Lithium ion battery using crosslinkable separator

Abstract

To provide: a separator for an electricity storage device that can exhibit both a shutdown function and high-temperature puncture resistance, while ensuring electricity storage device safety, output and / or cycle stability; and a novel crosslinking method suitable for its production process, and an assembly kit or production method for the electricity storage device.SOLUTION: The present invention provides: a separator for an electricity storage device comprising a silane-modified polyolefin, where silane crosslinking reaction of the silane-modified polyolefin is initiated when it contacts an electrolyte solution; and a method for producing the separator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator for an electricity storage device and a crosslinking method thereof, an electricity storage device assembly kit, a method for manufacturing an electricity storage device, and the like. [Background technology]

[0002] Microporous membranes are widely used as separation or permselective separation membranes for various substances, separators, etc., and examples of their applications include microfiltration membranes, separators for fuel cells and capacitors, base materials for functional membranes in which functional materials are filled into the pores to exhibit new functions, separators for electricity storage devices, etc. In particular, polyolefin microporous membranes are suitably used as separators for lithium ion batteries, which are widely used in notebook personal computers, mobile phones, digital cameras, etc.

[0003] To ensure battery safety, separators are required to achieve both a shutdown function and an improved membrane rupture temperature. For example, Patent Document 1 describes the adjustment of the high-order physical properties of polyolefin resins, which are essential components of lithium-ion battery separators. Furthermore, as shown in Patent Document 2, within a specific crystallinity and gel fraction range, the shutdown function suppresses heat generation due to short circuits within the battery, while the membrane does not rupture even if high-temperature areas occur locally within the battery cell (breakdown at 170°C or higher), thereby ensuring battery safety. Regarding Patent Documents 1 and 2, more specifically, it has been experimentally demonstrated that high-temperature membrane rupture can be achieved by constructing silane crosslinks (gelation structures) within polyolefin separators.

[0004] For example, Patent Documents 1 to 6 describe a silane crosslinked structure formed by contacting a separator containing silane-modified polyolefin with water. Patent Document 8 describes a crosslinked structure formed by ring-opening of norbornene by irradiation with ultraviolet light, electron beams, or the like. Patent Document 9 describes that the insulating layer of a separator contains a (meth)acrylic acid copolymer with a crosslinked structure, a styrene-butadiene rubber binder, or the like. Furthermore, for example, a separator has been proposed in which the thickness ratio between layer A having shutdown properties and layer B containing aramid resin and inorganic material is adjusted within a predetermined range (see Patent Document 11).

[0005] Lithium-ion batteries use components such as positive and negative electrode materials, electrolytes, and separators. Of these components, the separator, due to its insulating properties, is required to be inert to electrochemical reactions and surrounding components. Meanwhile, since the initial development of lithium-ion battery negative electrode materials, a technology has been established to suppress decomposition of the electrolyte on the negative electrode surface by forming a solid electrolyte interface (SEI) through a chemical reaction during the initial charge (Non-Patent Document 1). Even when polyolefin resin is used for the separator, oxidation reactions are induced on the positive electrode surface under high voltage, and cases of separator blackening and surface deterioration have been reported.

[0006] Based on the above concepts, polyolefin microporous membranes have been widely developed and put to practical use as separator materials for power storage devices, in order to adopt chemical structures inert to electrochemical reactions and other chemical reactions. However, as long as polyolefin is used as the resin, there are limitations to performance improvement, even if the separator's mechanical microporous structure is improved. For example, the separator's heat resistance stability above the melting point of polyolefin or the electronegativity of the olefin unit results in insufficient affinity or liquid retention with the electrolyte, resulting in insufficient permeability of Li ions or their solvated ion clusters through the separator.

[0007] As described above, due to the above limitations, it is not possible to expect current solutions to satisfy the high-speed charge / discharge or heat resistance stability required in modern battery development. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 9-216964 [Patent Document 2] International Publication No. 97 / 44839 [Patent Document 3] Japanese Patent Application Publication No. 11-144700 [Patent Document 4] Japanese Patent Application Publication No. 11-172036 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-176484 [Patent Document 6] Japanese Patent Application Laid-Open No. 2000-319441 [Patent Document 7] Japanese Patent Application Laid-Open No. 2017-203145 [Patent Document 8] Japanese Patent Application Laid-Open No. 2011-071128 [Patent Document 9] Japanese Patent Application Laid-Open No. 2014-056843 [Patent Document 10] Japanese Patent Application Publication No. 10-261435 [Patent Document 11] Japanese Patent Application Laid-Open No. 2007-299612 [Patent Document 12] International Publication No. 2010 / 134585 [Patent Document 13] Japanese Patent Application Laid-Open No. 2016-072150 [Non-patent literature]

[0009] [Non-Patent Document 1] Lithium-ion Secondary Batteries (2nd Edition) Published by Nikkan Kogyo Shimbun [Non-patent document 2] Basic Polymer Chemistry, Tokyo Kagaku Dojin Publishing Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, lithium-ion secondary batteries for mobile devices and automobiles have been achieving higher power output and higher energy density. Meanwhile, there is a demand for smaller battery cells and stable cycle discharge and charge performance during long-term use. To this end, separators used must be thin (e.g., 15 μm or less) and of high quality (e.g., uniform physical properties and no resin aggregates). Furthermore, battery safety standards have become stricter than before, and as described in Patent Documents 1 and 2, shutdown functionality and high-temperature membrane rupture resistance are required. Therefore, the development of separator resin compositions and manufacturing methods that enable stable production is anticipated. In this regard, a shutdown temperature of less than 150°C is desirable, and a higher membrane rupture temperature is desirable.

[0011] For example, the method described in Patent Document 3 uses a crosslinking catalyst masterbatch during the extrusion process to promote the crosslinking reaction of silane-modified polyethylene in the extruder, but this also results in the formation of resin aggregates, reducing the uniformity of the separator's physical properties. In contrast to this method, the methods described in Patent Documents 4, 5, and 6 address this issue by incorporating a plasticizer extraction process or a silane gel crosslinking process, controlling the gel fraction of the resin film, or molding the uncrosslinked resin by passing it through hot water and then dehydrating it. Patent Document 7 also proposes providing a heat-resistant resin microporous membrane with low heat shrinkage, low fluidity, and excellent meltdown resistance by adjusting the gel fraction, storage modulus at temperatures between 40°C and 250°C measured by dynamic viscoelasticity (DMA), maximum shrinkage measured by thermomechanical analysis (TMA), and radical content measured by electron spin resonance (ESR).

[0012] Furthermore, for separators for power storage devices, from the viewpoints of dimensional stability, maintaining the shutdown function while improving the membrane rupture temperature, and dimensional stability, it has been proposed to dispose an inorganic porous layer containing inorganic particles such as calcined kaolin or boehmite and a resin binder on at least one surface of a polyolefin microporous membrane (Patent Documents 12 and 13).

[0013] However, the method disclosed in Patent Document 4 does not allow the silane crosslinking reaction to proceed sufficiently, making it difficult to obtain high-temperature film rupture resistance.The plasticizer extraction process described in Patent Documents 3 and 4 uses a tin(II)-based crosslinking catalyst, which allows the crosslinking reaction to proceed, but there is concern that the crosslinking catalyst may remain afterwards.

[0014] The heat-resistant resin microporous membrane described in Patent Document 7 is obtained simply by applying a photopolymerizable coating solution to a membrane that has been made porous by a dry method. Furthermore, 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, if a low-molecular-weight silane coupling agent is used in a wet porosity-making method, it is expected that the low-molecular-weight silane coupling agent will not bond with the resin of the porous membrane because it easily reacts or bonds with the plasticizer used for porosity-making. Furthermore, batteries equipped with a heat-resistant resin microporous membrane as described in Patent Document 7 as a separator have poor cycle characteristics, and during long-term use, unexpected side reactions may occur within the battery, raising concerns about reduced battery safety.

[0015] Furthermore, the coating layer described in Patent Document 7 is formed by applying a compound having a polymerizable functional group to a resin porous membrane and then undergoing a crosslinking reaction in response to an external stimulus. Therefore, it is expected that the coating layer will partially penetrate the resin porous membrane upon application, and that a mixed region of the coating layer and the resin porous membrane will also form near the interface after the crosslinking reaction has progressed. While this provides good TMA heat shrinkage performance, it is expected that the battery cycle characteristics will deteriorate due to clogging of the resin porous membrane or that fuse (shutdown) performance will deteriorate due to melting of the resin porous membrane. Furthermore, a small amount of radical species compound was detected by ESR in the composite microporous membrane obtained by the method described in Patent Document 7. This residual radical species compound is expected to undergo a radical reaction with other components, particularly the electrolyte, when the composite microporous membrane is incorporated into a battery, leading to a chain reaction that decomposes the electrolyte and significantly impairs battery performance.

[0016] Furthermore, the microporous membranes and separators described in Patent Documents 1, 2, and 7 lack consideration of disposing an inorganic porous layer containing inorganic particles and a resin binder on their surfaces. Conventional separators with an inorganic porous layer on a microporous membrane appear to have a higher membrane rupture temperature on the temperature-resistance curve of an electricity storage device. However, in reality, resin may leach from the microporous membrane into the inorganic porous layer, which is expected to result in membrane loss throughout the separator and a resulting decrease in stress resistance. Therefore, while the multilayer porous membranes described in Patent Documents 12 and 13 include a polyolefin microporous membrane and an inorganic porous layer, there is room for consideration regarding the compatibility of low-temperature shutdown function and high-temperature membrane rupture resistance as separators for electricity storage devices, or the improvement of the cycle characteristics and nail penetration safety of the battery.

[0017] Furthermore, batteries using separators such as those described in Patent Documents 3 to 7 have poor cycle characteristics, and when used for a long period of time, unexpected side reactions are induced within the battery, raising concerns about a decrease in battery safety.

[0018] For typical molded products such as hot water pipes, a tin (Sn)-based catalyst is added to the extruder during the extrusion process. On the other hand, the wet manufacturing process for separators for energy storage devices typically involves steps such as extrusion and sheet molding, stretching, plasticizer extraction (porosification), heat treatment, and winding. If silane crosslinking is promoted in the extruder during the sheet molding process, gelled areas can lead to production defects and make it difficult to stretch the silane-crosslinked polyolefin in the subsequent stretching process. Therefore, there is still room for research into new separators for energy storage devices that are compatible with this manufacturing process.

[0019] Furthermore, the crosslinking methods described in Patent Documents 1 to 6, 8, and 9 are all performed in-process during separator film formation or in a batch immediately after separator film formation. Therefore, after forming the crosslinked structure described in Patent Documents 1 to 6, 8, and 9, the separator must be coated and slit, and the internal stress increases during the subsequent lamination and winding process with the electrodes, which can cause deformation of the manufactured battery. For example, if a crosslinked structure is formed by heating, the internal stress of the separator having the crosslinked structure can increase at room temperature or room temperature. Furthermore, when a crosslinked structure is formed by irradiation with light such as ultraviolet light or electron beams, the light irradiation may become uneven, resulting in an inhomogeneous crosslinked structure. This is thought to be because the periphery of the crystalline parts of the resin that constitutes the separator is easily crosslinked by the electron beam.

[0020] 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 solution. However, the technique described in Patent Document 10 does not aim to improve the cycle characteristics by specifying the structure of the separator.

[0021] Furthermore, the separators for electricity storage devices described in Patent Documents 1, 2 and 11 still have room for improvement in terms of improving the performance of the electricity storage device.

[0022] In view of the above problems, the present invention aims to provide a separator for an electricity storage device that combines a shutdown function with high-temperature rupture resistance and can ensure the safety, output, and / or cycle stability of the electricity storage device, and a novel crosslinking method that is compatible with the manufacturing process thereof, or an assembly kit or manufacturing method for an electricity storage device. [Means for solving the problem]

[0023] The above problems are solved by the following technical means. [1] A separator for an electric storage device, comprising a silane-modified polyolefin, wherein a silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator for an electric storage device comes into contact with an electrolyte. [2] 2. The separator for an electricity storage device according to item 1, wherein the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst that crosslinks the silane-modified polyolefin. [3] 3. The separator for an electricity storage device according to item 1 or 2, wherein the separator for an electricity storage device contains polyethylene in addition to the silane-modified polyolefin. [4] 4. The separator for an electricity storage device according to item 3, wherein the mass ratio of the silane-modified polyolefin to the polyethylene (mass of silane-modified polyolefin / mass of polyethylene) is 0.05 / 0.95 to 0.40 / 0.60. [5] A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (1): R ΔE’ =E' S / E' j (1) {where, E' j is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' Sis the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction, and E' j or E' S The conditions for measuring the storage modulus E' are defined by the following features (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample thickness: 5μm to 50μm Measurement temperature range: -50 to 225°C Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.5N Initial gap distance (at 25°C): 25mm Auto strain adjustment: Enabled (Range: Amplitude 0.05 to 25%, Sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal load is within 5 N and the increase in the amplitude value is within 25%, and the vibratory stress is measured. (iv) The relationship between the obtained sinusoidal load and amplitude value, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε* E * =E'+iE'' (In the formula, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus E' is calculated from The storage modulus change ratio (R ΔE’ ) is 1.5 to 20 times. [6] A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (3): R ΔE’’ =E'' S / E'' j (3) {in formula, E'' j is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' S is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction, and E'' j or E'' S The measurement conditions for the loss modulus E'' are defined by the following features (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample thickness: 5μm to 50μm Measurement temperature range: -50 to 225°C Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.5N Initial gap distance (at 25°C): 25mm Auto strain adjustment: Enabled (Range: Amplitude 0.05 to 25%, Sine wave load 0.02 to 5N) Do this. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal load is within 5 N and the increase in amplitude value is within 25%, and the vibratory stress is measured again. (iv) The obtained sinusoidal load and amplitude values, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε * E * =E'+iE'' (In the formula, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load Calculate the loss modulus E'' from The loss modulus change ratio (R ΔE’’ ) is 1.5 to 20 times. [7] A separator for an electricity storage device, characterized in that a silane crosslinking reaction of a silane-modified polyolefin occurs when the separator for an electricity storage device comes into contact with an electrolyte. [8] A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (2): R E’mix =E' a / E'0(2) {where, E' a is the storage modulus of the separator for an electric storage device measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for an electric storage device that does not contain the silane-modified polyolefin measured at 160°C to 220°C, and E' a The conditions for measuring the storage modulus E', which is E'0, are defined by the following features (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample thickness: 5μm to 50μm Measurement temperature range: -50 to 225°C Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.5N Initial gap distance (at 25°C): 25mm Auto strain adjustment: Enabled (Range: Amplitude 0.05 to 25%, Sine wave load 0.02 to 5N) Do this. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal load is within 5 N and the increase in the amplitude value is within 25%, and the vibratory stress is measured. (iv) The relationship between the obtained sinusoidal load and amplitude value, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε * E * =E'+iE'' (In the formula, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus E' is calculated from The mixed storage modulus ratio (R E’mix ) is 1.5 to 20 times. [9] A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (4): R E’’mix=E'' a / E''0(4) {in formula, E'' a is the loss modulus of the separator for an electric storage device measured at 160°C to 220°C, and E''0 is the loss modulus of the separator for an electric storage device that does not contain the silane-modified polyolefin measured at 160°C to 220°C, and E'' a The measurement conditions for the loss modulus E'' where E'' is 0 or E''0 are defined by the following configurations (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample thickness: 5μm to 50μm Measurement temperature range: -50 to 225°C Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.5N Initial gap distance (at 25°C): 25mm Auto strain adjustment: Enabled (Range: Amplitude 0.05 to 25%, Sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal load is within 20%. When the sinusoidal load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal load is within 5 N and the increase in amplitude value is within 25%, and the vibratory stress is measured again. (iv) The obtained sinusoidal load and amplitude values, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε * E * =E'+iE'' (In the formula, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load Calculate the loss modulus E'' from The mixed loss modulus ratio (R E’’mix ) is 1.5 to 20.0 times.

[10] Item 10. The separator for a storage battery device according to item 8 or 9, wherein the separator for a storage battery device that does not contain a silane-modified polyolefin is a microporous membrane made of a non-silane-modified polyolefin and has a gelation degree of 0% or more and 10% or less.

[11] A separator for an electric storage device comprising 5 to 40 mass% of a silane-modified polyolefin and 60 to 95 mass% of a polyolefin other than the silane-modified polyolefin, wherein the transition temperature between a rubber-like plateau region and a crystalline melt flow region in the temperature change of the storage modulus of the separator for an electric storage device is 135°C to 150°C.

[12] A separator for an electricity storage device made of a polyolefin microporous membrane, In measuring the solid viscoelasticity of the separator for an electricity storage device at temperatures of -50°C to 250°C, The minimum storage modulus is 1.0 MPa to 10 MPa, and the maximum storage modulus is 100 MPa to 10,000 MPa, and The minimum loss modulus is 0.1 MPa to 10 MPa, and the maximum loss modulus is 10 MPa to 10,000 MPa; The solid viscoelasticity measurement conditions for measuring the storage modulus and the loss modulus are the following conditions (i) to (iv): (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample film thickness: 200 μm to 400 μm (however, if the film thickness of a single sample is less than 200 μm, multiple samples should be stacked and the dynamic viscoelasticity measurement should be performed so that the total thickness is within the range of 200 μm to 400 μm.) Measurement temperature range: -50℃~250℃ Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.2N Initial gap distance (at 25°C): 10 mm Auto strain adjustment: Disabled Do with; (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load; (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.1%, and in the sinusoidal tensile mode, the gap distance and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 5%, and the vibratory stress is measured while the static tensile load is fixed at 0.1 N when the sinusoidal load becomes 0.1 N or less; (iv) The relationship between the obtained sinusoidal load and amplitude value, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E* ε * E * =E'+iE'' {where, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load Calculating the storage modulus and the loss modulus from A separator for an electricity storage device as defined in

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

[14] Item 14. The separator for an electricity storage device according to item 13, wherein the solid viscoelasticity measurement shows that the film softening transition temperature is 140°C to 150°C and the film rupture temperature is 180°C or higher.

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

[16] Item 16. The separator for an electricity storage device according to item 15, comprising 5% by mass to 40% by mass of a silane-modified polyolefin and 60% by mass to 95% by mass of a polyolefin other than the silane-modified polyolefin.

[17] A separator for an electricity storage device containing polyolefin, The polyolefin has one or more functional groups, and A separator for an electricity storage device, characterized in that after being housed in the electricity storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the electricity storage device, or (3) the functional groups react with other types of functional groups to form a crosslinked structure.

[18] Item 18. The separator for a storage battery device according to item 17, wherein the chemical substance is any one of an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof contained in the storage battery device.

[19] A separator for an electric storage device comprising a polyolefin, the separator having an amorphous portion crosslinked structure in which the amorphous portion of the polyolefin is crosslinked.

[20] The separator for an electricity storage device has the following formula (1): R E’X =E' Z / E' Z0 (1) {where, E' Z is the storage modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E' Z0 is the storage modulus measured in a temperature range of 160°C to 300°C before the electricity storage device separator is incorporated into the electricity storage device.} The mixed storage modulus ratio (R E’x 20. The separator for an electricity storage device according to item 19, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times. [twenty one] The separator for the electricity storage device has the following formula (3): R E’’X =E'' Z / E'' Z0 (3) {in formula, E'' Z is the loss modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E'' Z0is the loss modulus measured in a temperature range of 160°C to 300°C before the electricity storage device separator is incorporated into the electricity storage device.} The mixed loss modulus ratio (R E’’x 21. The separator for an electricity storage device according to item 19 or 20, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times. [twenty two] 22. The separator for an electricity storage device according to any one of items 19 to 21, wherein the amorphous portion is selectively crosslinked. [twenty three] The separator for the electricity storage device has the following formula (2): R E’mix =E' / E'0(2) In the formula, E' is the storage modulus measured at 160°C to 300°C when the electricity storage device separator has an amorphous crosslinked structure, and E'0 is the storage modulus of the separator for an electricity storage device that does not have an amorphous crosslinked structure, measured at 160°C to 300°C.} The mixed storage modulus ratio (R E’mix 23. The separator for an electricity storage device according to any one of items 17 to 22, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times. [twenty four] The separator for an electricity storage device has the following formula (4): R E’’mix =E'' / E''0(4) {wherein E'' is the loss modulus measured at 160°C to 300°C when the electricity storage device separator has an amorphous crosslinked structure, and E''0 is the loss modulus of the separator for an electricity storage device that does not have an amorphous crosslinked structure, measured at 160°C to 300°C.} The mixed loss modulus ratio (R E’’mix 24. The separator for an electricity storage device according to any one of items 17 to 23, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times. [twenty five] 25. The separator for an electricity storage device according to any one of items 17 to 24, wherein the polyolefin is polyethylene.

[26] 26. The separator for an electricity storage device according to any one of items 17 to 25, wherein the polyolefin is a functional group-modified polyolefin or a polyolefin copolymerized with a monomer having a functional group.

[27] 27. The separator for an electricity storage device according to any one of items 17 to 26, wherein the crosslinked structure is formed by a reaction mediated by any one of a covalent bond, a hydrogen bond, or a coordinate bond.

[28] The reaction via the covalent bond is the following reactions (I) to (IV): (I) Condensation reaction of multiple identical functional groups; (II) Reactions between multiple heterogeneous functional groups; (III) chain condensation reaction of functional groups with electrolytes; and (IV) reaction of functional groups with additives; Item 28. The separator for an electricity storage device according to Item 27, wherein the separator is at least one selected from the group consisting of:

[29] The reaction via the coordinate bond is the following reaction (V): (V) Reactions in which multiple identical functional groups crosslink through coordinate bonds with metal ions; Item 28. The separator for an electricity storage device according to Item 27,

[30] Item 29. The separator for an electrical storage device according to item 28, wherein the reaction (I) and / or (II) is catalytically promoted by a chemical substance inside the electrical storage device.

[31] Item 29. The separator for an electricity storage device according to item 28, wherein the reaction (I) is a condensation reaction of a plurality of silanol groups.

[32] Item 29. The separator for a power storage device according to Item 28, wherein the reaction (IV) is a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between a compound Rx constituting the power storage device separator and a compound Ry constituting the additive, wherein the compound Rx has a functional group x, and the compound Ry has a linking reaction unit y1.

[33] Reaction (IV) is a nucleophilic substitution reaction, The functional group x of the compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH; and The linking reaction unit y1 of the compound Ry is CH3SO2-, CF3SO2-, ArSO2-, CH3SO3-, CF3SO3-, ArSO3-, and the following formulas (y1-1) to (y1-6): [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} Item 33. The separator for an electricity storage device according to Item 32, wherein the group consisting of at least two monovalent groups represented by the following formula:

[34] Reaction (IV) is a nucleophilic substitution reaction, The compound Ry has a chain unit y2 in addition to the linking reaction unit y1, and The chain unit y2 is represented by the following formulae (y2-1) to (y2-6): [ka] {In the formula, m is an integer of 0 to 20, and n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} [ka] {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} Item 34. The separator for an electricity storage device according to Item 32 or 33, wherein the bivalent group is at least one selected from the group consisting of divalent groups represented by the following formula:

[35] Reaction (IV) is a nucleophilic addition reaction, The functional group x of the compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH; and The linking reaction unit y1 of the compound Ry is represented by the following formulae (Ay1-1) to (Ay1-6): [ka] [ka] [ka] [ka] {In the formula, R is a hydrogen atom or a monovalent organic group.} [ka] [ka] Item 33. The separator for an electricity storage device according to Item 32, wherein the group is at least one selected from the group consisting of groups represented by the following formula:

[36] the reaction (IV) is a ring-opening reaction, The functional group x of the compound Rx is at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH; and The linking reaction unit y1 of the compound Ry is represented by the following formula (ROy1-1): [ka] {In the formula, each of the multiple Xs independently represents a hydrogen atom or a monovalent substituent.} Item 33. The separator for an electricity storage device according to Item 32, wherein the group is at least two groups represented by the following formula:

[37] In the following reaction (V), the metal ion is Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ and Li + Item 30. The separator for an electricity storage device according to Item 29, wherein the separator is at least one selected from the group consisting of:

[38] A separator for an electrical storage device comprising a first porous layer (layer A) containing silane-modified polyolefin and capable of forming a crosslinked structure, and a second porous layer (layer B) containing inorganic particles, wherein the thermal shrinkage rate at 150°C after the formation of the crosslinked structure is 0.02 to 0.91 times the thermal shrinkage rate at 150°C before the formation of the crosslinked structure.

[39] Item 39. The separator for a storage battery device according to item 38, wherein the crosslinked structure in the layer A is formed by an acid, a base, swelling, or a compound generated within the storage battery device.

[40] a microporous membrane containing a silane-modified polyolefin; an inorganic porous layer containing inorganic particles and a resin binder, the inorganic porous layer being disposed on at least one surface of the microporous membrane; A separator for an electricity storage device comprising:

[41] Item 41. The separator for a power storage device according to Item 40, wherein the content of the inorganic particles in the inorganic porous layer is 5% by weight to 99% by weight.

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

[43] 43. The separator for an electricity storage device according to any one of items 40 to 42, wherein the inorganic particles are at least one selected from the group consisting of alumina (Al2O3), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxide hydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, diatomaceous earth, silica sand, and glass fiber.

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

[45] 45. The separator for a power storage device according to any one of items 40 to 44, wherein a silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator for a power storage device comes into contact with an electrolytic solution.

[46] The separator for an electricity storage device has a molecular weight of 1.01 or more, when measured excluding the inorganic porous layer, expressed by the following formula (1A): R △E’ =E' S / E' j (1A) {where, E' jis the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' S is the storage modulus measured at 160°C to 220°C of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction.} The storage modulus change ratio (R △E’ ) is 1.5 to 20 times, and / or the following formula (1B): R △E’’ =E'' S / E'' j (1B) {in formula, E'' j is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' S is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction.} The loss modulus change ratio (R △E 46. ​​The separator for an electricity storage device according to any one of items 40 to 45, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

[47] The electricity storage device separator has a molecular weight of 1000 or more when measured excluding the inorganic porous layer and has a molecular weight of 1000 or more as represented by the following formula (2A): R E’mix =E' / E'0(2A) {In the formula, E' is the storage modulus of the electricity storage device separator measured at 160°C to 220°C, and E'0 is the storage modulus of the electricity storage device separator that does not contain the silane-modified polyolefin measured at 160°C to 220°C.} The mixed storage modulus ratio (R E’mix ) is 1.5 to 20 times, and / or the following formula (2B): R E’’mix =E'' / E''0(2B) {In the formula, E" is the loss modulus of the electricity storage device separator measured at 160°C to 220°C, and E"0 is the loss modulus of the electricity storage device separator that does not contain the silane-modified polyolefin measured at 160°C to 220°C.} The mixed loss modulus ratio (R E’’mix 47. The separator for an electricity storage device according to any one of items 40 to 46, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

[48] 48. The separator for a power storage device according to any one of items 40 to 47, wherein the transition temperature between the rubber-like plateau region and the crystalline melt flow region in the change in storage modulus with temperature of the separator for a power storage device is 135°C to 150°C.

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

[50] An electricity storage device comprising a separator containing polyethylene and an electrolytic solution or an additive, in which a crosslinked structure is formed by a reaction between the functional group-modified polyethylene or the functional group-grafted copolymerized polyethylene and a chemical substance contained in the electrolytic solution or the additive.

[51] The following steps: (1) a sheet-forming step in which a mixture of silane-modified polyolefin, polyethylene, and a plasticizer is extruded, cooled and solidified, and formed into a sheet; (2) a stretching step of stretching the sheet in at least one direction to obtain a stretched product; (3) a porous body forming step of extracting the plasticizer from the stretched material in the presence of an extraction solvent to make the stretched material porous, and (4) a heat treatment step of subjecting the porous body to a heat treatment; 51. A method for producing a separator for an electricity storage device according to any one of items 1 to 50, comprising:

[52] The following steps: (1) A sheet-forming step in which the silane-modified polyolefin, polyethylene, and plasticizer are extruded into a sheet using an extruder, cooled and solidified, and processed into a sheet-shaped molded product; (2) a stretching step in which the sheet-like molded body is biaxially stretched at an areal 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 material 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) a coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinked precursor; (9) an assembly step of housing a laminate or a wound body of the electrodes and the silane cross-linked precursor, and a non-aqueous electrolyte solution in an outer casing, and bringing the silane cross-linked precursor into contact with the non-aqueous electrolyte solution; A method for producing a separator for an electricity storage device, comprising:

[53] The following two elements: (1) An exterior housing containing an electrode and a laminate or wound body of the separator for an electricity storage device according to any one of items 1 to 48; and (2) a container containing a nonaqueous electrolyte; An electricity storage device assembly kit comprising:

[54] Item 54. The electricity storage device assembly kit according to Item 53, wherein the non-aqueous electrolyte solution contains a fluorine (F)-containing lithium salt.

[55] Item 55. The electricity storage device assembly kit according to Item 53 or 54, wherein the non-aqueous electrolyte solution contains lithium hexafluorophosphate (LiPF6).

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

[57] The following steps: A step of preparing the electricity storage device assembly kit according to any one of items 53 to 56; a step of initiating a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator for the electricity storage device in element (1) of the electricity storage device assembly kit into contact with the nonaqueous electrolyte in element (2); A method for manufacturing an electricity storage device comprising:

[58] Further steps: a step of connecting a lead terminal to the electrode of the element (1); performing at least one charge / discharge cycle; Item 58. A method for producing an electricity storage device according to Item 57, comprising:

[59] A method for producing an electricity storage device using a separator containing polyolefin, comprising: The polyolefin comprises one or more types of functional groups, and the polyolefin is prepared by the steps of: (1) a cross-linking step of forming a cross-linked structure by condensing the functional groups together, (2) reacting the functional groups with chemicals inside the power storage device, or (3) reacting the functional groups with other types of functional groups. A method for manufacturing an electricity storage device comprising:

[60] Item 60. The method for producing an electricity storage device according to Item 59, wherein the crosslinking step is carried out at a temperature of 5°C to 90°C. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an electricity storage device separator that combines low-temperature shutdown function with high-temperature rupture resistance, and also to suppress the generation of unmelted resin aggregates in the manufacturing process, thereby contributing to productivity and economy, and further to provide an electricity storage device and an assembly kit therefor that have good cycle characteristics and high safety.

[0025] Furthermore, according to the present invention, since it is not necessary to form a crosslinked structure during or immediately after the film formation process, it is possible to suppress an increase in internal stress in the separator and deformation after fabrication of the electricity storage device, and / or it is possible to impart a crosslinked structure to the separator without using relatively high energy such as light irradiation or heating, thereby reducing uneven crosslinking. 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), thereby improving the strength between multiple components of the electricity storage device, and suppressing gaps that occur between the separator due to expansion and contraction of the electrodes during charge and discharge of the electricity storage device, thereby significantly improving cycle stability during long-term use. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is an example of a graph illustrating the relationship between temperature and storage modulus, comparing the storage modulus of a reference film and a crosslinked film within the temperature range of −50°C to 225°C, and showing the transition temperature between the rubber-like plateau region and the crystalline melt flow region. [Figure 2] FIG. 2 is an example of a graph illustrating the relationship between temperature and loss modulus, comparing the loss modulus of a reference film and a crosslinked film within the temperature range of −50°C to 225°C, and showing the transition temperature between the rubber-like plateau region and the crystalline melt flow region. [Figure 3] FIG. 3 is a graph showing the relationship between temperature and resistance of an electricity storage device including the separator obtained in Example I-1. [Figure 4] FIG. 4 is a graph illustrating the relationship between temperature, gap distance, storage modulus, and loss modulus in the viscoelasticity measurement of a separator for an electricity storage device, and illustrates graph (a) of Example II-1 and graph (b) of Comparative Example II-1. [Figure 5] FIG. 5 is a graph for determining the film-softening transition temperature based on the temperature, gap distance, and first derivative of gap displacement in the viscoelasticity measurement of a separator for an electricity storage device, and illustrates graph (a) of Example II-1 and graph (b) of Comparative Example II-1. [Figure 6]FIG. 6 is a schematic diagram illustrating a crystalline polymer having a higher-order structure divided into lamellae (crystalline portions), amorphous portions, and intermediate layer portions between them. [Figure 7] FIG. 7 is a schematic diagram for explaining the crystal growth of polyolefin molecules. [Figure 8] FIG. 8 is a graph of strain amount versus crystal refinement rate showing the change in X-ray crystal structure during a tensile fracture test for a film according to one embodiment of the present invention. [Figure 9] FIG. 9 is an example of a graph illustrating the relationship between temperature and storage modulus, comparing the storage modulus of a reference film and a crosslinked film within the temperature range of −50°C to 310°C, and showing the transition temperature between the rubber-like plateau region and the crystalline melt flow region. [Figure 10] FIG. 10 is an example of a graph illustrating the relationship between temperature and loss modulus, comparing the loss modulus of a reference film and a crosslinked film within the temperature range of −50°C to 310°C, and showing the transition temperature between the rubber-like plateau region and the crystalline melt flow region. [Figure 11] FIG. 11 shows (a) a 1 H-NMR chart and (b) a 13 C-NMR chart of silane-modified polyolefin raw material 1 obtained using polyolefin. [Figure 12] FIG. 12 shows (a) a 1 H-NMR chart and (b) a 13 C-NMR chart of silane-modified polyolefin raw material 2 obtained using polyolefin. [Figure 13] FIG. 13 shows (a) a 1 H-NMR chart and (b) a 13 C-NMR chart of the separator obtained in Example I-1 in a state before crosslinking. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist thereof.

[0028] In this specification, the symbol "to" means that the numerical values ​​at both ends of the symbol "to" are included as the upper and lower limits. In addition, in this specification, the upper and lower limits of a numerical range can be combined arbitrarily. For example, the upper limit of a preferred numerical range can be combined with the lower limit of a more preferred numerical range, or conversely, the upper limit of a more preferred numerical range can be combined with the lower limit of a preferred numerical range.

[0029] In this specification, the terms "on" and "formed on the surface" do not limit the positional relationship of each component to "directly on top." For example, the expressions "layer B formed on layer A" and "layer B formed on the surface of layer A" do not exclude an embodiment in which an arbitrary layer that does not fall into either of the categories of layer A and layer B is included between them.

[0030] The properties of only the microporous membrane described below can be measured after removing layers other than the microporous membrane (for example, the inorganic porous layer) from the electricity storage device separator.

[0031] <Separators for electricity storage devices> One embodiment of the present invention is a separator for an electrical storage device (hereinafter also simply referred to as "separator"). Separators are required to have insulating properties and ion permeability, and therefore generally include insulating materials having a porous structure, such as paper, polyolefin nonwoven fabric, or resin microporous membrane. In particular, for lithium-ion batteries, polyolefin microporous membranes are excellent because they can provide separators with oxidation-reduction degradation resistance and a dense, uniform porous structure. Here, the microporous membrane refers to a membrane (film) made of a porous body, and the average pore size thereof is preferably 10 nm or more and 500 nm or less, and more preferably 30 nm or more and 100 nm or less. When the separator is included in the power storage device, it is possible to remove the separator from the power storage device.

[0032] First, Second, Third, Fourth and Fifth Embodiments The separator according to the first embodiment contains a silane-modified polyolefin and may contain other polyolefins as desired. When the separator according to the first embodiment comes into contact with an electrolytic solution, a silane crosslinking reaction of the silane-modified polyolefin contained in the separator is initiated. Because the separator according to the first embodiment can crosslink the silane-modified polyolefin upon contact with the electrolytic solution, the timing of the crosslinking can be controlled, and therefore the crosslinking reaction can be carried out in the manufacturing process of the electricity storage device without carrying out the crosslinking reaction in the manufacturing process of the separator.

[0033] The separator according to the second embodiment is characterized in that a silane crosslinking reaction of the silane-modified polyolefin occurs upon contact with the electrolyte. In the second embodiment, regardless of whether the separator contains a silane-modified polyolefin, the location of the remaining silane-modified polyolefin, or whether the silane crosslinking reaction is initiated first, occurs sequentially, or occurs continuously upon contact with the electrolyte, the silane crosslinking reaction can be observed upon contact of the separator with the electrolyte. The silane crosslinking reaction of the silane-modified polyolefin that occurs upon contact of the separator according to the second embodiment with the electrolyte allows for control of the crosslinking timing, regardless of the separator's manufacturing or use process.

[0034] The separators according to the first and second embodiments can promote the crosslinking reaction when the electrolyte solution is poured into the exterior body that houses the separator, thereby avoiding production defects in the manufacturing process and achieving safety and high output of the electricity storage device in the manufacturing process of the electricity storage device. From the viewpoint of the components contained in the separator and the timing of the crosslinking reaction, it is preferable that the silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator and the electrolyte solution are mixed or contacted.

[0035] The separator according to the third embodiment contains 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, and in the viscoelasticity measurement (version 1) described in the examples, the following formula (1): R ΔE’ =E' S / E' j (1) {where, E' j is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' S is the storage modulus measured at 160°C to 220°C of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction.} The storage modulus change ratio (R ΔE’ ) is 1.5 to 20 times, and / or the following formula (3): R ΔE’’ =E'' S / E'' j (3) {in formula, E'' j is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' S is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction.} The loss modulus change ratio (R ΔE’’ In the third embodiment, the storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE’’ By setting the storage modulus change ratio (R) within the range of 1.5 to 20 times, it is possible to achieve both a shutdown function and high-temperature membrane rupture resistance. ΔE’ ) and / or the loss modulus change ratio (R ΔE’’ ) is preferably 2 to 18 times. j and E' S and E'' j and E'' Sare the average values ​​of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160 to 220°C. In addition, when the separator is in the form of a laminated film, the storage modulus E' is measured by removing only the silane-modified polyolefin-containing porous film from the laminated film. j and E' S and loss modulus E'' j and E'' S shall be measured.

[0036] The separator according to the fourth embodiment contains 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, and in the viscoelasticity measurement (version 1) described in the examples, the following formula (2): R E’mix =E' a / E'0(2) {where, E' a is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C, and E'0 is the storage modulus of the separator for an electricity storage device that does not contain a silane-modified polyolefin measured at 160°C to 220°C.} The mixed storage modulus ratio (R E’mix ) is 1.5 to 20 times, and / or the following formula (4): R E’’mix =E'' a / E''0(4) {in formula, E'' a is the loss modulus of the electricity storage device separator measured at 160°C to 220°C, and E''0 is the loss modulus of the electricity storage device separator that does not contain the silane-modified polyolefin measured at 160°C to 220°C.} The mixed loss modulus ratio (R E’’mix In the fourth embodiment, the mixed storage modulus ratio (R E’mix ) and / or the blend loss modulus ratio (R E’’mix By setting the mixed storage modulus ratio (R ) within the range of 1.5 to 20.0 times, it is possible to achieve both a shutdown function and high-temperature membrane rupture resistance.E’mix ) and / or the blend loss modulus ratio (R E’’mix ) is preferably 2 to 18 times. a and E'0 and E'' a 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 the widest temperature range is 160 to 220°C. When the separator is in the form of a laminated film, the storage modulus E' a and E'0 and loss modulus E'' a and E''0 shall be measured.

[0037] A separator according to a 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 silane-modified polyolefin. In the viscoelasticity measurement (version 1) described in the examples, the transition temperature between the rubbery plateau and the crystalline melting flow region is 135°C to 150°C in the temperature change of the storage modulus or loss modulus. In the fifth embodiment, the transition temperature between the rubbery plateau and the crystalline melting flow region is within the range of 135°C to 150°C, thereby achieving both a shutdown function and high-temperature membrane rupture resistance. The transition temperature between the rubbery plateau and the crystalline melting flow region is preferably 137°C to 147°C, more preferably 140°C to 145°C, and even more preferably 140°C to 143°C. When the separator is in the form of a laminated membrane, the transition temperature between the rubbery plateau and the crystalline melting flow region is measured by removing only the silane-modified polyolefin-containing porous membrane from the laminate.

[0038] Sixth and Seventh Embodiments The separator according to the sixth embodiment contains a polyolefin having one or more functional groups, and after being housed in an electricity storage device, (1) the functional groups of the polyolefin undergo a condensation reaction with each other, (2) the functional groups of the polyolefin react with chemicals inside the electricity storage device, or (3) the functional groups of the polyolefin react with other types of functional groups to form a crosslinked structure. It is believed that the functional groups contained in the polyolefin constituting the separator are not incorporated into the crystalline portion of the polyolefin but are crosslinked in the amorphous portion. Therefore, after being housed in an electricity storage device, the separator according to the sixth embodiment forms a crosslinked structure by utilizing the surrounding environment or chemicals inside the electricity storage device, thereby suppressing an increase in internal stress or deformation of the produced electricity storage device. On the other hand, if the crosslinking reaction is carried out before being installed in an electricity storage device and the electrode undergoes processes such as winding and slitting, the effects of stresses such as tension generated during these processes remain. In this case, if the stress is released after the electricity storage device is assembled, it is thought that this could cause deformation or damage to the electrode wound material due to stress concentration, which is undesirable.

[0039] In the sixth embodiment, (1) the condensation reaction between functional groups of a polyolefin can be, for example, a reaction via a covalent bond between two or more functional groups A contained in the polyolefin. (3) The reaction between a functional group of a polyolefin and another type of functional group can be, for example, a reaction via a covalent bond between a functional group A and a functional group B contained in the polyolefin.

[0040] Furthermore, (2) in the reaction between the functional group of the polyolefin and a chemical substance inside the electricity storage device, for example, functional group A contained in the polyolefin can form a covalent bond or a coordinate bond with any of the electrolyte, electrolytic solution, electrode active material, additive, or decomposition products thereof contained in the electricity storage device. Furthermore, reaction (2) forms a crosslinked structure not only inside the separator but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), thereby improving the strength between multiple components of the electricity storage device.

[0041] The separator according to the seventh embodiment contains a polyolefin and has an amorphous cross-linked structure in which the amorphous portion of the polyolefin is cross-linked. It is believed that the functional groups contained in the polyolefin constituting the separator are not incorporated into the crystalline portion of the polyolefin but are cross-linked in the amorphous portion. Therefore, compared to conventional cross-linked separators in which the crystalline portion and its periphery are easily cross-linked, the separator according to the seventh embodiment can suppress an increase in internal stress or deformation of the produced electricity storage device while achieving both a shutdown function and high-temperature membrane rupture resistance, thereby ensuring the safety of the electricity storage device. From the same perspective, the amorphous portion of the polyolefin contained in the separator according to the seventh embodiment is preferably selectively cross-linked, and more preferably, is significantly more cross-linked than the crystalline portion.

[0042] Although the crosslinking reaction mechanism and crosslinking structure of the seventh embodiment are not clear, the present inventors consider the following.

[0043] (1) Crystal structure in high-density polyethylene microporous membrane As shown in Figure 6, polyolefin resins, such as high-density polyethylene, are generally crystalline polymers with a higher-order structure divided into lamellae (crystalline portions), amorphous portions, and intermediate layers between them. In the crystalline portions and the intermediate layers between the crystalline and amorphous portions, the mobility of the polymer chains is low and they cannot be separated, but relaxation phenomena can be observed in the 0 to 120°C range in solid-state viscoelasticity measurements. On the other hand, the mobility of the polymer chains in the amorphous portions is very high, and these are observed in the -150 to -100°C range in solid-state viscoelasticity measurements. This is closely related to radical relaxation, radical transfer reactions, crosslinking reactions, and other reactions, which will be discussed later.

[0044] Furthermore, the polyolefin molecules that make up the crystals are not single; as shown in Figure 7, multiple polymer chains form small lamellae, which then aggregate to form crystals. This phenomenon is difficult to observe directly. In recent years, academic research using simulations has made it clearer. Note that here, a crystal is the smallest crystalline unit measured by X-ray structural analysis, and is the unit that can be calculated as the crystallite size. Thus, even within the crystalline portion (inside the lamellae), it is predicted that there are some parts that are not constrained and have somewhat high mobility.

[0045] (2) Crosslinking reaction mechanism by electron beam The reaction mechanism of electron beam crosslinking (hereafter abbreviated as EB crosslinking) of polymers is as follows: (i) irradiation of tens to hundreds of kGy of electron beams; (ii) penetration of the electron beam into the reaction target (polymer) and generation of secondary electrons; (iii) hydrogen abstraction in the polymer chain by the secondary electrons and generation of radicals; (iv) abstraction of adjacent hydrogen by the radicals and migration of active sites; and (v) crosslinking or polyene formation due to recombination of radicals. Radicals generated in the crystalline region have low mobility and therefore persist for long periods. Furthermore, impurities cannot penetrate the crystal, making the probability of reaction and quenching low. These radical species, known as stable radicals, remain for long periods of time (up to several months), and their lifetimes have been determined by ESR measurements. Consequently, crosslinking reactions within the crystal are thought to be limited. However, radicals generated in the small number of unconstrained molecular chains present within the crystal or in the surrounding crystalline-amorphous interlayer have somewhat longer lifetimes. Such radical species are called persistent radicals, and in a mobile environment, it is thought that cross-linking reactions between molecular chains will proceed with a high probability. On the other hand, since the mobility of the amorphous portion is very high, the generated radical species have a short lifespan, and it is thought that not only cross-linking reactions between molecular chains but also polyene reactions within a single molecular chain will proceed with a high probability. As described above, in a microscopic view at the crystal level, it can be assumed that the crosslinking reaction due to EB crosslinking is localized inside the crystal or its periphery.

[0046] (3) Crosslinking reaction mechanism by chemical reaction 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 electricity storage device, or a chemical substance contained in the electricity storage device, as a catalyst. As mentioned above, polyolefin resins have crystalline and amorphous regions. However, due to steric hindrance, the aforementioned functional groups are not present inside the crystals but are localized in the amorphous regions. This is generally known, and while units such as methyl groups present in small amounts in polyethylene chains may be incorporated into crystals, grafts that are bulkier than ethyl groups are not incorporated (Non-Patent Document 2). For this reason, crosslinking points resulting from reactions other than electron beam crosslinking are localized only in the amorphous regions.

[0047] (4) Relationship between differences in cross-linking structure and effects As described above, the morphology of the reaction product differs in the crosslinking reaction due to a chemical reaction inside the battery used in the seventh embodiment of the present invention. In research leading to the present invention, the following experiments were conducted to clarify the crosslinking structure and to clarify the changes in the physical properties of the microporous membrane that accompany the structural change. First, the mechanical properties of the membrane were investigated by tensile fracture tests. Simultaneously with the tensile fracture tests, changes in the crystal structure were analyzed by in-situ X-ray structural analysis using synchrotron radiation. The results, shown in Figure 8, indicate that, compared to membranes that had not undergone EB crosslinking or chemical crosslinking (before), the EB crosslinked membrane suppressed the subdivision of the crystalline region as the strain increased. This is due to selective crosslinking within or around the crystalline region. Accordingly, the Young's modulus and fracture strength improved significantly, demonstrating high mechanical strength. On the other hand, the chemically crosslinked membrane showed no difference in the subdivision of the crystals before and after the crosslinking reaction, suggesting that the non-crystalline region had been selectively crosslinked. Furthermore, there was no change in mechanical strength before and after the crosslinking reaction. Next, fuse / meltdown property tests were conducted to examine the behavior of both materials during crystalline melting. The results showed that the EB-crosslinked film exhibited a significantly higher fuse temperature, reaching a meltdown temperature of over 200°C. In contrast, the chemically crosslinked film showed no change in fuse temperature before and after crosslinking, but its meltdown temperature rose to over 200°C. Based on these findings, it is believed that the fuse (shutdown) characteristics caused by crystalline melting in the EB-crosslinked film were due to crosslinking around the crystalline region, resulting in an increase in melting temperature and a decrease in melting rate. On the other hand, the chemically crosslinked film did not have a crosslinked structure in the crystalline region, which led to the conclusion that this did not affect the shutdown characteristics. Furthermore, in the high-temperature range around 200°C, both materials retained a crosslinked structure after crystalline melting, allowing the entire resin to stabilize in a gel state, resulting in good meltdown properties.

[0048] The above findings are summarized in the table below. [Table 1]

[0049] In the separator according to the seventh embodiment, from the viewpoint of forming an amorphous crosslinked structure, achieving both a shutdown function and high-temperature membrane rupture resistance, etc., the viscoelasticity measurement (version 2) described in the examples is performed based on the following formula (1): R E’X =E' Z / E' z0 (1) {where, E' Z is the storage modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E' z0 is the storage modulus measured in a temperature range of 160°C to 300°C before the electricity storage device separator is incorporated into the electricity storage device.} The mixed storage modulus ratio (R E’x ) and / or the following formula (3): R E’’X =E'' Z / E'' Z0 (3) {in formula, E'' Z is the loss modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E'' Z0 is the loss modulus measured in a temperature range of 160°C to 300°C before the electricity storage device separator is incorporated into the electricity storage device.} The mixed loss modulus ratio (R E’’x ) is preferably 1.5 to 20 times, more preferably 3 to 18 times. Z and E' z0 and E'' Z and E'' z0 The storage modulus E' is the average value of the storage modulus or loss modulus measured within the set temperature range of the measuring device when the widest temperature range is 160°C to 300°C. In addition, when the separator is in the form of a laminated film, the storage modulus E' is measured by removing only the polyolefin porous film from the laminated film. Z and E' z0 and loss modulus E'' Z and E'' z0 shall be measured.

[0050] From the viewpoint of forming an amorphous crosslinked structure, achieving both a shutdown function and high-temperature membrane rupture resistance, etc., the separators according to the sixth and seventh embodiments are characterized in that, in the viscoelasticity measurement (version 2) described in the examples, the following formula (2): R E’mix =E' / E'0(2) In the formula, E' is the storage modulus of the separator for an electricity storage device having an amorphous crosslinked structure measured at 160°C to 300°C, and E'0 is the storage modulus measured at 160°C to 300°C of a separator for an electricity storage device that does not have an amorphous crosslinked structure.} The mixed storage modulus ratio (R E’mix ) and / or the following formula (4): R E’’mix =E'' / E''0(4) {wherein E'' is the loss modulus measured at 160°C to 300°C when the electricity storage device separator has an amorphous crosslinked structure, and E''0 is the loss modulus of the separator for an electricity storage device that does not have an amorphous crosslinked structure, measured at 160°C to 300°C.} The mixed loss modulus ratio (R E’’mix ) is preferably 1.5 to 20 times, more preferably 3 to 19 times, and even more preferably 5 to 18 times. 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, with the widest temperature range being 160°C to 300°C. When the separator is in the form of a laminated film, the storage modulus E' and E'0 and the loss modulus E'' and E''0 are measured by removing only the polyolefin porous film from the laminated film.

[0051] Eighth Embodiment Viscoelastic Behavior (Viscoelasticity Measurement Version 3 Explained in the Examples) The separator according to the eighth embodiment is made of a polyolefin microporous membrane, and in the viscoelasticity measurement (version 3) described in the examples, the separator has a minimum storage modulus (E') of 0.01% or less (E' min ) is 1.0MPa to 10MPa, and the maximum value of E' (E' max ) is 100 MPa to 10,000 MPa, and / or the minimum value of the loss modulus (E'') is min ) is 0.1MPa to 10MPa, and the maximum value of E'' (E'' max ) is 10MPa to 10,000MPa. 1.0MPa≦E' min ≦10MPa and 100MPa≦E' max ≦10,000 MPa and / or 0.1 MPa ≦ E'' min ≦10MPa and 10MPa≦E'' maxIf the pressure is in the range of 1.1 MPa ≦ E' ≦ 10,000 MPa, not only does the separator tend to have both a shutdown function and high-temperature membrane rupture resistance, but production defects can be avoided in the manufacturing process of the separator or the electricity storage device, and the stability and safety of the electricity storage device can be achieved. min ≦9.0MPa and / or 150MPa≦E' max ≦9,500 MPa is preferable, and 1.2 MPa≦E' min ≦8.0MPa and / or 233MPa≦E' max More preferably, 0.2 MPa≦E″≦9,000 MPa. min ≦9.0MPa and / or 56MPa≦E'' max ≦9,000 MPa is preferred, and 0.4 MPa ≦ E'' min ≦8.0MPa and / or 74MPa≦E'' max More preferably, it is ≦8,000 MPa.

[0052] In the solid viscoelasticity measurement (version 3), the average E' (E' ave ) is preferably 1.0 MPa to 12 MPa, more preferably 1.2 MPa to 10 MPa, and even more 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. When E' and / or E'' are within the above ranges at temperatures from the membrane softening transition temperature to the membrane rupture temperature, the cycle stability and safety of an electricity storage device including the separator tend to be improved.

[0053] In terms of achieving both a shutdown function and high-temperature membrane rupture resistance in solid viscoelasticity measurement (version 3), the membrane softening transition temperature of a separator made of a polyolefin microporous membrane is preferably 140°C to 150°C, more preferably 141°C to 149°C or 146°C to 149°C, and / or the membrane rupture temperature is preferably 180°C or higher, more preferably 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, or 240°C or higher, and even more preferably 250°C or higher. The upper limit of the membrane rupture temperature is not limited, and it is understood in this technical field that membrane rupture may occur even at temperatures higher than 250°C.

[0054] The conditions for measuring E' and E" in the solid viscoelasticity measurement (version 3) of the separator are explained in the Examples. When the separator is in the form of a laminated film, only the polyolefin microporous film is removed from the laminated film, and E' and E" of the removed polyolefin microporous film are measured. When the thickness of a single polyolefin microporous film is less than 200 μm, dynamic viscoelasticity measurement (version 3) is performed by stacking multiple polyolefin microporous films or folding a single polyolefin microporous film so that the total thickness is within the range of 200 μm to 400 μm.

[0055] The separators according to the first to eighth embodiments can include a microporous membrane and an inorganic porous layer containing inorganic particles and a resin binder, which is disposed on at least one surface of the microporous membrane, from the viewpoint of achieving both a shutdown function at a relatively low temperature and membrane rupture resistance at a relatively high temperature, and improving the cycle characteristics and safety of the electricity storage device. The separator can be in a state where the microporous membrane is used as a substrate and the substrate and the inorganic coating layer are combined.

[0056] <Ninth embodiment> The separator according to the ninth embodiment comprises: a microporous membrane comprising a silane-modified polyolefin; an inorganic porous layer including inorganic particles and a resin binder disposed on at least one surface of the microporous membrane; The separator according to the ninth embodiment may include a layer other than the microporous membrane and the inorganic porous layer, if desired.

[0057] In the ninth embodiment, the combination of a microporous membrane containing a silane-modified polyolefin and an inorganic porous layer tends to achieve both a shutdown function at temperatures below 150°C and membrane rupture resistance at relatively high temperatures, and also improves the cycle characteristics and nail penetration safety of the battery of the electricity storage device. Because the silane-modified polyolefin in the microporous membrane is silane-crosslinkable, silane crosslinking can increase the viscosity of the resin in the microporous membrane. Therefore, when a compressive force is applied between multiple electrodes at an abnormally high temperature in an electricity storage device containing the separator of the ninth embodiment, it is thought that the crosslinked, highly viscous resin is less likely to flow into the inorganic layer (i.e., less likely to be integrated), sufficient clearance between the electrodes can be secured, and battery short circuits can be suppressed.

[0058] When the separator according to the ninth embodiment comes into contact with the electrolyte, a silane crosslinking reaction of the silane-modified polyolefin is preferably initiated. More preferably, the silane crosslinking reaction is observed upon contact between the separator and the electrolyte, regardless of whether the silane crosslinking reaction is initiated first, occurs sequentially, or occurs continuously upon contact with the electrolyte. The silane crosslinking reaction of the silane-modified polyolefin that occurs upon contact between the separator and the electrolyte can control the timing of crosslinking of the separator, thereby avoiding production defects in the separator manufacturing process and achieving safety and high output in the manufacturing process of the power storage device. Furthermore, contacting the separator with the electrolyte can cause crosslinking reactions other than the silane crosslinking reaction.

[0059] In the viscoelasticity measurement (version 1) described in the examples, the separator according to the ninth embodiment has a viscoelasticity represented by the following formula (1A) when the inorganic porous layer is removed from the separator and the measurement is performed: R △E’ =E' S / E' j (1A) {where, E' j is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' S is the storage modulus measured at 160°C to 220°C of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction.} The storage modulus change ratio (R △E’ ) is preferably 1.5 to 20 times, and / or the following formula (1B): R △E’’ =E'' S / E'' j (1B) {in formula, E'' j is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' S is the loss modulus measured at 160°C to 220°C of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction.} The loss modulus change ratio (R △E The storage modulus change ratio (R △E’ ) and / or the loss modulus change ratio (R △E’’ When the storage modulus change ratio (R ΔE’ ) and / or the loss modulus change ratio (R ΔE’’ ) is more preferably 2 to 18 times. 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 the widest temperature range is 160 to 220°C. When the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, the storage modulus E' of the silane-modified polyolefin-containing microporous film is measured by removing only the silane-modified polyolefin-containing microporous film from the laminated film or composite film. j and E' Sand loss modulus E'' j and E'' S shall be measured.

[0060] In the viscoelasticity measurement (version 1) described in the examples, the separator according to the ninth embodiment has a viscoelasticity represented by the following formula (2A) when the inorganic porous layer is removed from the separator and the measurement is performed: R E’mix =E' / E'0(2A) {In the formula, E' is the storage modulus of the electricity storage device separator measured at 160°C to 220°C, and E'0 is the storage modulus of the electricity storage device separator that does not contain the silane-modified polyolefin measured at 160°C to 220°C.} The mixed storage modulus ratio (R E’mix ) is preferably 1.5 to 20 times, and / or the following formula (2B): R E’’mix =E'' / E''0(2B) {In the formula, E" is the loss modulus of the electricity storage device separator measured at 160°C to 220°C, and E"0 is the loss modulus of the electricity storage device separator that does not contain the silane-modified polyolefin measured at 160°C to 220°C.} The mixed loss modulus ratio (R E’’mix ) is preferably 1.5 to 20 times. E’mix ) and / or the blend loss modulus ratio (R E’’mix By setting the mixed storage modulus ratio (R ) within the range of 1.5 to 20 times, it is easy to achieve both shutdown function and high-temperature membrane rupture resistance. E’mix ) and / or the blend loss modulus ratio (R E’’mix) is more preferably 2 to 18 times. 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, with 160 to 220°C being the widest temperature range. When the separator is in the form of a laminated film or a composite film of a microporous film and an inorganic porous layer, the storage modulus E' and E'0 and the loss modulus E" and E"0 of the silane-modified polyolefin-containing microporous film are measured by removing only the silane-modified polyolefin-containing microporous film from the laminated film or composite film. Separators for electricity storage devices that do not contain silane-modified polyolefin will be described in detail in the Examples section.

[0061] From the viewpoint of achieving both a shutdown function and high-temperature membrane rupture resistance, the separator according to the ninth embodiment preferably has a transition temperature between the rubber-like plateau region and the crystalline melting flow region in the temperature change of its storage modulus of 135°C to 150°C. The transition temperature between the rubber-like plateau region and the crystalline melting flow region is preferably 137°C to 147°C, more preferably 140°C to 145°C, and even more preferably 140°C to 143°C. When the separator is in the form of a laminated membrane or a composite membrane of a microporous membrane and an inorganic porous layer, the transition temperature of the silane-modified polyolefin-containing microporous membrane is measured by removing only the silane-modified polyolefin-containing microporous membrane from the laminate or composite membrane.

[0062] <Tenth embodiment> According to a tenth embodiment, a separator for an electricity storage device (hereinafter simply referred to as "separator") includes a first porous layer (layer A) containing a silane-modified polyolefin and capable of forming a crosslinked structure, and a second porous layer (layer B) containing inorganic particles. Each of the layers A and B is a single layer or multiple layers. The layer B is formed on only one side or both sides of the layer A. In LIBs, a typical example of an energy storage device, lithium (Li) ions travel back and forth between the positive and negative electrodes. By placing a separator containing layers A and B between the positive and negative electrodes, it is possible to move Li ions between the electrodes at relatively high speed while preventing contact between the electrodes.

[0063] (thickness ratio) The A layer functions as a crosslinkable microporous membrane, and the B layer functions as an inorganic porous layer formed on the microporous membrane. Here, the ratio (TA / TB) of the thickness of the A layer (TA) to the thickness of the B layer (TB) is preferably 0.22 or more and 14 or less. If the ratio (TA / TB) is 0.22 or more, the proportion of the A layer in the separator can be sufficiently ensured, allowing the A layer to exhibit its functions. On the other hand, if the ratio (TA / TB) is 14 or less, the proportion of the B layer in the separator can be sufficiently ensured, allowing the B layer to exhibit its functions.

[0064] By providing the A layer and the B layer with specific structures and further setting the ratio (TA / TB) within the above range, a separator can be provided that can improve the cycle characteristics and safety of an electricity storage device. Such a separator can be suitably used as a constituent material for LIBs for use in mobile devices or automobiles, for example. From the viewpoint of the above effects, the ratio (TA / TB) is preferably 0.8 or more, more preferably 1.0 or more, while the ratio (TA / TB) is preferably 5.5 or less, more preferably 3.2 or less.

[0065] The ratio (TA / TB) may be set to, for example, less than 2.5, 2.0 or less, or 1.0 or less. In this case, the thickness (TA) of layer A is less than 2.5 times the thickness (TB) of layer B and is smaller than the thickness (TB) of layer B, making it easier to reduce the thickness of layer A, and therefore the thickness of the separator.

[0066] The total thickness (TA+TB) of the A layer and the B layer is preferably 3.0 μm or more and 22 μm or less. If the total thickness (TA+TB) is 3.0 μm or more, the membrane strength of the separator tends to be improved. On the other hand, if the total thickness (TA+TB) is 22 μm or less, the ion permeability of the separator tends to be improved. From the viewpoint of the above effects, the total thickness (TA+TB) is more preferably 3.5 μm or more, and even more preferably 4.0 μm or more. On the other hand, the total thickness (TA+TB) is more preferably 20 μm or less, and even more preferably 18 μm or less.

[0067] The total thickness (TA+TB) may be set to, for example, less than 11 μm, 10 μm or less, or 8 μm or less. Even with such a thin separator, as long as it is within the scope of the present invention, it is possible to improve the cycle characteristics and safety of the electricity storage device.

[0068] The ratio (TA / TB) and the total thickness (TA+TB) can be measured by the methods described in the Examples section, and can be controlled by adjusting the thickness (TA) and / or the thickness (TB). Layer A and layer B will be described later.

[0069] (Shutdown temperature and meltdown temperature) For Layer A, it is preferable that the shutdown temperature (sometimes referred to as fuse temperature) is 130°C to 160°C and the meltdown temperature (sometimes referred to as membrane rupture temperature) is 200°C or higher, measured based on electrical resistance under a pressure of 0.1 MPa to 10.0 MPa (preferably under a pressure of 10 MPa).

[0070] If the shutdown temperature is 130°C or higher, unnecessary activation of the shutdown function during normal reaction of the electricity storage device can be avoided, and sufficient output characteristics of the electricity storage device can be ensured. On the other hand, if the shutdown temperature is 160°C or lower, the shutdown function can be suitably activated during abnormal reaction of the electricity storage device. In addition, if the shutdown temperature is 200°C or higher, the abnormal reaction of the electricity storage device can be stopped before the temperature reaches an ultra-high temperature range, and melting and rupture of the separator can be prevented when the abnormal reaction of the electricity storage device occurs.

[0071] That is, by satisfying the above-mentioned conditions for the shutdown temperature and meltdown temperature, a separator can be realized that can provide an electricity storage device with excellent heat resistance, pore blocking characteristics (shutdown function), and melting and film rupture characteristics (meltdown function), and the separator itself can also ensure mechanical properties, ion permeability, etc. Therefore, by providing a separator whose shutdown temperature and meltdown temperature satisfy the above-mentioned conditions, the electricity storage device can achieve improved cycle characteristics and safety. From the viewpoint of the above effects, the shutdown temperature is preferably higher than 130° C., more preferably 135° C. or higher, and even more preferably 136° C. or higher. On the other hand, the shutdown temperature is preferably 150° C. or lower, more preferably 148° C. or lower, and even more preferably 146° C. or lower. Similarly, from the viewpoint of the above effects, the meltdown temperature is preferably 175° C. or higher, more preferably 178° C. or higher, and even more preferably 180° C. or higher. On the other hand, the meltdown temperature is preferably 230° C. or lower, more preferably 225° C. or lower, and even more preferably 220° C. or lower. Regarding the meltdown temperature, even if it becomes impossible to measure accurately above 200°C, as long as the temperature is 200°C or higher, the above requirement of "meltdown temperature is 200°C or higher" is met.

[0072] In this specification, the terms "shutdown temperature" and "meltdown temperature" refer to values ​​obtained by measuring electrical resistance under the above-mentioned applied pressure. That is, the above-mentioned pressure is applied to a laminate including a positive electrode, a separator, and a negative electrode, and the temperature of the laminate is increased. The shutdown temperature and meltdown temperature are derived based on the AC resistance (AC resistance between the electrodes) that increases as the pressure is applied. In a tenth embodiment, the shutdown temperature is defined as the temperature at which the AC resistance first exceeds a predetermined reference value (e.g., 1000 Ω). Further heating is then continued, and the temperature at which the AC resistance that had exceeded the reference value falls to or below the reference value (e.g., 1000 Ω) is defined as the meltdown temperature. A hydraulic jack can be used to pressurize the laminate, but this is not limiting and any other known pressurizing means may be used. An aluminum heater can be used to heat the laminate, but this is not limiting and any other known heating means may be used. The shutdown temperature and meltdown temperature can be measured by the methods described in the Examples section, and can also be controlled by adjusting the configuration or manufacturing method of the A layer.

[0073] (Heat shrinkage rate at 150℃) In Layer A, the heat shrinkage rate (T2) at 150°C after the formation of the crosslinked structure is 0.02 to 0.91 times the heat shrinkage rate (T1) at 150°C before the formation of the crosslinked structure. In other words, the ratio (T2 / T1) of the heat shrinkage rate (T2) at 150°C after the formation of the crosslinked structure to the heat shrinkage rate (T1) at 150°C before the formation of the crosslinked structure is 0.02 to 0.91. The heat shrinkage rate used here is the larger of the heat shrinkage rate in the machine direction (MD) of Layer A and the heat shrinkage rate in the transverse direction (TD) of Layer A. Because Layer A can form a crosslinked structure using silane-modified polyolefin, it becomes possible to focus on the change in the thermal shrinkage rate before and after the crosslinking.

[0074] If the ratio (T2 / T1) is 0.02 or more, the occurrence of a short circuit can be effectively suppressed, thereby reliably preventing a rise in temperature throughout the electricity storage device and the associated smoke and fire that may result. On the other hand, if the ratio (T2 / T1) is 0.91 or less, it can be determined that the crosslinking reaction in Layer A has progressed sufficiently. In other words, if the ratio (T2 / T1) is within the above range, a separator for an electricity storage device can be provided that can improve the cycle characteristics and safety of the electricity storage device. Therefore, from the viewpoint of the above-mentioned effects, the ratio (T2 / T1) is preferably 0.03 or more, more preferably 0.05 or more, and even more preferably 0.07 or more. On the other hand, the ratio (T2 / T1) is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.4 or less.

[0075] The thermal shrinkage (T1) at 150° C. before the formation of the crosslinked structure is preferably 70% or less, more preferably 60% or less. Furthermore, the heat shrinkage (T2) at 150°C after the formation of the crosslinked structure is preferably 60% or less, more preferably 50% or less. However, since the formation of the crosslinked structure tends to reduce the heat shrinkage compared to before the formation of the crosslinked structure, the heat shrinkage (T2) is generally smaller than the heat shrinkage (T1).

[0076] The heat shrinkage rate at 150°C can be measured by the method described in the Examples section, and can be controlled by adjusting the configuration or manufacturing method of the A layer.

[0077] The separators according to the above-described embodiments are interchangeable or can be combined with one another. The separator according to the ninth or tenth embodiment described above may include layers other than the microporous membrane and the inorganic porous layer, if desired. The components of the separators according to the first to tenth embodiments are described below.

[0078] [Microporous membrane] The microporous membrane can be formed from a polyolefin or a modified polyolefin.

[0079] The microporous membrane contains a silane-modified polyolefin and may contain other polyolefins as desired. Due to the silane crosslinkability of the silane-modified polyolefin, the microporous membrane can undergo a crosslinking reaction during the separator manufacturing process.

[0080] The polyolefin contained in the microporous membrane is not particularly limited, and examples thereof include homopolymers of ethylene or propylene, or copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these, high-density polyethylene (homopolymer) or low-density polyethylene is preferred, with high-density polyethylene (homopolymer) being more preferred, from the viewpoint of being able to perform heat setting (sometimes abbreviated as "HS") at higher temperatures without pore clogging. The polyolefins may be used alone or in combination of two or more.

[0081] From the viewpoints of resistance to oxidation-reduction degradation and a dense, uniform porous structure, the microporous membrane is preferably produced using both silane-modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) as raw materials. It is generally known that the weight-average molecular weight of ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more. More preferably, in the production of the microporous membrane or separator, the weight ratio of the silane-modified polyolefin to UHMWPE (silane-modified polyolefin weight / UHMWPE weight) is 0.05 / 0.95 to 0.40 / 0.60.

[0082] The content of polyolefin contained in the microporous membrane is preferably 50% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, and preferably 80% by weight or more and 100% by weight or less. Furthermore, the microporous membrane preferably contains a polyolefin having a weight-average molecular weight of 100,000 or more and less than 1,000,000 (preferably 40% by weight or more, more preferably 80% by weight or more, based on the total weight of the polyolefin). The weight-average molecular weight of the polyolefin is more preferably 120,000 or more and less than 950,000, and even more preferably 130,000 or more and less than 930,000. The use of a polyolefin having a weight-average molecular weight of 100,000 or more and less than 1,000,000 facilitates early relaxation of polymer shrinkage during heating tests of the electrical storage device, and tends to facilitate maintaining safety, particularly in heating safety tests. By adjusting the weight-average molecular weight of the microporous membrane to less than 1,000,000, it is possible to suppress molding defects (membrane patterns) during extrusion called melt fracture, while by adjusting the weight-average molecular weight of the microporous membrane to 100,000 or more, it is possible to suppress the transfer of dents when the microporous membrane is wound around a core.

[0083] The viscosity average molecular weight of the microporous membrane at the time of removing the inorganic porous layer and before crosslinking treatment is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less, from the viewpoint of preventing the generation of polymer powder due to frictional shear during roll transport of the separator.

[0084] The thickness of the microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more, 4.0 μm or more, or 4.5 μm or more. When the thickness of the microporous membrane is 1.0 μm or more, the membrane strength tends to be further improved. Furthermore, the thickness of the microporous membrane is preferably 500 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less, 22 μm or less, or 19 μm or less. When the thickness of the microporous membrane is 500 μm or less, the ion permeability tends to be further improved. The thickness of the microporous membrane can be measured by the method described in the Examples.

[0085] When the microporous membrane is used as a separator in recent relatively high-capacity lithium-ion secondary batteries, the membrane thickness is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, even more preferably 18 μm or less, and particularly preferably 16 μm or less. In this case, a membrane thickness of 25 μm or less tends to further improve permeability. In this case, the lower limit of the membrane thickness may be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, 6.0 μm or more, or 7.5 μm or more.

[0086] From the viewpoint of the high-temperature membrane rupture resistance of the separator for an electricity storage device and the safety of the electricity storage device, the microporous membrane used as the separator preferably has a melting and membrane rupture temperature of 180°C to 220°C, more preferably 180°C to 200°C, as measured by thermomechanical analysis (TMA). Generally, when an electricity storage device generates heat due to an unexpected runaway reaction, a polyolefin separator for the electricity storage device fuses at a low temperature (e.g., 150°C or below), quickly stopping the movement of Li ions and the accompanying discharge inside or outside the electricity storage device. The entire electricity storage device is then cooled by the ambient air or a refrigerant, preventing ignition of the electrolyte or an exothermic decomposition reaction of the electrolyte, thereby ensuring safety. However, if a runaway reaction occurs within the electricity storage device, it will not be stopped by the separator's fuse and will continue to generate heat, causing the separator to melt and rupture, making it impossible to ensure the safety of the device. Therefore, it is important that the separator does not melt and break down until the entire energy storage device has cooled sufficiently. Furthermore, if the temperature rises to an ultra-high temperature range of 220°C or higher, the decomposition reaction of the electrolyte or electrolyte will proceed vigorously, causing corrosion of the electrodes by the decomposition products, further generating heat and leading to an explosion. In this case, the separator will melt and break down, seeping into both electrodes and coating the active material, preventing the corrosion reaction.

[0087] [First porous layer (A layer)] The A layer contains a silane-modified polyolefin and is capable of forming a crosslinked structure. From the viewpoint of ensuring resistance to oxidation-reduction deterioration and ensuring a dense and uniform porous structure, the A layer preferably further contains polyethylene as a polyolefin different from the silane-modified polyolefin. The A layer may contain components other than the silane-modified polyolefin and polyethylene.

[0088] Examples of the polyolefin constituting the silane-modified polyolefin in Layer A include homopolymers of ethylene or propylene; and copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these, the polyolefin is preferably a homopolymer of ethylene (polyethylene), more preferably a high-density polyethylene and / or a low-density polyethylene, and even more preferably a high-density polyethylene, from the viewpoint of enabling heat fixation at higher temperatures while avoiding pore clogging. The polyolefin may be used alone or in combination of two or more types.

[0089] Layer A may contain a polymer (other polymer) that does not fall under either the silane-modified polyolefin or polyethylene, within the range that does not excessively impair the effects of the present invention. The weight average molecular weight of the entire layer A is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

[0090] (Thickness of layer A) The thickness (TA) of layer A is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. If the thickness (TA) is 1 μm or more, the membrane strength tends to be further improved. On the other hand, the thickness (TA) is preferably 500 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less. If the thickness (TA) is 500 μm or less, the ion permeability tends to be further improved. The thickness (TA) may be set to, for example, 1.00 μm or more, 2.00 μm or more, or 3.00 μm or more.

[0091] When the separator is a LIB separator, the thickness (TA) is preferably less than 22 μm, more preferably 21 μm or less, and even more preferably 20.5 μm or less. When the separator is a LIB separator, the upper limit of the thickness (TA) may be set to less than 13 μm or 8.5 μm or less. If the thickness (TA) is 25 μm or less, permeability tends to be further improved. The thickness (TA) may be set to, for example, less than 22.00 μm, 21.00 μm or less, 20.00 μm or less, less than 13.00 μm, or 8.50 μm or less. The lower limit of the thickness (TA) may be the same as above. The thickness (TA) can be measured by the method described in the Examples section, and can be controlled by changing the stretching ratio of the A layer, for example.

[0092] When Layer A is a single layer, the thickness of Layer A is treated as the thickness (TA). When Layer A is a multi-layer, the total thickness of the multi-layer A is treated as the thickness (TA).

[0093] (Temperature at which layer A breaks down) The film rupture temperature of the layer A measured by thermomechanical analysis (TMA) is preferably 180°C or higher and 220°C or lower. Even if an unexpected runaway reaction causes the energy storage device to overheat abnormally, the separator's shutdown function is expected to stop the movement of Li-ions and the resulting discharge inside or outside the energy storage device. The refrigerant is then expected to cool the entire energy storage device, ensuring safety. Meanwhile, by keeping the membrane rupture temperature within the above range, even if the entire energy storage device is not sufficiently cooled, or even if the temperature reaches an ultra-high temperature range, the separator melts and ruptures, permeating both electrodes and coating the active material, making it easier to suppress further heat generation. The film rupture temperature can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio in the production process.

[0094] (Porosity of microporous membrane or layer A) The porosity of the microporous membrane or Layer A is preferably 20% or more, more preferably 25% or more, and even more preferably 28% or more, 30% or more, 32% or more, or 35% or more. A porosity of 20% or more tends to further improve the ability to follow the rapid movement of Li ions. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and even more preferably 60% or less. A porosity of 90% or less tends to further improve the membrane strength and further suppress self-discharge. The porosity can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio in the production process.

[0095] (Air permeability of microporous membrane or layer A) The air permeability of the microporous membrane or layer A is preferably 1 second / 100 cm 3 More than 50 seconds / 100cm is preferable. 3 More preferably, 55 seconds / 100cm 3 More preferably, the air permeability is 1 sec / 100 cm or more, more preferably 70 seconds or more, 90 seconds or more, or 110 seconds or more. 3 If the thickness is 400 s / 100 cm or more, the balance between the membrane thickness, porosity, and average pore size tends to be improved. 3 Less than 300 seconds / 100cm, preferably less than 300 seconds / 100cm 3 , more preferably 270 seconds / 100 cm 3 Air permeability is 400 seconds / 100 cm or less. 3 If it is less than this, the ion permeability tends to be further improved. The air permeability can be measured by the method described in the Examples section, and can be controlled by changing the stretching temperature and / or stretching ratio in the production process.

[0096] (Puncture strength of microporous membrane or layer A) The pin 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 pin puncture strength is 200 gf / 20 μm or more, even if active material or the like falls off when winding a laminate of a separator and an electrode, it is easy to prevent membrane rupture due to the fallen active material or the like. It also makes it easy to reduce the possibility of short-circuiting due to expansion and contraction of the electrode during charge and discharge. On the other hand, the pin puncture strength is preferably 4000 gf / 20 μm or less, more preferably 3800 gf / 20 μm or less. If the pin puncture strength is 3500 gf / 20 μm or less, it is easy to reduce thermal contraction during heating. The pin puncture strength can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio in the production process.

[0097] [Tensile strength of microporous membrane or layer A] The tensile strength of the microporous membrane or layer A is preferably 1000 kgf / cm in both the MD (longitudinal direction of the membrane or layer A, machine direction or flow direction) and TD (direction perpendicular to the MD, width direction of the membrane or layer A). 2 More preferably, it is 1050 kgf / cm 2 More preferably, it is 1100 kgf / cm 2 The tensile strength is 1000kgf / cm 2 By satisfying this condition, breakage during slitting or winding of the electricity storage device tends to be further suppressed, or short circuits due to foreign matter or the like in the electricity storage device tend to be further suppressed. 2 More preferably, it is 4500 kgf / cm or less. 2 More preferably, it is 4000 kgf / cm or less. 2 Tensile strength is 5000kgf / cm or less. 2 or less, the microporous membrane or layer A will relax early during the heating test, weakening the contractile force, and as a result, safety tends to be enhanced.

[0098] [Tensile modulus of microporous membrane or layer A] The tensile modulus of the microporous membrane or Layer A is preferably 120 N / cm or less, more preferably 100 N / cm or less, and even 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 is not highly oriented for use in lithium-ion secondary batteries. In a heating test or the like, when a blocking agent such as polyethylene melts and shrinks, the polyethylene or the like undergoes early stress relaxation, which tends to suppress separator shrinkage in the battery and facilitate prevention of short-circuiting between electrodes (i.e., improve the safety of the separator during heating). Such a low tensile modulus is easily achieved by including polyethylene with a weight-average molecular weight of 500,000 or less in the polyolefin forming the microporous membrane or Layer A. On the other hand, the lower limit of the tensile modulus is not particularly limited, but is preferably 10 N / cm or more, more preferably 30 N / cm or more, and even more preferably 50 N / cm or more. The tensile modulus can be appropriately adjusted by adjusting the degree of stretching in the production process, or by performing relaxation after stretching as necessary.

[0099] <Polyolefin> The polyolefin is not particularly limited, but examples thereof include homopolymers of ethylene or propylene, and copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these, high-density polyethylene or low-density polyethylene is preferred, with high-density polyethylene being more preferred, from the viewpoint of being able to perform heat setting (sometimes abbreviated as "HS") at higher temperatures without pore clogging. The polyolefins may be used alone or in combination of two or more.

[0100] The separator preferably contains a polyolefin having a weight-average molecular weight (Mw) of less than 2,000,000, more preferably at least 40% by mass, and even more preferably at least 80% by mass, of the total polyolefin content. The use of a polyolefin having a Mw of less than 2,000,000 tends to facilitate early relaxation of polymer shrinkage during heating tests of the power storage device, making it easier to maintain safety, particularly in thermal safety tests. The use of a polyolefin having a Mw of less than 2,000,000 tends to result in a lower modulus of elasticity in the thickness direction of the resulting microporous membrane compared to the use of a polyolefin having a Mw of 1,000,000 or more, resulting in a microporous membrane to which the core's irregularities are more easily transferred. The weight average molecular weight of the entire polyolefin microporous film constituting the separator is preferably 100,000 or more and 2,000,000 or less, and more preferably 150,000 or more and 1,500,000 or less.

[0101] (Polyolefin having one or more functional groups) From the viewpoints of forming a crosslinked structure, resistance to oxidation-reduction degradation, and a dense, uniform porous structure, the separator preferably contains a polyolefin having one or more functional groups, such as a functional-group-modified polyolefin or a polyolefin copolymerized with a monomer having a functional group. In this specification, functional-group-modified polyolefin refers to a polyolefin to which a functional group has been bonded after production. The functional group can be bonded to the polyolefin backbone or can be introduced into a comonomer. Preferably, the functional group is involved in selective crosslinking of the amorphous portion of the polyolefin. For example, the functional group can 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 linear or cyclic heteroatom-containing hydrocarbon group, an amino group, a sulfhydryl group, a metal chelate group, and a halogen-containing group.

[0102] From the viewpoints of separator strength, ion permeability, resistance to oxidation-reduction degradation, and a dense, uniform porous structure, the separator preferably contains both a polyolefin having one or more functional groups and a silane-unmodified polyethylene. When a polyolefin having one or more functional groups and a silane-unmodified polyethylene are used in combination, the mass ratio of the polyolefin having one or more functional groups to the silane-unmodified polyethylene in the separator (mass of the polyolefin having one or more functional groups / mass of the silane-unmodified polyethylene) is preferably 0.05 / 0.95 to 0.80 / 0.20.

[0103] (Crosslinked structure) The crosslinked structure of the separator contributes to both the separator's shutdown function and high-temperature rupture resistance, as well as the safety of the storage battery device, and is preferably formed in the amorphous portion of the polyolefin contained in the separator. The crosslinked structure can be formed, for example, by a reaction mediated by a covalent bond, a hydrogen bond, or a coordinate bond. Among these, reactions mediated by a covalent bond include the following reactions (I) to (IV): (I) Condensation reaction of multiple identical functional groups (II) Reactions between multiple heterogeneous functional groups (III) Chain condensation reaction of functional groups with electrolytes (IV) Chain condensation reaction of functional groups with additives It is preferable that the compound is at least one selected from the group consisting of: The reaction via a coordinate bond is represented by the following reaction (V): (V) A reaction in which multiple identical functional groups crosslink with eluted metal ions through coordinate bonds. It is preferable that:

[0104] Reaction (I) A schematic scheme and specific examples of reaction (I) are shown below, where A represents the first functional group of the separator. [ka] {In the formula, R is an alkyl group or heteroalkyl group having 1 to 20 carbon atoms, which may have a substituent.}

[0105] When the functional group A for reaction (I) is a silanol group, the polyolefin contained in the separator is preferably silane-graft-modified. The silane-graft-modified polyolefin has a polyolefin main chain and a structure having alkoxysilyl grafts on the main chain. Examples of the alkoxide substituted with the alkoxysilyl include methoxide, ethoxide, and butoxide. For example, in the above formula, R can be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl. Furthermore, the main chain and the graft are connected by a covalent bond, and examples of such structures include alkyl, ether, glycol, and ester. Considering the manufacturing process of the separator according to this embodiment, the silane-graft-modified polyolefin preferably has a silicon-to-carbon (Si / C) ratio of 0.2 to 1.8%, more preferably 0.5 to 1.7%, prior to the crosslinking treatment step.

[0106] The preferred silane-grafted polyolefin has a density of 0.90 to 0.96 g / cm 3 and a melt flow rate (MFR) at 190°C of 0.2 to 5 g / min. From the viewpoints of suppressing the generation of resin aggregates during the separator manufacturing process and maintaining silane crosslinkability until contact with the electrolyte, it is preferable that the silane-grafted polyolefin is not a masterbatch resin containing a dehydration condensation catalyst. It is known that dehydration condensation catalysts also function as catalysts for the siloxane bond-forming reaction of alkoxysilyl group-containing resins. In this specification, a compound obtained by adding a dehydration condensation catalyst (e.g., an organometallic catalyst) to an alkoxysilyl group-containing resin or other kneaded resins in advance during a continuous resin kneading process using an extruder is referred to as a masterbatch resin.

[0107] Reaction (II) A schematic scheme and a specific example of reaction (II) are shown below, where the first functional group of the separator is A and the second functional group is B. [ka] [ka] [ka] [ka]

[0108] Reactions (I) and (II) can be catalyzed, for example, by a chemical substance within the electrical storage device that the separator is incorporated into. The chemical substance can be, for example, an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof, contained in the electrical storage device.

[0109] Reaction (III) A schematic scheme and a specific example of reaction (III) are shown below, where A represents the first functional group of the separator and Sol represents the electrolyte solution. [ka] [ka] [ka] [ka]

[0110] Reaction (IV) A schematic scheme of reaction (IV) is shown below, where A represents the first functional group of the separator, B represents the second functional group that is optionally incorporated, and Add represents the additive. [ka]

[0111] From the viewpoint of forming a covalent bond represented by the dotted line in the above scheme, reaction (IV) is preferably a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between compound Rx constituting the separator and compound Ry constituting the additive (Add). Compound Rx may be a polyolefin contained in the separator, such as polyethylene or polypropylene, and preferably the polyolefin is modified with functional group x, for example, at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH.

[0112] Since the multiple compounds Rx are crosslinked via the compound Ry as an additive, it is preferable that the compound Ry has two or more linking reaction units y1. The multiple linking reaction units y1 may have any structure or group, may be substituted or unsubstituted, may contain heteroatoms or inorganic substances, and may be the same or different from each other, as long as they can undergo a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction with the functional group x of the compound Rx. Furthermore, when the compound Ry has a chain structure, the multiple linking reaction units y1 can each independently be a terminal group, incorporated into the main chain, or a side chain or pendant.

[0113] When reaction (IV) is a nucleophilic substitution reaction, the following description will be given by regarding the functional group x of compound Rx as a nucleophilic group and the linking reaction unit y1 of compound Ry as a leaving group, merely as an example. In this embodiment, however, both the functional group x and the linking reaction unit y1 can become a leaving group depending on their nucleophilicity.

[0114] From the viewpoint of nucleophilic reagent, the functional group x of the compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of oxygen-based nucleophilic groups include hydroxyl groups, alkoxy groups, ether groups, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophilic groups include ammonium groups, primary amino groups, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of sulfur-based nucleophilic groups include -SH and thioether groups, with -SH being preferred.

[0115] When the reaction (IV) is a nucleophilic substitution reaction, the linking reaction unit y1 of the compound Ry, from the viewpoint of the leaving group, may be an alkylsulfonyl group such as CH3SO2- or CH3CH2SO2-; an arylsulfonyl group (-ArSO2-); a haloalkylsulfonyl group such as CF3SO2- or CCl3SO2-; - -, CH3CH2SO3 - -; aryl sulfonate groups (ArSO3 - -);CF3SO3 - -, CCl3SO3 - -; and heterocyclic groups are preferred, and these can be used alone or in combination of two or more. Heteroatoms contained in the heterocycle include nitrogen atoms, oxygen atoms, sulfur atoms, etc., and among these, nitrogen atoms are preferred from the viewpoint of leaving properties. Leaving groups containing a nitrogen atom in the heterocycle include those of the following formulae (y1-1) to (y1-6): [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} [ka] {In the formula, X is a hydrogen atom or a monovalent substituent.} A monovalent group represented by the following formula is preferred.

[0116] In formulae (y1-1) to (y1-6), X represents a hydrogen atom or a monovalent substituent. Examples of the monovalent substituent include an alkyl group, a haloalkyl group, an alkoxyl group, and a halogen atom.

[0117] When the reaction (IV) is a nucleophilic substitution reaction and the compound Ry has a chain structure, the compound Ry may contain, in addition to the linking reaction unit y1, the following formulae (y2-1) to (y2-6) as the chain unit y2: [ka] {In the formula, m is an integer of 0 to 20, and n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, n is an integer of 1 to 20.} [ka] {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} [ka] {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} It is preferable that the compound Ry has at least one selected from the group consisting of divalent groups represented by the following formula: 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.

[0118] In formula (y2-1), m is an integer of 0 to 20, and from the viewpoint of the crosslinked network, preferably 1 to 18. In formulas (y2-1) to (y2-6), n is an integer of 1 to 20, and from the viewpoint of the crosslinked network, preferably 2 to 19 or 3 to 16. In formulas (y2-5) to (y2-6), X is an alkylene group or arylene group having 1 to 20 carbon atoms, and from the viewpoint of the stability of the chain structure, preferably a methylene group, ethylene group, n-propylene group, n-butylene group, n-hexylene group, n-heptylene group, n-octylene group, n-dodecylene group, o-phenylene group, m-phenylene group, or p-phenylene group.

[0119] When reaction (IV) is a nucleophilic substitution reaction, preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 and chain unit y2 of compound Ry are shown in Tables 2 to 4 below.

[0120] [Table 2]

[0121] [Table 3]

[0122] [Table 4]

[0123] As a specific example 1 of the nucleophilic substitution reaction, the functional group x of the polyolefin is -NH2, the linking reaction unit y1 of the additive (compound Ry) is a skeleton derived from succinimide, and the chain unit y2 is -(O-C2H5) nThe reaction scheme for the case where - is shown below. [ka]

[0124] As specific example 2 of a nucleophilic substitution reaction, the reaction scheme is shown below when the functional groups x of the polyolefin are -SH and -NH, the linking reaction unit y1 of the additive (compound Ry) is a nitrogen-containing cyclic skeleton, and the chain unit y2 is o-phenylene. [ka]

[0125] When reaction (IV) is a nucleophilic addition reaction, the functional group x of compound Rx and the linking reaction unit y1 of compound Ry can undergo an addition reaction. In the nucleophilic addition reaction, the functional group x of compound Rx is preferably an oxygen-based nucleophilic group, a nitrogen-based nucleophilic group, or a sulfur-based nucleophilic group. Examples of oxygen-based nucleophilic groups include hydroxyl groups, alkoxy groups, ether groups, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophilic groups include ammonium groups, primary amino groups, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of sulfur-based nucleophilic groups include -SH and thioether groups, with -SH being preferred.

[0126] In the nucleophilic addition reaction, the linking reaction unit y1 of the compound Ry is selected from the group consisting of the following formulae (Ay1-1) to (Ay1-6), from the viewpoint of addition reactivity or availability of raw materials: [ka] [ka] [ka] [ka] {In the formula, R is a hydrogen atom or a monovalent organic group.} [ka] [ka] It is preferable that the group is at least one selected from the group consisting of groups represented by the following formula:

[0127] In formula (Ay1-4), R is a hydrogen atom or a monovalent organic group, and preferably a hydrogen atom, C 1~20 It is an alkyl group, an alicyclic group, or an aromatic group, and more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group.

[0128] When reaction (IV) is a nucleophilic addition reaction, preferred combinations of the functional group x of compound Rx and the linking reaction unit y1 of compound Ry are shown in Tables 5 and 6 below.

[0129] [Table 5]

[0130] [Table 6]

[0131] As a specific example of a nucleophilic addition reaction, the reaction scheme when the functional group x of the separator is -OH and the linking reaction unit y1 of the additive (compound Ry) is -NCO is shown below. [ka]

[0132] When reaction (IV) is a ring-opening reaction, the functional group x of compound Rx and the linking reaction unit y1 of compound Ry can undergo a ring-opening reaction, and from the viewpoint of easy availability of raw materials, it is preferable that the cyclic structure on the linking reaction unit y1 side opens. From the same viewpoint, it is more preferable that linking reaction unit y1 is an epoxy group, and it is even more preferable that compound Ry has at least two epoxy groups, and it is even more preferable that it is a diepoxy compound.

[0133] When the reaction (IV) is a ring-opening reaction, the functional group x of the compound Rx is preferably at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH, and / or the linking reaction unit y1 of the compound Ry is preferably a ring-opening reaction unit represented by the following formula (ROy1-1): [ka] {In the formula, each of the multiple Xs independently represents a hydrogen atom or a monovalent substituent.} In formula (ROy1-1), each of the multiple Xs independently represents a hydrogen atom or a monovalent substituent, and preferably represents a hydrogen atom, C 1~20 The functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry are preferably an alkyl group, an alicyclic group, or an aromatic group, and more preferably a hydrogen atom, a methyl group, an ethyl group, a cyclohexyl group, or a phenyl group. For the epoxy ring-opening reaction, preferred combinations of the functional group x of the compound Rx and the linking reaction unit y1 of the compound Ry are shown in Table 7 below.

[0134] [Table 7]

[0135] Reaction (V) The first functional group of the separator is A and the metal ion is M. n+ A schematic scheme of reaction (V) and examples of functional group A are shown below. [ka]

[0136] In the above scheme, the metal ion M n+ is preferably eluted from the electricity storage device (hereinafter also referred to as eluted metal ions), for example, Zn 2+ , Mn 2+ , Co 3+ , Ni 2+ and Li + The functional group A may be at least one selected from the group consisting of -COO - The coordinate bond in the case of is shown below. [ka]

[0137] Functional group A is -COOH and the eluted metal ion is Zn 2+ A specific scheme of reaction (V) in the case of is shown below. [ka]

[0138] In the above scheme, the hydrofluoric acid (HF) can be derived from, for example, the electrolyte, electrolytic solution, electrode active material, additive, or decomposition product or water-absorbed product thereof contained in the electricity storage device, depending on the charge / discharge cycle of the electricity storage device.

[0139] <Silane-modified polyolefin> Silane-modified polyolefins have a structure in which alkoxysilyl groups are grafted onto a polyolefin main chain. Silane-modified polyolefins can be obtained by grafting alkoxysilyl groups onto the main chain of a silane-unmodified polyolefin. It is believed that the alkoxysilyl group undergoes a hydrolysis reaction with water to convert to a silanol group, which then undergoes a crosslinking reaction to form a siloxane bond (see the formula below; the ratio of T1 structure, T2 structure, and T3 structure is arbitrary). Examples of alkoxides substituted on the alkoxysilyl group include methoxide, ethoxide, and butoxide. In the formula below, R includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl. [ka]

[0140] The main chain and the graft are connected by a covalent bond. Examples of structures that form such covalent bonds include alkyl, ether, glycol, and ester. Before the crosslinking reaction, the silane-modified polyolefin has a modified amount of silanol units of 2% or less relative to the main chain ethylene units.

[0141] The preferred silane-grafted polyolefin has a density of 0.90 to 0.96 g / cm 3 and the melt flow rate (MFR) at 190°C is 0.2 to 5 g / min.

[0142] To ensure that the effects of the present invention are satisfactorily achieved, the amount of 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 even more preferably 5% by mass or more or 6% by mass or more, based on the total amount of the microporous membrane or Layer A. To improve the cycleability and safety of the electricity storage device, the amount of 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. The amount of silane-modified polyolefin may be 30% by mass or more, 50% by mass or more, or even 100% by mass, based on the total amount of Layer A.

[0143] The crosslinked structure in the microporous membrane or layer A is preferably formed by a compound generated within the electricity storage device. That is, in the production process of an electricity storage device, when the separator is brought into contact with a non-aqueous electrolyte, a crosslinked structure in the microporous membrane or Layer A is preferably formed by forming an oligosiloxane bond using swelling of the microporous membrane or Layer A and / or a compound generated in the electricity storage device. In this case, the crosslinked structure is obtained by actively promoting the crosslinking reaction in the production process of the electricity storage device, rather than actively promoting the crosslinking reaction in the production process of the separator, and therefore the self-crosslinking properties of the separator can be maintained until it is housed in the electricity storage device.

[0144] From the viewpoints of suppressing the generation of resin aggregates during the separator manufacturing process and maintaining silane crosslinkability until contact with the electrolyte, it is preferable that the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst. Dehydration condensation catalysts are also known to function as catalysts for the siloxane bond-forming reaction of alkoxysilyl group-containing resins. In this specification, a masterbatch resin is a compound obtained by adding a dehydration condensation catalyst (e.g., an organometallic catalyst) to an alkoxysilyl group-containing resin or other kneaded resin in advance during a continuous process including a resin kneading step using an extruder.

[0145] (polyethylene) In this specification, polyethylene that can be further contained in addition to the silane-modified polyolefin (polyethylene further contained in the microporous membrane or layer A as a polyolefin other than the silane-modified polyolefin) refers to polyethylene that is a homoethylene polymer or a copolymer containing an alkane unit, whose weight-average molecular weight is from 100,000 to 10,000,000.

[0146] When the microporous membrane or layer A further contains polyethylene as a polyolefin different from the silane-modified polyolefin, the content thereof is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the silane-modified polyolefin and polyethylene. A polyethylene content of 20% by mass or more tends to ensure resistance to deterioration due to oxidation and reduction, and also tends to ensure a dense and uniform porous structure. On the other hand, the polyethylene content is preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. When the polyethylene content is 97% by mass or less, the content of silane-modified polyolefin in the microporous membrane or layer A can be ensured.

[0147] (Method for detecting silane-modified polyolefin contained in separators) When the silane-modified polyolefin contained in the separator is crosslinked, it is insoluble or has insufficient solubility in organic solvents, making it difficult to measure the content of the silane-modified polyolefin directly from the separator. In such cases, the silane-modified polyolefin contained in the separator can be detected by pretreating the sample using methyl orthoformate, which does not cause side reactions, to decompose the siloxane bonds into methoxysilanols, followed by solution NMR measurement. Pretreatment experiments can be performed with reference to Japanese Patent Nos. 3529854 and 3529858.

[0148] Specifically, the silane-modified polyolefin used as a raw material for separator production 1 H or 13 The NMR identification of C can be used to detect silane-modified polyolefins contained in separators. 1 H and 13 An example of a C NMR measurement technique is described below.

[0149] ( 1 H NMR measurement) The sample is dissolved in o-dichlorobenzene-d4 at 140°C, and a 1H-NMR spectrum is obtained with a proton resonance frequency of 600 MHz. 1 The H-NMR measurement conditions are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 1 sec Accumulation count: 1000 times or more Sample concentration: 1 wt / vol%

[0150] ( 13 C NMR measurement) The sample was dissolved in o-dichlorobenzene-d4 at 140°C. 13 Obtain a C-NMR spectrum. 13 The measurement conditions for C-NMR are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 5 seconds Accumulation count: 10,000 times or more Sample concentration: 10 wt / vol%

[0151] Figures 11 and 12 show the results of silane-modified polyolefin raw materials 1 and 2, which use two types of polyolefins. 1 H and 13 1 is a C-NMR chart, and raw materials 1 and 2 differ in melt index (MI), C3 graft amount, C4 graft amount, and / or silanol modification amount.

[0152] Figure 11 1 H and 13 The C-NMR measurement conditions are as follows: ( 1 H-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 1 H Observation frequency: 600MHz Pulse program: zg30 Pulse waiting time: 1sec Number of times accumulated: 1024 Measurement temperature: 130℃ Chemical shift reference: 7.219 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 1wt / vol% Sample tube: 5mmφ ( 13 C-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 13 C Observation frequency: 150.91MHz Pulse program: zgpg30 Pulse waiting time: 5 seconds Accumulation count: 24,000 or 12,800 Measurement temperature: 130℃ Chemical shift reference: 132.39 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 10wt / vol% Sample tube: 5mmφ

[0153] Figure 12 1 H and 13 The C-NMR measurement conditions are as follows: ( 1 H-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 1 H Observation frequency: 600MHz Pulse program: zg30 Pulse waiting time: 1sec Number of times accumulated: 1024 Measurement temperature: 130℃ Chemical shift reference: 7.219 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 1wt / vol% Sample tube: 5mmφ ( 13 C-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 13 C Observation frequency: 150.91MHz Pulse program: zgpg30 Pulse waiting time: 5 seconds Number of times: 12,800 Measurement temperature: 130℃ Chemical shift reference: 132.39 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 10wt / vol% Sample tube: 5mmφ

[0154] FIG. 13 shows a state before crosslinking of a separator produced using the silane-modified polyolefin raw material 1 shown in FIG. 11 in Example I-1 described later. 1 H and 13 13 is a C-NMR chart. 1 H and 13 The C-NMR measurement conditions are as follows: ( 1 H-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 1 H Observation frequency: 600MHz Pulse program: zg30 Pulse waiting time: 1sec Number of times accumulated: 1024 Measurement temperature: 130℃ Chemical shift reference: 7.219 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 1wt / vol% Sample tube: 5mmφ ( 13 C-NMR measurement conditions) Equipment: Bruker Avance NEO 600 Observation kernel: 13 C Observation frequency: 150.91MHz Pulse program: zgpg30 Pulse waiting time: 5 sec Accumulation count: 24,000 or 12,800 Measurement temperature: 130℃ Chemical shift reference: 132.39 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4 Sample concentration: 10wt / vol% Sample tube: 5mmφ

[0155] Furthermore, the separator in a crosslinked state can be measured by NMR similar to that shown in FIG. 13 after the pretreatment described above (not shown).

[0156] As shown in Figures 11 to 13, 1 H and / or 13 By measuring C NMR, it is possible to confirm the amount of silane unit modification in the silane-modified polyolefin and the amount of alkyl group modification in the polyolefin in the raw polyolefin material, and in the separator, it is possible to identify the content of silane-modified polyolefin (-CH2-Si: 1 H, 0.69 ppm, t; 13 C, 6.11 ppm, s) is possible.

[0157] [Combination of microporous membrane and inorganic porous layer] The combination of a microporous membrane containing silane-modified polyolefin and an inorganic porous layer tends to achieve both a shutdown function at temperatures below 150°C and membrane rupture resistance at relatively high temperatures, while also improving the cycle characteristics and nail penetration safety of the battery in an electricity storage device. Because the silane-modified polyolefin in the microporous membrane is silane-crosslinkable, silane crosslinking can increase the viscosity of the resin in the microporous membrane. Therefore, when a compressive force is applied between multiple electrodes at abnormally high temperatures in an electricity storage device containing a separator, the crosslinked, highly viscous resin is less likely to flow into the inorganic layer (i.e., less likely to integrate), ensuring sufficient clearance between the electrodes and preventing battery short circuits.

[0158] [Inorganic porous layer] The inorganic porous layer is a layer containing inorganic particles and a resin binder, and may further contain a dispersant that disperses the inorganic particles in the binder resin, if desired.

[0159] From the viewpoint of the ion permeability of the separator and the charge / discharge capacity or cycle stability of the electricity 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.

[0160] [Second porous layer (B layer)] The B layer contains inorganic particles. The B layer may further contain a resin binder. When the B layer contains inorganic particles and a resin binder, the B layer may be the inorganic porous layer described above. Note that the B layer may contain components other than the inorganic particles and the resin binder.

[0161] (Thickness of layer B) The thickness (TB) of layer B is preferably 0.2 μm or more, more preferably 0.5 μm or more. If the thickness (TB) is 0.5 μm or more, mechanical strength tends to be further improved. On the other hand, the thickness (TB) is preferably less than 22 μm, more preferably 20 μm or less, and even more preferably 15 μm or less. If the thickness (TB) is 30 μm or less, the volume occupied by the separator in the electricity storage device is reduced, which tends to be advantageous in terms of increasing the capacity of the electricity storage device. This is also preferable from the viewpoint of preventing an excessive increase in the air permeability of the separator. The thickness (TB) may be set, for example, to 0.50 μm or more, 0.80 μm or more, or 1.00 μm or more, or may be set to less than 22.00 μm, 20.00 μm or less, or 15.00 μm or less. The thickness (TB) can be measured by the method described in the Examples section, and can also be controlled by changing the coating amount of the coating liquid (slurry) for forming the B layer.

[0162] If the B layer is a single layer, the thickness of the B layer is treated as the above "Thickness (TB)". If the B layer is a single layer, the total thickness of the multiple B layers is treated as the above "Thickness (TB)". In addition, when Layer B is arranged on both one side and the other side of Layer A, the total thickness of Layer B arranged on one side and Layer B arranged on the other side is treated as the above-mentioned "thickness (TB)".

[0163] (Inorganic particles) Examples of inorganic particles include inorganic oxides (oxide ceramics) such as alumina (Al2O3), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxide hydroxide (AlO(OH)), potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These may be used alone or in combination of two or more.

[0164] The amount of inorganic particles is preferably 5% by mass or more, or 20% by mass or more, more preferably 30% by mass or more, based on the total amount of the inorganic porous layer or Layer B, from the viewpoint of ensuring heat resistance. The amount of inorganic particles may be set to 50% by mass or more, more than 80% by mass, or 85% by mass or more, based on the total amount of the inorganic porous layer or Layer B. On the other hand, the amount of inorganic particles is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, or 99% by mass or less. The amount of inorganic particles may be set to, for example, 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, or may be set to 99.90% by mass or less or 99.50% by mass.

[0165] The shape of the inorganic particles may be plate-like, scale-like, needle-like, columnar, spherical, polyhedral, spindle-like, or block-like. A combination of inorganic particles having these shapes may be used.

[0166] The number average particle size of the inorganic particles is, for example, 0.01 μm or more, 0.1 μm or more, or 0.3 μm or more, and preferably 0.5 μm or more. On the other hand, this number average particle size is, for example, 10.0 μm or less, 9.0 μm or less, or 6.0 μm or less, preferably 2.5 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less. Adjusting the number average particle size of the inorganic particles to within the above range is preferable from the viewpoint of improving safety in the event of a short circuit. Methods for adjusting the number average particle size of the inorganic particles include grinding the inorganic particles using an appropriate grinding device such as a ball mill, bead mill, or jet mill.

[0167] Regarding the particle size distribution of the inorganic particles, the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. The ratio of maximum particle size to average particle size is preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less. Adjusting the particle size distribution of the inorganic particles to within the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures. Furthermore, there may be multiple particle size peaks between the maximum particle size and the minimum particle size. Note that examples of methods for adjusting the particle size distribution of the inorganic particles include a method of pulverizing an inorganic filler using a ball mill, bead mill, jet mill, etc. to adjust it to the desired particle size distribution, and a method of preparing multiple fillers with multiple particle size distributions and then blending them.

[0168] (resin binder) The resin binder contains a resin that binds inorganic particles together. The resin binder has a glass transition temperature (Tg) of preferably −50° C. to 100° C., more preferably −35° C. to 95° C., from the viewpoint of ensuring the binding strength with the inorganic particles and the stability of the inorganic porous layer or layer B in the separator manufacturing process, or the electricity storage device manufacturing process or charge / discharge process.

[0169] The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the glass transition temperature can be determined as the temperature at the intersection of a line extending the low-temperature baseline of the DSC curve toward the high-temperature side and a tangent to the inflection point of the stepwise change in the glass transition. More specifically, the glass transition temperature can be determined according to the method described in the Examples. Furthermore, "glass transition" refers to a change in heat quantity that occurs on the endothermic side of a DSC test specimen due to a change in state of the polymer. Such a change in heat quantity is observed as a stepwise change in the DSC curve. The "stepwise change" refers to the portion of the DSC curve where the curve departs from the previous low-temperature baseline and transitions to a new high-temperature baseline. A combination of a stepwise change and a peak is also considered a stepwise change. Furthermore, the "inflection point" refers to the point at which the gradient of the stepwise change in the DSC curve is maximum. It can also be expressed as the point at which the upwardly convex curve changes to a downwardly convex curve, assuming the upper side is the heat-generating side. The "peak" refers to the portion of the DSC curve where the curve leaves the low-temperature baseline and returns to the same baseline. The "baseline" refers to the temperature range of the DSC curve where no transition or reaction occurs in the test specimen.

[0170] Examples of the resin binder include the following 1) to 7). These may be used alone or in combination of two or more. 1) Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; 3) Acrylic polymers: for example, methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers; 4) Polyvinyl alcohol-based resins: for example, polyvinyl alcohol and polyvinyl acetate; 5) Fluorine-containing resins: for example, PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; 6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0171] These types of resin binders can be obtained using desired monomers as raw materials through known manufacturing methods such as emulsion polymerization or solution polymerization. In the polymerization, the polymerization temperature, pressure during polymerization, method of adding the monomers, and additives used (polymerization initiator, molecular weight adjuster, pH adjuster, etc.) are not limited.

[0172] The amount of resin binder is, for example, 0.5% by mass or more or 1.0% by mass or more, and, for example, 50% by mass or less or 30% by mass or less, based on the total amount of the inorganic porous layer or layer B. As described above, since the resin binder is an optional component of layer B, the amount of resin binder contained in layer B may be less than 20% by mass, 15% by mass or less, or 0% by mass, based on the total amount of layer B. If the amount of resin binder contained in layer B is reduced, there is more room for incorporating the inorganic particles into layer B.

[0173] (dispersant) The dispersant adsorbs to the surface of inorganic particles in the slurry used to form the inorganic porous layer or layer B, stabilizing the inorganic particles through electrostatic repulsion or the like, and may be, for example, a polycarboxylate, a sulfonate, a polyoxyether, a surfactant, or the like. In addition to the components described above, the inorganic porous layer or layer B may further contain other components that are typically added to aqueous paints or the like, within the scope of their effects. Such other components are not particularly limited, and examples include thickeners, film-forming aids, plasticizers, crosslinking agents, antifreeze agents, antifoaming agents, dyes, preservatives, UV absorbers, and light stabilizers. These other components may be used alone or in combination of two or more.

[0174] (additives) The microporous membrane, inorganic porous layer, Layer A, and / or Layer B may contain known additives as needed, such as organometallic catalysts (dehydration condensation catalysts), plasticizers, phenolic, phosphorus-based, and sulfur-based antioxidants, metal soaps such as calcium stearate and zinc stearate, thickeners, film-forming aids, crosslinking agents, antifreeze agents, antifoaming agents, preservatives, UV absorbers, light stabilizers, antistatic agents, antifogging agents, dyes, and coloring pigments. Layer B may also contain a crosslinking agent, which may contain a functional group reactive with the inorganic particles.

[0175] <Separator properties> When the separator is used in a relatively high-capacity lithium-ion secondary battery, the thickness of the entire separator is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, even more preferably 18 μm or less, and particularly preferably 16 μm or less. A separator thickness of 25 μm or less tends to further improve ion permeability. The lower limit of the thickness of the entire 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.

[0176] The separator's air permeability is 50 seconds / 100 cm 3 ~400 seconds / 100cm 3is preferable, and more preferably 75 seconds / 100 cm 3 ~275 seconds / 100cm 3 , and more preferably 100 seconds / 100 cm 3 ~200 seconds / 100cm 3 The separator is 50 seconds / 100 cm 3 If the air permeability is above 400 seconds / 100cm, the material has adequate mechanical strength. 3 If the air permeability is within this range, the battery characteristics are improved from the viewpoint of permeability, which is preferable.

[0177] [Electricity storage device assembly kit] In another aspect of the present invention, there is provided an electricity storage device assembly kit including the above-described electricity storage device separator. The electricity storage device assembly kit includes the following two elements: (A) an exterior housing that houses a laminate or a wound body of electrodes and the separator for an electricity storage device according to each embodiment described above; and (B) a container containing a nonaqueous electrolyte; When using the electricity storage device assembly kit, a cross-linked structure is formed in the separator by bringing the separator in element (A) into contact with the nonaqueous electrolyte in element (B), bringing the electrolyte into contact with the laminate or wound body within the exterior body, and / or by continuing the charge / discharge cycle of the assembled electricity storage device, thereby making it possible to form an electricity storage device that is both safe and has high output.

[0178] Without wishing to be bound by theory, it is believed that when the electrolyte or electrolyte solution comes into contact with the electrodes and / or when the energy storage device is charged or discharged, a substance that catalyzes the crosslinking reaction or a substance having functional groups that become part of the crosslinked structure is present in the electrolyte solution, on the inner surface of the exterior body, or on the surface of the electrodes. These substances dissolve in the electrolyte solution and uniformly swell and diffuse into the amorphous portion of the polyolefin, thereby uniformly promoting the crosslinking reaction of the separator-containing laminate or wound body. The substance that catalyzes the crosslinking reaction may be in the form of an acid solution or film. When the electrolyte contains lithium hexafluorophosphate (LiPF), it can be hydrogen fluoride (HF) or a fluorine-containing organic substance derived from hydrogen fluoride (HF). The substance having functional groups that become part of the crosslinked structure can be, for example, a compound having the functional groups A and / or B described above, the electrolyte solution itself, various additives, etc.

[0179] In order to promote the cross-linking reaction of the separator, the non-aqueous electrolyte solution contained in element (2) is preferably a fluorine (F)-containing lithium salt such as LiPF6 that generates HF, or an electrolyte having an unshared electron pair such as LiN(SO2CF3)2 or LiSO3CF3, or alternatively LiBF4, LiBC4O8 (LiBOB), etc.

[0180] In order to promote the cross-linking reaction of the separator, the electricity storage device assembly kit may include, as an accessory (or element (C)), a separate container for storing a catalyst for promoting the cross-linking reaction, such as a mixture of an organometallic catalyst and water, an acid solution, or a base solution.

[0181] [Electricity storage device] The separator described above can be used in an electricity storage device. The electricity storage device includes a positive electrode, a negative electrode, a separator according to the present embodiment disposed between the positive and negative electrodes, an electrolyte solution, and, if desired, an additive. When the separator is housed in a device exterior, the functionally modified polyethylene or functionally grafted polyethylene reacts with chemicals contained in the electrolyte solution or additives to form a crosslinked structure, resulting in a crosslinked structure in the electricity storage device. The functionally modified polyethylene or functionally grafted polyethylene can be derived from, but is not limited to, the polyolefin raw material of the microporous membrane or a polyolefin modified during the manufacturing process of the microporous membrane.

[0182] Specific examples of the power storage device include lithium batteries, lithium secondary batteries, lithium ion secondary batteries, sodium secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, calcium secondary batteries, calcium ion secondary batteries, aluminum secondary batteries, aluminum ion secondary batteries, nickel-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 viewpoint of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-metal hydride batteries, and lithium ion capacitors are preferred, and lithium batteries or lithium ion secondary batteries are more preferred. The additives may be, for example, dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, coloring pigments, and the like.

[0183] [Lithium-ion secondary battery] A lithium-ion secondary battery is a storage battery that uses a lithium transition metal oxide such as lithium cobalt oxide or lithium cobalt composite oxide as a positive electrode, a carbon material such as graphite as a negative electrode, and an organic solvent containing a lithium salt such as LiPF as an electrolyte. The electrolyte described above for the electricity storage device assembly kit may also be used for a lithium-ion secondary battery. When a lithium-ion secondary battery is charged or discharged, ionized lithium travels back and forth between the electrodes. Since the ionized lithium needs to travel between the electrodes at a relatively high speed while preventing contact between the electrodes, a separator is placed between the electrodes.

[0184] <Method for manufacturing separator for power storage device> Another aspect of the present invention is a method for producing a separator for an electricity storage device. The method for producing a separator can include, for example, a step of producing a microporous membrane or an A layer, and, if desired, a step of producing an inorganic porous layer on the microporous membrane, or a step of producing a B layer on the A layer. Unless otherwise specified, the materials used in the separator production method may be those described in the first to tenth embodiments.

[0185] <Eleventh embodiment> The method for producing a separator according to the eleventh embodiment will be described below for a microporous membrane (flat membrane), but is not intended to exclude forms other than flat membranes. The method for producing a microporous membrane according to the eleventh embodiment includes the following steps: (1) Sheet forming process; (2) Stretching process; (3) porous body forming step; and (4) Heat treatment process; By carrying out steps (1) to (4), the above-described layer A can also be formed.

[0186] The method for producing a separator according to the eleventh embodiment may, if desired, include the following steps in addition to steps (1) to (4): (8B) a coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinked precursor; (9) an assembly step of housing a laminate or a wound body of the electrodes and the silane cross-linked precursor, and a non-aqueous electrolyte solution in an outer casing, and bringing the silane cross-linked precursor into contact with the non-aqueous electrolyte solution; In the eleventh embodiment, an inorganic porous layer is applied to a microporous membrane that maintains silane crosslinkability in step (8B), and then the separator in the electricity storage device is brought into contact with the electrolyte in step (9), thereby improving the stress resistance of the electricity storage device and the separator therein, and thereby achieving the cycle stability and safety of the electricity storage device.

[0187] The method for producing a microporous membrane according to the eleventh embodiment may optionally include a kneading step before the sheet-forming step (1) and / or a winding and slitting step after the heat-treatment step (3), but from the viewpoint of maintaining silane crosslinkability until contact with the electrolytic solution, it is preferable not to include a silane crosslinking treatment step. The silane crosslinking treatment step is generally a step in which an object to be treated containing a silane-modified polyolefin is brought into contact with a mixture of an organometallic catalyst and water or immersed in a basic solution or an acid solution to carry out a silane dehydration condensation reaction to form oligosiloxane bonds.

[0188] The metal of 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. Examples of organometallic catalysts include dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctoate. These catalysts are known to dramatically accelerate the reaction rate using the reaction mechanism proposed by Weij et al. (FW van. der. Weij: Macromol. Chem., 181, 2541, 1980). In recent years, in order to avoid the environmental and human health hazards posed by organotins, it has been discovered that the Lewis function of copper and / or titanium chelate complexes can be combined with an organic base to accelerate the reaction of forming siloxane bonds between alkoxysilyl groups, similar to organotin complexes.

[0189] The base solution has a pH greater than 7 and may contain, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, amine compounds, etc. Among these, from the viewpoints of safety and silane crosslinkability of the electricity storage device, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0190] The acid solution has a pH of less than 7 and may contain, for example, an inorganic acid, an organic acid, etc. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0191] In the kneading step, in this embodiment, a kneader is used to knead the silane-modified polyolefin, and, if desired, a plasticizer or inorganic material and other polyolefins. From the viewpoints of suppressing the generation of resin aggregates in the production process and maintaining silane crosslinkability until contact with the electrolytic solution, it is preferable not to add a masterbatch resin containing a dehydration condensation catalyst to the kneaded mixture.

[0192] The plasticizer is not particularly limited, but examples thereof include organic compounds that can form a homogeneous solution with polyolefin at temperatures below the boiling point. More specific examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. One plasticizer may be used alone, or two or more may be used in combination. The proportion of the plasticizer is not particularly limited, but from the viewpoint of the porosity of the resulting microporous film, the proportion of the polyolefin and silane-modified polyolefin is preferably 20% by mass or more of the total mass, as needed, and from the viewpoint of viscosity during melt-kneading, preferably 90% by mass or less.

[0193] The sheet forming step is a step in which the obtained kneaded product or a mixture of silane-modified polyolefin, polyethylene, and plasticizer is extruded, cooled and solidified, and molded into a sheet to obtain a sheet. The sheet forming method is not particularly limited, but an example is a method in which the melt-kneaded and extruded molten product is solidified by compression cooling. Cooling methods include direct contact with a cooling medium such as cold air or cooling water, and contact with a roll and / or press cooled with a refrigerant, but the method of contact with a roll and / or press cooled with a refrigerant is preferred because of its excellent film thickness controllability.

[0194] From the viewpoint of resin aggregates in the separator or the maximum internal heat generation rate, the mass ratio of the silane-modified polyolefin to the polyethylene (mass of the silane-modified polyolefin / mass of the polyethylene) in the sheet molding process is preferably 0.05 / 0.95 to 0.4 / 0.6, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0195] From the viewpoint of improving safety by suppressing thermal runaway when the electricity storage device is destroyed while maintaining low-temperature shutdown properties of 150°C or less and resistance to membrane rupture at high temperatures of 180 to 220°C, it is preferable that the silane-modified polyolefin in the sheet molding step is not a masterbatch resin that contains a dehydration condensation catalyst that crosslinks the silane-modified polyolefin before the sheet molding step.

[0196] The stretching step involves extracting plasticizers and / or inorganic materials from the resulting sheet as needed, and then stretching the sheet in one or more directions. Examples of sheet stretching methods include MD uniaxial stretching using a roll stretching machine, TD uniaxial stretching using a tenter, sequential biaxial stretching using a combination of a roll stretching machine and a tenter, or a combination of a tenter and a tenter, and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. Simultaneous biaxial stretching is preferred from the viewpoint of obtaining a more uniform film. The total areal stretching ratio is preferably 8 times or more, more preferably 15 times or more, and even more preferably 20 times or more or 30 times or more, from the viewpoints of uniformity of film thickness and the balance between tensile elongation, porosity, and average pore size. A total areal stretching ratio of 8 times or more tends to facilitate the production of a film with high strength and good thickness distribution. Furthermore, from the viewpoint of preventing breakage, the areal stretching ratio may be 250 times or less.

[0197] The porous body forming step is a step of extracting a plasticizer from the stretched product after the stretching step to make the stretched product porous. The plasticizer extraction method is not particularly limited, but examples include a method of immersing the stretched product in an extraction solvent and a method of showering the stretched product with the extraction solvent. The extraction solvent is not particularly limited, but for example, it is preferable that it is a poor solvent for polyolefins and a good solvent for plasticizers and / or inorganic materials, and has a boiling point lower than the melting point of polyolefins. Examples of such extraction solvents are not particularly limited, but examples include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropanol; ketones such as acetone and 2-butanone; and alkaline water. The extraction solvents may be used alone or in combination.

[0198] The heat treatment step is a step in which, after the stretching step, plasticizer is extracted from the sheet as needed, followed by further heat treatment to obtain a microporous membrane. The heat treatment method is not particularly limited, but examples include a heat setting method in which stretching and relaxation are performed using a tenter and / or roll stretching machine. The relaxation operation refers to a shrinking operation performed in the machine direction (MD) and / or transverse direction (TD) of the membrane at a predetermined temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation, or the value obtained by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation, or, when both MD and TD are relaxed, the value obtained by multiplying the MD relaxation rate by the TD relaxation rate.

[0199] [Inorganic Porous Layer Coating Process] The inorganic porous layer coating step (8B) is a step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the microporous membrane obtained above. The coating step (8B) can be performed while maintaining the silane crosslinkability of the silane-modified polyolefin.

[0200] The coating step (8B) can also be performed to form the above-described layer B. A known manufacturing method can be used to form the layer B. Examples of methods for producing a laminate including the layer A and the layer B include a method of coating the layer A with a slurry containing inorganic particles, a method of laminating and extruding the raw materials for the layer B and the raw materials for the layer A by co-extrusion, and a method of separately producing the layer A and the layer B and then bonding them together.

[0201] The inorganic porous layer can be formed, for example, by applying a slurry containing inorganic particles, a resin binder, water or an aqueous solvent (e.g., a mixture of water and alcohol), and optionally a dispersant to at least one surface of the microporous membrane. The inorganic particles, resin binder, and dispersant may be as described in the first to tenth embodiments.

[0202] The solvent contained in the slurry is preferably one that can uniformly and stably disperse or dissolve the inorganic particles, such as N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0203] Examples of methods for preparing the inorganic particle-containing slurry include mechanical stirring methods using a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a stirring blade.

[0204] Examples of methods for applying the inorganic particle-containing slurry 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 doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0205] Methods for removing the solvent from such a coated film include drying at a temperature below the melting point of the material constituting the microporous membrane, drying under reduced pressure at a low temperature, etc. Some of the solvent may remain as long as it does not significantly affect the device characteristics.

[0206] [Winding / Slitting process] The winding step is a step in which the obtained microporous membrane or the microporous membrane coated with the inorganic porous layer is slit as necessary and wound around a predetermined core.

[0207] [Electricity storage device assembly process] The electricity storage device assembly process is a process in which a separator precursor (hereinafter also referred to as a silane-crosslinked precursor) that has maintained silane crosslinkability and an electrode are stacked to form a laminate, the laminate is further wound as desired to form a wound body, and the laminate or wound body and a non-aqueous electrolyte are housed in an outer casing to bring the silane-crosslinked precursor into contact with the non-aqueous electrolyte. The electricity storage device assembly process suppresses thickness loss of the microporous membrane, maintains morphology, and suppresses penetration of the polyolefin resin from the microporous membrane into the inorganic porous layer, thereby improving the stress resistance of the electricity storage device or separator.

[0208] The silane-modified polyolefin crosslinks during or after the electricity storage device assembly step (9), and therefore is compatible with conventional electricity storage device manufacturing processes, while allowing a silane crosslinking reaction to occur in the separator after the electricity storage device is manufactured, thereby improving the safety of the electricity storage device.

[0209] In the energy storage device assembly process, from the viewpoint of ease of handling the electrolyte, it is preferable to encase the laminate or wound body in an outer casing and then pour the nonaqueous electrolyte into the outer casing, or to pour the electrolyte into the outer casing and then encase the laminate or wound body in the outer casing.

[0210] From the viewpoint of promoting the cross-linking reaction of the separator, the electrolyte of the nonaqueous electrolytic solution may be a fluorine (F)-containing lithium salt such as LiPF6 that generates hydrogen fluoride (HF), or an electrolyte having an unshared electron pair such as LiN(SO2CF3)2 or LiSO3CF3, or may be LiBF4 or LiBC4O8 (LiBOB).

[0211] Without wishing to be bound by theory, it is believed that the methoxysilane graft moieties are converted to silanols by the presence of trace amounts of moisture in the energy storage device (e.g., moisture contained in components such as electrodes, separators, and electrolytes), undergo crosslinking, and convert to siloxane bonds. Furthermore, when the electrolyte or electrolyte comes into contact with the electrodes, a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte or on the electrode surface. This substance dissolves in the electrolyte and uniformly swells and diffuses into the amorphous portion of the polyolefin where the silane-modified graft moieties are present, thereby uniformly promoting the crosslinking reaction of the separator-containing laminate or wound body. The substance that catalyzes the silane crosslinking reaction may be in the form of an acid solution or film. When the electrolyte contains lithium hexafluorophosphate (LiPF), it may be HF generated by the reaction of LiPF with moisture, or a fluorine-containing organic substance derived from HF.

[0212] From the viewpoint of the efficiency of the silane crosslinking reaction, it is preferable to house the laminate or wound body and the nonaqueous electrolyte in the exterior housing of the energy storage device, and then connect lead terminals to the electrodes and perform at least one charge / discharge cycle. It is believed that the charge / discharge cycle generates a substance that has a catalytic effect on the silane crosslinking reaction in the electrolyte or on the electrode surface, thereby achieving the silane crosslinking reaction. The cycle charge / discharge can be performed using known methods and devices, specifically the methods described in the Examples.

[0213] [Method for manufacturing an electricity storage device] Another embodiment of the present invention is a method for manufacturing an electricity storage device.

[0214] <Twelfth embodiment> A method for manufacturing an electricity storage device according to a twelfth embodiment includes the following steps: (A) preparing the above-described electricity storage device assembly kit; (A) initiating a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator in element (1) of the electricity storage device assembly kit into contact with the nonaqueous electrolyte in element (2); (c) optionally connecting lead terminals to the electrodes of element (1); (d) optionally, performing at least one charge / discharge cycle; Steps (a) to (d) can be performed by a method known in the art, except for using the separator for an electricity storage device according to this embodiment, and steps (a) to (d) can use a positive electrode, a negative electrode, an electrolyte, an exterior body, and a charge / discharge device known in the art.

[0215] For step (a), a separator having a vertically elongated shape with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be produced. Next, in step (a), positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are stacked in this order and wound into a circular or flat spiral to obtain a wound body. In steps (b) and (c), the wound body is placed in a device can (e.g., a battery can) and a non-aqueous electrolyte is poured into the can, thereby producing an electricity storage device. Alternatively, an electricity storage device can be produced by folding the electrodes and separator to form a wound body, placing the wound body in a device container (e.g., an aluminum film), and pouring a non-aqueous electrolyte into the can.

[0216] At this time, the wound body can be pressed. Specifically, the separator, the current collector, and the electrode having the active material layer formed on at least one surface of the current collector can be stacked and pressed.

[0217] The pressing temperature is preferably, for example, 20°C or higher, which is a temperature at which adhesiveness can be effectively exhibited. Furthermore, from the viewpoint of preventing clogging of pores in the separator or thermal shrinkage due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the microporous membrane, more preferably 120°C or lower. From the viewpoint of preventing clogging of pores in the separator, the pressing pressure is preferably 20 MPa or lower. The pressing time may be 1 second or less when using a roll press, or may be surface pressing for several hours, but is preferably 2 hours or less from the viewpoint of productivity. The above manufacturing process can prevent press-back when a wound body made of electrodes and a separator is press-formed, which is preferable because it can prevent a decrease in yield in the device assembly process and shorten the production process time.

[0218] From the viewpoint of ensuring the silane crosslinking reaction of the separator after step (a), it is preferable to perform steps (c) and (d). It is thought that a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte or on the electrode surface by the charge-discharge cycle, thereby achieving the silane crosslinking reaction.

[0219] For example, in the separator manufacturing method described above, if the manufacturing method of the A layer does not include a silane crosslinking treatment step, the crosslinking reaction can be actively promoted by contacting the separator with a non-aqueous electrolyte. Without wishing to be bound by theory, it is believed that the silane-modified graft moieties are converted to silanols by the small amount of moisture contained in the power storage device (such as the small amount of moisture contained in the electrodes, separator, non-aqueous electrolyte, etc.), undergo a crosslinking reaction, and convert to siloxane bonds. Furthermore, when the non-aqueous electrolyte comes into contact with the electrodes, a substance that catalyzes the silane crosslinking reaction is generated in the non-aqueous electrolyte or on the electrode surface. Such a substance that catalyzes the silane crosslinking reaction dissolves in the non-aqueous electrolyte and uniformly swells and diffuses into the amorphous portion of the polyolefin where the silane-modified graft moieties are present, thereby uniformly promoting the crosslinking reaction of the separator-containing laminate or wound body.

[0220] The substance that catalyzes the silane crosslinking reaction may be in the form of an acid solution or a film. When the electrolyte contains lithium hexafluorophosphate (LiPF), LiPF reacts with water to generate hydrogen fluoride (HF) or a fluorine-containing organic compound derived from hydrogen fluoride (HF). These compounds are treated as the substance that catalyzes the silane crosslinking reaction (compounds generated in the energy storage device).

[0221] <Thirteenth embodiment> A thirteenth embodiment is a method for producing an electricity storage device using a separator including a polyolefin having one or more types of functional groups, the method comprising the following steps: (1) A cross-linking process in which functional groups are condensed with each other, (2) functional groups are reacted with chemicals inside the energy storage device, or (3) functional groups of polyolefins are reacted with other types of functional groups to form cross-linked structures. Includes.

[0222] 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 be carried out using the compounds in the electricity storage device and the environment surrounding the device, it does not require excessive conditions such as electron beams or high temperatures of 100°C or higher, and can be carried out under mild conditions such as temperatures of 5°C to 90°C and / or in the ambient atmosphere.

[0223] By carrying out a crosslinking step in the manufacturing process of an electricity storage device, it is possible to omit the formation of a crosslinked structure during or immediately after the separator film-forming process, thereby alleviating or eliminating stress distortion after the production of the electricity storage device, and / or imparting a crosslinked structure to the separator without using relatively high energy such as light irradiation or heating, thereby reducing uneven crosslinking, the occurrence of unmelted resin aggregates, and the burden on the environment.

[0224] During the crosslinking process, (2) functional groups are reacted with chemicals inside the energy storage device, or (3) functional groups of the polyolefin are reacted with other types of functional groups, thereby forming crosslinked structures not only inside the separator but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), thereby improving the strength between multiple components of the energy storage device.

[0225] The separator described above contains silane-modified polyolefin that crosslinks when it comes into contact with an electrolyte solution, making it compatible with conventional manufacturing processes for electricity storage devices while allowing a silane crosslinking reaction to occur after the electricity storage device is manufactured, thereby improving the safety of the electricity storage device. [Example]

[0226] The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. The physical properties in the examples were measured by the following methods.

[0227] <Weight average molecular weight> A calibration curve was created by measuring standard polystyrene under the following conditions using a Waters ALC / GPC 150C (trademark). Chromatograms of the following polymers were also measured under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the following method. Column: Tosoh GMH6-HT (trademark) x 2 + GMH6-HTL (trademark) x 2 Mobile phase: o-dichlorobenzene Detector: Differential refractometer Flow rate: 1.0ml / min Column temperature: 140℃ Sample concentration: 0.1 wt% (weight average molecular weight of polyethylene) Each molecular weight component in the obtained calibration curve was multiplied by 0.43 (Q factor of polyethylene / Q factor of polystyrene=17.7 / 41.3) to obtain a molecular weight distribution curve converted into polyethylene, and the weight average molecular weight was calculated. (Weight average molecular weight of resin composition) The weight average molecular weight was calculated using the Q factor value of the polyolefin with the largest mass fraction, in the same manner as for polyethylene.

[0228] <Viscosity average molecular weight (Mv)> The intrinsic viscosity [η] in decalin solvent at 135°C was determined based on ASTM-D4020. The Mv of polyethylene was calculated using the following formula: [η]=6.77×10 -4 Mv 0.67

[0229] <Melt mass-flow rate (MFR) (g / 10 min)> Using a melt mass flow rate measuring instrument (Melt Indexer F-F01) manufactured by Toyo Seiki Seisaku-sha, the weight of the resin extruded for 10 minutes under conditions of 190°C and a load of 2.16 kg was determined as the MFR value.

[0230] <Measurement of glass transition temperature> An appropriate amount of the aqueous dispersion containing the resin sample (solid content = 38-42 wt %, pH = 9.0) was placed on an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes to obtain a dry film. Approximately 17 mg of this dry film was placed in an aluminum container for measurement, and a DSC curve under a nitrogen atmosphere and a DSC curve were obtained using a DSC measurement device (Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows: First stage temperature increase program: Start at 70°C, increase temperature at a rate of 15°C per minute, and maintain at 110°C for 5 minutes. Second stage temperature reduction program: Reduce the temperature from 110°C at a rate of 40°C per minute. After reaching -50°C, maintain the temperature for 5 minutes. Third-stage temperature increase program: Temperature increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were collected during this third-stage temperature increase. The glass transition temperature (Tg) was determined as the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve toward higher temperatures) and the tangent at the inflection point (the point where the upward convex curve changes to a downward convex curve).

[0231] <Film thickness (μm)> Using a micro-thickness gauge manufactured by Toyo Seiki and KBM (trademark), the film thickness of the microporous membrane or separator was measured at room temperature of 23 ± 2°C and relative humidity of 60%. Specifically, across the entire width in the TD direction, the film thickness at 5 points was measured at approximately equal intervals, and the average value thereof was obtained. The thickness of the inorganic porous layer can be calculated by subtracting the film thickness of the microporous membrane from the thickness of the separator composed of the microporous membrane and the inorganic porous layer.

[0232] <Thickness of layer A (TA), and thickness of layer B (TB)> Using a micro-thickness gauge manufactured by Toyo Seiki and KBM (trademark), the thickness of layer A (TA) was measured at room temperature of 23 ± 2°C and relative humidity of 60%. Specifically, across the entire width in the TD direction, the film thickness at 5 points was measured at approximately equal intervals, and the average value thereof was obtained. Also, by the same method, the thickness of the laminate including layer A and layer B was obtained. Then, the thickness of layer B (TB) was obtained by subtracting the thickness of layer A (TA) from the thickness of the obtained laminate. The thickness of the obtained laminate was treated as the total thickness (TA + TB) of layer A and layer B. Also, the ratio of thickness (TA / TB) was obtained by dividing the thickness (TA) by the thickness (TB).

[0233] <Porosity (%)> (i) Calculated from the density of the mixed composition A 10 cm × 10 cm square sample was cut from the microporous membrane, and its volume (cm 3 ) and mass (g) were determined. From these and the density (g / cm 3 ), the porosity was calculated using the following formula. The density of the mixed composition was the value calculated and obtained from the densities of each of the raw materials used and the mixing ratio. Porosity (%) = (Volume - Mass / Density of mixed composition) / Volume × 100

[0234] (ii) Calculated from the film density Alternatively, from the volume, mass, and film density (g / cm 3 ), the porosity of the microporous membrane was calculated by the following formula. Porosity (%) = (Volume - Mass / Film density) / Volume × 100 In the present disclosure, the film density refers to a value measured according to the D) density gradient tube method described in JIS K7112 (1999).

[0235] (iii) Porosity of the A layer A 10 cm × 10 cm square sample was cut from the A layer, and its volume (cm 3 ) and mass (g) were determined. Then, the porosity was calculated using the following formula from these values and the density (g / cm 3 ). The density of the mixed composition was a value calculated from the density of each raw material used and the mixing ratio. Porosity (%) = (Volume - Mass / Density of the mixed composition) / Volume × 100

[0236] <Air permeability (sec / 100 cm 3 )> In accordance with JIS P-8117 (2009), the Gurley air permeability meter, model G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd., was used to measure the air permeability of the sample or the A layer.

[0237] <Puncture strength of the A layer> Using a handy compression tester KES-G5 (model name) manufactured by Kato Tech Co., Ltd., the A layer was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central part of the fixed A layer at a puncture speed of 2 mm / second in an atmosphere of 25°C using a needle with a tip curvature radius of 0.5 mm to measure the maximum puncture load. The value obtained by converting the maximum puncture load per 20 μm thickness was defined as the puncture strength (gf / 20 μm). When the thermoplastic polymer exists only on one side of the substrate, the needle can be punctured from the surface where the thermoplastic polymer exists.

[0238] <Quantification of resin aggregates in the separator> Resin aggregates in the separator are defined as regions having an area of 100 μm in length × 100 μm or more in width and not allowing light to pass through when the separator obtained through the film-forming processes of the examples and comparative examples described later is observed with a transmission optical microscope. In the observation with a transmission optical microscope, in a separator area of 1000 m 2 ​The number of resin aggregates per unit area was measured.

[0239] <Storage modulus, loss modulus and transition temperature (version 1)> Dynamic viscoelasticity measurements of separators can be performed using a dynamic viscoelasticity measuring device, and the storage modulus (E'), loss modulus (E''), and the transition temperature between the rubber-like plateau region and the crystalline melting flow region can be calculated. ΔE’ ) is calculated by the following formula (1), and the mixed storage modulus ratio (R E’mix ) is calculated as the loss modulus change ratio (R ΔE’’ ) is calculated by the following formula (3): E’’mix ) were calculated according to the following formula (4). The measurement conditions were as follows (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Atmosphere: Nitrogen Measurement device used: RSA-G2 (TA Instruments) Sample thickness: 5μm to 50μm Measurement temperature range: -50 to 225°C Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.5N Initial gap distance (at 25°C): 25mm Auto strain adjustment: Enabled (Range: Amplitude 0.05 to 25%, Sine wave load 0.02 to 5N) It was carried out at. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load. (iii) Sine wave tension mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.2%, and the vibration stress was measured by varying the gap distance and static tensile load so that the difference between the static tensile load and the sinusoidal load was within 20%. When the sinusoidal load became 0.02 N or less, the amplitude was amplified so that the sinusoidal load was within 5 N and the increase in amplitude was within 25%, and the vibration stress was measured. (iv) The relationship between the obtained sinusoidal load and amplitude value, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε * E * =E'+iE'' {where, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus and loss modulus were calculated from the data. E' S and E' j and E'' S and E'' j E' was the average value of each storage modulus or each loss modulus at 160°C to 220°C in the dynamic viscoelasticity measurement data. a and E'0 and E'' a and E''0 were taken as the average values ​​of the storage moduli or loss moduli at 160°C to 220°C in the dynamic viscoelasticity measurement data. R ΔE’ =E' S / E' j (1) Comparison before and after injection into the cell RE’mix =E' a / E'0(2) Comparison of presence and absence of silane crosslinking R ΔE’’ =E'' S / E'' j (3) Comparison before and after injection into the cell R E’’mix =E'' a / E''0(4) Comparison of silane crosslinking and non-silane crosslinking

[0240] An example of a graph illustrating the relationship between temperature and storage modulus is shown in Figure 1. As shown in Figure 1, by comparing the storage modulus of a reference film (a separator for an electricity storage device that does not contain silane-modified polyolefin) and the crosslinked film within a temperature range of -50°C to 225°C, the transition temperature between the rubber-like plateau region and the crystalline melting flow region can be confirmed in Figure 1. The transition temperature is defined as the temperature at the intersection of a straight line extending the high-temperature baseline toward the low-temperature side and a tangent line drawn at the inflection point of the curve for the crystalline melting transition region. An example of a graph illustrating the relationship between temperature and loss modulus is shown in Figure 2. Figure 2 compares the loss modulus of a reference film (a separator for an electricity storage device that does not contain silane-modified polyolefin) and a crosslinked film within a temperature range of -50°C to 220°C, and shows the transition temperatures determined by the same method as in Figure 1. In this technical field, the storage modulus and loss modulus are determined by the following formula: tanδ=E'' / E' {wherein tan δ represents the loss tangent, E′ represents the storage modulus, and E″ represents the loss modulus.} It is compatible according to The mixed storage modulus ratio (R E’mix ) or mixed loss modulus ratio (R E’’mix In the measurement of E', a microporous membrane made of silane-unmodified polyolefin with a gelation degree of approximately 0% was used as a separator for an electricity storage device that did not contain silane-modified polyolefin. a , E' 0、 E'' aFor E''0 and E'', if no breakage of the sample (a sudden drop in elastic modulus) was observed between 160°C and 220°C, they were calculated from the average value between 160°C and 220°C, and if breakage of the sample was observed between 160°C and 220°C, they were calculated from the average value between 160°C and the temperature at the breakage point. For example, the reference film shown in Figures 1 and 2 broke at 207°C.

[0241] <Storage modulus, loss modulus and transition temperature (version 2)> Dynamic viscoelasticity measurements of separators can be performed using a dynamic viscoelasticity measuring device, and the storage modulus (E'), loss modulus (E''), and the transition temperature between the rubber-like plateau region and the crystalline melting flow region can be calculated. ΔE’X ) is calculated by the following formula (1), and the mixed storage modulus ratio (R E’mix ) is calculated by the following formula (2): E’’x ) is calculated by the following formula (3): E’’mix ) were calculated according to the following formula (4). The measurement conditions were a TA Instruments RSA-G2 dynamic viscoelasticity measuring device, measuring frequency 1 Hz, strain 0.2%, in a nitrogen atmosphere, and a temperature range of -50°C to 310°C. Other conditions were in accordance with the above version 1 for measuring the storage modulus and loss modulus. Z and E' Z0 and E'' Z and E'' Z0 was 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, and E'' and E''0 were the average values ​​of each storage modulus or each loss modulus at 160°C to 300°C in the dynamic viscoelasticity measurement data. R ΔE’X =E' Z / E' Z0 (1) Comparison before and after injection into the cell R E’mix =E' / E'0(2) Comparison of the presence or absence of amorphous cross-linked structure R E’’X =E'' Z / E'' Z0 (3) Comparison before and after injection into the cell RE’’mix =E'' / E''0(4) Comparison of the presence or absence of amorphous cross-linked structure

[0242] An example of a graph illustrating the relationship between temperature and storage modulus is shown in Figure 9. As shown in Figure 9, by comparing the storage modulus of a reference film (a separator for an electricity storage device that does not have an amorphous crosslinked structure) and the crosslinked film within a temperature range of -50°C to 310°C, the transition temperature between the rubber-like plateau region and the crystalline melting flow region can be confirmed in Figure 9. The transition temperature is defined as the temperature at the intersection of a straight line extending the high-temperature baseline toward the low-temperature side and a tangent line drawn at the inflection point of the curve for the crystalline melting transition region.

[0243] An example of a graph illustrating the relationship between temperature and loss modulus is shown in Figure 10. Figure 10 compares the loss modulus of a reference film (a separator for an electricity storage device that does not contain silane-modified polyolefin) and a crosslinked film within a temperature range of -50°C to 310°C, and shows the transition temperatures determined by the same method as in Figure 9. In this technical field, the storage modulus and loss modulus are determined by the following formula: tanδ=E'' / E' {wherein tan δ represents the loss tangent, E′ represents the storage modulus, and E″ represents the loss modulus.} It is compatible according to

[0244] The mixed storage modulus ratio (R E’mix ) or mixed loss modulus ratio (R E’’mix In the measurement of E', E', a polyolefin microporous membrane with a gelation degree of approximately 0% was used as a separator for an electricity storage device that does not have an amorphous crosslinked structure. 0、 Regarding E'' and E''0, if no breakage of the sample (a sudden drop in elastic modulus) was observed between 160°C and 300°C, they were calculated from the average value between 160°C and 300°C, and if breakage of the sample was observed between 160°C and 300°C, they were calculated from the average value between 160°C and the temperature at the breakage point. For example, the reference film shown in Tables 11 and 12 and Figures 9 and 10 showed breakage at 210°C.

[0245] In this specification, a separator for a storage battery device that does not have an amorphous crosslinked structure can be a separator manufactured using any one selected from the group consisting of polyethylene:X (viscosity-average molecular weight: 100,000 to 400,000), PE:Y (viscosity-average molecular weight: 400,000 to 800,000), and PE:Z (viscosity-average molecular weight: 800,000 to 9,000,000), or a mixture of two or three selected from the group consisting of X, Y, and Z, in any ratio. Polyolefins composed solely of a hydrocarbon skeleton, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and olefin-based thermoplastic elastomers, may also be added to the mixed composition. More specifically, a separator for a storage battery device that does not have an amorphous crosslinked structure can refer to a polyolefin microporous membrane that exhibits a change in solid content (hereinafter referred to as "gelation degree") of 10% or less before and after heating in a decalin solution at 160°C. Note that when measuring the gelation degree, the solid content refers to only the resin and does not include other materials such as inorganic substances. On the other hand, the gelation degree of a polyolefin microporous membrane having an amorphous part crosslinked structure such as a silane crosslinked structure is preferably 30% or more, more preferably 70% or more.

[0246] <Storage modulus, loss modulus, film softening transition temperature, and film rupture temperature (version 3)> The solid viscoelasticity of the separator was measured using a dynamic viscoelasticity measuring device, and the storage modulus (E'), loss modulus (E''), and film-softening transition temperature could be calculated. The solid viscoelasticity measurement conditions were as follows (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (TA Instruments) Sample film thickness: 200 μm to 400 μm (however, if the film thickness of a single sample is less than 200 μm, multiple samples should be stacked and the dynamic viscoelasticity measurement should be performed so that the total thickness is within the range of 200 μm to 400 μm.) Measurement temperature range: -50℃~250℃ Heating rate: 10℃ / min ·Measurement frequency: 1Hz Deformation mode: Linear tension Initial static tensile load: 0.2N Initial gap distance (at 25°C): 10 mm Auto strain adjustment: Disabled This is done. (ii) The static tensile load refers to the midpoint between the maximum stress and the minimum stress in each cyclic motion, and the sinusoidal load refers to the oscillating stress centered on the static tensile load; (iii) The sinusoidal tension mode refers to measuring the vibration stress while performing periodic motion with a fixed amplitude of 0.1%. In the sinusoidal tension mode, the gap distance and static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 5%, and the vibration stress is measured. When the sinusoidal load falls below 0.1 N, the static tensile load is fixed at 0.1 N and the vibration stress is measured again. (iv) The relationship between the obtained sinusoidal load and amplitude value, and the following equation: σ * =σ0·Exp[i(ωt+δ)], ε * =ε0·Exp(iωt), σ * =E * ε * E * =E'+iE'' {where, σ * : Vibration stress, ε * : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibration stress and strain, E * : Complex modulus, E': Storage modulus, E'': Loss modulus Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus (E') and loss modulus (E'') are calculated from the above. The average of the maximum and minimum values ​​of E' is taken as the average E' (E' ave) is calculated, and the average value of the maximum and minimum values of E’’ is defined as the average E’’ (E’’ ave ) is calculated.

[0247] Note that E’ and E’’ are calculated from 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, when no breakage (sudden decrease in 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 breakage of the sample is observed at -50°C to 250°C is taken as the minimum value. Also, in the technical field, the storage modulus and the loss modulus are interchangeable according to the following formula: tanδ = E’’ / E’ {In the formula, tanδ represents the loss tangent, E’ represents the storage modulus, and E’’ represents the loss modulus.} are interchangeable according to.

[0248] The film softening transition point temperature is defined as the temperature of the minimum value obtained by differentiating the curve of the sample gap distance in the dynamic viscoelasticity measurement data by the first order. Also, the film breakage temperature is defined as the temperature at which breakage (sudden decrease in modulus) of the sample is observed in the dynamic viscoelasticity measurement data, and the measurement limit temperature may be defined as 250°C from the viewpoint that the thermal decomposition reaction of the polyolefin resin progresses. However, since the phenomenon can be understood similarly even in measurements at temperatures higher than 250°C, in this embodiment, a separator for a power storage device having a film breakage temperature of 180°C or higher can be implemented.

[0249] <Film breakage temperature of layer A> Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, the environmental temperature was changed from 25 to 250°C, and the temperature at the moment when the load was completely released was defined as the TMA film breakage temperature (the film breakage temperature of layer A measured by TMA). Specifically, a 3mm TD and 14mm MD sample was taken from layer A and used as a test piece (a test piece with the long side in the MD). Both ends of the test piece in the MD were set on a dedicated probe so that the chuck distance was 10mm, and a load of 1.0g was applied to the test piece. The furnace containing the test piece was heated, and the temperature at which the load reached 0g was taken as the film rupture temperature (°C). When measuring a sample piece TD where the TD is the long side, layer A is taken at TD 14 mm and MD 3 mm and used as the sample piece. Both ends of TD are chucked to a dedicated probe, the distance between the chucks is set to 10 mm, an initial load of 1.0 g is applied, and the same operation as above is carried out.

[0250] <Heat shrinkage rate at 150℃> A 100 mm TD and 100 mm MD sample was taken from a laminate (a laminate including layers A and B) before the formation of a crosslinked structure, and used as a sample piece. The sample piece was then placed in an oven at 150°C for 1 hour. The sample piece was sandwiched between two pieces of paper to prevent direct exposure to hot air. The sample piece was removed from the oven and cooled, after which the area of ​​the sample piece was measured, and the thermal shrinkage (T1) at 150°C before the formation of a crosslinked structure was calculated using the following formula: Heat shrinkage rate at 150°C (%) = (10,000 (mm 2 ) - Area of ​​the sample piece after heating (mm 2 ))×100 / 10,000 In addition, a sample of 100 mm in TD and 100 mm in MD was taken from the laminate after the formation of the crosslinked structure, and the same operation as above was carried out to calculate the thermal shrinkage (T2) at 150°C after the formation of the crosslinked structure. The ratio (T2 / T1) was obtained by dividing the thermal shrinkage (T2) by the thermal shrinkage (T1). This ratio (T2 / T1) corresponds to the rate of change in the thermal shrinkage (T2) at 150°C after the formation of the crosslinked structure relative to the thermal shrinkage (T1) at 150°C before the formation of the crosslinked structure.

[0251] <Battery Destruction Safety Test 1> Battery Destruction Safety Test 1 involves driving an iron nail into a battery charged to 4.5V at a speed of 20mm / sec, penetrating it and causing an internal short circuit. This test can clarify the phenomenon that occurs during an internal short circuit by measuring the time course of the battery's voltage drop and the battery surface temperature rise due to an internal short circuit. In addition, insufficient shutdown function of the separator or rupture at low temperatures during an internal short circuit can cause the battery to suddenly heat up, which can then cause the electrolyte to ignite, resulting in smoke and / or explosion.

[0252] (Preparation of batteries used in battery breakdown safety test 1) 1a. Preparation of the positive electrode The positive electrode active material was 92.2 mass% lithium-cobalt composite oxide LiCoO2, the conductive materials were 2.3 mass% each of flake graphite and acetylene black, and the resin binder was 3.2 mass% polyvinylidene fluoride (PVDF). These were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil that served as a positive electrode current collector using a die coater, dried at 130 °C for 3 minutes, and then compression molded using a roll press. At this time, the amount of applied positive electrode active material was 250 g / m 2 , the bulk density of the active material is 3.00 g / cm 3 It was adjusted to be.

[0253] 1b. Preparation of negative electrode A slurry was prepared by dispersing 96.9% by mass of artificial graphite as the negative electrode active material, and 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of styrene-butadiene copolymer latex as the resin binder in purified water. This slurry was applied to one side of a 12 μm-thick copper foil that served as the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press. The amount of active material applied to the negative electrode was 106 g / m. 2 , the active material bulk density is 1.35 g / cm 3 It was adjusted to be.

[0254] 1c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0255] 1d. Battery assembly The separator was cut into strips measuring 60 mm in the transverse (TD) direction and 1000 mm in the longitudinal (MD) direction, folded zigzag, and stacked alternately between the separators (12 positive electrodes, 13 negative electrodes). The positive electrodes measured 30 mm x 50 mm, and the negative electrodes measured 32 mm x 52 mm. The zigzag stack was placed in a laminated bag, and the nonaqueous electrolyte prepared in step c above was poured into the bag and sealed. After leaving the battery at room temperature for one day, the battery was charged at 3 mA (0.5 C) in a 25°C atmosphere up to a battery voltage of 4.2 V. After reaching 4.2 V, the current was reduced from 3 mA to maintain the battery voltage at 4.2 V. This method performed the initial charge after battery fabrication for a total of 6 hours. The battery was then discharged at 3 mA (0.5 C) down to a battery voltage of 3.0 V.

[0256] (Maximum heat generation rate) After an iron nail was inserted into the resulting battery, the battery surface temperature was measured over 300 seconds using a thermocouple. From the temperature change graph, the rate at which the temperature change per second was greatest was determined to be the maximum heat generation rate.

[0257] (Voltage drop time) An iron nail was inserted into the resulting battery, and the time required for the voltage to drop from 4.5 V to 3 V was determined as the voltage drop time (3 V drop time).

[0258] <Evaluation of cycle characteristics and method of fabricating the battery> A battery for evaluating cycle characteristics was fabricated according to the same methods as 1a. to 1c. of the battery fabrication method used in the above item <Battery Destruction Safety Test 1>, except that assembly was performed according to the following 1d-2.

[0259] 1d-2. Battery assembly The separator was cut into 18 mm diameter circles, and the positive and negative electrodes were cut into 16 mm diameter circles. The positive electrode, separator, and negative electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other, and then placed in a lidded stainless steel container. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode and the lid in contact with the aluminum foil of the positive electrode. The nonaqueous electrolyte obtained in Item 1c of "Battery Destruction Safety Test 1" above was poured into the container and sealed. After leaving the battery at room temperature for one day, the battery was charged at a current of 3 mA (0.5 C) in a 25°C atmosphere up to a battery voltage of 4.2 V. After reaching this voltage, the current was reduced from 3 mA to maintain the battery voltage at 4.2 V. This was the first charge after battery fabrication, for a total of 6 hours. The battery was then discharged at a current of 3 mA (0.5 C) down to a battery voltage of 3.0 V.

[0260] The resulting battery was subjected to 100 charge / discharge cycles at 60°C. The battery was charged at a current of 6.0mA (1.0C) up to a battery voltage of 4.2V, and then the current was reduced from 6.0mA to maintain 4.2V. This was done for a total of 3 hours. The battery was discharged at a current of 6.0mA (1.0C) down to a battery voltage of 3.0V.

[0261] (Cycle characteristic evaluation 1) The capacity retention rate was calculated from the discharge capacity at the 100th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0262] (Cycle characteristic evaluation 2) The capacity retention rate (%) was calculated from the discharge capacity at the 300th cycle and the discharge capacity at the 1st cycle according to the following formula: When the capacity retention rate was high, it was evaluated as having good cycle characteristics. Evaluation result (%) = (100 x retention capacity after 300 cycles / discharge capacity at the first cycle)

[0263] <Fuse / Meltdown (F / MD) characteristics> (i) 0.5 MPa pressure and 2°C / min heating rate The positive electrode, separator, and negative electrode were cut into a circular shape with a diameter of 200 mm and stacked. A nonaqueous electrolyte was added to the resulting laminate and allowed to soak completely. The laminate was then sandwiched in the center of a circular aluminum heater with a diameter of 600 mm, and the aluminum heater was pressurized from above and below to 0.5 MPa using a hydraulic jack. The measurement was completed. The resistance (Ω) between the electrodes was measured while the laminate was heated with the aluminum heater at a temperature increase rate of 2°C / min. The resistance between the electrodes, including the separator fuse, increased, and the temperature at which the resistance first exceeded 1000 Ω was recorded as the fuse temperature (shutdown temperature). Further heating was continued, and the temperature at which the resistance dropped below 1000 Ω was recorded as the meltdown temperature (film rupture temperature).

[0264] (ii) Maximum pressure of 10 MPa and heating rate of 15°C / min The positive electrode, separator, and negative electrode were cut into a circular shape with a diameter of 200 mm and stacked together to obtain a laminate. A nonaqueous electrolyte was added and allowed to soak throughout the laminate. The laminate was sandwiched in the center of a circular aluminum heater with a diameter of 600 mm, and a pressure of 10 MPa was applied to the aluminum heater from above and below using a hydraulic jack. The measurement preparation was completed. The resistance (Ω) between the electrodes was measured while the laminate was heated with the aluminum heater at a temperature increase rate of 15°C / min. The temperature at which the resistance between the electrodes increased and exceeded 1000 Ω for the first time was recorded as the shutdown temperature (°C). Further heating was continued, and the temperature at which the resistance dropped below 1000 Ω was recorded as the meltdown temperature (°C).

[0265] For both evaluations (i) and (ii), a resistance measurement wire was attached with conductive silver paste to the back of the aluminum foil of the positive electrode prepared in "1a. Preparation of positive electrode" in the above section <Battery Destruction Safety Test 1>. Also, a resistance measurement wire was attached with conductive silver paste to the back of the copper foil of the negative electrode prepared in "1b. Preparation of negative electrode" in the above section <Battery Destruction Safety Test 1>. Furthermore, the electrolyte-containing electrolyte prepared in "1c. Preparation of non-aqueous electrolyte" in the above section <Battery Destruction Safety Test 1> was also used for the F / MD characteristic test.

[0266] <Safety test (nail penetration test) 2> 2a. Preparation of the positive electrode The positive electrode active material was nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) 90.4 mass%, graphite powder (KS6) (density 2.26 g / cm) as a conductive additive 3 1.6 mass% of acetylene black powder (AB) (density 1.95 g / cm 3 3.8 mass% of PVDF (density 1.75 g / cm , number average particle diameter 48 nm) as a resin binder. 3 The mixture was mixed at a ratio of 4.2% by mass and dispersed in NMP to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression molded using a roll press to prepare a positive electrode. At this time, the amount of the positive electrode active material applied was 109 g / m 2 It was.

[0267] 2b. Preparation of negative electrode Graphite powder A (density 2.23 g / cm) was used as the negative electrode active material. 3 , number average particle diameter 12.7 μm) 87.6 mass%, and graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7% by mass of carboxymethylcellulose (number average particle diameter 6.5 μm) and 1.4% by mass (solids content equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solids content of 1.83% by mass) and 1.7% by mass (solids content equivalent) of diene rubber latex (aqueous solution with a solids content of 40% by mass) in purified water as a resin binder. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The coating amount of the negative electrode active material was 52 g / m. 2 It was.

[0268] 2c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0269] 2d. Battery construction Using the positive electrode, negative electrode, and nonaqueous electrolyte solution obtained in 2a to 2c above, as well as a separator (a separator of the example or a separator of the comparative example), a laminate-type secondary battery having a size of 100 mm x 60 mm and a capacity of 3 Ah was fabricated by constant current constant voltage (CCCV) charging for 3 hours under conditions of a current value of 1 A (0.3 C) and an end-of-battery voltage of 4.2 V.

[0270] 2e. Nail penetration evaluation The fabricated laminated secondary battery was placed on an iron plate in a temperature-controlled explosion-proof booth. The temperature in the explosion-proof booth was set to 40°C, and a 3.0 mm diameter iron nail was driven into the center of the laminated secondary battery at a speed of 2 mm / sec, and the nail was maintained in the penetrated state. After the nail penetrated, a thermocouple was installed inside the nail to measure the temperature inside the laminated battery, and the presence or absence of ignition was evaluated. The evaluation was repeated using newly prepared laminated secondary batteries in the same manner, and the number of samples that did not ignite (no ignition) was calculated as a percentage using the following formula. Evaluation result (%) = (100 x number of samples that did not ignite / total number of samples) The pass rate for the nail penetration evaluation is preferably, for example, 50% or more after 200 cycles and 5% or more after 1000 cycles.

[0271] <Experimental Group I> [Method for producing silane-grafted polyolefin] The raw polyolefin used for silane-grafted polyolefins may have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. Propylene or butene copolymerized α-olefins may also be used. While melt-blending the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane is added to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-tetrabutyl-4-hydroxyphenyl)propionate]) is added to adjust the radical concentration in the system and suppress chain reactions (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin is cooled in water and processed into pellets, which are then dried by heating at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is approximately 10 to 1500 ppm. The silane-grafted modified polyolefin obtained by the above-mentioned production method is referred to in Table 8 as "silane-modified polyolefin (B)."

[0272] [Example I-1] A mixture was obtained by dry blending 79.2% by mass of homopolymer polyethylene (A) with a weight-average molecular weight of 500,000 with 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) with a MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 with trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 0.8 and 0.2, respectively). 1% by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1400 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set as follows: MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7 × 6 times), and biaxial stretching temperature 125°C. Next, the stretched gel sheet was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 125°C and a stretch ratio of 1.8 times, followed by a relaxation operation of 0.5 times in the TD direction (i.e., an HS relaxation rate of 0.5 times) to obtain a microporous membrane. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a separator for evaluation.

[0273] [Examples I-2 to I-6] The microporous membranes shown in Table 8 were obtained in the same manner as in Example I-1 above, except that the ratio of components A and B and the crosslinking method and conditions were changed as shown in Table 8.

[0274] [Comparative Examples I-1, I-2] A mixture was obtained by dry blending 79.2% by mass of homopolymer polyethylene (A) with a weight-average molecular weight of 500,000 with 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) with a MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 with trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 0.8 and 0.2, respectively). 1% by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1400 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set as follows: MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7 × 6 times), and biaxial stretching temperature 125°C. Next, the stretched gel sheet was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 125°C and a stretch ratio of 1.8 times, followed by a relaxation operation of 0.5 times in the TD direction (i.e., the HS relaxation rate was 0.5 times). The heat-treated porous body was then introduced into an ethanol bath (affinity treatment tank) and allowed to remain there while being immersed for 60 seconds to carry out affinity treatment, thereby obtaining an affinity-treated porous body. Furthermore, in Comparative Example I-1, the affinity-treated porous body was introduced into a 25% aqueous caustic soda solution (temperature 80°C, pH 8.5 to 14), and in Comparative Example I-2, into a 10% aqueous hydrochloric acid solution (temperature 60°C, pH 1 to 6.5), where it was immersed and retained for 60 seconds, thereby crosslinking the affinity-treated porous body and obtaining a crosslinked porous body. The crosslinked porous body was then introduced into water (a water-washing bath) and immersed there for 60 seconds to rinse it, then introduced into a conveyor dryer and dried at 120°C for 60 seconds to obtain a microporous membrane. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a separator for evaluation.

[0275] [Evaluation results] The microporous membranes and batteries obtained in Examples I-1 to I-6 and Comparative Examples I-1 and I-2 were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 8. The relationship between temperature and resistance of a 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 shutdown temperature of the separator obtained in Example I-1 was 143°C and the membrane rupture temperature was 200°C or higher. Furthermore, the separator obtained in Example I-1 in its pre-crosslinked state was 1 H and 13 The C-NMR chart (b) is shown in Figure 13.

[0276] [Table 8]

[0277] In Table 8, "Silane-modified polyethylene (B)" is a polyethylene having a density of 0.95 g / cm3 obtained by modifying a polyolefin having a viscosity-average molecular weight of 20,000 with a trimethoxyalkoxide-substituted vinylsilane. 3 and a silane-modified polyethylene having a melt flow rate (MFR) of 0.4 g / min at 190°C.

[0278] <Experimental Group IIa> [Method for producing silane-grafted polyolefin] The raw polyolefin used for silane-grafted polyolefins has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It may be an ethylene homopolymer or an α-olefin copolymer of ethylene and propylene or butene. While melt-kneading the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane is added to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-tetrabutyl-4-hydroxyphenyl)propionate]) is added to adjust the radical concentration in the system and suppress chain reaction (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water and pelletized, followed by heating and drying at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1500 ppm or less. The silane-grafted modified polyethylene obtained by the above-mentioned production method is referred to in Table 9 as "silane-modified polyethylene (B)." Example II-1 A mixture was obtained by dry blending 80% by mass of homopolymer polyethylene (polyethylene (A)) with a weight-average molecular weight of 700,000 with 20% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) with a MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 10,000 with a trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 80% and 20%, respectively). 1% by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1100 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product under the following conditions: MD magnification 7.0 times, TD magnification 6.2 times, and biaxial stretching temperature 120°C. Next, the stretched gel sheet was introduced into a dichloromethane tank and thoroughly immersed in dichloromethane to extract and remove the liquid paraffin, and then the dichloromethane was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 133°C and a stretch ratio of 2.1 times, followed by a relaxation operation to a stretch ratio of 2.0 times in the TD direction. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a separator for evaluation.

[0279] [Examples II-2 to II-8, Comparative Examples II-1 to II-3] The microporous membranes shown in Table 9 were obtained by the same procedure as in Example II-1, except that the ratio of components A and B, the presence or absence of other resins (C) as additional components, membrane properties, and crosslinking method and conditions were changed as shown in Table 9. Note that the component "PP" in Table 9 refers to a PP having an MFR of 2.5 g / 10 min or less and a density of 0.89 g / cm, measured under conditions of a temperature of 230°C and a mass of 2.16 kg. 3 The above silane-unmodified polypropylene was used. In the crosslinking method "alkali-treated crosslinking" in Table 9, the sample was treated with a 25% aqueous solution of caustic soda (temperature 80°C, pH 8.5 to 14).

[0280] [Evaluation results] The microporous membranes and batteries obtained in Examples II-1 to II-8 and Comparative Examples II-1 to II-3 were evaluated according to the above-described evaluation methods, and the evaluation results are also shown in Table 9. Regarding viscoelasticity measurements of the obtained microporous membranes used as separators for electricity storage devices, the relationships between temperature, gap distance, storage modulus, and loss modulus are shown in Figure 4(a) for Example II-1 and Figure 4(b) for Comparative Example II-1. Furthermore, the membrane softening transition temperature determined based on the first derivative of temperature, gap distance, and gap displacement is shown in Figure 5(a) for Example II-1 and Figure 5(b) for Comparative Example II-1. In Examples II-1 to II-8 and Comparative Example II-3, no membrane rupture was observed at the measurement limit temperature of 250°C. In Example II-1 and Comparative Example II-1, 26 8-μm-thick membranes were stacked, and the storage modulus, loss modulus, membrane softening transition temperature, and membrane rupture temperature were measured under the condition that the total sample thickness was 208 μm.

[0281] [Table 9A]

[0282] [Table 9B]

[0283] <Experiment Series IIb> [Reference membrane] As a separator for an electricity storage device that does not contain silane-modified polyolefin (hereinafter referred to as the "reference membrane"), a silane-grafted unmodified polyolefin microporous membrane was used, which had a change in solid content (hereinafter referred to as the "gelation degree") of approximately 0% before and after heating in a decalin solution at 160°C. When measuring the gelation degree, the solid content refers to only the resin and does not include other materials such as inorganic substances. In this specification, a separator for an electricity storage device that does not contain a silane-grafted modified polyolefin can be produced using any one selected from the group consisting of polyethylene (PE):X (viscosity average molecular weight 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 a mixture of two or three selected from the group consisting of X, Y, and Z, in any ratio. A polyolefin composed solely of a hydrocarbon skeleton, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), or an olefin-based thermoplastic elastomer, may also be added to the mixed composition.

[0284] [Crosslinked membrane] The polyolefin microporous membrane of Example II-1 after contact with the above-described electrolyte solution or the polyolefin microporous membrane of Example II-1 removed from the cell after the first charge / discharge was dried and used as a separator for an electricity storage device after silane crosslinking (hereinafter referred to as "crosslinked membrane"). The gelation degree of the crosslinked membrane was 30% or more or 70% or more.

[0285] [Viscoelastic behavior] The reference membrane and the crosslinked membrane were measured for the above items (storage modulus, loss modulus, membrane softening transition temperature, and membrane rupture temperature (version 3)). The measurement results are shown in Table 10.

[0286] [Table 10]

[0287] <Experimental Group III>

[0288] [Method for producing silane-grafted polyolefin] The raw polyolefin used for silane-grafted polyolefins has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It may also be a propylene or butene copolymerized α-olefin. While melt-kneading the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane is added to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-tetrabutyl-4-hydroxyphenyl)propionate]) is added to adjust the radical concentration in the system and suppress chain reaction (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin is cooled in water and processed into pellets, which are then dried by heating at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is approximately 1000 to 1500 ppm. The silane-grafted modified polyolefin obtained by the above-mentioned method is shown in Tables 11 and 12 as "silane-modified polyethylene."

[0289] [Production methods for modified PE and copolymers with various functional groups other than silane-modified PE] Modified PEs and copolymers having various functional groups other than silane-modified PE were produced by the following methods. For all raw materials, the molecular weight of the raw materials used was adjusted so that the MI was within the range of 0.5 to 10. Hydroxyl-modified PE was produced by saponifying and neutralizing EVA copolymer. Amine-modified, oxazoline-modified, and other modified resins were produced by polymerizing PE using a chromium catalyst, then converting the terminal vinyl groups of the PE to epoxy groups using a tungsten-based catalyst under hydrogen peroxide conditions. Subsequently, the target reactive sites were converted to the desired functional groups using known organic functional group conversion reactions to obtain various modified PEs. For example, in the case of amine-modified PE, primary or secondary amines were injected as liquids into an extruder while the epoxy-modified PE was melt-kneaded at 200°C. The unreacted amines were then removed through a pressure reducing valve, and the resulting amine-modified resin was extruded into strands and cut into pellets. The modified PE obtained by the above-mentioned production method is shown in Tables 11 and 12 as one type of "modified PE or copolymer (B)".

[0290] [Example III-1] A mixture was obtained by dry blending 79.2% by mass of homopolymer polyethylene (A) with a weight-average molecular weight of 500,000 with 19.8% by mass of silane-grafted polyethylene (PE(B)) with a MFR of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 with trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 0.8 and 0.2, respectively). 1% by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1400 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set as follows: MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7 × 6 times), and biaxial stretching temperature 125°C. Next, the stretched gel sheet was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 125°C and a stretch ratio of 1.8 times, followed by a relaxation operation of 0.5 times in the TD direction (i.e., an HS relaxation rate of 0.5 times) to obtain a microporous membrane. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a separator for evaluation. The separator and battery for evaluation were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are shown in Table 11.

[0291] [Examples III-2 to III-18] The microporous membranes and batteries shown in Table 11 or Table 12 were obtained by the same procedure as in Example III-1, except that the types, ratios, and crosslinking methods and conditions of Resins A and B were changed as shown in Table 11 or Table 12. The obtained microporous membranes and batteries were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 11 or Table 12. In Examples III-8 to III-10 and III-15 to III-18, an appropriate amount of an additive listed in Table 11 or Table 12 was dissolved in the electrolyte beforehand when the electrolyte was poured.

[0292] [Comparative Examples III-1, III-2] The same operations as in Example III-1 were performed to obtain the microporous membranes shown in Table 12, except that the types, amount ratios, and crosslinking methods and conditions of Resins A and B were changed as shown in Table 12. The obtained microporous membranes were irradiated with a predetermined dose of electron beam to perform electron beam crosslinking. The obtained electron beam-crosslinked microporous membranes and batteries were subjected to various evaluations according to the above-described evaluation methods, and the evaluation results are also shown in Table 12.

[0293] The strain amount-crystal refinement rate graph for Comparative Example III-2 and Example III-1 is shown in Figure 8 to observe the change in X-ray crystal structure during the tensile fracture test. In Figure 8, the microporous membrane of Comparative Example III-2 is represented by the dotted line "EB crosslinking," and the microporous membrane of Example III-1 is represented by the solid line "before chemical crosslinking" and the dashed line "after chemical crosslinking."

[0294] [Table 11A]

[0295] [Table 11B]

[0296] [Table 12A]

[0297] [Table 12B]

[0298] Explanation of Abbreviations in Table 11 and Table 12 * "Silane-modified polyethylene" is obtained by a modification reaction with trimethoxyalkoxide-substituted vinyl silane using a polyolefin with a viscosity-average molecular weight of 20,000 as a raw material, and has a density of 0.95 g / cm 3 and is a silane-modified polyethylene with a melt flow rate (MFR) of 0.4 g / min at 190 °C. "-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 [Production Method of Modified PEs and Copolymers Having Various Functional Groups Other than Silane-modified PE]. ** (I) Condensation reaction of multiple identical functional groups (II) Reaction between multiple different functional groups (III) Chain condensation reaction of functional groups and electrolyte (IV) Reaction of functional groups and additives (V) Reaction in which multiple identical functional groups crosslink through coordination bonds with eluted metal ions *** EC: Ethylene carbonate **** BS(PEG)5: Succinimide at both ends, EO unit repeating number 5 Diisocyanate: A compound in which isocyanates at both ends are linked to hexane units through urethane bonds Diepoxy compound: A compound in which epoxide groups at both ends are linked to butane units

[0299] <Experimental Group IV>

[0300] [Example IV-1] [Preparation of A Layer] (Preparation of Silane Graft-modified Polyolefin) The raw polyethylene was polyethylene with a viscosity-average molecular weight of 120,000. While melt-kneading the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) was added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane was added, and an addition reaction was carried out to introduce alkoxysilyl groups into the α-olefin polymer, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-tetrabutyl-4-hydroxyphenyl)propionate]) was added to adjust the radical concentration in the reaction system and suppress chain reaction (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then heated and dried at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1500 ppm or less. The modification reaction using trimethoxyalkoxide-substituted vinylsilane as described above yielded a silane-modified polyethylene with an MFR (190° C.) of 0.4 g / min.

[0301] (Preparation of layer A) A resin blend was prepared by combining 65% by mass of homopolymer polyethylene having a weight-average molecular weight of 800,000 with 35% by mass of the silane-modified polyethylene obtained above. 1% by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to the blend, and the mixture was dry-blended using a tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also used. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. In an extruder, the mixture and liquid paraffin were melt-kneaded, and the feeder and pump were adjusted so that the mass ratio of the liquid paraffin in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220 °C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / hour. Subsequently, the melt-kneaded material was extruded and cast onto a cooling roll controlled at a surface temperature of 25 °C through a T-die to obtain a gel sheet (sheet-shaped molded body) with an original film thickness of 1400 μm.

[0302] Next, the sheet-shaped molded body was introduced into a simultaneous biaxial tenter stretching machine for biaxial stretching to obtain a stretched product. The set stretching conditions were 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. Next, the stretched gel sheet was introduced into a dichloromethane bath, fully immersed in dichloromethane to extract and remove the liquid paraffin, and then the dichloromethane was removed by drying to obtain a porous body. Next, the porous body was introduced into a TD tenter to perform heat setting (HS) at a heat setting temperature of 133 °C and a stretching ratio of 1.8 times. Then, a relaxation operation was performed up to 1.7 times in the TD direction to obtain a microporous membrane. Thereafter, the obtained microporous membrane was cut at the ends and wound up as a mother roll with a width of 1,100 mm and a length of 5,000 m. At the time of the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as the evaluation A layer. For the obtained evaluation A layer, the film thickness, air permeability, porosity, etc. were measured and shown in Table 13.

[0303] <Production of B layer> A dispersion was prepared by uniformly dispersing 95 parts by mass of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solids content equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco, solids concentration 40%) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was crushed in a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, producing an inorganic particle-containing slurry. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0304] [Examples IV-2 to IV-5 and Comparative Examples IV-1 to IV-2] At least one of the weight-average molecular weight of the polyethylene homopolymer, the set stretching conditions, the heat setting conditions, and the relaxation operation conditions was changed to achieve the physical property values ​​shown in Table 13. In addition, the composition of Layer B was changed as shown in Table 13. Apart from these changes, a separator was produced in the same manner as in Example IV-1, and the above evaluations were carried out using the obtained separator. The evaluation results are shown in Table 13. [Table 13]

[0305] <Experimental Group V> [Method for producing silane-grafted polyolefin] The raw polyolefin used for silane-grafted polyolefins may have a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. Propylene or butene copolymerized α-olefins may also be used. While melt-blending the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane is added to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-tetrabutyl-4-hydroxyphenyl)propionate]) is added to adjust the radical concentration in the system and suppress chain reactions (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin is cooled in water and processed into pellets, which are then dried by heating at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is approximately 10 to 1500 ppm. The silane-grafted polyolefin obtained by the above-mentioned production method is referred to as "silane-modified polyethylene (B)" in Tables 14 to 16. The silane-grafted polyolefin used here had a density of 0.94 g / cm 3 and the MFR is 0.65 g / min.

[0306] [Example V-1] (Formation of microporous membrane) A mixture was obtained by dry blending 79.2 wt% of homopolymer polyethylene (A) with a weight-average molecular weight of 500,000 with 19.8 wt% of silane-grafted polyethylene (silane-modified polyethylene (B)) with a MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 with trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 80% and 20%, respectively). 1 wt% of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the 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. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1400 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set as follows: MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7 × 6 times), and biaxial stretching temperature 125°C. Next, the stretched gel sheet was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 125°C and a stretch ratio of 1.8 times, followed by a relaxation operation of 0.5 times in the TD direction (i.e., an HS relaxation rate of 0.5 times) to obtain a microporous membrane. Thereafter, the ends of the obtained microporous membrane were cut off and taken up as a microporous membrane mother roll having a width of 1,100 mm and a length of 5,000 m.

[0307] (Acrylic latex manufacturing method) The acrylic latex used as the resin binder is produced by the following method. A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation). The temperature inside the reaction vessel was then raised to 80°C, and while maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes. The above emulsion was prepared by mixing a mixture of: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi 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 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex with a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

[0308] (Formation of inorganic porous layer) A dispersion was prepared by uniformly dispersing 95 parts by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by weight (solids equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids concentration) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion was milled using a bead mill (cell volume 200 cc, zirconia beads 0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. An inorganic particle-containing slurry was prepared by adding 4.6 parts by weight (solids equivalent) of acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) as a resin binder to the dispersion after particle size adjustment. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0309] [Examples V-2 to V-12, Comparative Example V-2] The microporous membranes shown in Tables 14 to 16 were obtained by performing the same operations as in Example V-1, except that the ratio of components A and B, the presence or absence or composition of an inorganic layer, and the crosslinking method and conditions were changed as shown in Tables 14 to 16.

[0310] [Comparative example V-1] A mixture was obtained by dry blending 79.2 wt% of homopolymer polyethylene (A) with a weight-average molecular weight of 500,000 with 19.8 wt% of silane-grafted polyethylene (silane-modified polyethylene (B)) with a MFR (190°C) of 0.4 g / min, obtained by modifying a polyolefin with a viscosity-average molecular weight of 20,000 with trimethoxyalkoxide-substituted vinylsilane (resin compositions of (A) and (B) are 80% and 20%, respectively). 1 wt% of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant. The mixture was then fed into a twin-screw extruder under a nitrogen atmosphere via a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the 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. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1400 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set as follows: MD magnification 7.0 times, TD magnification 6.0 times (i.e., 7 × 6 times), and biaxial stretching temperature 125°C. Next, the stretched gel sheet was introduced into a methyl ethyl ketone tank and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 125°C and a stretch ratio of 1.8 times, followed by a relaxation operation of 0.5 times in the TD direction (i.e., the HS relaxation rate was 0.5 times). In Comparative Example V-1, in order to use the heat-treated porous body as a separator, the end portions of the obtained porous body were cut off and wound up into a mother roll having a width of 1,100 mm and a length of 5,000 m. For Comparative Example V-1, during the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a separator for evaluation.

[0311] [Evaluation results] The microporous membranes and batteries obtained in Examples V-1 to V-12 and Comparative Examples V-1 and V-2 were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Tables 14 to 16.

[0312] [Table 14]

[0313] [Table 15]

[0314] [Table 16]

[0315] <Experimental Group VI> Porous membranes were formed in the same manner as in Examples 1 to 3 and Comparative Examples 2 to 3 shown in Patent Document 5 (JP 2001-176484 A), and designated as porous membranes V-1 to V-5, respectively. 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. Furthermore, the storage modulus and loss modulus change ratio R of porous membrane V-4 before and after contact with the electrolyte solution was measured according to the above item <Storage modulus, loss modulus, and transition temperature (version 1)> of this specification. △E’ and R △E’’ The results are shown in Table 17.

[0316] [Table 17]

[0317] The following points are clear from Table 17: (a) Even for porous membrane V-4 (Comparative Example 2 of Patent Document 5, gel fraction 36%), which has the lowest gel fraction, the elastic modulus change ratio remains at 1. This proves that the crosslinking reaction has already been completed for all of porous membranes V-1 to V-5, and that the porous membranes described in Patent Document 5 do not have self-crosslinking properties (uncrosslinked portions). (b) Comparative Example 1 in Patent Document 5 is an unmodified silane product.

[0318] (c) The separator according to the seventh embodiment of the present invention described above is valuable in that it selectively chemically crosslinks the amorphous zone between the crystalline and crystalline regions. When the silane-unmodified polyolefin and the silane-modified polyolefin form mixed crystals, the modified units are expelled into the amorphous regions and randomly dispersed. In this state, the adjacent crosslinked units come into contact with each other, and the crosslinking reaction proceeds. On the other hand, if multiple crosslinking units are far apart from each other, even if there are crosslinking units, they cannot contribute to the crosslinking reaction. In particular, the crosslinking reaction from silanol to siloxane in the porous membrane proceeds immediately once (all) reaction conditions are met, and the units that can contribute to crosslinking can be sufficiently crosslinked, so further crosslinking of the remaining units cannot proceed in the battery containing the porous membrane. Therefore, even if residual silanol groups remain in the porous membranes as in the porous membranes V-1 to V-5, if a crosslinking treatment is performed in the manufacturing process of those membranes, the crosslinking reaction will not proceed in the battery containing those membranes (i.e., the residual silanol groups cannot contribute to the crosslinked structure).

[0319] (d) For the separator according to the seventh embodiment of the present invention, we experimentally found a crystalline structure with a crystalline distance and a dispersion distribution of crosslinking units that allows the crosslinking reaction of the crosslinking units to proceed with high probability by adjusting the molecular weight, copolymer concentration, and blending ratio of the raw resin, and further combining this with a film-stretching process. This enabled us to improve the fracture resistance and heat-resistant safety of the battery, and also suppress the deterioration of battery cycle performance due to residual heterofunctional groups.

Claims

1. A separator for an electric storage device, comprising a silane-modified polyolefin, wherein a silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator for an electric storage device comes into contact with an electrolyte.

2. 2. The electricity storage device separator according to claim 1, wherein the silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst that crosslinks the silane-modified polyolefin.

3. The separator for an electricity storage device according to claim 1 or 2, wherein the separator for an electricity storage device contains polyethylene in addition to the silane-modified polyolefin.

4. 4. The separator for an electricity storage device according to claim 3, wherein the mass ratio of the silane-modified polyolefin to the polyethylene (mass of silane-modified polyolefin / mass of polyethylene) is 0.05 / 0.95 to 0.40 / 0.

60.

5. A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (1): R ΔＥ’ =E' Ｓ / E' ｊ (1) {In the formula, E' ｊ is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' Ｓ is the storage modulus of the separator for an electrical storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction, and E' ｊ or E' Ｓ The conditions for measuring the storage modulus E' are defined by the following features (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (manufactured by TA Instruments) - Sample film thickness: range of 5 μm to 50 μm - Measurement temperature range: -50 to 225°C Temperature increase rate: 10°C / min ・Measurement frequency: 1Hz Deformation mode: Linear tension Initial value of static tensile load: 0.5N Initial gap distance (at 25°C): 25 mm Auto strain adjustment: Enabled (range: amplitude 0.05 to 25%, sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal wave load is within 5 N and the increase in the amplitude value is within 25%, and the vibratory stress is measured. (iv) The relationship between the obtained sinusoidal load and the amplitude value, and the following formula: s ＊ =s ０ ・Exp[i(ωt+d)], e ＊ =e ０ ・Exp(iot) s ＊ =E ＊ ・e ＊ E ＊ =E'++E'' (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 of elasticity, E': storage modulus of elasticity, E'': loss modulus of elasticity Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus E' is calculated from The storage modulus change ratio (R ΔＥ’ ) is 1.5 to 20 times.

6. A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (3): R ΔＥ’’ =E'' Ｓ / E'' ｊ (3) {In the formula, E'' ｊ is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' Ｓ is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C after the silane-modified polyolefin has undergone a crosslinking reaction, and E'' ｊ or E'' Ｓ The measurement conditions for the loss modulus E″ are defined by the following configurations (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (manufactured by TA Instruments) - Sample film thickness: range of 5 μm to 50 μm - Measurement temperature range: -50 to 225°C Temperature increase rate: 10°C / min ・Measurement frequency: 1Hz Deformation mode: Linear tension Initial value of static tensile load: 0.5N Initial gap distance (at 25°C): 25 mm Auto strain adjustment: Enabled (range: amplitude 0.05 to 25%, sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal wave load is within 5 N and the increase in amplitude value is within 25%, and the vibratory stress is measured. (iv) The obtained sinusoidal load and amplitude values, and the following formula: s ＊ =s ０ ・Exp[i(ωt+d)], e ＊ =e ０ ・Exp(iot) s ＊ =E ＊ ・e ＊ E ＊ =E'++E'' (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 of elasticity, E': storage modulus of elasticity, E'': loss modulus of elasticity Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The loss modulus E'' is calculated from The loss modulus change ratio (R ΔＥ’’ ) is 1.5 to 20 times.

7. A separator for an electricity storage device, characterized in that a silane crosslinking reaction of a silane-modified polyolefin occurs when the separator for an electricity storage device comes into contact with an electrolyte.

8. A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (2): R Ｅ’ｍｉｘ =E' ａ / E' ０ (2) {In the formula, E' ａ is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C, and E' ０ is the storage modulus of the separator for an electrical storage device that does not contain the silane-modified polyolefin, measured at 160°C to 220°C, and E' ａ or E' ０ The conditions for measuring the storage modulus E' are defined by the following features (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (manufactured by TA Instruments) - Sample film thickness: range of 5 μm to 50 μm - Measurement temperature range: -50 to 225°C Temperature increase rate: 10°C / min ・Measurement frequency: 1Hz Deformation mode: Linear tension Initial value of static tensile load: 0.5N Initial gap distance (at 25°C): 25 mm Auto strain adjustment: Enabled (range: amplitude 0.05 to 25%, sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal wave load is within 5 N and the increase in the amplitude value is within 25%, and the vibratory stress is measured. (iv) The relationship between the obtained sinusoidal load and the amplitude value, and the following formula: s ＊ =s ０ ・Exp[i(ωt+d)], e ＊ =e ０ ・Exp(iot) s ＊ =E ＊ ・e ＊ E ＊ =E'++E'' (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 of elasticity, E': storage modulus of elasticity, E'': loss modulus of elasticity Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The storage modulus E' is calculated from The mixed storage modulus ratio (R Ｅ’ｍｉｘ ) is 1.5 to 20 times.

9. A separator for an electricity storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, the separator comprising a polyolefin represented by the following formula (4): R Ｅ’’ｍｉｘ =E'' ａ / E'' ０ (4) {In the formula, E'' ａ is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C, and E'' ０ is the loss modulus of the separator for an electrical storage device that does not contain the silane-modified polyolefin, measured at 160°C to 220°C, and E'' ａ or E'' ０ The measurement conditions for the loss modulus E″ are defined by the following configurations (i) to (iv). (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (manufactured by TA Instruments) - Sample film thickness: range of 5 μm to 50 μm - Measurement temperature range: -50 to 225°C Temperature increase rate: 10°C / min ・Measurement frequency: 1Hz Deformation mode: Linear tension Initial value of static tensile load: 0.5N Initial gap distance (at 25°C): 25 mm Auto strain adjustment: Enabled (range: amplitude 0.05 to 25%, sine wave load 0.02 to 5N) This is done. (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillating stress centered on the static tensile load. (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.2%. In the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal wave load is within 20%. When the sinusoidal wave load becomes 0.02 N or less, the amplitude value is amplified so that the sinusoidal wave load is within 5 N and the increase in amplitude value is within 25%, and the vibratory stress is measured. (iv) The obtained sinusoidal load and amplitude values, and the following formula: s ＊ =s ０ ・Exp[i(ωt+d)], e ＊ =e ０ ・Exp(iot) s ＊ =E ＊ ・e ＊ E ＊ =E'++E'' (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 of elasticity, E': storage modulus of elasticity, E'': loss modulus of elasticity Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load The loss modulus E'' is calculated from The mixed loss modulus ratio (R Ｅ’’ｍｉｘ ) is 1.5 to 20.0 times.

10. The separator for an electricity storage device according to claim 8 or 9, wherein the separator for an electricity storage device that does not contain the silane-modified polyolefin is a microporous film made of a silane-unmodified polyolefin and has a gelation degree of 0% or more and 10% or less.

11. A separator for an electric storage device comprising 5 to 40 mass % of a silane-modified polyolefin and 60 to 95 mass % of a polyolefin other than the silane-modified polyolefin, wherein the transition temperature between a rubber-like plateau region and a crystalline melt flow region in the temperature change of the storage modulus of the separator for an electric storage device is 135°C to 150°C.

12. A separator for an electricity storage device made of a polyolefin microporous membrane, In measuring the solid viscoelasticity of the separator for an electricity storage device at temperatures of −50° C. to 250° C., The minimum storage modulus is 1.0 MPa to 10 MPa, and the maximum storage modulus is 100 MPa to 10,000 MPa; and The minimum value of the loss modulus is 0.1 MPa to 10 MPa, and the maximum value of the loss modulus is 10 MPa to 10,000 MPa; The solid viscoelasticity measurement conditions for measuring the storage modulus and the loss modulus are the following conditions (i) to (iv): (i) Dynamic viscoelasticity measurement was performed under the following conditions: Measurement device used: RSA-G2 (manufactured by TA Instruments) Sample film thickness: 200 μm to 400 μm (however, if the film thickness of a single sample is less than 200 μm, multiple samples are stacked together and the dynamic viscoelasticity measurement is performed so that the total thickness is within the range of 200 μm to 400 μm.) - Measurement temperature range: -50℃ to 250℃ Temperature increase rate: 10°C / min ・Measurement frequency: 1Hz Deformation mode: Linear tension ・Initial value of static tensile load: 0.2N Initial gap distance (at 25°C): 10 mm Auto strain adjustment: Disabled Do it with; (ii) The static tensile load refers to the intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillatory stress centered on the static tensile load; (iii) The sinusoidal tensile mode refers to measuring the vibratory stress while performing periodic motion at a fixed amplitude of 0.1%, and in the sinusoidal tensile mode, the vibratory stress is measured by varying the gap distance and the static tensile load so that the difference between the static tensile load and the sinusoidal load is within 5%, and when the sinusoidal load becomes 0.1 N or less, the static tensile load is fixed at 0.1 N and the vibratory stress is measured; (iv) The relationship between the obtained sinusoidal load and the amplitude value, and the following formula: s ＊ =s ０ ・Exp[i(ωt+d)], e ＊ =e ０ ・Exp(iot) s ＊ =E ＊ ・e ＊ E ＊ =E'++E'' {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 of elasticity, E': storage modulus of elasticity, E'': loss modulus of elasticity Vibration stress: sinusoidal load / initial cross-sectional area Static tensile load: Load at the minimum point of vibration stress at each cycle (minimum point of gap distance at each cycle) Sinusoidal load: the difference between the measured oscillatory stress and the static tensile load. Calculating the storage modulus and the loss modulus from A separator for an electricity storage device as defined in

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

14. The separator for an electricity storage device according to claim 13, wherein, in the solid viscoelasticity measurement, the film softening transition temperature is 140°C to 150°C and the film rupture temperature is 180°C or higher.

15. The separator for an electricity storage device according to any one of claims 12 to 14, comprising a silane-modified polyolefin and a polyolefin other than the silane-modified polyolefin.

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

17. A separator for an electricity storage device containing polyolefin, The polyolefin has one or more functional groups, and A separator for an electricity storage device, characterized in that after being housed in the electricity storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the electricity storage device, or (3) the functional groups react with other types of functional groups to form a crosslinked structure.

18. 18. The separator for a storage battery device according to claim 17, wherein the chemical substance is any one of an electrolyte, an electrolytic solution, an electrode active material, an additive, or a decomposition product thereof contained in the storage battery device.

19. A separator for an electric storage device comprising a polyolefin, the separator having an amorphous portion crosslinked structure in which the amorphous portion of the polyolefin is crosslinked.

20. The separator for an electricity storage device has the following formula (1): R Ｅ’Ｘ =E' Ｚ / E' Ｚ０ (1) {In the formula, E' Ｚ is the storage modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E' Ｚ０ is the storage modulus measured in a temperature range of 160°C to 300°C before the separator for an electricity storage device is incorporated into the electricity storage device.} The mixed storage modulus ratio (R Ｅ’ｘ 20. The separator for an electricity storage device according to claim 19, wherein the ratio of the total mass of the separator to the total mass of the battery is 1.5 to 20 times.

21. The separator for an electricity storage device has the following formula (3): R Ｅ’’Ｘ =E'' Ｚ / E'' Ｚ０ (3) {In the formula, E'' Ｚ is the loss modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the separator for an electricity storage device has progressed in the electricity storage device, and E'' Ｚ０ is the loss modulus measured in a temperature range of 160°C to 300°C before the electricity storage device separator is incorporated into the electricity storage device.} The mixed loss modulus ratio (R Ｅ’’ｘ 21. The separator for an electricity storage device according to claim 19 or 20, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

22. The electricity storage device separator according to any one of claims 19 to 21, wherein the amorphous portion is selectively crosslinked.

23. The separator for an electricity storage device has the following formula (2): R Ｅ’ｍｉｘ =E' / E' ０ (2) In the formula, E' is a storage modulus measured at 160°C to 300°C when the electricity storage device separator has an amorphous crosslinked structure, and E' ０ is the storage modulus of the separator for an electricity storage device that does not have an amorphous crosslinked structure, measured at 160°C to 300°C.} The mixed storage modulus ratio (R Ｅ’ｍｉｘ 23. The separator for an electricity storage device according to any one of claims 17 to 22, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

24. The separator for an electricity storage device has the following formula (4): R Ｅ’’ｍｉｘ =E'' / E'' ０ (4) {In the formula, E" is the loss modulus measured at 160°C to 300°C when the electricity storage device separator has an amorphous crosslinked structure, and E'' ０ is the loss modulus of the separator for an electricity storage device that does not have an amorphous crosslinked structure, measured at 160°C to 300°C.} The mixed loss modulus ratio (R Ｅ’’ｍｉｘ 24. The separator for an electricity storage device according to any one of claims 17 to 23, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

25. The separator for an electricity storage device according to any one of claims 17 to 24, wherein the polyolefin is polyethylene.

26. The separator for an electricity storage device according to any one of claims 17 to 25, wherein the polyolefin is a functional group-modified polyolefin or a polyolefin copolymerized with a monomer having a functional group.

27. The separator for an electricity storage device according to any one of claims 17 to 26, wherein the crosslinked structure is formed by a reaction mediated by any one of a covalent bond, a hydrogen bond, or a coordinate bond.

28. The reaction via the covalent bond is represented by the following reactions (I) to (IV): (I) Condensation reaction of multiple identical functional groups; (II) Reactions between multiple different functional groups; (III) a chain condensation reaction between the functional group and the electrolyte; and (IV) reaction of the functional group with the additive; 28. The separator for an electricity storage device according to claim 27, which is at least one selected from the group consisting of:

29. The reaction via a coordinate bond is the following reaction (V): (V) A reaction in which multiple identical functional groups crosslink via coordinate bonds with metal ions; The separator for an electricity storage device according to claim 27,

30. 29. The separator for an electrical storage device according to claim 28, wherein the reaction (I) and / or (II) is catalytically promoted by a chemical substance inside the electrical storage device.

31. 29. The electricity storage device separator according to claim 28, wherein the reaction (I) is a condensation reaction of a plurality of silanol groups.

32. The reaction (IV) is a nucleophilic substitution reaction, a nucleophilic addition reaction, or a ring-opening reaction between a compound Rx constituting the electricity storage device separator and a compound Ry constituting the additive, wherein the compound Rx has a functional group x, and the compound Ry has a linking reaction unit y １ The separator for an electricity storage device according to claim 28 , having

33. Reaction (IV) is a nucleophilic substitution reaction, The functional group x of the compound Rx is —OH, —NH ２ , —NH—, —COOH, and —SH, and The linking reaction unit y of the compound Ry １ But CH ３ SO ２ -, CF ３ SO ２ -, ArSO ２ -, CH ３ SO ３ -, CF ３ SO ３ -, ArSO ３ - and the following formula (y １ −1) to (y １ -6): 【Chemistry 1】 {In the formula, X is a hydrogen atom or a monovalent substituent.} 【Chemistry 2】 {In the formula, X is a hydrogen atom or a monovalent substituent.} 【Transformation 3】 {In the formula, X is a hydrogen atom or a monovalent substituent.} 【Chemistry 4】 {In the formula, X is a hydrogen atom or a monovalent substituent.} 【Transformation 5】 {In the formula, X is a hydrogen atom or a monovalent substituent.} 【Transformation 6】 {In the formula, X is a hydrogen atom or a monovalent substituent.} The separator for an electricity storage device according to claim 32, wherein the group consisting of at least two monovalent groups represented by the following formula:

34. Reaction (IV) is a nucleophilic substitution reaction, The compound Ry is a ligation reaction unit y １ In addition to the chain unit y ２ and The chain unit y ２ is expressed by the following formula (y ２ −1) to (y ２ -6): 【Transformation 7】 {wherein m is an integer from 0 to 20, and n is an integer from 1 to 20.} 【Transformation 8】 {wherein n is an integer from 1 to 20.} 【Chemistry 9】 {wherein n is an integer from 1 to 20.} 【Chemistry 10】 {wherein n is an integer from 1 to 20.} 【Chemistry 11】 {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} 【Chemistry 12】 {In the formula, X is an alkylene group or an arylene group having 1 to 20 carbon atoms, and n is an integer of 1 to 20.} The separator for an electricity storage device according to claim 32 or 33, wherein the group is at least one selected from the group consisting of divalent groups represented by the following formula:

35. Reaction (IV) is a nucleophilic addition reaction, The functional group x of the compound Rx is —OH, —NH ２ , —NH—, —COOH, and —SH, and The linking reaction unit y of the compound Ry １ is expressed by the following formula (Ay １ -1) to (Ay １ -6): 【Chemistry 13】 【Chemistry 14】 【Chemistry 15】 【Chemistry 16】 {In the formula, R is a hydrogen atom or a monovalent organic group.} 【Chemistry 17】 [Chemistry 18] The separator for an electricity storage device according to claim 32, wherein the group is at least one selected from the group consisting of groups represented by the following formula:

36. the reaction (IV) is a ring-opening reaction, The functional group x of the compound Rx is —OH, —NH ２ , —NH—, —COOH, and —SH, and The linking reaction unit y of the compound Ry １ is expressed by the following formula (ROy １ -1): 【Chemistry 19】 {In the formula, each of the multiple Xs independently represents a hydrogen atom or a monovalent substituent.} The separator for an electricity storage device according to claim 32 , wherein the group is at least two groups represented by the following formula:

37. In the following reaction (V), the metal ion is Zn ２＋ , Mn ２＋ , Co ３＋ , Ni ２＋ and Li ＋ 30. The separator for an electricity storage device according to claim 29, wherein the separator is at least one selected from the group consisting of:

38. A separator for an electric storage device, comprising a first porous layer (layer A) containing a silane-modified polyolefin and capable of forming a crosslinked structure, and a second porous layer (layer B) containing inorganic particles, wherein the heat shrinkage rate at 150°C after the formation of the crosslinked structure is 0.02 to 0.91 times the heat shrinkage rate at 150°C before the formation of the crosslinked structure.

39. 39. The separator for an electricity storage device according to claim 38, wherein the crosslinked structure in the layer A is formed by an acid, a base, swelling, or a compound generated within the electricity storage device.

40. a microporous membrane containing a silane-modified polyolefin; an inorganic porous layer containing inorganic particles and a resin binder, the inorganic porous layer being disposed on at least one surface of the microporous membrane; A separator for an electricity storage device comprising:

41. The electricity storage device separator according to claim 40, wherein the content of the inorganic particles in the inorganic porous layer is 5% by weight to 99% by weight.

42. 42. The power storage device separator according to claim 40, wherein the content of the silane-modified polyolefin in the microporous film is 0.5% by weight to 40% by weight.

43. The inorganic particles are alumina (Al ２ O ３ ), silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxide hydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, diatomaceous earth, silica sand, and glass fiber. The separator for an electricity storage device according to any one of claims 40 to 42, which is at least one selected from the group consisting of:

44. The separator for an electricity storage device according to any one of claims 40 to 43, wherein the resin binder has a glass transition temperature (Tg) of -50°C to 100°C.

45. The separator for an electricity storage device according to any one of claims 40 to 44, wherein a silane crosslinking reaction of the silane-modified polyolefin is initiated when the separator for an electricity storage device comes into contact with an electrolyte solution.

46. The separator for an electricity storage device has a molecular weight of 1.01 or more, when measured excluding the inorganic porous layer, expressed by the following formula (1A): R △Ｅ’ =E’ Ｓ / E’ ｊ (1A) {In the formula, E' ｊ is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E' Ｓ is the storage modulus of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction, measured at 160°C to 220°C.} The storage modulus change ratio (R △Ｅ’ ) is 1.5 to 20 times, and / or the following formula (1B): R △Ｅ’’ =E’’ Ｓ / E’’ ｊ (1B) {In the formula, E'' ｊ is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C before the silane-modified polyolefin undergoes a crosslinking reaction, and E'' Ｓ is the loss modulus of the separator for an electricity storage device after the silane-modified polyolefin has undergone a crosslinking reaction, measured at 160°C to 220°C.} The loss modulus change ratio (R △Ｅ The separator for an electricity storage device according to any one of claims 40 to 45, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

47. The separator for an electricity storage device has a molecular weight of 1000 or more when measured excluding the inorganic porous layer and has a molecular weight of 1000 or more as represented by the following formula (2A): R Ｅ’ｍｉｘ =E’ / E’ ０ (2A) {wherein E' is the storage modulus of the separator for an electricity storage device measured at 160°C to 220°C, and E' ０ is the storage modulus measured at 160°C to 220°C of a separator for an electricity storage device that does not contain the silane-modified polyolefin.} The mixed storage modulus ratio (R Ｅ’ｍｉｘ ) is 1.5 to 20 times, and / or the following formula (2B): R Ｅ’’ｍｉｘ =E'' / E'' ０ (2B) {wherein E" is the loss modulus of the separator for an electricity storage device measured at 160°C to 220°C, and E" ０ is the loss modulus of the separator for an electricity storage device that does not contain the silane-modified polyolefin, measured at 160°C to 220°C.} The mixed loss modulus ratio (R Ｅ’’ｍｉｘ 47. The separator for an electricity storage device according to any one of claims 40 to 46, wherein the ratio of the surface area to the surface area of ​​the separator is 1.5 to 20 times.

48. The separator for a storage device according to any one of claims 40 to 47, wherein the transition temperature between the rubber-like plateau region and the crystalline melt flow region in the change in storage modulus with temperature of the separator for a storage device is 135°C to 150°C.

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

50. An electricity storage device comprising a separator containing polyethylene and an electrolytic solution or an additive, in which a crosslinked structure is formed by a reaction between the functional group-modified polyethylene or the functional group-grafted copolymerized polyethylene and a chemical substance contained in the electrolytic solution or the additive.

51. The following steps: (1) a sheet-forming step of extruding a mixture of silane-modified polyolefin, polyethylene, and a plasticizer, cooling and solidifying the mixture, and forming the mixture into a sheet; (2) a stretching step of stretching the sheet in at least one direction to obtain a stretched product; (3) a porous body forming step of extracting the plasticizer from the stretched material in the presence of an extraction solvent to make the stretched material porous, thereby forming a porous body; and (4) a heat treatment step of subjecting the porous body to a heat treatment; A method for producing the separator for an electricity storage device according to any one of claims 1 to 50, comprising:

52. The following steps: (1) a sheet-forming step in which the silane-modified polyolefin, polyethylene, and plasticizer are extruded into a sheet using an extruder, cooled and solidified, and processed into a sheet-shaped molded product; (2) a stretching step in which the sheet-like molded body is biaxially stretched at an areal stretching ratio of 20 times to 250 times to form a stretched body; (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) a coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the heat-treated porous body to form a silane crosslinked precursor; (9) an assembly step of housing a laminate or a wound body of the electrodes and the silane cross-linked precursor, and a non-aqueous electrolyte solution in an outer casing, and bringing the silane cross-linked precursor into contact with the non-aqueous electrolyte solution; A method for producing a separator for an electricity storage device, comprising:

53. The following two elements: (1) an exterior housing containing an electrode and a laminate or wound body of the separator for an electricity storage device according to any one of claims 1 to 48; and (2) a container containing a non-aqueous electrolyte; An electricity storage device assembly kit comprising:

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

55. The non-aqueous electrolyte is lithium hexafluorophosphate (LiPF ６ 55. The electricity storage device assembly kit according to claim 53 or 54, comprising:

56. The electricity storage device assembly kit according to any one of claims 53 to 55, wherein the non-aqueous electrolyte solution is an acid solution and / or a base solution.

57. The following steps: A step of preparing the electricity storage device assembly kit according to any one of claims 53 to 56; a step of initiating a silane crosslinking reaction of the silane-modified polyolefin by bringing the separator for the electricity storage device in element (1) of the electricity storage device assembly kit into contact with the nonaqueous electrolyte in element (2); A method for manufacturing an electricity storage device comprising:

58. Further steps: A step of connecting a lead terminal to the electrode of the element (1); performing at least one charge / discharge cycle; The method for manufacturing the electricity storage device according to claim 57, comprising:

59. A method for producing an electricity storage device using a separator containing polyolefin, comprising: The polyolefin comprises one or more types of functional groups, and the process comprises: (1) a cross-linking step of forming a cross-linked structure by condensing the functional groups together, (2) reacting the functional groups with chemical substances inside the electrical storage device, or (3) reacting the functional groups with other types of functional groups. A method for manufacturing an electricity storage device comprising:

60. The method for manufacturing an electricity storage device according to claim 59, wherein the crosslinking step is carried out at a temperature of 5°C to 90°C.

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