φ

[0667] Solvent: o-dichlorobenzene-d4

[0668] Measurement temperature: 130 °C

[0669] Pulse angle: 30°

[0670] Pulse waiting time: 5 sec

[0671] Number of accumulations: 10,000 times or more

[0672] Sample concentration: 10 wt / vol%

[0673] Figure 11 and 12 are ¹H and ¹³C-NMR spectra of silane-modified polyolefin raw materials 1 and 2 using two types of polyolefins, and the melt index (MI), C3 grafting amount, C4 grafting amount, and / or silanol modification amount of raw materials 1 and 2 are different. 1 ¹H and 13 ¹³C-NMR measurement conditions are as follows.

[0674] Figure 11 of 1 ¹H and 13 ¹³C-NMR measurement conditions are as follows.

[0675] ( 1 ¹H-NMR measurement conditions)

[0676] Apparatus: Bruker Avance NEO 600

[0677] Observed nucleus: 1 ¹H

[0678] Observed frequency: 600 MHz

[0679] Pulse program: zg30

[0680] Pulse waiting time: 1 sec

[0681] Number of accumulations: 1024 times

[0682] Measurement temperature: 130 °C

[0683] Chemical shift reference: 7.219 ppm (o-DCBz)

[0684] Solvent: o-dichlorobenzene-d4

[0685] Sample concentration: 1 wt / vol%

[0686] Sample tube: 5 mm φ

[0687] ( 13 C-NMR measurement conditions)

[0688] Instrument: Bruker Avance NEO 600

[0689] Observed nucleus: 13 C

[0690] Observation frequency: 150.91 MHz

[0691] Pulse program: zgpg30

[0692] Pulse waiting time: 5 sec

[0693] Number of accumulations: 24,000 times or 12,800 times

[0694] Measurement temperature: 130 °C

[0695] Chemical shift reference: 132.39 ppm (o-DCBz)

[0696] Solvent: o-dichlorobenzene-d4

[0697] Sample concentration: 10 wt / vol%

[0698] Sample tube: 5 mm φ

[0699] Figure 12 of 1 H and 13 The C-NMR measurement conditions are as follows.

[0700] ( 1 H-NMR measurement conditions)

[0701] Instrument: Bruker Avance NEO 600

[0702] Observed nucleus: 1 H

[0703] Observation frequency: 600 MHz

[0704] Pulse program: zg30

[0705] Pulse waiting time: 1 sec

[0706] Number of accumulations: 1024 times

[0707] Measurement temperature: 130 °C

[0708] Chemical shift reference: 7.219 ppm (o-DCBz)

[0709] Solvent: o - dichlorobenzene - d4

[0710] Sample concentration: 1 wt / vol%

[0711] Sample tube: 5 mm φ

[0712] ( 13 C - NMR measurement conditions)

[0713] Instrument: Bruker Avance NEO 600

[0714] Observed nucleus: 13 C

[0715] Observation frequency: 150.91 MHz

[0716] Pulse program: zgpg30

[0717] Pulse waiting time: 5 sec

[0718] Number of accumulations: 12,800 times

[0719] Measurement temperature: 130 °C

[0720] Chemical shift reference: 132.39 ppm (o - DCBz)

[0721] Solvent: o - dichlorobenzene - d4

[0722] Sample concentration: 10 wt / vol%

[0723] Sample tube: 5 mm φ

[0724] Figure 13 It is the state before cross - linking of the separator made of the silane - modified polyolefin raw material 1 used in Example I - 1 described below Figure 11 shown 1 H and 13 C - NMR spectrogram. Figure 13 of 1 H and 13 The C - NMR measurement conditions are as follows.

[0725] ( 1 H - NMR measurement conditions)

[0726] Instrument: Bruker Avance NEO 600

[0727] Observed nucleus: 1 H

[0728] Observation frequency: 600 MHz

[0729] Pulse program: zg30

[0730] Pulse waiting time: 1 sec

[0731] Number of accumulations: 1024 times

[0732] Measured temperature: 130 °C

[0733] Chemical shift reference: 7.219 ppm (o-DCBz)

[0734] Solvent: o-dichlorobenzene-d4

[0735] Sample concentration: 1 wt / vol%

[0736] Sample tube: 5 mm φ

[0737] ( 13 C-NMR measurement conditions)

[0738] Apparatus: Bruker Avance NEO 600

[0739] Observed nucleus: 13 C

[0740] Observation frequency: 150.91 MHz

[0741] Pulse program: zgpg30

[0742] Pulse waiting time: 5 sec

[0743] Number of accumulations: 24000 times or 12800 times

[0744] Measured temperature: 130 °C

[0745] Chemical shift reference: 132.39 ppm (o-DCBz)

[0746] Solvent: o-dichlorobenzene-d4

[0747] Sample concentration: 10 wt / vol%

[0748] Sample tube: 5 mm φ

[0749] In addition, for the crosslinked separator, after the pretreatment described above, it can be measured by the same NMR as (not shown). Figure 13 the same

[0750] As Figures 11 to 13 shown, by 1 H and / or 13 C NMR measurement, in the polyolefin raw material, the modification amount of the silane unit in the silane-modified polyolefin, the alkyl modification amount of the polyolefin, etc. can be confirmed, and in the separator, the presence of the silane-modified polyolefin (-CH2 -Si: 1 H, 0.69 ppm, t; 13 C, 6.11 ppm, s).

[0751] [Combination of microporous membrane and inorganic porous layer]

[0752] The combination of a microporous membrane containing a silane-modified polyolefin and an inorganic porous layer has a tendency to balance the shut-off function at temperatures lower than 150 °C and the film-breaking property at higher temperatures, and to improve the cycle characteristics and the battery nail penetration safety of the electric storage device. It is speculated that since the silane-modified polyolefin in the microporous membrane is silane crosslinkable, if silane crosslinking occurs, the viscosity of the resin in the microporous membrane sometimes increases. Therefore, when a compressive force is applied between multiple electrodes at an abnormally high temperature in an electric storage device including a separator, the crosslinked high-viscosity resin hardly flows into the inorganic layer (i.e., it is difficult to integrate), the gap between the electrodes can be sufficiently ensured, and battery short-circuiting can be suppressed.

[0753] [Inorganic porous layer]

[0754] The inorganic porous layer is a layer containing inorganic particles and a resin binder, and may further contain a dispersant for dispersing the inorganic particles in the binder resin, as desired.

[0755] From the viewpoints of the ion permeability of the separator and the charge-discharge capacity or cycle stability of the electric storage device, 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. The thickness of the inorganic porous layer can be determined by the method described in the examples.

[0756] [Second porous layer (layer B)]

[0757] Layer B contains inorganic particles. Layer B may further contain a resin binder. When layer B contains inorganic particles and a resin binder, layer B may be the inorganic porous layer described above. It should be noted that layer B may contain components other than inorganic particles and a resin binder.

[0758] (Thickness of layer B)

[0759] The thickness (TB) of the B layer is preferably 0.2 μm or more, more preferably 0.5 μm or more. If the thickness (TB) is 0.5 μm or more, there is a tendency for the mechanical strength to be further improved. On the other hand, the thickness (TB) is preferably less than 22 μm, more preferably 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 for it to be advantageous in terms of increasing the capacity of the power storage device. In addition, it is also preferable from the perspective of preventing the air permeability of the separator from rising excessively. It should be noted that the thickness (TB) can be set, for example, to 0.50 μm or more, 0.80 μm or more, or 1.00 μm or more, and in addition, it can be set to less than 22.00 μm, 20.00 μm or less, or 15.00 μm or less.

[0760] The thickness (TB) can be measured by the method described in the Examples column, and in addition, it can be controlled by changing the coating amount of the coating liquid (slurry) used to form the B layer.

[0761] 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 multi-layer, the total thickness of the multi-layer B layer is regarded as the above-mentioned "thickness (TB)".

[0762] In addition, in the case where the B layer is disposed on both sides, i.e., one side and the other side of the A layer, the total thickness of the B layer disposed on this one side and the B layer disposed on the other side is regarded as the above-mentioned "thickness (TB)".

[0763] (Inorganic particles)

[0764] Examples of the inorganic particles include: inorganic oxides (oxide-based ceramics) such as alumina (Al2O3), silica, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; inorganic nitrides (nitride-based ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxyhydroxide (AlO(OH)), potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and quartz sand; and glass fiber. These can be used alone or in combination of two or more.

[0765] 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.

[0766] It should be noted that the amount of the inorganic particles can be set, for example, 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. On the other hand, it can be set to 99.90% by mass or less, or 99.50% by mass or less.

[0767] Examples of the shape of the inorganic particles include: flake shape, scale shape, needle shape, column shape, spherical shape, polyhedron shape, spindle shape, and block shape. A variety of inorganic particles having these shapes can be used in combination.

[0768] The number-average particle diameter 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 diameter 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 further preferably 1.5 μm or less. From the viewpoint of improving the safety during short circuit, it is preferable to adjust the number-average particle diameter of the inorganic particles to the above range. As a method for adjusting the number-average particle diameter of the inorganic particles, there can be mentioned a method of pulverizing the inorganic particles using an appropriate pulverizing device such as a ball mill, a bead mill, or a jet mill.

[0769] Regarding the particle size distribution of the inorganic particles, the minimum particle diameter is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle diameter is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 7 μm or less. In addition, the ratio of the maximum particle diameter to the average particle diameter is preferably 50 or less, more preferably 30 or less, and further preferably 20 or less. From the viewpoint of suppressing thermal shrinkage at high temperatures, it is preferable to adjust the particle size distribution of the inorganic particles to the above range. In addition, there may be multiple particle diameter peaks between the maximum particle diameter and the minimum particle diameter. It should be noted that, as a method for adjusting the particle size distribution of the inorganic particles, for example, there can be mentioned: a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill, etc. and adjusting it to a desired particle size distribution, a method of mixing a plurality of fillers having a plurality of particle size distributions after preparation, etc.

[0770] (Resin binder)

[0771] The resin binder contains a resin that bonds inorganic particles together. From the perspective of ensuring the adhesion between inorganic particles and the stability of the inorganic porous layer or the B layer during the manufacturing process of the separator, the manufacturing process of the energy storage device, or the charge and discharge process, the glass transition temperature (Tg) of the resin binder is preferably -50°C to 100°C, more preferably -35°C to 95°C.

[0772] The glass transition temperature is determined based on the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of the straight line obtained by extending the baseline on the low-temperature side of the DSC curve to the high-temperature side and the tangent line at the inflection point of the stepped change portion of the glass transition can be used as the glass transition temperature. More specifically, it can be determined according to the method described in the examples. In addition, "glass transition" means that in DSC, a heat change accompanied by a change in the state of the polymer as the test piece occurs on the endothermic side. This heat change is observed as a stepped change shape in the DSC curve. "Stepped change" refers to the portion of the DSC curve from when the curve departs from the previous low-temperature baseline until it moves to the new high-temperature baseline. It should be noted that the combination of stepped changes and peaks is also included in the stepped changes. Furthermore, "inflection point" refers to the point where the slope of the DSC curve of the stepped change portion reaches the maximum. In addition, in the stepped change portion, when the upper side is the exothermic side, it can also be expressed as the point where the upward convex curve changes to the downward convex curve. "Peak" refers to the portion of the DSC curve from when the curve departs from the low-temperature baseline until it returns to the same baseline again. "Baseline" refers to the DSC curve in the temperature region where no transition and reaction occur in the test piece.

[0773] Examples of the resin binder include the following 1) to 7). These can be used alone or in combination of two or more.

[0774] 1) Polyolefins: such as polyethylene, polypropylene, ethylene-propylene rubber, and their modified products;

[0775] 2) Conjugated diene polymers: such as styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene-styrene copolymers and their hydrogenated products;

[0776] 3) Acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;

[0777] 4) Polyvinyl alcohol resins: such as polyvinyl alcohol and polyvinyl acetate;

[0778] 5) Fluorine-containing resins: such as PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer;

[0779] 6) Cellulose derivatives: such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and

[0780] 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: such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0781] These types of resin binders can be obtained by using a desired monomer as a raw material according to known production methods such as emulsion polymerization or solution polymerization. In the polymerization, the polymerization temperature, the pressure during polymerization, the monomer addition method, and the additives used (polymerization initiators, molecular weight regulators, pH regulators, etc.) are not limited.

[0782] The amount of the resin binder is, based on the total amount of the inorganic porous layer or the B layer, for example, 0.5% by mass or more, or 1.0% by mass or more. On the other hand, it is, for example, 50% by mass or less, or 30% by mass or less. In addition, as described above, with respect to the B layer, the resin binder is an optional component. Therefore, the amount of the resin binder contained in the B layer, based on the total amount of the B layer, can be set to less than 20% by mass, 15% by mass or less, or 0% by mass. If the amount of the resin binder contained in the B layer decreases, the room for containing the above inorganic particles in the B layer can be increased accordingly.

[0783] (Dispersant)

[0784] The dispersant is a substance that adsorbs on the surface of inorganic particles in the slurry used to form the inorganic porous layer or the B layer and stabilizes the inorganic particles by electrostatic repulsion or the like. For example, it can be polycarboxylate, sulfonate, polyoxyether, surfactant, etc. In the inorganic porous layer or the B layer, in addition to the above components, within the range of their effects, other components that are usually added and blended in aqueous paints or the like can be further contained. As such other components, there is no particular limitation, and examples include: thickeners, film-forming aids, plasticizers, crosslinking agents, antifreezing agents, defoaming agents, dyes, preservatives, ultraviolet absorbers, light stabilizers, etc. These other components can be used alone, or two or more of them can be used in combination.

[0785] (Additives)

[0786] The microporous membrane, inorganic porous layer, layer A and / or layer B may contain known additives as required. Examples of the additives include organometallic catalysts (dehydration condensation catalysts); plasticizers; antioxidants such as phenols, phosphorus compounds, and sulfur compounds; metal soaps such as calcium stearate and zinc stearate; thickeners; film-forming aids; crosslinking agents; antifreeze agents; defoaming agents; preservatives; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; dyes; and coloring pigments.

[0787] In addition, layer B may contain a crosslinking agent. The crosslinking agent may contain a functional group reactive with the above inorganic particles.

[0788] <Physical properties of the separator>

[0789] When the separator is used in a lithium ion secondary battery with a higher capacity, the overall film thickness of the separator is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, still more 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 for the ion permeability to be further improved. The lower limit value of the overall film thickness of the separator may 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.

[0790] The air permeability of the separator is preferably 50 seconds / 100 cm 3 to 400 seconds / 100 cm 3 , more preferably 75 seconds / 100 cm 3 to 275 seconds / 100 cm 3 , still more preferably 100 seconds / 100 cm 3 to 200 seconds / 100 cm 3 . If the separator has an air permeability of 50 seconds / 100 cm 3 or more, it has appropriate mechanical strength. If the air permeability is 400 seconds / 100 cm 3 or less, the battery characteristics are improved from the perspective of permeability, and thus it is preferred.

[0791] [Battery assembly kit]

[0792] Another aspect of the present invention provides a battery assembly kit including the separator for a battery device described above. The battery assembly kit includes the following two elements:

[0793] (A) A housing that houses a laminate or a wound body of electrodes and the separator for a battery device of each of the above-described embodiments; and

[0794] (B) A container that houses a non-aqueous electrolyte.

[0795] When using the assembled battery device kit, by bringing the separator in element (A) into contact with the non-aqueous electrolyte in element (B), bringing the electrolyte into contact with the laminate or wound body in the outer casing, and / or by continuously performing charge and discharge cycles of the assembled battery device, a crosslinked structure is formed within the separator, and a battery device that balances safety and output can be formed.

[0796] Although not wishing to be bound by theory, it is considered that when the electrolyte or non-aqueous electrolyte comes into contact with the electrode and / or when the battery device is charged and discharged, substances that catalyze the crosslinking reaction or substances having functional groups that form part of the crosslinked structure are present in the electrolyte, on the inner surface of the outer casing, or on the electrode surface. They dissolve into the electrolyte and uniformly swell and diffuse into the amorphous portion of the polyolefin, thereby uniformly promoting the crosslinking reaction of the laminate or wound body containing the separator. The substance that catalyzes the crosslinking reaction can be in the form of an acid solution or a film. In the case where the electrolyte contains lithium hexafluorophosphate (LiPF6), it can be hydrogen fluoride (HF) or a fluorine-containing organic compound derived from hydrogen fluoride (HF). Substances having functional groups that form part of the crosslinked structure can be, for example, compounds having functional groups A and / or B as described above, the electrolyte itself, various additives, etc.

[0797] Regarding the non-aqueous electrolyte accommodated in element (2), from the perspective of promoting the crosslinking reaction of the separator, the electrolyte can be a fluorine (F)-containing lithium salt such as LiPF6 that generates HF, an electrolyte having a lone pair of electrons such as LiN(SO2CF3)2, LiSO3CF3, etc., or can also be LiBF4, LiBC4O8 (LiBOB), etc.

[0798] Regarding the assembled battery device kit, from the perspective of promoting the crosslinking reaction of the separator, it can be equipped with an accessory (or element (C)) such as another container that accommodates a catalyst for promoting the crosslinking reaction, for example, a mixture containing an organometallic catalyst and water, an acid solution, an alkali solution, etc.

[0799] [Battery device]

[0800] The separator described above can be used in a battery device. The battery device includes a positive electrode, a negative electrode, the separator of the present embodiment disposed between the positive and negative electrodes, an electrolyte, and optionally additives. Once the separator is accommodated in the device outer casing, the functional group-modified polyethylene or functional group-grafted copolymerized polyethylene reacts with the chemical substances contained in the electrolyte or additives, thereby forming a crosslinked structure. Therefore, there is a crosslinked structure in the manufactured battery device. The functional group-modified polyethylene or functional group-grafted copolymerized polyethylene is not limited and can be derived from the polyolefin raw material of the microporous membrane or from the polyolefin modified in the manufacturing process of the microporous membrane.

[0801] Examples of the power storage device include: lithium batteries, lithium secondary batteries, lithium-ion secondary batteries, sodium secondary batteries, sodium-ion secondary batteries, magnesium secondary batteries, magnesium-ion secondary batteries, calcium secondary batteries, calcium-ion secondary batteries, aluminum secondary batteries, aluminum-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, electric double layer capacitors, lithium-ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, zinc-air batteries, etc. Among these, from the perspective of practicality, lithium batteries, lithium secondary batteries, lithium-ion secondary batteries, nickel-metal hydride batteries, or lithium-ion capacitors are preferred, and lithium batteries or lithium-ion secondary batteries are more preferred.

[0802] Additives can be, for example, dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, coloring pigments, etc.

[0803] [Lithium-ion secondary battery]

[0804] The lithium-ion secondary battery is a storage battery as follows: lithium transition metal oxides such as lithium cobaltate and lithium cobalt composite oxides are used as the positive electrode, carbon materials such as graphite and plumbago are used as the negative electrode, and an organic solvent containing a lithium salt such as LiPF6 is used as the electrolyte. Regarding the power storage device assembly kit, the electrolyte described above can also be used for the lithium-ion secondary battery.

[0805] During charging / discharging of the lithium-ion secondary battery, ionized lithium reciprocates between the electrodes. In addition, while suppressing the contact between the electrodes, it is necessary to move the ionized lithium between the electrodes at a relatively high speed. Therefore, a separator is disposed between the electrodes.

[0806] [Manufacturing method of separator for power storage device]

[0807] Another aspect of the present invention is a manufacturing method of a separator for a power storage device. The manufacturing method of the separator may include, for example, a manufacturing process of a microporous membrane or an A layer, and an optional manufacturing process of an inorganic porous layer on the microporous membrane or a B layer on the A layer. The materials used in the manufacturing method of the separator can be the materials described in the first to tenth embodiments without special description.

[0808] [Eleventh Embodiment]

[0809] As the manufacturing method of the separator of the eleventh embodiment, the case of a microporous membrane (flat film) will be described below, but it is not intended to exclude forms other than the flat film. The manufacturing method of the microporous membrane of the eleventh embodiment includes the following steps:

[0810] (1) Sheet forming step;

[0811] (2) Stretching step;

[0812] (3) Porous body forming step; and

[0813] (4) Heat treatment step.

[0814] By performing steps (1) to (4), the A layer described above can also be formed.

[0815] The manufacturing method of the separator of the eleventh embodiment may further include the following steps based on steps (1) to (4) as desired:

[0816] (8B) Coating step, forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinking precursor;

[0817] (9) Assembly step, accommodating an electrode, a laminate or a wound body thereof of the silane crosslinking precursor, and a non-aqueous electrolyte in a housing, and bringing the silane crosslinking precursor into contact with the non-aqueous electrolyte.

[0818] In the eleventh embodiment, after coating the inorganic porous layer on the microporous membrane maintaining silane crosslinkability in step (8B), in step (9), the separator in the power storage device is brought into contact with the electrolyte, so that the stress tolerance of the power storage device and the separator therein is improved, and further the cycle stability and safety of the power storage device can be achieved.

[0819] The manufacturing method of the microporous membrane of the eleventh embodiment may include, as desired, a kneading step before the sheet forming step (1) and / or a winding / slitting step after the heat treatment step (3). From the perspective of maintaining silane crosslinkability until contact with the electrolyte, it is preferably not to include a silane crosslinking treatment step. The silane crosslinking treatment step is generally a step of forming a low oligomeric siloxane bond by subjecting an object to be treated containing a silane-modified polyolefin to contact a mixture containing an organometallic catalyst and water, or impregnating it in an alkali solution or an acid solution to perform a silane dehydration condensation reaction.

[0820] The metal containing the organometallic catalyst may be, for example, at least one selected from the group consisting of scandium, titanium, vanadium, copper, zinc, aluminum, zirconium, palladium, gallium, tin, and lead. Regarding the organometallic catalyst, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctanoate, etc. can be cited. 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.). In addition, in recent years, in order to avoid the environmental and human health hazards caused by organotin, it is known that by utilizing the Lewis function of a chelate complex of copper and / or titanium and combining it with an organic base, the reaction of forming a siloxane bond between alkoxysilyl groups can be promoted in the same manner as an organotin complex.

[0821] The pH of the alkaline solution exceeds 7 and may include, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, amine compounds, etc. Among these, from the viewpoints of the safety of the power storage device and the silane crosslinkability, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is further preferred.

[0822] The pH of the acidic solution is less than 7 and may include, for example, inorganic acids, organic acids, etc. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids or phosphoric acids.

[0823] In the kneading step, a kneader is used. In the present embodiment, a silane-modified polyolefin, a plasticizer or an inorganic material as desired, and other polyolefins can be kneaded. From the viewpoints of suppressing the generation of resin aggregates in the manufacturing process and maintaining the silane crosslinkability until contact with the electrolyte, it is preferred not to add a masterbatch resin containing a dehydration condensation catalyst to the kneaded product.

[0824] The plasticizer is not particularly limited. For example, organic compounds that can form a homogeneous solution with polyolefins at temperatures below the boiling point can be cited. More specifically, examples include: decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, paraffin oil, etc. Among these, paraffin oil and dioctyl phthalate are preferred. The plasticizer can be used alone or in combination of two or more. The proportion of the plasticizer is not particularly limited. From the viewpoint of the porosity of the obtained microporous membrane, the polyolefin and the silane-modified polyolefin are preferably 20% by mass or more based on the total mass as needed. From the viewpoint of the viscosity during melt kneading, it is preferably 90% by mass or less.

[0825] The sheet forming step is a step of extruding the obtained kneaded product, or a mixture of a silane-grafted modified polyolefin, polyethylene and a plasticizer, cooling and solidifying it, and molding it into a sheet to obtain a sheet. The method of sheet forming is not particularly limited. For example, a method of solidifying a melt kneaded and extruded product by compression cooling can be cited. As the cooling method, examples include: a method of directly contacting a cooling medium such as cold air or cooling water; a method of contacting a roll and / or a press cooled by a refrigerant, etc. The method of contacting a roll and / or a press cooled by a refrigerant is preferred in terms of excellent film thickness controllability.

[0826] From the viewpoints of resin aggregates in the separator or the maximum internal heat generation rate, in the sheet forming step, the mass ratio of the silane-modified polyolefin to polyethylene (mass of the silane-modified polyolefin / mass of polyethylene) is preferably 0.05 / 0.95 to 0.4 / 0.6, more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0827] From the perspective of simultaneously suppressing thermal runaway during the destruction of the power storage device and improving safety while having low-temperature shut-off properties below 150°C and burst film resistance at high temperatures of 180 to 220°C, it is preferable in the sheet forming process that the silane-modified polyolefin does not contain a masterbatch resin containing a dehydration condensation catalyst for crosslinking the silane-modified polyolefin before the sheet forming process.

[0828] The stretching process is a process of extracting a plasticizer and / or an inorganic material from the obtained sheet as needed and further stretching the sheet in a direction of one axis or more. As a method for stretching the sheet, examples include: MD uniaxial stretching based on a roll stretcher, TD uniaxial stretching based on a tenter, successive biaxial stretching based on a combination of a roll stretcher and a tenter or a combination of two tenters, simultaneous biaxial stretching based on a simultaneous biaxial tenter or blow molding, etc. From the perspective of obtaining a more uniform film, simultaneous biaxial stretching is preferable. In terms of the uniformity of the film thickness, the balance between the stretching elongation rate, porosity, and average pore diameter, the total surface magnification is preferably 8 times or more, more preferably 15 times or more, and further preferably 20 times or more or 30 times or more. By making the total surface magnification 8 times or more, there is a tendency to easily obtain a sheet with high strength and a good thickness distribution. In addition, from the perspective of preventing breakage, etc., the surface magnification can be 250 times or less.

[0829] The porous body forming process is a process of extracting a plasticizer from the stretched product after the stretching process and making the stretched product porous. As a method for extracting the plasticizer, there is no particular limitation, and examples include: a method of immersing the stretched product in an extraction solvent, a method of spraying the extraction solvent onto the stretched product, etc. As the extraction solvent, there is no particular limitation, and for example, a solvent that is a poor solvent for polyolefin and a good solvent for the plasticizer and / or inorganic material and has a boiling point lower than the melting point of polyolefin is preferable. As such an extraction solvent, there is no particular limitation, and examples include: hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropanol; ketones such as acetone and 2-butanone; alkaline water, etc. The extraction solvent can be used alone as 1 type or in combination of 2 types or more.

[0830] The heat treatment process is a process of further extracting a plasticizer from the sheet as needed after the stretching process and further performing heat treatment to obtain a microporous membrane. As the heat treatment method, there is no particular limitation, and examples thereof include heat setting methods such as stretching and relaxation operations using a tenter and / or a roller stretching machine. The relaxation operation refers to a shrinking operation performed at a specified temperature and relaxation rate in the machine direction (MD) and / or the width direction (TD) of the membrane. The relaxation rate is 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 of the membrane after the relaxation operation by the TD size of the membrane before the operation, or in the case of performing relaxation in both MD and TD, it is a value obtained by multiplying the relaxation rate of MD by the relaxation rate of TD.

[0831] [Coating process of inorganic porous layer]

[0832] The coating process (8B) of the inorganic porous layer is a process 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 process (8B) can be performed while maintaining the silane crosslinkability of the silane-modified polyolefin.

[0833] The B layer described above can also be formed by performing the coating process (8B). As a method for forming the B layer, known manufacturing methods can be adopted. As a method for producing a laminate including the A layer and the B layer, for example, there can be mentioned: a method of coating a slurry containing inorganic particles on the A layer, a method of co-extruding the raw material of the B layer and the raw material of the A layer by a co-extrusion method, a method of laminating and bonding them after separately producing the A layer and the B layer, etc.

[0834] The inorganic porous layer can be formed, for example, by coating a slurry containing inorganic particles, a resin binder, water or an aqueous solvent (such as a mixture of water and alcohol, etc.) and, if desired, a dispersant on 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.

[0835] As the solvent contained in the slurry, a solvent that can uniformly and stably disperse or dissolve the inorganic particles is preferably used. As such a solvent, for example, there can be mentioned: N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, dichloromethane and hexane.

[0836] As a method for preparing the slurry containing inorganic particles, for example, there can be mentioned mechanical stirring methods based on a ball mill, a bead mill, a planetary ball mill, a vibratory ball mill, a sand mill, a colloid mill, a grinder, a roller mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, a stirring blade, etc.

[0837] As a coating method for a slurry containing inorganic particles, examples include: gravure coater method, small-diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air knife coater method, blade coater method, rod coater method, extrusion coater method, casting coater method, die coater method, screen printing method, spray coating method, etc.

[0838] Regarding the method for removing the solvent from the coated film, examples include: a method of drying at a temperature below the melting point of the material constituting the microporous membrane, a method of drying under reduced pressure at a low temperature, etc. In addition, if it is within a range that does not significantly affect the device characteristics, a part of the solvent can be left behind.

[0839] [Winding / Slitting Process]

[0840] The winding process is a process of slitting the obtained microporous membrane or the microporous membrane coated with an inorganic porous layer as needed and winding it around a specified core.

[0841] [Battery Assembly Process]

[0842] The battery assembly process is a process as follows: 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 winding the laminate to form a wound body as desired, accommodating the laminate or the wound body and a non-aqueous electrolyte in an outer casing, and bringing the silane crosslinking precursor into contact with the non-aqueous electrolyte. Through the battery assembly process, it is possible to suppress the film weight reduction of the microporous membrane, maintain the morphology, suppress the penetration of the polyolefin resin from the microporous membrane into the inorganic porous layer, and further improve the stress tolerance of the battery or the separator.

[0843] In the battery assembly process (9) or after the process (9), the silane-modified polyolefin is crosslinked. Therefore, it is possible to be suitable for the existing manufacturing process of the battery while initiating the silane crosslinking reaction of the separator after the battery is manufactured, thereby improving the safety of the battery.

[0844] In the battery assembly process, from the perspective of the processability of the electrolyte, it is preferable to inject the non-aqueous electrolyte into the outer casing after accommodating the laminate or the wound body in the outer casing, or to accommodate the laminate or the wound body in the outer casing after injecting the electrolyte into the outer casing.

[0845] From the perspective of promoting the crosslinking reaction of the separator, the electrolyte of the non-aqueous electrolyte can be a fluorine (F)-containing lithium salt such as LiPF6 that generates hydrogen fluoride (HF), an electrolyte having a lone pair of electrons such as LiN(SO2CF3)2, LiSO3CF3, etc., or can also be LiBF4, LiBC4O8 (LiBOB), etc.

[0846] Although not wishing to be bound by theory, it is presumed that the methoxysilane grafted portion is converted into silanol due to trace amounts of moisture contained in the electric storage device (moisture contained in components such as electrodes, separators, and electrolytes), undergoes a crosslinking reaction, and changes into siloxane bonds. In addition, it is considered that once the electrolyte or the electrolytic solution comes into contact with the electrode, substances that catalyze the silane crosslinking reaction are generated in the electrolytic solution or on the surface of the electrode, dissolve into the electrolytic solution, and swell and diffuse uniformly into the amorphous portion of the polyolefin where the silane-modified grafted portion exists, thereby uniformly promoting the crosslinking reaction of the laminate or wound body including the separator. The substances that catalyze 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), it can be HF generated by the reaction of LiPF6 with moisture, or a fluorine-containing organic compound derived from HF.

[0847] From the perspective of the efficiency of the silane crosslinking reaction, it is preferable to perform at least one cycle of charge and discharge by connecting a lead terminal to the electrode after accommodating the laminate or wound body and the non-aqueous electrolyte in the outer casing of the electric storage device. It is considered that through the charge and discharge cycle, substances that catalyze the silane crosslinking reaction are generated in the electrolytic solution or on the surface of the electrode, thereby realizing the silane crosslinking reaction. The cyclic charge and discharge can be carried out by known methods and devices, and specifically can be the methods described in the examples.

[0848] [Method for manufacturing an electric storage device]

[0849] Another aspect of the present invention is a method for manufacturing an electric storage device.

[0850] [Twelfth Embodiment]

[0851] The method for manufacturing the electric storage device according to the twelfth embodiment includes the following steps;

[0852] (I) A step of preparing the electric storage device assembly kit described above;

[0853] (II) A step of starting the silane crosslinking reaction of the silane-modified polyolefin by bringing the separator in element (1) of the electric storage device assembly kit into contact with the non-aqueous electrolyte in element (2);

[0854] (III) A step of connecting a lead terminal to the electrode of element (1) as desired; and

[0855] (IV) A step of performing at least one cycle of charge and discharge as desired.

[0856] Steps (I) to (IV) can be carried out by known methods in the art except for using the separator for the electric storage device of the present embodiment. In addition, in steps (I) to (IV), known positive electrodes, negative electrodes, electrolytes, outer casings, and charge and discharge devices in the art can be used.

[0857] For process (I), a longitudinally elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be manufactured. Subsequently, in process (I), they 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 processes (II) and (III), by accommodating the wound body in a device can (such as a battery can) and further injecting a non-aqueous electrolyte, an electrical storage device can be manufactured. In addition, an electrical storage device can also be manufactured by a method of loading a wound body formed by folding an electrode and a separator into a device container (such as an aluminum film) and injecting a non-aqueous electrolyte.

[0858] At this time, the wound body can be pressed. Specifically, the separator and an electrode having a current collector and an active material layer formed on at least one side of the current collector can be overlapped and pressed.

[0859] Regarding the pressing temperature, as a temperature at which adhesiveness can be effectively exhibited, for example, it is preferably 20°C or higher. In addition, from the perspective of suppressing clogging of pores in the separator or thermal shrinkage caused by hot pressing, the pressing temperature is preferably lower than the melting point of the material contained in the microporous membrane, and more preferably 120°C or lower. Regarding the pressing pressure, from the perspective of suppressing clogging of pores in the separator, it is preferably 20 MPa or lower. Regarding the pressing time, it can be 1 second or less when using roll pressing, or it can be surface pressing for several hours. From the perspective of productivity, it is preferably 2 hours or less.

[0860] By undergoing the above manufacturing process, it is possible to suppress the press back when the wound body composed of an electrode and a separator is press-formed. Therefore, it is possible to suppress a reduction in the yield rate in the device assembly process and shorten the production process time, which is preferable.

[0861] From the perspective of reliably performing the silane crosslinking reaction of the separator after process (II), it is preferable to perform processes (III) and (IV). It is considered that through charge-discharge cycles, a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte or on the electrode surface, thereby realizing the silane crosslinking reaction.

[0862] For example, in the method for manufacturing a separator, when the method for manufacturing the A layer described above does not include a silane crosslinking treatment step, the crosslinking reaction can be actively promoted by bringing the separator into contact with a non-aqueous electrolyte. Although not wishing to be bound by theory, it is presumed that the silane-modified graft portion is converted into silanol due to trace amounts of moisture contained in the electric storage device (moisture slightly contained in the electrodes, separator, non-aqueous electrolyte, etc.), and a crosslinking reaction occurs, changing into a siloxane bond. In addition, it is considered that once the non-aqueous electrolyte comes into contact with the electrode, a substance that catalyzes the silane crosslinking reaction is generated in the non-aqueous electrolyte or on the electrode surface. It is considered that this substance that catalyzes the silane crosslinking reaction dissolves in the non-aqueous electrolyte and swells and diffuses uniformly into the amorphous portion of the polyolefin where the silane-modified graft portion exists, thereby uniformly promoting the crosslinking reaction of the laminate or wound body including the separator.

[0863] The substance that catalyzes the silane crosslinking reaction can be in the form of an acid solution or a film. When the electrolyte contains lithium hexafluorophosphate (LiPF6), LiPF6 reacts with moisture, and the resulting hydrogen fluoride (HF) or a fluorine-containing organic compound derived from hydrogen fluoride (HF) is regarded as a substance that catalyzes the silane crosslinking reaction (a compound generated in the electric storage device).

[0864] <The Thirteenth Embodiment>

[0865] The thirteenth embodiment is a method for manufacturing an electric storage device using a separator including a polyolefin having one or two or more functional groups, and includes the following steps:

[0866] (1) A crosslinking step of forming a crosslinked structure by causing a condensation reaction between functional groups, or (2) causing a reaction between a functional group and a chemical substance inside the electric storage device, or (3) causing a reaction between a functional group of the polyolefin and other types of functional groups.

[0867] The crosslinking step can be carried out in the same manner as the reaction for forming the crosslinked structure of the separator described above. In addition, since the crosslinking step can utilize the compounds inside the electric storage device and the environment around the device, excessive conditions such as electron beams and high temperatures above 100 °C are not required, and mild conditions such as a temperature of 5 °C to 90 °C and / or the ambient atmosphere can be adopted.

[0868] By performing the crosslinking step in the manufacturing process of the electric storage device, the formation of the crosslinked structure can be omitted in the film-forming process of the separator or immediately after it, the stress and strain after the production of the electric storage device can be relaxed or eliminated, and / or a crosslinked structure can be imparted to the separator without using high energies such as light irradiation or heating, reducing the generation of crosslinking unevenness, unmolten resin aggregates, and the burden on the environment.

[0869] In the crosslinking step, by reacting the functional groups with the chemical substances inside the power storage device through (2), or reacting the functional groups of polyolefin with other types of functional groups through (3), 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), which can improve the strength between multiple components of the power storage device.

[0870] Since the separator described above undergoes crosslinking when contacting with the electrolyte solution, it can initiate the silane crosslinking reaction after the manufacture of the power storage device while being suitable for the manufacturing process of the existing power storage device, thereby improving the safety of the power storage device.

[0871] Examples

[0872] Examples and comparative examples are given to illustrate the present invention more specifically, but the present invention is not limited to the following examples as long as it does not exceed its gist. It should be noted that the physical properties in the examples are measured by the following methods.

[0873] <Weight-average molecular weight>

[0874] Use the ALC / GPC 150C type (trademark) manufactured by Waters Corporation to measure standard polystyrene under the following conditions and make a calibration curve. In addition, for each of the following polymers, the chromatogram is also measured under the same conditions, and the weight-average molecular weight of each polymer is calculated based on the calibration curve according to the following method.

[0875] Chromatographic column: 2 pieces of GMH6-HT (trademark) manufactured by Tosoh Corporation + 2 pieces of GMH6-HTL (trademark)

[0876] Mobile phase: o-dichlorobenzene

[0877] Detector: Differential refractometer

[0878] Flow rate: 1.0 ml / min

[0879] Column temperature: 140 °C

[0880] Sample concentration: 0.1 wt%

[0881] (Weight-average molecular weight of polyethylene)

[0882] The weight-average molecular weight is calculated by multiplying each molecular weight component in the obtained calibration curve by 0.43 (Q factor of polyethylene / Q factor of polystyrene = 17.7 / 41.3) to obtain the molecular weight distribution curve in terms of polyethylene.

[0883] (Weight-average molecular weight of the resin composition)

[0884] Use the Q factor value of the polyolefin with the largest mass fraction, and calculate the weight-average molecular weight in the same way as in the case of polyethylene except for this.

[0885] <Viscosity-average molecular weight (Mv)>

[0886] Based on ASTM-D4020, the intrinsic viscosity [η] at 135 °C in decalin solvent was determined. The Mv of polyethylene was calculated according to the following formula.

[0887] [η] = 6.77×10 -4 Mv 0.67

[0888] <Melt mass flow rate (MFR) (g / 10 min)>

[0889] Using a melt mass flow rate measuring machine (MELT INDEXER F-F01) manufactured by Toyo Seiki Seisaku-sho, Ltd., the weight of the resin extruded in 10 minutes under the conditions of 190 °C and a load of 2.16 kg was determined as the MFR value.

[0890] <Measurement of glass transition temperature>

[0891] An appropriate amount of the aqueous dispersion containing the resin sample (solid content = 38 - 42 wt%, pH = 9.0) was taken into an aluminum dish and dried for 30 minutes with a hot air dryer at 130 °C to obtain a dried film. Approximately 17 mg of this dried film was filled into a measurement aluminum container, and DSC curves and DSC curves were obtained using a DSC measuring device (manufactured by Shimadzu Corporation, model "DSC6220") under a nitrogen atmosphere. The measurement conditions are as described below.

[0892] First heating program: Start from 70 °C and increase the temperature at a rate of 15 °C per minute. After reaching 110 °C, maintain for 5 minutes.

[0893] Second cooling program: Start from 110 °C and decrease the temperature at a rate of 40 °C per minute. After reaching -50 °C, maintain for 5 minutes.

[0894] Third heating program: Start from -50 °C and increase the temperature to 130 °C at a rate of 15 °C per minute. DSC and DDSC data were obtained during this third heating.

[0895] The intersection point of the baseline (a straight line obtained by extending the baseline in the DSC curve obtained to the high temperature side) and the tangent line at the inflection point (the point where the upward convex curve changes to the downward convex curve) was taken as the glass transition temperature (Tg).

[0896] <Film thickness (μm)>

[0897] 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 their average value 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.

[0898] <Thickness of layer A (TA), and thickness of layer B (TB)>

[0899] 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 their average value 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.

[0900] 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.

[0901] <Porosity (%)>

[0902] (i) Calculated based on the density of the mixed composition

[0903] 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.

[0904] Porosity (%) = (Volume - Mass / Density of mixed composition) / Volume × 100

[0905] (ii) Calculated based on the film density

[0906] Alternatively, the porosity of the microporous membrane is calculated from the volume, mass, and film density (g / cm 3 ) using the following formula.

[0907] Porosity (%) = (Volume - Mass / Film density) / Volume × 100

[0908] 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).

[0909] (iii) Porosity of Layer A

[0910] Cut a 10 cm × 10 cm square sample from Layer A, and determine its volume (cm 3 ) and mass (g). Based on these and the density (g / cm 3 ), calculate the porosity using the following formula. The density of the mixed composition is the value calculated and obtained based on the respective densities and mixing ratios of the raw materials used.

[0911] Porosity (%) = (Volume - Mass / Density of the mixed composition) / Volume × 100

[0912] <Air permeability (sec / 100 cm 3 )>

[0913] According to JIS P - 8117 (2009), use a GURLEY - type air permeability tester, G - B2 (trademark) manufactured by Toyo Seiki Co., Ltd. to measure the air permeability of the sample or Layer A.

[0914] <Puncture strength of Layer A>

[0915] Use a handheld compression tester KES - G5 (model) manufactured by KATO TECH Co., Ltd. Fix Layer A with a sample holder having an opening diameter of 11.3 mm. Then, for the central part of the fixed Layer A, use a needle with a tip curvature radius of 0.5 mm and perform a puncture test at a puncture speed of 2 mm / second in an atmosphere of 25°C to measure the maximum puncture load. Convert this maximum puncture load to a value equivalent to a thickness of 20 μm, and use this value as the puncture strength (gf / 20 μm). In the case where the thermoplastic polymer exists only on one side of the substrate, the needle can be punctured from the side where the thermoplastic polymer exists.

[0916] <Quantification of resin aggregates in the separator>

[0917] Resin aggregates in the separator are defined as regions that are opaque and have an area of 100 μm in length × 100 μm in width or more when observing the separator obtained through the film - forming process of the following Examples and Comparative Examples using a transmission - type optical microscope. In the observation based on the transmission - type optical microscope, measure the number of resin aggregates per 1000 m 2 separator area.

[0918] <Storage modulus, loss modulus, and transition temperature (version 1)>

[0919] The dynamic viscoelasticity of the separator is measured using a dynamic viscoelasticity measuring device, and the storage modulus (E’), loss modulus (E”), and transition temperature between the rubbery plateau region and the crystal melting flow region can be calculated. The storage modulus change ratio (R ΔE’ ) is calculated according to the following formula (1), the mixed storage modulus ratio (R E’mix ) is calculated according to the following formula (2), the loss modulus change ratio (R ΔE” ) is calculated according to the following formula (3), and the mixed loss modulus ratio (R E”mix ) is calculated according to the following formula (4), respectively. It should be noted that the measurement conditions are as follows (i) to (iv).

[0920] (i) The dynamic viscoelasticity measurement is carried out under the following conditions:

[0921] · Atmosphere: Nitrogen

[0922] · Measuring device used: RSA-G2 (manufactured by TA Instruments)

[0923] · Sample film thickness: in the range of 5 μm to 50 μm

[0924] · Measurement temperature range: -50 to 225 °C

[0925] · Heating rate: 10 °C / min

[0926] · Measurement frequency: 1 Hz

[0927] · Deformation mode: Sinusoidal wave tensile mode (Linear tension)

[0928] · Initial value of static tensile load: 0.5 N

[0929] · Initial (at 25 °C) distance between gaps: 25 mm

[0930] · Automatic strain adjustment: Enabled (range: amplitude value 0.05 to 25%, sinusoidal wave load 0.02 to 5 N).

[0931] (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each cycle of motion, and the sinusoidal wave load refers to the vibration stress centered on the static tensile load.

[0932] (iii) The sine wave stretching mode means measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%. At this time, the vibration stress is measured by changing the distance between the gaps and the static tensile load in such a way that the difference between the static tensile load and the sine wave load is within 20%. It should be noted that when the sine wave load is below 0.02 N, the vibration stress is measured by increasing the amplitude value in such a way that the sine wave load is within 5 N and the increase amount of the amplitude value is within 25%.

[0933] (iv) Calculate the storage modulus and loss modulus according to the relationship between the obtained sine wave load and the amplitude value and the following formula:

[0934] σ * = σ0·Exp[i(ωt + δ)],

[0935] ε * = ε0·Exp(iωt),

[0936] σ * = E * ·ε *

[0937] E * = E’ + iE”

[0938] {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

[0939] Vibration stress: Sine wave load / Initial cross-sectional area

[0940] Static tensile load: Load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between the gaps in each cycle)

[0941] Sine wave load: Difference between the measured vibration stress and the static tensile load}.

[0942] E’ S and E’ j as well as E” S and E” j Adopt the average value of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelastic measurement data. E’ a and E’0 as well as E” a and E”0 adopt the average value of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelastic measurement data.

[0943] R ΔE’ = E’S / E’ j (1) Comparison before and after battery insertion

[0944] R E’mix = E’ a / E’0 (2) Comparison with and without silane crosslinking

[0945] R ΔE” = E” S / E” j (3) Comparison before and after battery insertion

[0946] R E”mix = E” a / E”0 (4) Comparison with and without silane crosslinking

[0947] An example of a graph for explaining the relationship between temperature and storage modulus is shown in Figure 1 . As Figure 1 shown, by comparing the storage modulus of a standard membrane (a separator for an electric storage device that does not contain a silane-modified polyolefin) and the crosslinked membrane within the temperature range of -50°C to 225°C, the transition temperature between the rubbery plateau region and the crystalline melting flow region can be confirmed in Figure 1 . It should be noted that the transition temperature is the temperature of the intersection of a straight line obtained by extending the baseline on the high-temperature side to the low-temperature side and a tangent line drawn at the inflection point of the curve in the crystalline melting change portion.

[0948] An example of a graph for explaining the relationship between temperature and loss modulus is shown in Figure 2 . Figure 2 In it, by comparing the loss modulus of a standard membrane (a separator for an electric storage device that does not contain a silane-modified polyolefin) and the crosslinked membrane within the temperature range of -50°C to 220°C, the transition temperature determined by the same method as Figure 1 is shown. In this technical field, the storage modulus and the loss modulus can be interchanged according to the following formula:

[0949] tanδ = E” / E’

[0950] {In the formula, tanδ represents the loss tangent, E’ represents the storage modulus, and E” represents the loss modulus.}.

[0951] It should be noted that in the measurement of the hybrid storage modulus ratio (R E’mix ) or the hybrid loss modulus ratio (R E”mix ), as the separator for an electric storage device that does not contain a silane-modified polyolefin, a microporous membrane made of a silane-unmodified polyolefin with a gelation degree of about 0% is used. In addition, regarding E’ a , E’0, E” aFor “E’0” and “E”0”, when no fracture (sharp decrease in elastic modulus) of the sample is observed at 160°C to 220°C, it is calculated based on the average value from 160°C to 220°C. When fracture of the sample occurs at 160°C to 220°C, it is calculated based on the average value from 160°C to the temperature at the fracture point. For example Figure 1 and 2 the standard film shown in 2 fractures at 207°C.

[0952] <Storage Modulus, Loss Modulus, and Transition Temperature (version 2)>

[0953] By using a dynamic viscoelasticity measuring device to measure the dynamic viscoelasticity of the separator, the storage modulus (E’), loss modulus (E”), and the transition temperature between the rubbery plateau region and the crystal melting flow region can be calculated. The storage modulus change ratio (R ΔE’X ) is calculated according to the following formula (1), the mixed storage modulus ratio (R E’mix ) is calculated according to the following formula (2), the mixed loss modulus ratio (R E”X ) is calculated according to the following formula (3), and the mixed loss modulus ratio (R E”mix ) is calculated according to the following formula (4), respectively. It should be noted that for the measurement conditions, use the RSA-G2 dynamic viscoelasticity measuring device manufactured by TA Instruments, the measurement frequency is 1 Hz, the strain is 0.2%, and in the nitrogen atmosphere in the temperature range of -50°C to 310°C. For other conditions, according to the above version 1, measure the storage modulus and loss modulus. E’ Z and E’ Z0 as well as E” Z and E” Z0 Adopt the average value of each storage modulus or each loss modulus at 160°C to 300°C in the dynamic viscoelasticity measurement data. E’ and E’0 as well as E” and E”0 adopt the average value of each storage modulus or each loss modulus at 160°C to 300°C in the dynamic viscoelasticity measurement data.

[0954] R ΔE’X = E’ Z / E’ Z0 (1) Comparison before and after inserting the battery

[0955] R E’mix = E’ / E’0 (2) Comparison with or without an amorphous crosslinked structure

[0956] R E”X = E” Z / E” Z0 (3) Comparison before and after inserting the battery

[0957] R E”mix= E” / E”0 (4) Comparison of the presence or absence of an amorphous crosslinked structure

[0958] An example of a graph for explaining the relationship between temperature and storage modulus is shown in Figure 9 . As Figure 9 shown, by comparing the storage modulus of a standard film (a separator for a storage device without an amorphous crosslinked structure) and the crosslinked film in the temperature range of -50°C to 310°C, the transition temperature between the rubbery plateau region and the crystal melting flow region can be confirmed in Figure 9 . It should be noted that the transition temperature is the temperature of 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 part.

[0959] An example of a graph for explaining the relationship between temperature and loss modulus is shown in Figure 10 . In Figure 10 , by comparing the loss modulus of a standard film (a separator for a storage device without silane-modified polyolefin) and the crosslinked film in the temperature range of -50°C to 310°C, the transition temperature determined by the same method as Figure 9 is shown. In this technical field, the storage modulus and the loss modulus can be interchanged according to the following formula:

[0960] tanδ = E” / E’

[0961] {In the formula, tanδ represents the loss tangent, E’ represents the storage modulus, and E” represents the loss modulus.}.

[0962] It should be noted that in the measurement of the mixed storage modulus ratio (R E’mix ) or the mixed loss modulus ratio (R E”mix ), as a separator for a storage device without an amorphous crosslinked structure, a micro-porous film made of polyolefin with a gelation degree of about 0% is used. In addition, regarding E’, E’0, E”, and E”0, when no fracture (sharp decrease in elastic modulus) of the sample is observed at 160°C to 300°C, it is calculated based on the average value at 160°C to 300°C. When fracture of the sample occurs at 160°C to 300°C, it is calculated based on the average value from 160°C to the temperature of the fracture point. For example, the standard films shown in Table 11 and Table 12 and Figure 9 and Figure 10 fracture at 210°C.

[0963] In this specification, the separator for a power storage device without an amorphous part crosslinked structure may be a separator made of a composition prepared by using any one selected from the group consisting of polyethylene: X (viscosity-average molecular weight of 100,000 to 400,000), PE: Y (viscosity-average molecular weight of 400,000 to 800,000), and PE: Z (viscosity-average molecular weight of 800,000 to 9,000,000), or two or three selected from the group consisting of X, Y, and Z and mixed in any proportion. It should be noted that polyolefins composed only of hydrocarbon skeletons such as low-density polyethylene: LDPE, linear low-density polyethylene: LLDPE, polypropylene: PP, and olefin-based thermoplastic elastomers can be added to the mixed composition. More specifically, the separator for a power storage device without an amorphous part crosslinked structure may refer to a polyolefin microporous membrane with a change rate of solid components (hereinafter referred to as "gelation degree") of 10% or less before and after heating at 160 °C in a decalin solution. It should be noted that when measuring the gelation degree, the solid components refer only to the resin and do not include other materials such as inorganic substances.

[0964] On the other hand, the gelation degree of the polyolefin microporous membrane having an amorphous part crosslinked structure such as a silane crosslinked structure is preferably 30% or more, and more preferably 70% or more.

[0965] <Storage modulus, loss modulus, film softening transition temperature, and film fracture temperature (version 3)>

[0966] The solid viscoelasticity of the separator can be measured using a dynamic viscoelasticity measuring device, and the storage modulus (E'), loss modulus (E"), and film softening transition temperature can be calculated. It should be noted that the conditions for the solid viscoelasticity measurement are as follows (i) to (iv).

[0967] (i) The dynamic viscoelasticity measurement is carried out under the following conditions:

[0968] · Measuring device used: RSA-G2 (manufactured by TA Instruments)

[0969] · Sample film thickness: 200 μm to 400 μm (wherein, when the film thickness of a single sample is less than 200 μm, multiple samples are stacked so that the total thickness is in the range of 200 μm to 400 μm for dynamic viscoelasticity measurement.)

[0970] · Measurement temperature range: -50 °C to 250 °C

[0971] · Heating rate: 10 °C / min

[0972] · Measurement frequency: 1 Hz

[0973] · Deformation mode: sine wave tensile mode (Linear tension)

[0974] · Initial value of static tensile load: 0.2 N

[0975] · Initial (at 25 °C) distance between gaps: 10 mm

[0976] · Automatic strain adjustment (automatic strain adjustment): Disabled.

[0977] (ii) The static tensile load refers to the median value between the maximum stress and the minimum stress under each cycle of motion, and the sine-wave load refers to the vibration stress centered on the static tensile load;

[0978] (iii) The sine-wave tensile mode refers to measuring the vibration stress while performing cyclic motion with a fixed amplitude of 0.1%. In the sine-wave tensile mode, the distance between gaps and the static tensile load are changed in such a way that the difference between the static tensile load and the sine-wave load is within 5% to measure the vibration stress. When the sine-wave load is 0.1 N or less, the static tensile load is fixed at 0.1 N to measure the vibration stress.

[0979] (iv) Calculate the storage modulus (E’) and the loss modulus (E”) based on the relationship between the obtained sine-wave load and amplitude value and the following formula:

[0980] σ * = σ0·Exp[i(ωt + δ)],

[0981] ε * = ε0·Exp(iωt),

[0982] σ * = E * ·ε *

[0983] E * = E’ + iE”

[0984] {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

[0985] Vibration stress: Sine-wave load / Initial cross-sectional area

[0986] Static tensile load: Load at the minimum point of the vibration stress in each cycle (the minimum point of the distance between gaps in each cycle)

[0987] Sine-wave load: Difference between the measured vibration stress and the static tensile load}.

[0988] In addition, the average value of the maximum and minimum values of E’ is calculated and denoted as average E’ (E’ ave ), and the average value of the maximum and minimum values of E” is calculated and denoted as average E” (E” ave ).

[0989] It should be noted that E’ and E” calculate the maximum and minimum values of each storage modulus or each loss modulus at -50°C to 250°C in the dynamic viscoelasticity measurement data. More specifically, in the case where no fracture (sharp decrease in elastic modulus) of the sample is observed at -50°C to 250°C, the maximum and minimum values at -50°C to 250°C are calculated, and the value at the temperature at which the sample fractures at -50°C to 250°C is taken as the minimum value. In addition, in the present technical field, the storage modulus and the loss modulus can be interchanged according to the following formula:

[0990] tanδ = E” / E’

[0991] {In the formula, tanδ represents the loss tangent, E’ represents the storage modulus, and E” represents the loss modulus.}.

[0992] The film softening transition point temperature is the temperature of the minimum value obtained by taking the first derivative of the curve of the sample gap distance in the dynamic viscoelasticity measurement data. In addition, the film fracture temperature is the temperature at which fracture (sharp decrease in elastic modulus) of the sample is observed in the dynamic viscoelasticity measurement data, and its measurement limit temperature is sometimes set at 250°C from the perspective of the thermal decomposition reaction of the polyolefin resin. However, the phenomenon can be similarly understood through measurement at a high temperature above 250°C. Therefore, in the present embodiment, a separator for a power storage device having a film fracture temperature of 180°C or higher can be implemented.

[0993] <Film breakage temperature of layer A>

[0994] Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, the environmental temperature is changed between 25 and 250°C, and the temperature at the moment when the load is completely released is determined as the TMA film breakage temperature (the film breakage temperature of layer A measured by TMA).

[0995] Specifically, TD3 mm and MD14 mm are taken from layer A and used as specimen pieces (specimen pieces with MD as the long side). The two ends of the MD of the specimen piece are installed on a special probe with a clamp distance of 10 mm, and a load of 1.0 g is applied to the specimen piece. The furnace carrying the test piece is heated, and the temperature at which the load display is 0 g is taken as the film breakage temperature (°C).

[0996] Note that when measuring the TD of the specimen piece with TD as the long side, take TD 14 mm and MD 3 mm from layer A as the specimen piece, clamp both ends of TD with a special probe, set the distance between the clamps to 10 mm, initially apply a load of 1.0 g, and perform the same operations as above.

[0997] <Thermal shrinkage rate at 150°C>

[0998] Take TD 100 mm and MD 100 mm from the laminate (laminate including layer A and layer B) before forming the crosslinked structure as the specimen piece. And let the specimen piece stand in an oven at 150°C for 1 hour. At this time, sandwich the specimen piece with two pieces of paper so that the hot air does not directly blow on the specimen piece. After taking out the specimen piece from the oven and cooling it, measure the area of the specimen piece, and calculate the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure according to the following formula.

[0999] Thermal shrinkage rate at 150°C (%) = (10,000 (mm 2 ) - Area of the specimen piece after heating (mm 2 )) × 100 / 10,000

[1000] In addition, for the laminate after forming the crosslinked structure, take TD 100 mm and MD 100 mm as the specimen piece, perform the same operations as above, and thus calculate the thermal shrinkage rate (T2) at 150°C after forming the crosslinked structure.

[1001] Then, by dividing the thermal shrinkage rate (T2) by the thermal shrinkage rate (T1), the ratio (T2 / T1) is obtained. The value of this ratio (T2 / T1) corresponds to the change magnification of the thermal shrinkage rate (T2) at 150°C after forming the crosslinked structure relative to the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure.

[1002] <Battery destruction safety test 1>

[1003] Battery destruction safety test 1 is a test in which a nail is knocked into a battery charged to 4.5 V at a speed of 20 mm / sec and made to penetrate to cause an internal short circuit. By measuring the time-varying behavior of the voltage drop of the battery caused by the internal short circuit and the behavior of the surface temperature rise of the battery caused by the internal short circuit in this test, the phenomena during the internal short circuit can be clarified. In addition, due to the insufficient closing function of the separator or the film breakage at low temperature during the internal short circuit, sometimes the battery will heat up rapidly, and then sometimes the electrolyte will catch fire, and the battery will emit smoke and / or explode.

[1004] (Manufacture of the battery used in Battery destruction safety test 1)

[1005] 1a. Manufacture of the positive electrode

[1006] Take 92.2 mass% of lithium cobalt composite oxide LiCoO2 as the positive electrode active material, 2.3 mass% each of flake graphite and acetylene black as the conductive materials, and 3.2 mass% of polyvinylidene fluoride (PVDF) as the resin binder, and disperse them in N-methylpyrrolidone (NMP) to prepare a slurry. Coat this slurry on one side of an aluminum foil with a thickness of 20 μm that constitutes the positive electrode current collector, dry it at 130 °C for 3 minutes, and then perform compression molding with a roll press. At this time, adjust the coating amount of the positive electrode active material to 250 g / m 2 , and adjust the volume density of the active material to 3.00 g / cm 3 .

[1007] 1b. Fabrication of the negative electrode

[1008] Disperse 96.9 mass% of artificial graphite as the negative electrode active material, 1.4 mass% of ammonium salt of carboxymethyl cellulose and 1.7 mass% of styrene-butadiene copolymer latex as the resin binders in purified water to prepare a slurry. Coat this slurry on one side of a copper foil with a thickness of 12 μm that constitutes the negative electrode current collector, dry it at 120 °C for 3 minutes, and then perform compression molding with a roll press. At this time, adjust the coating amount of the negative electrode active material to 106 g / m 2 , and adjust the volume density of the active material to 1.35 g / cm 3 .

[1009] 1c. Preparation of the non-aqueous electrolyte

[1010] Dissolve LiPF6 as the solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[1011] 1d. Battery assembly

[1012] Cut the separator to a width (TD) of 60 mm and a length (MD) of 1000 mm, fold the separator repeatedly, and alternately stack the positive electrode and the negative electrode (12 positive electrodes and 13 negative electrodes) in layers between the separators. It should be noted that materials with an area of 30 mm × 50 mm are used for the positive electrode and 32 mm × 52 mm for the negative electrode. After loading the repeatedly folded laminate into a laminated bag, inject the non-aqueous electrolyte obtained in c. above and seal it. After leaving it at room temperature for 1 day, charge it at a current value of 3 mA (0.5C) in an atmosphere of 25 °C until the battery voltage reaches 4.2 V. After reaching this voltage, decrease the current value from 3 mA while maintaining 4.2 V, and perform the initial charge after battery fabrication for a total of 6 hours in this way. Then, discharge it at a current value of 3 mA (0.5C) until the battery voltage reaches 3.0 V.

[1013] (Maximum heat generation rate)

[1014] After driving an iron nail through the obtained battery, based on 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 rises the most per 1 second is determined as the maximum heat generation rate.

[1015] (Voltage drop time)

[1016] After driving an iron nail through the obtained battery, the time required for the voltage to drop from 4.5V to 3V is determined as the voltage drop time (the time to drop to 3V).

[1017] (Evaluation of cycle characteristics and manufacturing method of battery)

[1018] In accordance with the same method as 1a. to 1c. in the manufacturing method of the battery used in the above item <Battery destruction safety test 1>, but assemble a battery for evaluating cycle characteristics according to 1d-2. below.

[1019] 1d-2. Battery assembly

[1020] Cut the separator into a circle with a diameter of 18 mm, cut the positive electrode and the negative electrode into circles with a diameter of 16 mm, and stack the positive electrode, the separator, and the negative electrode in sequence with the active material surfaces of the positive electrode and the negative electrode facing each other, and place them in a stainless steel container with a lid. The container is insulated from the lid, the container is in contact with the copper foil of the negative electrode, and the lid is in contact with the aluminum foil of the positive electrode. Inject the non-aqueous electrolyte obtained in 1c. of the above item <Battery destruction safety test 1> into the container and seal it. After leaving it at room temperature for 1 day, charge it at a current value of 3 mA (0.5C) in an atmosphere of 25°C until the battery voltage reaches 4.2V, and after reaching, reduce the current value from 3 mA while maintaining 4.2V, and perform the initial charging of the battery for a total of 6 hours in this way. Then, discharge it at a current value of 3 mA (0.5C) until the battery voltage reaches 3.0V.

[1021] The charge and discharge of the obtained battery are carried out for 100 cycles in an atmosphere of 60°C. Charge it at a current value of 6.0 mA (1.0C) until the battery voltage reaches 4.2V, and after reaching, reduce the current value from 6.0 mA while maintaining 4.2V, and perform the charging for a total of 3 hours in this way. Discharge it at a current value of 6.0 mA (1.0C) until the battery voltage reaches 3.0V.

[1022] (Cycle characteristic evaluation 1)

[1023] Based on the discharge capacity of the 100th cycle and the discharge capacity of the 1st cycle, calculate the capacity retention rate. A high capacity retention rate is evaluated as having good cycle characteristics.

[1024] (Cycle characteristic evaluation 2)

[1025] Based on the discharge capacity of the 300th cycle and the discharge capacity of the 1st cycle, the capacity retention rate (%) is calculated according to the following formula. A higher capacity retention rate is evaluated as having good cycle characteristics.

[1026] Evaluation result (%) = (100 × Retained capacity after 300 cycles / Discharge capacity of the 1st cycle)

[1027] <Fusing / Melting Rupture (F / MD) Characteristics>

[1028] (i) Pressurization at 0.5 MPa and heating rate of 2 °C / min

[1029] The positive electrode, separator, and negative electrode are cut into circular shapes with a diameter of 200 mm and overlapped. A non-aqueous electrolyte is added to the resulting laminate and permeates throughout. The laminate is clamped at the center of a circular aluminum heater with a diameter of 600 mm, and the aluminum heater is pressurized to 0.5 MPa from above and below with a hydraulic jack to complete the preparation for measurement. While heating the laminate with the aluminum heater at a heating rate of 2 °C / min, the resistance (Ω) between the electrodes is measured. The temperature at which the separator fuses and the resistance between the electrodes increases and the resistance first exceeds 1000 Ω is taken as the fusing temperature (shut-off temperature). In addition, heating is further continued, and the temperature at which the resistance drops below 1000 Ω is taken as the melting rupture temperature (membrane rupture temperature).

[1030] (ii) Maximum pressurization of 10 MPa and heating rate of 15 °C / min

[1031] The positive electrode, separator, and negative electrode are cut into circular shapes with a diameter of 200 mm, and a non-aqueous electrolyte is added to the laminate obtained by overlapping and permeates throughout. The laminate is clamped at the center of a circular aluminum heater with a diameter of 600 mm, and the aluminum heater is pressurized from above and below with a hydraulic jack to 10 MPa to complete the preparation for measurement. While heating the laminate with the aluminum heater at a heating rate of 15 °C / min, the resistance (Ω) between the electrodes is measured. The temperature at which the resistance between the electrodes increases and the resistance first exceeds 1000 Ω is taken as the shut-off temperature (°C). In addition, heating is further continued, and the temperature at which the resistance drops below 1000 Ω is taken as the melting rupture temperature (°C).

[1032] It should be noted that for any one of the evaluations in (i) and (ii), a resistance measurement wire is bonded to the back of the aluminum foil of the positive electrode fabricated through "1a. Fabrication of the Positive Electrode" in the above-mentioned item <Battery Destruction Safety Test 1> with a conductive silver paste. In addition, a resistance measurement wire is bonded to the back of the copper foil of the negative electrode fabricated through "1b. Fabrication of the Negative Electrode" in the above-mentioned item <Battery Destruction Safety Test 1> with a conductive silver paste. Furthermore, the electrolyte-containing electrolytic solution prepared through "1c. Preparation of the Non-aqueous Electrolyte" in the above-mentioned item <Battery Destruction Safety Test 1> is also used for the F / MD characteristic test.

[1033] <Safety Test (Stab Test) 2>

[1034] 2a. Fabrication of the Positive Electrode

[1035] Mix nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) at 90.4 mass%, graphite powder (KS6) (density 2.26 g / cm 3 , number average particle size 6.5 μm) at 1.6 mass%, acetylene black powder (AB) (density 1.95 g / cm 3 , number average particle size 48 nm) at 3.8 mass%, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm 3 ) at 4.2 mass% in a certain ratio, disperse them in NMP to prepare a slurry. Use a die coater to coat this slurry on one side of an aluminum foil with a thickness of 20 μm that constitutes the positive electrode current collector, dry it at 130 °C for 3 minutes, and then use a roll press for compression molding to fabricate the positive electrode. At this time, the coating amount of the positive electrode active material is 109 g / m 2 .

[1036] 2b. Fabrication of the Negative Electrode

[1037] Graphite powder A (density 2.23 g / cm 3 , number average particle size 12.7 μm) at 87.6 mass% and graphite powder B (density 2.27 g / cm 3, 9.7 mass% of the number average particle size of 6.5 μm, 1.4 mass% of the ammonium salt of carboxymethyl cellulose as a resin binder (in terms of solid content) (aqueous solution with a solid content concentration of 1.83 mass%), and 1.7 mass% of a diene rubber latex (in terms of solid content) (aqueous solution with a solid content concentration of 40 mass%) were dispersed in purified water to prepare a slurry. The slurry was coated on one side of a copper foil with a thickness of 12 μm that constitutes the negative electrode current collector, dried at 120 °C for 3 minutes, and then compression-molded using a roll press to fabricate the negative electrode. At this time, the coating amount of the negative electrode active material was 52 g / m 2 .

[1038] 2c. Preparation of non-aqueous electrolyte

[1039] LiPF6 as a solute was dissolved in a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[1040] 2d. Battery fabrication

[1041] Using the positive electrode, negative electrode, and non-aqueous electrolyte obtained in the above 2a to 2c, and a separator (the separator of the example or the separator of the comparative example), a laminated secondary battery with a size of 100 mm × 60 mm and a capacity of 3 Ah was fabricated, which was charged under constant current and constant voltage (CCCV) conditions of a current value of 1 A (0.3C) and a terminal battery voltage of 4.2 V for 3 hours.

[1042] 2e. Nail penetration evaluation

[1043] The fabricated laminated secondary battery was placed on an iron plate in an explosion-proof chamber with adjustable temperature. The temperature in the explosion-proof chamber was set to 40 °C, and an iron nail with a diameter of 3.0 mm was penetrated through the central part of the laminated secondary battery at a speed of 2 mm / second, and the nail maintained the penetrated state. The temperature of a thermocouple set inside the nail in such a way that the temperature inside the laminated battery could be measured after the nail penetration was measured to evaluate the presence or absence of ignition.

[1044] The evaluation was repeated using a newly fabricated laminated secondary battery by the same method, and the number of samples without ignition was calculated as a percentage value according to the following formula.

[1045] Evaluation result (%) = (100 × number of samples without ignition / total number of samples)

[1046] Regarding the pass rate of the nail penetration evaluation, for example, it is preferably 50% or more at 200 cycles and 5% or more at 1000 cycles.

[1047] <Experimental Group I>

[1048] [Manufacturing method of silane-grafted modified polyolefin]

[1049] The raw polyolefin used in the silane-grafted modified polyolefin may 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 may be a propylene or butene copolymerized α-olefin. While melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added. After generating free radicals in the polymer chain of the α-olefin, trimethoxyalkoxide-substituted vinylsilane is injected, and an alkoxysilyl group is introduced into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, in order to adjust the free radical concentration in the system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heated and dried at 80 °C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is about 10 to 1500 ppm.

[1050] The silane-grafted modified polyethylene obtained by the above manufacturing method is used as "silane-modified polyolefin (B)" in Table 8.

[1051] [Example I-1]

[1052] To 79.2% by mass of polyethylene (A), a homopolymer with a weight-average molecular weight of 500,000, 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (at 190 °C) of 0.4 g / min, which is obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 as a raw material through a trimethoxyalkoxide-substituted vinylsilane reaction (thus, the resin compositions of (A) and (B) are 0.8 and 0.2 respectively), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant are added, and dry mixing is carried out using a drum mixer to obtain a mixture. The obtained mixture is fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78 °C is 7.59×10 -5 m 2 / s) is injected into the extruder barrel through a plunger pump.

[1053] The mixture and liquid paraffin are melt-kneaded in the extruder, and the feeder and pump are adjusted so that the amount ratio of 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 speed of 240 rpm, and a discharge rate of 18 kg / h.

[1054] Next, the molten mixture was extruded through a T-die onto a cooling roll with a surface temperature controlled at 25°C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) with a blank film thickness of 1400 μm.

[1055] Next, the sheet-shaped molded body was guided to a simultaneous biaxial tentering machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to an MD magnification of 7.0 times, a TD magnification of 6.0 times (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1056] Next, the stretched gel sheet was guided to a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove liquid paraffin, and then dried to remove methyl ethyl ketone, obtaining a porous body.

[1057] Next, in order to perform heat setting (HS), the porous body was guided to a TD tenter, and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8 times. Then, a relaxation operation of 0.5 times in the TD direction (i.e., the HS relaxation ratio was 0.5 times) was performed to obtain a microporous membrane.

[1058] Then, for the obtained microporous membrane, the ends were cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1059] During the above evaluation, the microporous membrane unwound from the master roll was slit as needed and used as a separator for evaluation.

[1060] [Examples I-2 to I-6]

[1061] As recorded in Table 8, the amount ratio of Components A and B and the crosslinking method / conditions were changed. Except for this, the same operations as in Example I-1 above were performed to obtain the microporous membranes shown in Table 8.

[1062] [Comparative Examples I-1, I-2]

[1063] To 79.2% by mass of polyethylene (A), a homopolymer with a weight average molecular weight of 500,000, 19.8% by mass of a silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (190°C) of 0.4 g / minute, which was obtained by modifying a polyolefin with a viscosity average molecular weight of 20,000 as a raw material through a reaction of substituting vinyl silane with trimethoxyalkoxide (thus, the resin compositions of (A) and (B) were 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were dry-blended using a drum mixer to obtain a mixture. The obtained mixture was fed into a twin-screw extruder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C was 7.59×10 -Inject into the extruder drum at 5 m² / s.

[1064] In the extruder, melt and knead the mixture and liquid paraffin, and adjust the feeder and pump so that the amount of 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 speed of 240 rpm, and a discharge rate of 18 kg / h.

[1065] Next, extrude the melt-kneaded material through a T-die 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.

[1066] 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 6.0 times (i.e., 7×6 times), and a biaxial stretching temperature of 125 °C.

[1067] Next, guide the stretched gel sheet to a methyl ethyl ketone bath, fully immerse it in methyl ethyl ketone to extract and remove the liquid paraffin, and then dry to remove the methyl ethyl ketone to obtain a porous body.

[1068] Next, in order to perform heat setting (HS), guide the porous body to a TD tenter, perform HS at a heat setting temperature of 125 °C and a stretching ratio of 1.8 times, and then perform a relaxation operation of 0.5 times in the TD direction (i.e., the HS relaxation ratio is 0.5 times).

[1069] Furthermore, guide it into an ethanol bath (affinity treatment tank), immerse it and stay for 60 seconds to perform the affinity treatment of the heat-treated porous body to obtain an affinity-treated porous body.

[1070] Furthermore, in Comparative Example I-1, guide the affinity-treated porous body into a 25% aqueous sodium hydroxide solution (temperature 80 °C, pH 8.5 - 14), and in Comparative Example I-2, guide the affinity-treated porous body into a 10% aqueous hydrochloric acid solution (temperature 60 °C, pH 1 - 6.5), immerse it and stay for 60 seconds to perform the crosslinking treatment of the affinity-treated porous body to obtain a crosslinked-treated porous body.

[1071] Furthermore, guide the crosslinked-treated porous body into water (water washing treatment tank), immerse it and stay for 60 seconds to wash the crosslinked-treated porous body. Guide it to a conveyor dryer and dry it under the conditions of 120 °C for 60 seconds to obtain a microporous membrane.

[1072] 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.

[1073] In the above evaluation, the microporous membrane released from the master roll is slit as needed and used as a separator for evaluation.

[1074] [Evaluation results]

[1075] For the microporous membranes and batteries obtained in Examples I-1 to I-6 and Comparative Examples I-1 to I-2, various evaluations were carried out according to the above evaluation method, and the evaluation results are also shown in Table 8. In addition, the relationship between the temperature and resistance of the battery equipped with the microporous membrane obtained in Example I-1 as a separator is shown in Figure 3 . From Figure 3 and Table 8, it can be seen that the closing temperature of the separator obtained in Example I-1 is 143 °C, and the film-breaking temperature is 200 °C or higher. Furthermore, the 1 H and 13 C-NMR spectra (b) of the separator obtained in Example I-1 in the state before crosslinking are shown in Figure 13 .

[1076] [Table 8]

[1077]

[1078] It should be noted that "silane-modified polyethylene (B)" in Table 8 is a silane-modified polyethylene obtained by using a polyolefin with a viscosity-average molecular weight of 20,000 as a raw material and through a modification reaction based on trimethoxyalkoxide-substituted vinylsilane, with a density of 0.95 g / cm 3 and a melt mass flow rate (MFR) of 0.4 g / minute at 190 °C.

[1079] <Experimental Group IIa>

[1080] [Manufacturing method of silane-grafted modified polyolefin]

[1081] The raw polyolefin used in the silane-grafted modified polyolefin may 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 may be a homopolymer of ethylene or a copolymer of ethylene with propylene or butene. While melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added, and after generating free radicals in the polymer chain of the α-olefin, trimethoxyalkoxide-substituted vinyl silane is injected, and an alkoxysilyl group is introduced into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, in order to adjust the free radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then dried by heating at 80 °C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 1500 ppm or less.

[1082] The silane-grafted modified polyethylene obtained by the above manufacturing method is used as "silane-modified polyethylene (B)" in Table 9.

[1083] [Example II-1]

[1084] To 80% by mass of polyethylene (polyethylene (A)) which is a homopolymer with a weight-average molecular weight of 700,000, 20% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (at 190 °C) of 0.4 g / minute obtained by modifying a polyolefin with a viscosity-average molecular weight of 10,000 as a raw material through trimethoxyalkoxide-substituted vinyl silane is added (thus, the resin compositions of (A) and (B) are 80% and 20% respectively), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant is added, and dry mixing is performed using a roller mixer to obtain a mixture. The obtained mixture is fed into a twin-screw extruder by a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78 °C is 7.59×10 -5 m 2 / s) is injected into the extruder barrel through a plunger pump.

[1085] The mixture and liquid paraffin are melt-kneaded in the extruder, and the feeder and pump are adjusted so that the amount ratio of 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 speed of 240 rpm, and a discharge rate of 18 kg / h.

[1086] Next, the melt-kneaded mixture was extruded through a T-die onto a cooling roll with a surface temperature controlled at 25°C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) with a blank film thickness of 1100 μm.

[1087] Next, the sheet-shaped molded body was guided to a simultaneous biaxial tentering machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to an MD magnification of 7.0 times, a TD magnification of 6.2 times, and a biaxial stretching temperature of 120°C.

[1088] Next, the stretched gel sheet was guided to a dichloromethane bath, fully immersed in dichloromethane to extract and remove liquid paraffin, and then dried to remove dichloromethane, obtaining a porous body.

[1089] Next, in order to perform heat setting (HS), the porous body was guided to a TD tenter, and HS was performed at a heat setting temperature of 133°C and a stretching ratio of 2.1 times. Then, a relaxation operation was performed to 2.0 times in the TD direction.

[1090] Then, for the obtained microporous membrane, the ends were cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1091] During the above evaluation, the microporous membrane unwound from the master roll was slit as needed and used as a separator for evaluation.

[1092] [Examples II-2 to II-8, Comparative Examples II-1 to II-3]

[1093] As shown in Table 9, the amount ratio of Components A and B, the presence or absence of (C) other resins as additional components, the film physical properties, and the crosslinking method / conditions were changed. Except for these, the same operations as in Example II-1 were performed to obtain the microporous membranes shown in Table 9. It should be noted that as the component "PP" in Table 9, a silane-unmodified polypropylene with an MFR of 2.5 g / 10 min or less and a density of 0.89 g / cm 3 at the above were used. In addition, in the crosslinking method "alkali treatment crosslinking" in Table 9, the samples were treated with a 25% aqueous sodium hydroxide solution (temperature 80°C, pH 8.5 to 14).

[1094] [Evaluation Results]

[1095] 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 above evaluation methods, and the evaluation results are also shown in Table 9. In addition, regarding the viscoelasticity measurement when using the obtained microporous membrane as a separator for a power storage device, the temperature, gap distance, and the relationship between the storage modulus and the loss modulus of Example II-1 are shown in Figure 4(a) of Comparative Example II-1 is shown in Figure 4 (b) thereof. 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 Comparative Example II-1 is shown in Figure 5 (b) thereof. No film breakage was observed in Examples II-1 to II-8 and Comparative Example II-3 at the measurement limit temperature of 250°C. It should be noted that in Example II-1 and Comparative Example II-1, 26 films with a thickness of 8 μm were overlapped, and the storage modulus, loss modulus, film softening transition temperature, and film breakage temperature were measured under the condition that the total film thickness of the sample was 208 μm.

[1096] [Table 9A]

[1097]

[1098] [Table 9B]

[1099]

[1100] [Experimental Series IIb]

[1101] [Standard Film]

[1102] As a separator for an electric storage device that does not contain a silane-modified polyolefin (hereinafter referred to as "standard film"), a silane-grafted unmodified polyolefin microporous film with a change rate of solid components (hereinafter referred to as "gelation degree") of about 0% before and after heating at 160°C in a decalin solution is used. When measuring the gelation degree, the solid components refer only to the resin and do not include other materials such as inorganic substances.

[1103] It should be noted that in this specification, a separator for an electric storage device that does not contain a silane-grafted modified polyolefin can be manufactured using any one selected from the group consisting of polyethylene (PE): X (viscosity-average molecular weight of 100,000 to 400,000), PE: Y (viscosity-average molecular weight of 400,000 to 800,000), and PE: Z (viscosity-average molecular weight of 800,000 to 9,000,000), or can be manufactured from a composition in which two or three selected from the group consisting of X, Y, and Z are mixed in any proportion. It should be noted that polyolefins composed only of a hydrocarbon skeleton such as low-density polyethylene: LDPE, linear low-density polyethylene: LLDPE, polypropylene: PP, and olefin-based thermoplastic elastomers can be added to the mixed composition.

[1104] [Crosslinked Film]

[1105] As a separator for an electric storage device after silane crosslinking reaction (hereinafter referred to as "crosslinked film"), the polyolefin microporous film of Example II-1 after contacting with the electrolyte described above, or the polyolefin microporous film of Example II-1 taken out from the battery after the first charge and discharge is dried and used. The degree of gelation of the crosslinked film is 30% or more or 70% or more.

[1106] [Viscoelastic behavior]

[1107] The above items <storage modulus, loss modulus, film softening transition temperature, and film fracture temperature (version 3)> are measured for the standard film and the crosslinked film. The measurement results are shown in Table 10.

[1108] [Table 10]

[1109]

[1110] <Experimental Group III>

[1111] [Manufacturing method of silane-grafted modified polyolefin]

[1112] The raw material polyolefin used in the silane-grafted 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, or can be a propylene or butene copolymerized α-olefin. While melt-kneading the raw material polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added. After generating free radicals in the α-olefin polymer chain, trimethoxyalkoxide-substituted vinylsilane is injected, and an alkoxysilyl group is introduced into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, at the same time, in order to adjust the free radical concentration in the system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heated and dried at 80 °C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is about 1000 - 1500 ppm.

[1113] The silane-grafted modified polyolefin obtained by the above manufacturing method is shown as "silane-modified polyethylene" in Table 11 and Table 12.

[1114] [Manufacturing method of modified PE and copolymer with various functional groups other than silane-modified PE]

[1115] Modified PE and copolymer with various functional groups other than silane-modified PE are manufactured by the following method.

[1116] For any raw material, it is adjusted with the molecular weight of the raw material used so that the MI is in the range of 0.5 to 10. The modified PE having a hydroxyl group is produced by saponifying and neutralizing an EVA copolymer. Modified resins such as amine modification and oxazoline modification cause a tungsten-based catalyst to act on the terminal vinyl group of PE polymerized using a chromium catalyst under hydrogen peroxide conditions to convert the vinyl group into an epoxy group. Thereafter, using a known organic reaction for functional group conversion, the target reaction site is converted into a target functional group to obtain various modified PEs. For example, in the case of amine-modified PE, while melt-kneading the modified PE having an epoxy group in an extruder at 200 °C, a primary amine or a secondary amine is injected in a liquid state and reacted. Then, the unreacted amines are removed through a pressure reducing valve, and the obtained amine-modified resin is extruded into a wire shape and cut into a pellet shape.

[1117] The modified PE obtained by the above manufacturing method is represented as one of "modified PE or copolymer (B)" in Tables 11 and 12.

[1118] [Example III-1]

[1119] To 79.2% by mass of polyethylene (A), a homopolymer having a weight average molecular weight of 500,000, 19.8% by mass of silane-grafted polyethylene (PE (B)) having an MFR of 0.4 g / minute, which is obtained by modifying a polyolefin having a viscosity average molecular weight of 20,000 as a raw material through a trimethoxyalkoxide-substituted vinylsilane reaction (whereby the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant are dry-blended using a drum mixer to obtain a mixture. The obtained mixture is fed by a feeder into a twin-screw extruder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 °C is 7.59×10 -5 m 2 / s) is injected into the extruder barrel through a plunger pump.

[1120] The mixture and the liquid paraffin are melt-kneaded in the extruder, and the feeder and the pump are adjusted 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 / h.

[1121] Next, the melt-kneaded material is extruded through a T-die onto a cooling roll with a surface temperature controlled at 25 °C and cast to obtain a gel sheet (sheet-shaped molded body) having a blank film thickness of 1400 μm.

[1122] Next, the sheet-shaped molded body is guided to a simultaneous biaxial tentering machine for biaxial stretching to obtain a stretched product. The stretching conditions are set as MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7×6 times), and biaxial stretching temperature 125°C.

[1123] Next, the stretched gel sheet is guided to a methyl ethyl ketone tank, fully impregnated in methyl ethyl ketone to extract and remove liquid paraffin, and then dried to remove methyl ethyl ketone to obtain a porous body.

[1124] Next, in order to perform heat setting (HS), the porous body is guided to a TD tenter, and HS is performed at a heat setting temperature of 125°C and a stretching ratio of 1.8 times. Then, a relaxation operation of 0.5 times in the TD direction (i.e., HS relaxation ratio is 0.5 times) is performed to obtain a microporous membrane.

[1125] Then, for the obtained microporous membrane, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1126] During the above evaluation, the microporous membrane unwound from the master roll is slit as needed and used as an evaluation separator.

[1127] For the evaluation separator and the battery, various evaluations are performed according to the above evaluation method, and the evaluation results are shown in Table 11.

[1128] [Examples III-2 to III-18]

[1129] As shown in the description of Table 11 or Table 12, the types, mass ratios, and crosslinking methods / conditions of Resins A and B are changed. In addition, the same operations as in Example III-1 are performed to obtain the microporous membranes and batteries shown in Table 11 or Table 12. For the obtained microporous membranes and batteries, various evaluations are performed according to the above evaluation method, and the evaluation results are also shown in Table 11 or Table 12. It should be noted that in Examples III-8 to III-10 and III-15 to III-18, when injecting the electrolyte, an electrolyte in which an appropriate amount of the additive described in Table 11 or Table 12 is pre-dissolved is used.

[1130] [Comparative Examples III-1, III-2]

[1131] As shown in the description of Table 12, the types, mass ratios, and crosslinking methods / conditions of Resins A and B are changed. In addition, the same operations as in Example III-1 are performed to obtain the microporous membrane shown in Table 12. The obtained electron beam crosslinked microporous membrane and battery are irradiated with a specified dose and then various evaluations are performed according to the above evaluation method, and the evaluation results are also shown in Table 12.

[1132] Regarding Comparative Example III-2 and Example III-1, the strain-crystal subdivision rate diagrams are shown in Figure 8 , and the X-ray crystal structure changes during the tensile fracture test are observed. Figure 8 In, the microporous membrane of Comparative Example III-2 is represented by a dotted line for "EB crosslinking", and the microporous membrane of Example III-1 is represented by a solid line for "before chemical crosslinking" and a dashed line for "after chemical crosslinking".

[1133] [Table 11A]

[1134]

[1135] [Table 11B]

[1136]

[1137] [Table 12A]

[1138]

[1139] [Table 12B]

[1140]

[1141] Explanation of Abbreviations in Tables 11 and 12

[1142] * "Silane-modified polyethylene" is a silane-modified polyethylene obtained by using polyolefin with a viscosity-average molecular weight of 20,000 as a raw material and through a modification reaction based on the substitution of vinyl silane with trimethoxyalkoxide, having a density of 0.95 g / cm 3 and a melt mass flow rate (MFR) of 0.4 g / minute at 190 °C.

[1143] "-COOH modified PE", "-oxazoline modified PE", "-oxazoline, -OH modified PE", "-OH modified PE", "-OH, -NH- modified PE", and "-OH, amine modified PE" are all modified PEs obtained by the above [manufacturing methods of modified PEs and copolymers with various functional groups other than silane-modified PE].

[1144] ** (I) Condensation reaction of multiple identical functional groups

[1145] (II) Reaction between multiple different functional groups

[1146] (III) Chain condensation reaction of functional groups with electrolyte

[1147] (IV) Reaction of functional groups with additives

[1148] (V) Reaction in which multiple identical functional groups are crosslinked by means of coordination bonds with dissolved metal ions

[1149] *** EC: Ethylene carbonate

[1150] **** BS(PEG)5: Succinimide at both ends, number of repeated EO units is 5

[1151] Diisocyanate: A compound in which isocyanates at both ends are connected to a hexane unit by means of a urethane bond

[1152] Diepoxide: A compound in which epoxy groups at both ends are connected to a butane unit

[1153] <Experimental Group IV>

[1154] [Example IV-1]

[1155] <Fabrication of Layer A>

[1156] (Fabrication of silane-grafted polyolefin)

[1157] Using polyethylene with a viscosity-average molecular weight of 120,000 as the raw material polyethylene, while melt-kneading the raw material polyethylene with an extruder, adding an organic peroxide (di-tert-butyl peroxide), generating free radicals in the polymer chain of the alpha-olefin, injecting trimethoxyalkoxide-substituted vinyl silane, and introducing an alkoxysilyl group into the alpha-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, simultaneously, in order to adjust the free radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the alpha-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heated and dried at 80 °C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinyl silane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinyl silane in the pellets is about 1500 ppm or less.

[1158] As described above, through the modification reaction using trimethoxyalkoxide-substituted vinyl silane, silane-modified polyethylene with an MFR (190 °C) of 0.4 g / minute is obtained.

[1159] (Fabrication of Layer A)

[1160] Mix 35% by mass of the above-obtained silane-modified polyethylene with 65% by mass of a homopolymer polyethylene having a weight-average molecular weight of 800,000 to form a resin blend. Add 1% by mass of pentaerythritol tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant to the blend and perform dry mixing using a roller 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.

[1161] Melt-knead the mixture and liquid paraffin in the extruder, and adjust the feeder and the pump so that the amount ratio of liquid paraffin in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-kneading conditions are a set temperature of 220 °C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / hour. 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.

[1162] 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.

[1163] 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.

[1164] Next, guide the porous body to a TD tenter for heat setting (HS) at a heat setting temperature of 133 °C and a stretching ratio of 1.8 times. Then, perform a relaxation operation to a TD of 1.7 times to obtain a microporous membrane.

[1165] 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.

[1166] At the above evaluation, slit the microporous membrane unwound from the master roll as needed and use it as the evaluation A layer.

[1167] For the obtained evaluation A layer, measure the film thickness, air permeability, porosity, etc., as shown in Table 13.

[1168] <Fabrication of B layer>

[1169] 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (in terms of solid content) of an aqueous ammonium polycarboxylate solution (SNDispersant 5468 manufactured by SAN NOPCO LIMITED, solid content concentration 40%) as an ionic dispersant were uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion was subjected to a crushing treatment using a bead mill (tank volume 200 cc, zirconia beads with a diameter of 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, and a slurry containing inorganic particles was produced.

[1170] Next, the microporous membrane was continuously discharged from the above-mentioned microporous membrane master roll, and the slurry containing inorganic particles was coated on one side of the microporous membrane using a gravure reverse coater. Then, the water was removed by drying with a dryer at 60°C, and it was wound up to obtain a master roll of the separator.

[1171] At the time of evaluation, the separator discharged from the master roll was cut as needed and used as the separator for evaluation.

[1172] [Examples IV-2 to IV-5 and Comparative Examples IV-1 to IV-2]

[1173] Taking the physical property values described in Table 13 as the target, the weight average molecular weight of the polyethylene of the homopolymer was changed, and at least any one of the stretching conditions, heat setting conditions, and relaxation operation conditions was set. In addition, the composition of the B layer was changed as described in Table 13.

[1174] Except for these changes, the separator was produced by the same method as in Example IV-1, and the above evaluation was carried out using the obtained separator. The evaluation results are shown in Table 13.

[1175] [Table 13]

[1176]

[1177] <Experimental Group V>

[1178] [Manufacturing Method of Silane-Grafted Modified Polyolefin]

[1179] The raw polyolefin used in the silane-grafted modified polyolefin may 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, or it may be a propylene or butene copolymerized α-olefin. While melt-kneading the raw polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) is added. After generating free radicals in the polymer chain of the α-olefin, trimethoxyalkoxide-substituted vinylsilane is injected, and an alkoxysilyl group is introduced into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, in order to adjust the free radical concentration in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heated and dried at 80 °C for 2 days to remove moisture or unreacted trimethoxyalkoxide-substituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is about 10 to 1500 ppm.

[1180] The silane-grafted modified polyolefin obtained by the above manufacturing method is used as "silane-modified polyethylene (B)" in Tables 14 to 16. It should be noted that the density of the silane-grafted modified polyolefin used this time is 0.94 g / cm 3 and the MFR is 0.65 g / min.

[1181] [Example V-1]

[1182] (Formation of microporous membrane)

[1183] To 79.2% by weight of polyethylene (A), which is a homopolymer with a weight-average molecular weight of 500,000, 19.8% by weight of silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (at 190 °C) of 0.4 g / min, which is obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 as a raw material through a trimethoxyalkoxide-substituted vinylsilane reaction (thus, the resin composition of (A) and (B) is 80% and 20%), and 1% by weight of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant are added, and dry mixing is performed using a drum mixer to obtain a mixture. The obtained mixture is fed into a twin-screw extruder by a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78 °C is 7.59×10 -5 m 2 / s) is injected into the extruder barrel through a plunger pump.

[1184] The mixture and liquid paraffin are melt-kneaded in an extruder, and the feeder and pump are adjusted so that the amount of liquid paraffin in the extruded polyolefin composition is 70% by weight (i.e., the polymer concentration is 30% by weight). The melt-kneading conditions are a set temperature of 220°C, a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[1185] Next, the melt-kneaded material is extruded through a T-die onto a cooling roll with a surface temperature controlled at 25°C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) with a blank film thickness of 1400 μm.

[1186] Next, the sheet-shaped molded body is guided to a simultaneous biaxial tentering machine and biaxially stretched to obtain a stretched product. The set stretching conditions are set to an MD magnification of 7.0 times, a TD magnification of 6.0 times (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[1187] Next, the stretched gel sheet is guided to a methyl ethyl ketone bath, fully impregnated in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, obtaining a porous body.

[1188] Next, in order to perform heat setting (HS), the porous body is guided to a TD tenter, and HS is performed at a heat setting temperature of 125°C and a stretching ratio of 1.8 times. Then, a relaxation operation of 0.5 times in the TD direction (i.e., the HS relaxation ratio is 0.5 times) is performed to obtain a microporous membrane.

[1189] Then, for the obtained microporous membrane, the ends are cut off and wound into a microporous membrane master roll with a width of 1,100 mm and a length of 5,000 m.

[1190] (Manufacturing method of acrylic latex)

[1191] The acrylic latex used as a resin binder can be manufactured by the following method.

[1192] 70.4 parts by mass of ion-exchanged water, 0.5 part by mass of "Aquaron KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 part by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) are added to a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer. Next, the temperature inside the reaction vessel is raised to 80°C, and 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate are added while maintaining the temperature at 80°C to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution is completed, the emulsion is dropped from the dropping tank into the reaction vessel over 150 minutes.

[1193] It should be noted that the above emulsion is prepared by mixing the following substances with a homogenizing mixer for 5 minutes: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aquaron KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and a mixture of 52 parts by mass of ion-exchanged water.

[1194] After the dropping of the emulsion is completed, the temperature inside the reaction vessel is maintained at 80 °C for 90 minutes, and then cooled to room temperature. The resulting emulsion is adjusted to pH = 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water is added to obtain an acrylic latex with a solid content of 40%. The number average particle diameter of the resulting acrylic latex is 145 nm, and the glass transition temperature is -23 °C.

[1195] (Formation of inorganic porous layer)

[1196] 95 parts by weight of aluminum hydroxide (average particle diameter 1.4 μm) as inorganic particles and 0.4 parts by weight (in terms of solid content) of an aqueous ammonium polycarboxylate solution (SNDispersant 5468 manufactured by SAN NOPCO LIMITED, solid content concentration 40%) as an ionic dispersant are uniformly dispersed in 100 parts by weight of water to prepare a dispersion. The resulting dispersion is subjected to a crushing treatment with a bead mill (tank volume 200 cc, zirconia microbead diameter 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. 4.6 parts by weight (in terms of solid content) 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 is added to the dispersion with the adjusted particle size distribution to prepare a slurry containing inorganic particles.

[1197] Next, the microporous membrane is continuously discharged from the above microporous membrane master roll, and the slurry containing inorganic particles is coated on one side of the microporous membrane with a gravure reverse coater, and then dried with a dryer at 60 °C to remove water, and wound up to obtain a master roll of the separator.

[1198] During evaluation, the separator discharged from the master roll is slit as needed and used as the evaluation separator.

[1199] [Examples V-2 to V-12, Comparative Example V-2]

[1200] As shown in Tables 14 to 16, by changing the quantitative ratio of Components A and B, the presence or composition of the inorganic layer, and the crosslinking method / conditions, and in addition, performing the same operations as in Example V-1, the microporous membranes shown in Tables 14 to 16 were obtained.

[1201] [Comparative Example V-1]

[1202] To 79.2% by weight of polyethylene (A), a homopolymer with a weight-average molecular weight of 500,000, 19.8% by weight of a silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (at 190 °C) of 0.4 g / minute, which was obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 as a raw material through a trimethoxyalkoxide-substituted vinyl silane modification reaction (thus, the resin compositions of (A) and (B) were 80% and 20% respectively), and 1% by weight 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 to obtain a mixture. The obtained mixture was fed from a feeder into a twin-screw extruder under a nitrogen atmosphere.Moreover, liquid paraffin (kinematic viscosity at 37.78 °C: 7.59×10 - 5 m2 / s) was injected into the extruder barrel through a plunger pump.

[1203] In the extruder, the mixture and liquid paraffin were melt-kneaded, and the feeder and pump were adjusted so that the quantitative ratio of 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 rate of 18 kg / h.

[1204] Next, the melt-kneaded material was extruded through a T-die onto a cooling roll with a surface temperature controlled at 25 °C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) with a blank film thickness of 1400 μm.

[1205] Next, the sheet-shaped molded body was guided to a simultaneous biaxial tentering machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to an MD magnification of 7.0 times, a TD magnification of 6.0 times (i.e., 7×6 times), and a biaxial stretching temperature of 125 °C.

[1206] Next, the stretched gel sheet was guided to a methyl ethyl ketone bath, sufficiently impregnated in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone to obtain a porous body.

[1207] Next, in order to perform heat setting (HS), the porous body was guided to a TD tenter, and HS was performed at a heat setting temperature of 125 °C and a stretching ratio of 1.8 times. Then, a relaxation operation with a ratio of 0.5 times in the TD direction (i.e., the HS relaxation ratio was 0.5 times) was performed.

[1208] In Comparative Example V-1, in order to use the heat-treated porous body as a separator, for the obtained porous body, the ends were cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[1209] Regarding Comparative Example V-1, at the above evaluation, the microporous membrane unwound from the master roll was slit as needed and used as an evaluation separator.

[1210] [Evaluation Results]

[1211] For the microporous membranes and batteries obtained in Examples V-1 to V-12 and Comparative Examples V-1 to V-2, various evaluations were carried out according to the above evaluation method, and the evaluation results are also shown in Tables 14 to 16.

[1212] [Table 14]

[1213]

[1214] [Table 15]

[1215]

[1216] [Table 16]

[1217]

[1218] <Experimental Group VI>

[1219] 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 Laid-Open No. 2001-176484), and are respectively designated as Porous Membranes V-1 to V-5. For Porous Membranes V-1 to V-5, the gel fraction (%), heat resistance temperature (°C), and needle penetration strength (gf / 25 μm) were evaluated according to the method described in Patent Document 5. Further, according to the above item <Storage Modulus, Loss Modulus, and Transition Temperature (version 1)> of this specification, the change ratios R △E’ and R △E” of the storage modulus and loss modulus of Porous Membrane V-4 before and after contacting the electrolytic solution were measured. The results are shown in Table 17.

[1220] [Table 17]

[1221]

[1222] The following points can be clarified from Table 17.

[1223] (a) Even for the porous membrane V-4 with the lowest gel fraction (Comparative Example 2 of Patent Document 5, gel fraction: 36%), the magnification of the elastic modulus change remains 1. Therefore, it was confirmed that the porous membranes V-1 to V-5 have all undergone thorough crosslinking reactions, and the porous membranes described in Patent Document 5 do not have self-crosslinking properties (uncrosslinked portions).

[1224] (b) Additionally, Comparative Example 1 of Patent Document 5 is an unmodified silane product.

[1225] (c) The value of the separator of the seventh embodiment of the present invention described above lies in selectively chemically crosslinking the amorphous region between crystals and crystal parts. When an unmodified silane polyolefin and a modified silane polyolefin form mixed crystals, the modified units are repelled by the amorphous part and are irregularly dispersed. In this state, the connected crosslinking units come into contact and undergo a crosslinking reaction.

[1226] On the other hand, if multiple crosslinking units are far from each other, even if crosslinking units exist, they cannot contribute to the crosslinking reaction. Especially once the crosslinking reaction from silanol to siloxane in the porous membrane satisfies its (all) reaction conditions, the reaction immediately proceeds, and the units capable of participating in crosslinking can be fully crosslinked. Therefore, it is impossible to further crosslink the remaining units in the battery including the porous membrane.

[1227] Therefore, even if there are remaining silanol groups in the porous membranes such as V-1 to V-5, as long as crosslinking treatment is performed during the manufacturing process of these membranes, the crosslinking reaction in the battery containing the membrane will not occur (that is, the remaining silanol groups cannot contribute to the crosslinked structure).

[1228] (d) Regarding the separator of the seventh embodiment of the present invention, by adjusting the molecular weight of the raw material resin, copolymer concentration, compounding ratio, etc., and further combining with the stretching film-forming process, it was experimentally found that the intercrystalline distance at which the crosslinking reaction of crosslinking units can occur with a high probability and the crystal structure with a dispersed distribution of crossl...

Claims

1. A separator for an electricity storage device, which includes a silane-modified polyolefin, a first porous layer (layer A) capable of forming a crosslinked structure, and a second porous layer (layer B) containing inorganic particles, wherein, In the manufacturing process of the separator for the electricity storage device, no crosslinking reaction is carried out, and when the separator for the electricity storage device comes into contact with the electrolyte, the silane crosslinking reaction of the silane-modified polyolefin starts; the thermal shrinkage rate of the separator for the electricity storage device at 150 °C after forming the crosslinked structure is 0.02 times or more and 0.91 times or less of the thermal shrinkage rate at 150 °C before forming the crosslinked structure; the ratio TA / TB of the thickness TA of the A layer to the thickness TB of the B layer is 0.22 or more and 14 or less, and the thickness TB of the B layer is 1.00 μm or more and 15.00 μm or less; the content of the silane-modified polyolefin in the A layer is 0.5% by weight to 40% by weight, the A layer further contains polyethylene, and the content of the polyethylene in the A layer is 20% by mass or more and 97% by mass or less based on the total amount of the silane-modified polyolefin and the polyethylene.

2. The separator for an electricity storage device according to claim 1, wherein, The crosslinked structure in the A layer is formed by an acid, a base, swelling, or a compound generated in the electricity storage device.

3. The separator for an electric storage device according to claim 1 or 2, wherein, The content of the inorganic particles in the B layer is 5% by weight to 99% by weight.

4. The separator for an electric storage device according to claim 1 or 2, wherein, The inorganic particles are at least one selected from the group consisting of alumina (Al2O3), silica, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxyhydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand, and glass fiber.

5. An electricity storage device, which includes an electrode, the separator for the electricity storage device according to any one of claims 1 to 4, and a non-aqueous electrolyte.

6. A method for manufacturing a separator for an electricity storage device, which is the method for manufacturing the separator for the electricity storage device according to any one of claims 1 to 4, and includes the following steps: (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. (2) A stretching step of stretching the sheet in at least a uniaxial direction to obtain a stretched product. (3) A porous body forming step of extracting the plasticizer from the stretched product in the presence of an extraction solvent to make the stretched product porous and form a porous body; and (4) A heat treatment step of subjecting the porous body to heat treatment.

7. A method for manufacturing an electricity storage device according to claim 5, which includes the following steps: (1) A sheet forming step of extruding a silane-modified polyolefin, polyethylene, and a plasticizer into a sheet by an extruder, cooling and solidifying, and processing into a sheet-shaped body. (2) A stretching step of biaxially stretching the sheet-shaped body at a surface magnification of 20 times or more and 250 times or less to form a stretched product. (3) A porous body forming step of extracting the plasticizer from the stretched product to form a porous body. (4) A heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing in the width direction to obtain a heat-treated porous body. (8B) Coating step: an inorganic porous layer containing inorganic particles and a resin binder is formed on at least one surface of the heat-treated porous body to form a silane crosslinking precursor; (9) Assembly step: an electrode, a laminate or a wound body of the silane crosslinking precursor, and a non-aqueous electrolyte are accommodated in a housing, and the silane crosslinking precursor is brought into contact with the non-aqueous electrolyte; In the step (8B), the heat-treated porous body maintains silane crosslinkability, and in or after the step (9), the silane-modified polyolefin crosslinks.

8. A battery device assembly kit, which comprises the following two elements: Element 1: a housing that houses a laminate or a wound body of an electrode and a separator for a battery device according to any one of claims 1 to 4; and Element 2: a container that houses a non-aqueous electrolyte.

9. The battery storage device assembly kit according to claim 8, wherein, The non-aqueous electrolyte contains a fluorine (F)-containing lithium salt.

10. The battery assembly kit according to claim 8, wherein, The non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6).

11. The battery storage device assembly kit according to claim 8, wherein, The non-aqueous electrolyte is an acid solution and / or a base solution.

12. A method for manufacturing a battery device, which includes the following steps; A step of preparing a battery device assembly kit according to any one of claims 8 to 11, and A step of starting a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator for a battery device in Element 1 of the battery device assembly kit into contact with the non-aqueous electrolyte in Element 2.

13. The method for manufacturing a battery device according to claim 12, which further includes the following steps: A step of connecting a lead terminal to the electrode in Element 1, and A step of performing at least one cycle of charge and discharge.

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