KR102280521B1 - Polyolefin laminated microporous membrane - Google Patents

Abstract

[Problem] An object of the present invention is to improve the film resistance of the microporous film under high temperature without impairing the strength and porosity of the microporous film, and to achieve both device characteristics and safety of an electrical storage device including the microporous film as a separator. do it with
[Solutions] The microporous film for an electrical storage device has a laminated structure, and at least one layer of the laminated structure contains a polyolefin having one or more functional groups, and the microporous film for an electrical storage device is stored in the electrical storage device. After that, (1) the functional groups are subjected to a condensation reaction, (2) the functional group reacts with a chemical substance inside the power storage device, or (3) the functional group reacts with a different type of functional group, thereby forming a crosslinked structure, Moreover, ratio MD/TD of the orientation ratio of the width direction (TD) with respect to the machine direction (MD) when at least one layer containing the said polyolefin is measured by wide-angle X-ray scattering satisfy|fills 1.3 or more.

Description

Polyolefin laminated microporous membrane {POLYOLEFIN LAMINATED MICROPOROUS MEMBRANE}

The present invention relates to a microporous membrane for electrical storage devices and the like.

Microporous membranes are widely used as separation or selective permeation separation membranes for various substances, as separators, and the like, and examples of their use include microfiltration membranes, separators for fuel cells, capacitors, or functional materials filled in pores to express new functions. The base material of a functional film, the separator for electrical storage devices, etc. are mentioned. Especially, the microporous film made from polyolefin is used as a separator for lithium ion batteries widely used for a notebook-type personal computer, a cellular phone, a digital camera, etc.

In order to ensure battery safety, it has been proposed to form a crosslinked structure in a separator to achieve both expression of a shutdown function and improvement in film breaking temperature (Patent Documents 1 to 8). For example, Patent Documents 1 to 6 describe a silane crosslinked structure formed by contact of a silane-modified polyolefin-containing separator with water or the like. Patent Document 7 describes a cross-linked structure formed by ring-opening of norbornene by irradiation with ultraviolet rays, electron beams, or the like. Patent Document 8 describes that the insulating layer of the separator includes a (meth)acrylic acid copolymer having a crosslinked structure, a styrene-butadiene rubber binder, and the like.

As a member of a lithium ion battery, a positive electrode, a negative electrode material, electrolyte solution, and a separator are used. Among these members, the separator has been required to be inert to an electrochemical reaction or a peripheral member from its qualification as an insulating material. Regarding the negative electrode material of a lithium ion battery, from the beginning of its development, a technique has been established for suppressing the decomposition of the electrolyte on the surface of the negative electrode by forming a solid electrolyte interface (SEI) by a chemical reaction during the first charge (Non-Patent Document 1) . Moreover, even when a polyolefin resin is used for a separator, the case where oxidation reaction is induced in the positive electrode surface under high voltage, blackening of a separator, surface deterioration, etc. are also reported.

Japanese Patent Laid-Open No. 9-216964 International Publication No. 97/44839 Japanese Patent Laid-Open No. 11-144700 Japanese Patent Laid-Open No. 11-172036 Japanese Patent Laid-Open No. 2001-176484 Japanese Patent Laid-Open No. 2000-319441 Japanese Patent Laid-Open No. 2011-071128 Japanese Patent Laid-Open No. 2014-056843

Lithium-ion secondary battery (2nd edition) Nikkan High School deep borax publication

In recent years, with increasing output and high energy density of lithium ion secondary batteries for mobile device mounting or vehicle mounting, miniaturization of battery cells and stable cycle charge/discharge performance during long-term use are demanded. Therefore, strength and porosity are required for manufacture of the microporous film which can be used as a battery separator. In addition, the level of battery safety is also stricter than before, and as described in Patent Documents 1 and 2, a separator having a shutdown function and high temperature film breakability, and a stable manufacturing method thereof are expected. In this regard, as the level of the shutdown temperature, lower than 150° C. is preferable, and as the level of the film breaking temperature, higher is more preferable.

However, all of the bridge|crosslinking methods described in patent documents 1-8 are performed by the phosphorus process of a microporous membrane, or arrangement|positioning immediately after preparation of a microporous membrane. Therefore, after the formation of the crosslinked structure described in Patent Documents 1 to 8, coating processing and slitting of the microporous film must be performed for use as a separator, and internal stress increases in the subsequent lamination and winding process with the electrode, The produced power storage device may be deformed. For example, when a crosslinked structure is formed by heating, the internal stress of a separator having the crosslinked structure may increase at room temperature or room temperature. Moreover, when a crosslinked structure is formed by light irradiation of an ultraviolet-ray, electron beam, etc. to a microporous film, irradiation of light will become non-uniform|heterogenous, and a crosslinked structure may become heterogeneous. This is considered to be because the periphery of the crystal part of the resin constituting the microporous film is easily crosslinked by the electron beam.

In view of the above problems, the present invention improves the film resistance under high temperature of the microporous film without impairing the strength and porosity of the microporous film, and achieves both device characteristics and safety of an electrical storage device including the microporous film as a separator. aims to make

The above problem is solved by the following technical means.

[One]

A microporous film for electrical storage devices having a laminated structure and comprising polyolefin in at least one layer of the laminated structure, the microporous film comprising:

The said polyolefin has 1 type, or 2 or more types of functional groups,

After storage in the electrical storage device, (1) the functional groups are condensation-reacted, (2) the functional group reacts with a chemical substance inside the electrical storage device, or (3) the functional group reacts with a different type of functional group, A cross-linked structure is formed, and also

Ratio of the orientation ratio of the width direction (TD) to the machine direction (MD) when at least one layer of the laminated structure contains polypropylene, and the layer containing the polypropylene is measured as a single layer by wide-angle X-ray scattering MD/TD satisfies 1.3 or more, The microporous film for electrical storage devices characterized by the above-mentioned.

[2]

The said crosslinked structure is (1) The microporous film for electrical storage devices as described in item 1 which is formed by the said functional group condensation-reacting.

[3]

The said crosslinked structure is (2) The microporous film for electrical storage devices according to item 1 which is formed by the said functional group reacting with the chemical substance inside the said electrical storage device.

[4]

The microporous membrane for power storage devices according to item 1 or 3, wherein the chemical substance is any of an electrolyte, an electrolyte solution, an electrode active material, an additive, or a decomposition product thereof contained in the power storage device.

[5]

The said crosslinked structure is (3) The microporous film for electrical storage devices according to item 1 which is formed by the said functional group reacting with a functional group of a different type.

[6]

At least one layer comprising the polyolefin, the following formula (I):

R _E'X =E' _Z /E' _Z0 (I)

{wherein, E' _Z is, after at least one reaction of (1) to (3) of the microporous membrane for the electrical storage device proceeds in the electrical storage device, the storage measured in a temperature range of 160°C to 300°C is the modulus of elasticity, and also

E' _Z0 is the storage elastic modulus measured in a temperature range of 160°C to 300°C before the microporous membrane for the electrical storage device is embedded in the electrical storage device, and the measurement conditions of the storage elastic modulus that are _{E' Z} or E' _{Z0 are} , is defined by the following structures (i) to (iv).

(i) dynamic viscoelasticity measurement under the following conditions:

・Atmosphere: nitrogen

・Used measuring device: RSA-G2 (manufactured by TA Instruments)

・Sample film thickness: in the range of 5 µm to 50 µm (measured with one sheet regardless of the film thickness of the sample)

・Measurement temperature range: -50 to 300°C

·Temperature increase rate: 10℃/min

・Measurement frequency: 1Hz

Deformation mode: sine wave tension mode (Linear tension)

·Initial value of static tensile load: 0.5N

・Initial gap distance (at 25℃): 25mm

Auto strain adjustment: Enabled (Range: amplitude value 0.05 to 25%, sinusoidal load 0.02 to 5N)

was done in

(ii) The static tensile load refers to an intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillation 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 0.2%. At that time, the distance between the gaps and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 20%. Vibration stress was measured. Incidentally, when the sine wave load was 0.02 N or less, the amplitude value was amplified so that the sine wave load was within 5 N and the amount of increase in the amplitude value was within 25%, and the vibration stress was measured.

(iv) the relation between the obtained sine wave load and the amplitude value, and the following formula:

σ ^* =σ ₀ Exp[i(ωt+δ)],

ε ^* =ε ₀ Exp(iωt),

σ ^* =E ^* ε ^*

E ^* =E'+iE''

(where, σ ^* : vibrational stress, ε ^* : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E ^* : complex elastic modulus, E': storage modulus , E'': loss modulus

Vibration stress: sinusoidal load/initial cross-sectional area

Static tensile load: the load at the minimum of the vibration stress in each period (minimum of the inter-gap distance in each period)

Sine wave load: difference between measured vibration stress and static tensile load)

Calculate the storage modulus from

The microporous membrane for electrical storage devices according to any one of items 1 to 5, wherein the mixed storage elastic modulus ratio ( _{RE'x ) defined by is 1.2 to 20 times.}

[7]

A microporous film for electrical storage devices having a laminated structure and comprising polyolefin in at least one layer of the laminated structure, the microporous film comprising:

The polyolefin has an amorphous portion crosslinked structure in which an amorphous portion is crosslinked, and

Ratio of the orientation ratio of the width direction (TD) to the machine direction (MD) when at least one layer of the laminated structure contains polypropylene, and the layer containing the polypropylene is measured as a single layer by wide-angle X-ray scattering MD/TD satisfies 1.3 or more, The microporous film for electrical storage devices characterized by the above-mentioned.

[8]

The microporous film for electrical storage devices according to item 7, wherein the amorphous portion is selectively crosslinked.

[9]

At least one layer comprising the polyolefin, the following formula (II):

R _E'mix =E'/E' ₀ (II)

{wherein, E' is the storage modulus measured at 160°C to 300°C when the microporous membrane for electrical storage device has the amorphous part crosslinked structure, and

E' ₀ is the storage elastic modulus measured at 160 ° C. to 300 ° C. of the microporous film for electrical storage devices that does not have an amorphous part crosslinked structure, and the measurement conditions for the storage elastic modulus of _{E' or E' 0 are the following configuration (i)} to (iv).

(i) dynamic viscoelasticity measurement under the following conditions:

・Atmosphere: nitrogen

・Used measuring device: RSA-G2 (manufactured by TA Instruments)

・Sample film thickness: in the range of 5 µm to 50 µm (measured with one sheet regardless of the film thickness of the sample)

・Measurement temperature range: -50 to 300°C

·Temperature increase rate: 10℃/min

・Measurement frequency: 1Hz

Deformation mode: sine wave tension mode (linear tension)

·Initial value of static tensile load: 0.5N

・Initial gap distance (at 25℃): 25mm

Automatic strain adjustment: available (Range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5N)

was done in

(ii) The static tensile load refers to an intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillation 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 0.2%. At that time, the distance between the gaps and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 20%. Vibration stress was measured. Incidentally, when the sine wave load was 0.02 N or less, the amplitude value was amplified so that the sine wave load was within 5 N and the amount of increase in the amplitude value was within 25%, and the vibration stress was measured.

(iv) the relation between the obtained sine wave load and the amplitude value, and the following formula:

σ ^* =σ ₀ Exp[i(ωt+δ)],

ε ^* =ε ₀ Exp(iωt),

σ ^* =E ^* ε ^*

E ^* =E'+iE''

(where, σ ^* : vibrational stress, ε ^* : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E ^* : complex elastic modulus, E': storage modulus , E'': loss modulus

Vibration stress: sinusoidal load/initial cross-sectional area

Static tensile load: the load at the minimum of the vibration stress in each period (minimum of the inter-gap distance in each period)

Sine wave load: difference between measured vibration stress and static tensile load)

Calculate the storage modulus from

The microporous membrane for electrical storage devices according to item 7 or 8, wherein the mixed storage elastic modulus ratio ( _{RE'mix ) defined by is 1.2 to 20 times.}

According to the present invention, without impairing the strength and porosity of the microporous membrane for a power storage device, it is possible to achieve an improvement in the film resistance under high temperature, and the battery characteristics of the power storage device having the microporous membrane as a separator and the puncture test, etc. High safety is compatible. In addition, according to the present invention, since it is not necessary to form a crosslinked structure during or immediately after the film forming process, an increase in the internal stress of the separator and deformation after fabrication of the electrical storage device can be suppressed and/or relatively high due to light irradiation or heating. A crosslinked structure can be provided to a separator without using energy.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating the crystalline polymer which has a higher order structure divided into the lamella (crystal part) of a crystal structure, an amorphous part, and the intermediate|middle layer part between them.
2 is a schematic diagram for explaining crystal growth of polyolefin molecules.
3 is a diagram for explaining an example of azimuthal distribution of scattering intensity in the transmission method wide-angle X-ray scattering (WAXS) measurement of a polyolefin microporous membrane, a peak, and an example of peak separation by Gaussian function approximation, and the unit "arb.u " represents an arbitrary unit.

EMBODIMENT OF THE INVENTION Hereinafter, the form (it abbreviates to "embodiment" hereafter) for implementing this invention is demonstrated in detail. Incidentally, the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist.

[Microporous membrane for power storage device]

The microporous membrane may be formed of a single or a plurality of types of polyolefin-based resin, or may be a composite resin film having a polyolefin-based resin and other resins, and has a large number of fine pores. The microporous membrane (henceforth a polyolefin microporous membrane) containing polyolefin resin as a main component contains 50 mass % or more of polyolefin resin with respect to the mass of a membrane|membrane.

The polyolefin microporous film is preferably used for formation of an electrical storage device from the viewpoint of oxidation-reduction degradation resistance and a dense and uniform porous structure, more preferably used as a constituent material of the electrical storage device, as a separator for electrical storage devices It is more preferred to be used, and particularly preferred to be used as a separator for lithium ion batteries. In the present specification, a separator for an electrical storage device (hereinafter, may be abbreviated as “separator”) refers to a member disposed between a plurality of electrodes in an electrical storage device and having ion permeability and, if necessary, a shutdown characteristic. . A separator may contain a microporous membrane and may further be equipped with arbitrary functional layers as needed.

[First Embodiment]

The microporous membrane according to the first embodiment has a laminated structure, and at least one of the multilayers constituting the laminated structure contains polyolefin having one or more functional groups, and after being accommodated in the electrical storage device, (1) the functional groups of the polyolefin are subjected to a condensation reaction, (2) the functional group of the polyolefin reacts with a chemical substance inside the electrical storage device, or (3) the functional group of the polyolefin reacts with a different type of functional group to form a crosslinked structure . In the first embodiment, the microporous membrane can secure strength, impart a function, or be suitable for various uses, a porosity process, or a processing process by virtue of the laminated structure, and furthermore, the above (1) to (3) ), the strength and the film resistance under high temperature of 150 ° C. or higher can be improved by the cross-linked structure formed by the reaction of any of ), and when stored in an electrical storage device as a separator, for example, there is a tendency for compatibility of device characteristics and safety. there is.

In the first embodiment, functional groups contained in polyolefins such as polyethylene and polypropylene are not introduced into the crystalline portion of the polyolefin and are considered to be crosslinked in the amorphous portion. Therefore, after the microporous membrane is stored in the electrical storage device, the surrounding environment Alternatively, a cross-linked structure may be formed using a chemical substance inside the electrical storage device, thereby suppressing an increase in internal stress or deformation of the manufactured electrical storage device, thereby contributing to safety.

On the other hand, when a crosslinking reaction is performed before the microporous membrane is accommodated in an electrical storage device, and it passes through processes, such as winding-up and a slit, the influence of stresses, such as tension|tensile_strength generated at the time of the process, remains. When this stress is released after assembly of the electrical storage device, it is not preferable because it is considered to cause deformation of the electrode wound or the like or damage due to stress concentration.

Further, in the first embodiment, since it is not necessary to form a crosslinked structure during or immediately after the film forming process, when the microporous film is used as a separator, an increase in internal stress and deformation after fabrication of the electrical storage device can be suppressed and/or crosslinked It can contribute to energy saving by not using light irradiation or heating to form the structure.

Further, in the first embodiment, among the multilayers constituting the laminate structure of the microporous film, at least one layer containing polypropylene is a single layer in the width direction with respect to the machine direction (MD) when measured by wide-angle X-ray scattering. Ratio MD/TD of the orientation ratio of (TD) is 1.3 or more. In the first embodiment, when the ratio MD/TD of the orientation ratio of the polypropylene-containing monolayer is 1.3 or more, the strength, film formability, productivity and porosity of the microporous membrane having a laminate structure tend to improve, and further The microporosity, cross-linked structure and ion permeability of the microporous membrane can be adapted to desired device properties. The lower limit of the ratio MD/TD of the orientation ratio is preferably 1.4 or more or 1.5 or more, more preferably 1.6 or more, from the viewpoint of suitable film properties and device characteristics. The higher the upper limit of the ratio MD/TD of the orientation ratio, the easier it is to puncture the polyolefin molded body and the better the orientation of the microporous film. For example, depending on the film forming process or lamination process, 12.0 or less, 11.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.5 or less, or 5.0 or less.

[Second Embodiment]

The microporous film according to the second embodiment has a laminated structure, at least one of the multilayers constituting the laminated structure contains polyolefin, and the polyolefin has an amorphous portion crosslinked structure in which an amorphous portion is crosslinked. The microporous membrane according to the second embodiment can secure strength, impart a function, or be suitable for various uses, a porosity process, or a processing process by virtue of its laminated structure. Further, since the microporous membrane according to the second embodiment has a crosslinked structure of an amorphous portion of polyolefin such as polyethylene or polypropylene, it has a shut down function, compared with a conventional crosslinked microporous film in which the crystal portion and its surroundings are easily crosslinked. An increase in internal stress or deformation of the manufactured electrical storage device can be suppressed, and the safety|security of an electrical storage device can be ensured by making compatible with the film breakage resistance under high temperature of 150 degreeC or more. From the same viewpoint, the amorphous portion of the polyolefin contained in the microporous film according to the second embodiment is preferably crosslinked selectively, and more preferably, is crosslinked significantly more than the crystal portion.

Further, in the second embodiment, among the multilayers constituting the laminate structure of the microporous film, at least one layer containing polypropylene is a single layer in the width direction with respect to the machine direction (MD) when measured by wide-angle X-ray scattering. Ratio MD/TD of the orientation ratio of (TD) is 1.3 or more. In the second embodiment, when the ratio MD/TD of the orientation ratio of the polypropylene-containing monolayer is 1.3 or more, the strength, film formability, productivity, and porosity of the microporous membrane having a laminate structure tend to improve, and further The microporosity, cross-linked structure and ion permeability of the microporous membrane can be adapted to desired device properties. The lower limit of the ratio MD/TD of the orientation ratio is preferably 1.4 or more or 1.5 or more, more preferably 1.6 or more, from the viewpoint of suitability of film properties and device characteristics. The higher the upper limit of the ratio MD/TD of the orientation ratio, the easier it is to puncture the polyolefin molded body, and the orientation of the microporous membrane is also improved. For example, depending on the film forming process or lamination process, 12.0 or less, 11.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.5 or less, or 5.0 or less.

Incidentally, in the first and second embodiments, the monolayer measured by wide-angle X-ray scattering is made of only polypropylene or is added to polypropylene and contains components other than polypropylene, for example, polyolefin excluding polypropylene. , may contain resins or additives other than polyolefin.

[Crosslinking Reaction Mechanism]

Although it is not clear about a crosslinking reaction mechanism and a crosslinking structure in 1st and 2nd embodiment, the present inventors think as follows (A) - (D).

(A) Crystal structure in polyolefin microporous membrane

Polyolefin resins typified by polyethylene, etc., are generally crystalline polymers, as shown in FIG. 1, and have a higher-order structure divided into lamellar (crystal part) of a crystal structure, an amorphous part, and an intermediate|middle layer part between them. In the crystalline part and the intermediate layer between the crystalline part and the amorphous part, the polymer chains have low mobility and cannot be separated, but a relaxation phenomenon can be observed in the range of 0°C to 120°C in the solid viscoelasticity measurement. On the other hand, the amorphous part has very high polymer chain mobility, and is observed in the range of -150°C to -100°C in the solid viscoelasticity measurement. This point relates to the relaxation of radicals, a radical transfer reaction, a crosslinking reaction, and the like, which will be described later.

In addition, the polyolefin molecules constituting the crystal are not single, and as illustrated in FIG. 2 , a plurality of polymer chains form small lamellas, and then the lamellas aggregate to form crystals. This phenomenon is difficult to observe directly, and in recent years, scientific research has progressed and clarified by simulation. Incidentally, in the present specification, a crystal is a unit of a minimum crystal measured by X-ray structural analysis, and is a unit that can be calculated as a crystallite size. In this way, even in the crystal part (inside the lamella), it is predicted that there is a part with a slightly high mobility without being partially constrained during the crystal.

(B) Crosslinking reaction mechanism by electron beam

Next, the reaction mechanism of the electron beam crosslinking to the polymer (hereinafter referred to as EB crosslinking) is as follows.

(i) irradiation of electron beams of several tens of kGy to several hundred kGy;

(ii) transmission of electron beams to the reaction target (polymer) and generation of secondary electrons;

(iii) hydrogen extraction reaction and radical generation in the polymer chain by secondary electrons;

(iv) extraction of adjacent hydrogens by radicals and movement of active sites;

(v) Crosslinking reaction or polyene formation by recombination of radicals.

Here, with respect to the radical generated in the crystal part, since movement is insufficient, it exists over a long period of time, and since impurities or the like cannot enter the crystal, the probability of reaction and quenching is low. Such radical species are called stable radicals, remain for a long period of several months, and the lifespan is revealed by ESR measurement. As a result, it is thought that the crosslinking reaction in a crystal|crystallization is insufficient. However, in the unconstrained molecular chains slightly present in the crystal or in the surrounding crystalline-amorphous intermediate layer portion, the generated radicals have a slightly longer lifetime. Such radical species are called Persistent Radical, and it is thought that the crosslinking reaction between molecular chains advances with a high probability under a motility environment. On the other hand, since the amorphous part has very high mobility, the generated radical species have a short lifetime, and it is considered that not only the crosslinking reaction between molecular chains but also the polyene reaction within one molecular chain proceeds with high probability.

As described above, in the microscopic view of the crystal level, it can be inferred that the crosslinking reaction by EB crosslinking is localized inside or around the crystal.

(C) Crosslinking reaction mechanism by chemical reaction

As described above, a crystalline portion and an amorphous portion exist in the polyolefin resin. However, the functional group described above does not exist inside the crystal due to steric hindrance, but is localized in the amorphous portion. This is generally known, and a unit such as a methyl group slightly contained on a polyethylene chain may be introduced in the crystal, but a graft bulkier than an ethyl group is not introduced ("Basic Polymer Chemistry" published by Tokyo Chemical Co.) . For this reason, the crosslinking point by the reaction other than electron beam crosslinking is localized only in the amorphous part.

(D) Relationship between the difference in the cross-linking structure and the effect

In order to form a crosslinked structure in a microporous film, it is preferable to use the combination of the functional group in polyolefin resin and the chemical substance contained in an electrical storage device, or to use the chemical substance contained in an electrical storage device as a catalyst. In the crosslinking reaction by the chemical reaction inside an electrical storage device, the morphology of a reaction product differs with the raw material used, a catalyst, etc. In the research up to the present invention, in order to elucidate the cross-linked structure and to elucidate the change in the physical properties of the microporous membrane accompanying the structural change, the following experiments led to the elucidation of the present situation.

For the film without EB crosslinking or chemical crosslinking (before), and for the chemically crosslinked film, the behavior at the time of crystal melting of both was investigated by a fuse/meltdown characteristic test. As a result, in the film subjected to the EB crosslinking treatment, the fuse temperature becomes remarkably high, and the meltdown temperature rises to 200°C or higher. On the other hand, in the chemical crosslinked film, it was confirmed that the fuse temperature did not change before and after the crosslinking treatment, and the meltdown temperature rose to 200°C or higher. Therefore, in the fuse characteristics generated by crystal melting, the EB crosslinked film is considered to be caused by an increase in the melting temperature and a decrease in the melting rate because the periphery of the crystal portion is crosslinked. On the other hand, since the chemically crosslinked film does not have a crosslinked structure in the crystal part, it is determined that the fuse characteristics are not changed. In addition, in the high temperature region around 200° C., since both have a crosslinked structure after crystal melting, the entire resin material can be stabilized in a gel state, and good meltdown properties are obtained.

The above findings are summarized in Table 1 below.

In the first embodiment, (1) the condensation reaction between the functional groups of polyolefins such as polyethylene and polypropylene may be, for example, a reaction through a covalent bond between two or more functional groups A contained in the polyolefin. Further, (3) the reaction between the functional group of the polyolefin and the functional group of another type may be, for example, a reaction through a covalent bond between the functional group A and the functional group B included in the polyolefin.

In the first embodiment, (2) in the reaction between the functional group of polyolefin such as polyethylene and polypropylene and the chemical substance inside the electrical storage device, for example, the functional group A included in the polyolefin is an electrolyte or electrolyte solution included in the electrical storage device. , may form a covalent bond or a coordination bond with any of the electrode active materials, additives, or decomposition products thereof. Further, according to reaction (2), a crosslinked structure is formed not only inside the separator but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), so that the strength between the plurality of members of the electrical storage device can be improved.

The microporous membranes according to the first and second embodiments have the following formula (I) from the viewpoint of formation of an amorphous part crosslinked structure, coexistence of a shutdown function and high temperature rupture resistance, and the like:

R _E'X =E' _Z /E' _Z0 (I)

{wherein, E' _Z is the storage modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the microporous membrane proceeds in the electrical storage device, and

E' _z0 is the storage modulus of elasticity measured in a temperature range of 160°C to 300°C before the microporous membrane is embedded in the electrical storage device}

The mixed storage modulus ratio (R _E'x ) and/or the formula (III) defined by

R _E''X =E'' _Z /E'' _Z0 (III)

{wherein, E'' _Z is a loss modulus measured in a temperature range of 160°C to 300°C after the crosslinking reaction of the microporous membrane proceeds in the electrical storage device, and

E'' _Z0 is the loss modulus of elasticity measured in a temperature region of 160°C to 300°C before the microporous membrane is embedded in the electrical storage device}

The mixing loss elastic modulus ratio ( _RE''x ) defined by is preferably from 1.2 times to 20 times, more preferably from 2.0 times to 18 times, still more preferably from 3.5 times to 16.5 times. In addition, E' _Z and E' _z0 and E'' _Z and E'' _z0 are the storage modulus measured within the set temperature range of the measuring device when 160 to 300°C is the widest temperature range, respectively, or It is the average value of the loss modulus. Further, since the microporous membranes according to the first and second embodiments are laminated films having a laminated structure, the storage elastic modulus E' _Z and E' _z0 and the loss elastic modulus E'' only for the polyolefin-based microporous film peeled off from the laminated film. _{Let Z} and E'' _z0 be measured. The measurement conditions for the elastic modulus that are E' _Z , E' _z0 , E'' _Z or E'' _{z0 are described in Examples.}

The microporous membranes according to the first and second embodiments have the following formula (II) from the viewpoint of formation of an amorphous part crosslinked structure, coexistence of a shutdown function and high temperature rupture resistance, and the like:

R _E'mix =E'/E' ₀ (II)

{wherein, E' is the storage modulus measured at 160°C to 300°C of the microporous membrane having an amorphous part crosslinked structure, and

E′ ₀ is the storage modulus measured at 160° C. to 300° C. of the microporous membrane having no amorphous cross-linked structure}

A mixed storage modulus ratio (R _E'mix ) defined by , and/or the formula (IV):

R _E''mix =E''/E'' ₀ (IV)

{Wherein, E'' is the loss modulus measured at 160°C to 300°C of the microporous membrane having an amorphous part crosslinked structure, and

E'' ₀ is the loss modulus measured at 160°C to 300°C of the microporous membrane having no amorphous cross-linked structure}

The mixing loss elastic modulus ratio ( _RE''mix ) defined by is preferably from 1.2 times to 20 times, more preferably from 2.0 times to 18 times, still more preferably from 4.0 times to 17 times. In other words, E' and E' ₀ and E'' and E'' ₀ are the storage modulus or loss modulus measured within the set temperature range of the measuring device, respectively, when 160°C to 300°C is the widest temperature range. is the average value of In addition, since the microporous membranes according to the first and second embodiments are laminated films having a laminated structure, only the polyolefin-based microporous membranes peeled off from the laminated film have storage modulus E' and E' ₀ and loss modulus E'' and Let E'' ₀ be measured. The measurement conditions for the elastic modulus of E', E' ₀ , E'' or E'' _{0 are described in Examples.}

Components of the microporous membrane according to the first and second embodiments will be described below.

[Laminated Structure]

The microporous membrane may be formed in the form of a laminate. The laminate may consist of a plurality of layers of the same type with respect to constituent raw materials, structure, composition, etc., or may consist of a plurality of layers different from each other, and from the viewpoint of the total thickness or handling properties of the laminate, preferably two or more layers 10 Layers or less, more preferably 2 or more and 7 or less layers, still more preferably 2 or 3 layers.

When a monolayer of a resin in which 50 mol% or more of monomeric structural units are ethylene is represented as a polyethylene (PE) layer, and a monolayer of a resin in which 50 mol% or more of monomeric structural units are propylene is represented as a polypropylene (PP) layer, The laminated structure consisting of two layers does not distinguish between the back surface and the surface, and has the following:

PE layer/PE layer

PP layer/PP layer

PE layer/PP layer

Any of these is preferable, and the PE layer/PP layer is more preferable from the viewpoint of improving the strength and the film-resistance under high temperature. Here, the mark "/" indicates an interface.

The laminate structure consisting of three layers does not distinguish between the back surface and the surface, and has the following:

PP layer/PE layer/PP layer

PE layer/PP layer/PE layer

PE layer/PE layer/PP layer

PP layer/PP layer/PE layer

Any one is preferable, and from the viewpoint of improving strength and film resistance under high temperature, PP layer/PE layer/PP layer, PE layer/PP layer/PE layer, and PE layer/PE layer/PP layer are more preferable. . Here, the mark "/" indicates an interface.

The laminated structure of the microporous membrane has other layers, for example, a resin layer other than polyolefin (for example, a layer such as an acrylic resin), a non-resin layer (for example, an inorganic coating layer, etc.) as long as it contains at least one polyolefin-containing layer. ) may be included. In the laminated structure, the polyolefin-containing layer having a crosslinking reaction mechanism described above and the polypropylene-containing layer having a ratio MD/TD of 1.3 or more may be the same as or different from each other.

[Polyolefin]

Although it does not specifically limit as polyolefin constituting the microporous membrane, For example, a homopolymer of ethylene or propylene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbor and a copolymer formed from at least two monomers selected from the group consisting of nene. Among these, high-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene (UHMWPE), polypropylene, polybutene, or a combination thereof is preferable from the viewpoint of easy porosity in wet or dry processing. Generally, it is known that the weight average molecular weight of UHMWPE is 1,000,000 or more. In addition, polyolefin may be used individually by 1 type, or may use 2 or more types together.

Further, the weight average molecular weight (Mw) of the polyolefin is preferably 10,000 to 2,000,000, more preferably 20,000 to 1,500,000, still more preferably 30,000 to 1,500,000 from the viewpoint of heat shrinkability of the microporous membrane and safety of the electrical storage device. am.

[polyethylene]

From the viewpoints of the strength of the microporous membrane, ion permeability, resistance to oxidation-reduction degradation, and a dense and uniform porous structure, at least one layer of the laminated structure preferably contains polyethylene, and more preferably contains homopolyethylene. .

From the viewpoint of strength, film formability, productivity and porosity of the microporous membrane, the melt flow rate (MFR) of polyethylene is preferably less than 1.0 g/10 min, when measured under the conditions of a temperature of 190 ° C. and a mass of 2.16 kg, More preferably, it is 0.70 g/10min or less, More preferably, it is 0.20 g/10min - 0.50 g/10min. From the same viewpoint, the dispersion degree (Mw/Mn), which is a value obtained by dividing the weight average molecular weight (Mw) of polyethylene by the number average molecular weight (Mn), is preferably 11 or less, and more preferably 7 to 10. From the same viewpoint, the density of polyethylene is preferably 0.91 g/cm 3 or more and 0.97 g/cm 3 or less, and more preferably 0.92 g/cm 3 or more and less than 0.97 g/cm 3 .

[polypropylene]

From the viewpoints of the strength of the microporous membrane, ion permeability, oxidation-reduction degradation resistance, and a dense and uniform porous structure, at least one layer in the laminated structure preferably contains polypropylene, and more preferably contains homopolypropylene desirable.

From the viewpoint of strength, film formability, productivity and porosity of the microporous membrane, the MFR of polypropylene is preferably 2.5 g/10 min or less, more preferably less than or equal to 2.5 g/10 min, when measured under the conditions of a temperature of 230°C and a mass of 2.16 kg. 0.25 g/10 min to 1.4 g/10 min. From the same viewpoint, the dispersion degree (Mw/Mn), which is a value obtained by dividing the weight average molecular weight (Mw) of the polypropylene by the number average molecular weight (Mn), is preferably 10 or less, more preferably 5.2 to 9.0. From the same viewpoint, the density of polypropylene is preferably 0.89 g/cm 3 or more, more preferably 0.90 g/cm 3 or more and 0.96 g/cm 3 or less, or 0.90 g/cm 3 or more and 0.93 g/cm 3 or less.

[Polyolefin having 1 type or 2 or more types of functional groups]

The microporous membrane is a polyolefin having one or more functional groups from the viewpoint of formation of a cross-linked structure, resistance to oxidation-reduction degradation, and a dense and uniform porous structure, a functional group-modified polyolefin, or a polyolefin copolymerized with a monomer having a functional group. It is preferable to include Incidentally, in this specification, the functional group-modified polyolefin means what couple|bonded the functional group after manufacture of polyolefin. The functional group is bonded to the polyolefin backbone or can be introduced into the comonomer, and is preferably involved in the selective crosslinking of the polyolefin amorphous portion, for example, a carboxyl group, a hydroxyl group, a carbonyl group, a polymerizable unsaturated hydrocarbon group, an isocyanate group, an epoxy group, a silanol group, a hydrazide group, a carbodiimide group, an oxazoline group, an acetoacetyl group, an aziridine group, an ester group, an active ester group, a carbonate group, an azide group, a chain or cyclic hetero atom-containing hydrocarbon group; It may be at least one selected from the group consisting of an amino group, a sulfhydryl group, a metal chelate group, and a halogen-containing group.

The content of the polyolefin having one or two or more functional groups described above is preferably 5% by mass to 20% by mass based on the total mass of the polyolefin constituting one polyolefin-containing layer.

When one or more functional groups described above are introduced into polyethylene, the content ratio of polyethylene having one or more functional groups is based on the total mass of polyolefin constituting one polyolefin-containing layer, Preferably it is 5 mass % - 20 mass %.

When one or more functional groups described above are introduced into polypropylene, the content ratio of polypropylene having one or more functional groups is based on the total mass of polyolefin constituting one polyolefin-containing layer. Therefore, it is preferably 5% by mass to 20% by mass, and from the viewpoint of balance between strength and crosslinkability, it is preferably 30% by mass or less based on the total mass of polypropylene constituting one polypropylene-containing layer, more Preferably it is 4-25 mass %, More preferably, it is 5-20 mass %.

[Crosslinking Reaction]

The crosslinked structure of the microporous film contributes to both the shutdown function and high-temperature rupture resistance when used as a separator, and the safety of the electrical storage device, and is preferably formed in an amorphous portion of polyolefin. A crosslinked structure may be formed, for example, by a reaction via any of a covalent bond, a hydrogen bond, or a coordination bond. Among them, the reaction via a covalent bond is preferably (I) a condensation reaction of a plurality of identical functional groups.

reaction (I)

A schematic scheme and specific examples of the reaction (I) are shown below by making the first functional group of the microporous membrane A.

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

When the functional group A for the reaction (I) is a silanol group, it is preferable that the polyolefin contained in the microporous membrane is subjected to silane graft modification. The silane graft-modified polyolefin is constituted by a structure in which a main chain is a polyolefin and an alkoxysilyl is grafted onto the main chain. In addition, the alkoxide substituted with the said alkoxysilyl is methoxide, ethoxide, butoxide etc. are mentioned, for example. For example, in the above formula, R may be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, or the like. In addition, the main chain and the graft are connected by a covalent bond, and structures such as alkyl, ether, glycol or ester are mentioned. Considering the manufacturing process of the microporous membrane according to the present embodiment, the silane graft-modified polyolefin preferably has a silicon to carbon ratio (Si/C) of 0.2 to 1.8% in the step before the crosslinking treatment process, 0.5 It is more preferable that it is 1.7 %.

In the above scheme, without wishing to be bound by theory, the alkoxysilane graft portion is converted into silanol with slight moisture contained in the electrical storage device (moisture contained in members such as electrodes, separators, electrolytes, etc.) and cross-linked. , it is presumed to change with the siloxane bond. In addition, when the electrolyte or the electrolyte is in contact with the electrode, substances that catalyze the silane crosslinking reaction are generated in the electrolyte or on the electrode surface, and they are dissolved in the electrolyte, and uniformly in the amorphous portion of the polyolefin in which the silane-modified graft portion exists. It swells and diffuses, and it is thought that it accelerates|stimulates the crosslinking reaction of the microporous film used as a separator uniformly. The substance that catalyzes the silane crosslinking reaction may be in the form of an acid solution or a film, and when the electrolyte _{contains lithium hexafluorophosphate (LiPF 6} ), LiPF ₆ and moisture react with hydrogen fluoride (HF) , or a fluorine-containing organic material derived from HF. HF may be derived from any of an electrolyte, an electrolyte solution, an electrode active material, an additive, or those decomposition products or absorbents contained in an electrical storage device according to the charge/discharge cycle of an electrical storage device, for example.

(Other inclusions)

The microporous membrane is added to polyolefin as desired, and known additives such as a dehydration condensation catalyst, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments. may be included.

[Characteristics of microporous membrane]

Since the microporous film for electrical storage devices according to the first and second embodiments has a laminated structure, the following characteristic values are measured after separating layers other than the microporous film from the laminated film and in the state of the laminated film. there may be cases

The porosity of the microporous membrane is preferably 20% or more, more preferably 30% or more, and still more preferably 39% or more or 42% or more when measured in the state of a single-layer membrane. When the porosity of the microporous membrane is 20% or more and it is used as a separator of a lithium ion electrical storage device, there is a tendency for the followability to the rapid movement of lithium ions to be further improved. On the other hand, the porosity of the microporous membrane is preferably 90% or less, more preferably 80% or less, still more preferably 50% or less. When the porosity of the microporous film is 90% or less, the film strength is further improved and self-discharge tends to be more suppressed.

The air permeation resistance of the microporous membrane having a laminated structure, when measured in the state of the laminated membrane, is preferably 1 second or more, more preferably 50 seconds or more, and still more preferably 75 seconds or more, per 100 ml of the volume of the membrane. , more preferably 100 seconds or more or 125 seconds or more. When the air permeation resistance of the microporous membrane is 1 second or more, the balance between the membrane thickness, the porosity, and the average pore diameter tends to be further improved. Moreover, when the air permeation resistance of the microporous membrane which has a laminated structure is measured in the state of a laminated|multilayer film, Preferably it is 450 second or less, More preferably, it is 441 second or less, or 422 second or less. When the air permeation resistance of the microporous membrane is 450 seconds or less, the ion permeability tends to be further improved.

The tensile strength of the microporous film having a laminated structure, when measured in the state of the laminated film, is preferably 900 kg/cm 2 to 3000 kg with respect to MD (machine direction) with respect to the ratio MD/TD of the orientation ratio described above. /cm 2 , more preferably 1000 kg/cm 2 to 2500 kg/cm 2 , more preferably 1210 kg/cm 2 to 2050 kg/cm 2 , with respect to TD (direction orthogonal to MD, film width direction), preferably 100 kg/cm 2 to 500 kg/cm 2 , more preferably 110 kg/cm 2 to 250 kg/cm 2 , and still more preferably 120 kg/cm 2 to 200 kg/cm 2 .

The total thickness of the microporous membrane having a laminated structure is preferably 1.0 µm or more, more preferably 2.0 µm or more, and still more preferably 3.0 µm or more, 4.0 µm or more, or 5.5 µm or more. When the total thickness of the microporous membrane is 1.0 µm or more, the membrane strength tends to be further improved. The total thickness of the microporous membrane having a laminated structure is preferably 500 µm or less, more preferably 100 µm or less, and still more preferably 50 µm or less, 25 µm or less, 20 µm or less, or 15 µm or less. am. When the total thickness of the microporous membrane is 500 µm or less, the ion permeability tends to be further improved. When the microporous membrane is used as a separator for a lithium ion secondary battery, the total thickness of the microporous membrane having a laminate structure is preferably 1.0 μm to 25 μm, more preferably 3.0 μm to 22 μm, still more preferably 12 μm to 15 μm.

The puncture strength of the microporous film having a laminated structure, when measured in the state of the laminated film, is preferably 200 gf to 500 gf, more preferably 205 gf to 450 gf, more preferably from the viewpoint of balancing film resistance and device safety. Preferably it is 211 gf to 425 gf.

[Method for producing a microporous membrane having a laminated structure]

The manufacturing method of the microporous membrane which has a laminated structure, for example, the following process:

(A) Forming process of polyolefin resin composition;

(B) a step of forming a laminate including a polyolefin-containing layer;

(C) the step of making the polyolefin molded body pore-opening; and

(D) heat treatment process of the perforated material;

may include.

In the step (A), the polyolefin resin composition can be produced by a melt-kneading method of a single screw or twin screw extruder using a polyolefin resin and other materials. The material to be kneaded in the kneading step can be determined according to the pore opening step (c) performed thereafter. This is because the pore making step (c) can be performed by a known dry method and/or a wet method.

In step (b), for example, a laminate of a plurality of polyolefin-containing layers, a laminate of a polyolefin-containing layer and another resin layer, a laminate of a polyolefin-containing layer and a non-resin layer (eg, inorganic coating layer, etc.) is formed Examples of the lamination method include binding of a plurality of resin molded articles (eg, resin films), bonding of a plurality of resin films, co-extrusion of a plurality of resin compositions, and the like. In steps (b) and (c), their order may be interchanged or may be performed simultaneously. When the pore making step (c) is performed by the dry method described later, from the viewpoint of productivity or handling properties of the microporous membrane having the laminate structure according to the present embodiment, after forming the laminate in the step (b), the step ( In c), it is preferable to open the laminated body.

A polyolefin molded body, for example, a film, a sheet, a laminated body, etc. can be made to open|perforate in the perforation process (c). The pore opening method of the polyolefin molded body may be performed by a known dry method and/or a wet method.

Examples of the dry method include a method in which an unstretched sheet containing incompatible particles such as inorganic particles and a polyolefin is provided for stretching and extraction to peel off an interface of a dissimilar material to form a hole, a lamella opening method, a β crystal opening method, and the like.

The lamellar opening method is a method of obtaining an unstretched sheet having a crystalline lamellar structure by controlling melt crystallization conditions at the time of forming a sheet by melt extrusion of a resin, and cleaving the lamellar interface by stretching the obtained unstretched sheet to form holes. . In the lamellar opening method, for example, a die extrusion method can be used. In the die extrusion method, for example, a highly crystalline MD oriented raw fabric can be obtained by extruding the melt-kneaded material of the polypropylene resin composition from T-die and extruding it to MD.

In the β crystal opening method, an unstretched sheet having a β crystal having a relatively low crystal density is produced during melt extrusion of polypropylene (PP), and crystal is transferred to an α crystal having a relatively high crystal density by stretching the produced unstretched sheet. This is a method of forming holes by the difference in crystal density between the two. As the β crystal nucleating agent, for example, 2,6-naphthalenedicarboxylic acid dicyclohexylamide and the like can be used, and preferably a β crystal nucleating agent and an antioxidant are used in combination.

As the wet method, a polyolefin, optionally other resin, and a plasticizer or inorganic material are kneaded using a kneader, molded into a sheet shape, stretched as necessary, and then a hole forming material is extracted from the sheet, polyolefin resin After dissolution of the composition, a method of immersing the polyolefin in a poor solvent to solidify the polyolefin and at the same time remove the solvent can be used.

Although it does not specifically limit as a plasticizer, For example, the organic compound which can form a polyolefin and a uniform solution at the temperature below a boiling point is mentioned. More specifically, decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil, etc. are mentioned. there is. Among these, paraffin oil and dioctyl phthalate are preferable. A plasticizer may be used individually by 1 type, or may use 2 or more types together.

Even if either the dry method or the wet method is used, from the viewpoint of maintaining the crosslinkability of the microporous film until it is housed in an electrical storage device, the method for producing a microporous film includes a crosslinking agent, other reactive compound, and other It is preferable not to include a step of contacting the functional group of the compound, a catalyst for promoting crosslinking, or the like. In the polyolefin resin composition, as long as the crosslinkability of the microporous film is maintained, additives include, for example, fluorine-based flow modifiers, waxes, crystal nucleating materials, antioxidants, metal soaps such as aliphatic carboxylic acid metal salts, and ultraviolet absorbers. , light stabilizers, antistatic agents, antifogging agents, colored pigments, and the like.

The heat treatment step (d) of the perforated material may be performed for the purpose of heat setting after the stretching step or after the hole formation in order to suppress the shrinkage of the microporous membrane. As the heat treatment, stretching operation performed in a predetermined temperature atmosphere and predetermined elongation rate for the purpose of adjusting physical properties, and/or relaxation operation performed in a predetermined temperature atmosphere and predetermined relaxation rate for the purpose of reducing stretching stress is performed. can be heard After performing an extending|stretching operation, you may perform a relaxation|relaxation operation. These heat treatments can be performed using a tenter or a roll stretching machine.

[Separator for power storage device and power storage device]

The microporous membranes according to the first and second embodiments can be used in an electrical storage device. Generally, an electrical storage device is provided with an exterior body, the separator arrange|positioned between a positive electrode, a negative electrode, and a positive electrode, and electrolyte solution. When the microporous membrane according to these embodiments is housed in a device exterior body, the functional group-modified polyolefin or functional group graft copolymerized polyolefin formed during the manufacturing process of the microporous membrane and the chemical substance contained in the electrolyte solution or additive react to form a crosslinked structure Therefore, the produced electrical storage device has a crosslinked structure. It is preferable that a microporous membrane is arrange|positioned between positive and negative electrodes as a separator from a viewpoint of maintaining the crosslinkability of a microporous membrane until accommodated in an electrical storage device, and improving the safety|security of an electrical storage device after that. When a microporous film is accommodated in an electrical storage device as a separator, since a crosslinked structure is formed, while being suitable for the manufacturing process of the conventional electrical storage device, it can raise|generate a crosslinking reaction after device manufacture and can improve the safety|security of an electrical storage device.

Specific examples of the electrical storage device include a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a sodium secondary battery, a sodium ion secondary battery, a magnesium secondary battery, a magnesium ion secondary battery, a calcium secondary battery, a calcium ion secondary battery, an aluminum secondary battery. , an aluminum ion secondary battery, a nickel hydride battery, a nickel cadmium battery, an electric double layer capacitor, a lithium ion capacitor, a redox flow battery, a lithium sulfur battery, a lithium air battery, and a zinc air battery. Among these, a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a nickel hydride battery, or a lithium ion capacitor is preferable from a practical viewpoint, and a lithium battery or a lithium ion secondary battery is more preferable.

[Lithium Ion Secondary Battery]

A lithium ion secondary battery is a lithium-transition metal oxide such as lithium cobaltate and lithium cobalt composite oxide as a positive electrode, a carbon material such as graphite and graphite as a negative electrode, and an organic solvent containing a lithium salt such _{as LiPF 6 as an electrolyte solution.} used battery. At the time of charging and discharging a lithium ion secondary battery, ionized lithium reciprocates between electrodes. In addition, since it is necessary for the ionized lithium to move between the electrodes at a relatively high speed while suppressing the contact between the electrodes, a separator is disposed between the electrodes.

[Example]

Although an Example and a comparative example are given and the present invention is demonstrated more concretely, this invention is not limited to the following example, unless the summary is exceeded. Incidentally, the raw material used and the evaluation method of various characteristics of the microporous membrane are as follows.

[Measurement of melt flow rate (MFR)]

Melt flow rate (MFR) was measured in accordance with JIS K 7210, the MFR of the polypropylene resin is expressed as a value measured under the conditions of a temperature of 230 ° C. and a mass of 2.16 kg, and the MFR of the polyethylene resin is expressed at a temperature of 190 ° C. and a mass of 2.16. It is expressed as a value measured under the condition of kg (all units are g/10 min).

[Measurement of GPC (Gel Permeation Chromatography)]

A calibration curve was prepared by measuring standard polystyrene under the following conditions using Agilent PL-GPC220. In addition, the chromatograph was measured under the same conditions for each of the following polymers, and based on the prepared calibration curve, a value obtained by dividing the weight average molecular weight Mw of each polymer by the number average molecular weight Mn was calculated by the following method.

Column: 2 TSKgel GMHHR-H (20) HT (7.8 mm I.D. × 30 cm)

Mobile phase: 1,2,4-trichlorobenzene

Detector: RI

Column temperature: 160°C

Sample concentration: 1 mg/ml

Calibration Curve: Polystyrene

[Measurement of wide-angle X-ray scattering]

The (110) crystal peak area ratio (MD/TD) of the polypropylene microporous membrane was measured by transmission wide-angle X-ray scattering (WAXS). The WAXS measurement was performed under the following conditions.

Device Name: NANOPIX, Rigakusa

X-ray wavelength λ: 0.154 nm

Optics: Point Collimation

1st slit: 0.55mmφ

2nd slit: Open

3rd slit: 0.35mmφ

Exposure time: 900 seconds

Detector: HyPix-6000 (two-dimensional detector)

Camera Length: 85.7mm

With respect to one sample film, X-rays were incident from the film normal direction, and transmitted and scattered light was detected. In order to reduce scattering from other than the sample as much as possible, measurement was performed using a vacuum chamber in which the beam stop from the sample was installed in a vacuum. Incidentally, since HyPix-6000 has a dead region in the detector, two-dimensional data without a dead region was obtained by combining the results of two measurements by moving the detector in the vertical direction. Transmittance correction and empty cell scattering correction were performed on the obtained two-dimensional WAXS pattern. Then, the scattering data was made one-dimensional by performing annular averaging, and Bragg angles θs and θe corresponding to the lower ends of the small-angle side and the wide-angle side of the crystal peak derived from the (110) plane of polypropylene were determined. Then, for the two-dimensional WAXS pattern that has been subjected to transmittance correction and empty cell scattering correction, the azimuthal distribution of the scattering intensity in the range of 2θs<2θ<2θe (azimuth distribution of the crystal diffraction peak intensity derived from the (110) plane) is calculated. did. Fig. 3 shows an example of the obtained azimuth distribution of the scattering intensity in the range of 2θs<2θ<2θe. In the azimuthal distribution diagram of the scattering intensity in the range of 2θs<2θ<2θe, the (110) peak derived from the c-axis oriented crystal with the c-axis oriented in the MD is TD, and the a-axis oriented crystal is derived from the crystal a-axis oriented in the MD. The (110) peak of is observed near MD. The peak derived from the c-axis oriented crystal was approximated by one Gaussian function, and the peak derived from the a-axis oriented crystal was approximated by two Gaussian functions, and the peaks were separated. An example thereof is shown in FIG. 3 . For peak separation, WaveMetrics software IgorPro8ver.8.0.0.10 was used. S_MD is the peak area derived from the c-axis orientation crystal (crystal oriented in the c-axis MD) obtained by such peak separation, and the peak area derived from the a-axis orientation crystal (crystal orientation close to the c-axis TD). Assuming that (the sum of the areas of two Gaussian functions) is S_TD, the (110) crystal peak area ratio (MD/TD) is defined as S_MD/S_TD. Incidentally, in the azimuthal distribution diagram of the scattering intensity, as shown in FIG. 3 , a peak derived from a c-axis oriented crystal and a peak derived from an a-axis oriented crystal are observed at two locations. Therefore, the average of each peak area was designated as S_MD and S_TD.

[Thickness (㎛)]

The thickness of the porous film was measured at room temperature 23±2° C. using a Digimatic indicator IDC112 manufactured by Mitsutoyo Corporation.

[Porosity (%)]

A rectangular sample having a side of 5 cm x 5 cm was cut out from the porous film, and the porosity was calculated from the volume and mass of the sample using the following equation.

Porosity (%) = (volume (cm 3 ) - mass (g)/density of resin composition (g/cm 3 ))/volume (cm 3 )×100

[Air permeation resistance (sec/100cc)]

The air permeation resistance of the microporous membrane was measured with a Gurley type air permeability meter conforming to JIS P-8117.

[Strike Strength]

A needle having a hemispherical tip having a radius of 0.5 mm was prepared, the microporous membrane was sandwiched between two plates having an opening of 11 mm in diameter, and the needle, the microporous membrane and the plate were set. Using MX2-50N (product name) manufactured by Imada Corporation, a puncture test was performed under the conditions of a radius of curvature of the needle tip of 0.5 mm, an opening diameter of 11 mm of the microporous membrane retaining plate, and a piercing speed of 25 mm/min, and the needle and the microporous membrane were contact to determine the maximum stab load (ie, stab strength (gf)).

[Measurement of storage modulus, loss modulus and transition temperature]

The dynamic viscoelasticity of the microporous membrane before and after crosslinking is measured using a dynamic viscoelasticity measuring device, and the storage modulus (E'), the loss modulus (E''), and the transition temperature between the rubbery flat region and the crystal melting flow region are calculated. did. The storage elastic modulus change ratio (R _E'X ) is the following formula (I), the mixed storage elastic modulus ratio ( _RE'mix ) is the following formula (II), and the loss elastic modulus ratio (R _E''X ) is the following formula ( III), the mixing loss elastic modulus ratio ( _RE''mix ) was calculated according to the following formula (IV), respectively. Incidentally, the measurement conditions were as follows (i) to (iv).

(i) dynamic viscoelasticity measurement under the following conditions:

・Atmosphere: nitrogen

・Used measuring device: RSA-G2 (manufactured by TA Instruments)

・Sample film thickness: in the range of 5 µm to 50 µm (measured with one sheet regardless of the film thickness of the sample)

・Measurement temperature range: -50 to 300°C

·Temperature increase rate: 10℃/min

・Measurement frequency: 1Hz

Deformation mode: sine wave tension mode (linear tension)

·Initial value of static tensile load: 0.5N

・Initial gap distance (at 25℃): 25mm

Automatic strain adjustment: available (Range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5N)

was done in

(ii) The static tensile load refers to an intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillation 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 0.2%. At that time, the distance between the gaps and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 20%. Vibration stress was measured. Incidentally, when the sine wave load was 0.02 N or less, the amplitude value was amplified so that the sine wave load was within 5 N and the amount of increase in the amplitude value was within 25%, and the vibration stress was measured.

(iv) the relation between the obtained sine wave load and the amplitude value, and the following formula:

σ ^* =σ ₀ Exp[i(ωt+δ)],

ε ^* =ε ₀ Exp(iωt),

σ ^* =E ^* ε ^*

E ^* =E'+iE''

{wherein, σ ^* : vibrational stress, ε ^* : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E ^* : complex elastic modulus, E': storage modulus , E'': loss modulus

Vibration stress: sinusoidal load/initial cross-sectional area

Static tensile load: the load at the minimum of the vibration stress in each period (minimum of the inter-gap distance in each period)

Sine wave load: difference between measured vibration stress and static tensile load}

Storage modulus and loss modulus were calculated from

E' _Z and E' _Z0 and E'' _Z and E'' _Z0 were made into the maximum value of each storage elastic modulus or each loss elastic modulus at 160 degreeC - 300 degreeC among dynamic viscoelasticity measurement data. E' and E' ₀ and E'' and E'' ₀ were made into the average value of each storage elastic modulus or each loss elastic modulus at 160 degreeC - 300 degreeC among dynamic viscoelasticity measurement data.

R _E'X =E' _Z /E' _Z0 (I) Contrast before and after injection into the cell

R _E'mix =E'/E' ₀ (II) Contrast with or without cross-linked structure of amorphous part

R _E''X =E'' _Z /E'' _Z0 (III) Contrast before and after injection into the cell

R _E''mix =E''/E'' ₀ (IV) Contrast with or without cross-linked structure

In the art, the storage modulus and the loss modulus are expressed by the following formula:

tanδ=E''/E'

{wherein, tanδ represents loss tangent, E' represents storage modulus, and E'' represents loss modulus}

compatible according to

Incidentally, in the measurement of the mixed storage elastic modulus ratio ( _RE'mix ) or the mixed loss elastic modulus ratio ( _RE''mix ), a silane having a gelation degree of about 0% as a separator for electrical storage devices that does not have an amorphous crosslinked structure. An unmodified polyolefin microporous membrane was used.

[Tensile Test]

The tensile strength in the MD and TD directions was measured using an Instron Model 4201 according to the procedure of ASTM-882, and was determined as the breaking strength.

[Fuse/meltdown (F/MD) characteristics]

a. Production of positive electrode

92.2 mass % lithium cobalt composite oxide LiCoO ₂ as a positive electrode active material, 2.3 mass % of flaky graphite and acetylene black as a conductive material, and 3.2 mass % of polyvinylidene fluoride (PVDF) as a binder, N-methylpyrrolidone (NMP) ) to prepare a slurry. This slurry was applied to one side of an aluminum foil having a thickness of 20 µm to serve as a positive electrode current collector by a die coater, dried at 130°C for 3 minutes, and then compression molded with a roll press machine. At this time, the amount of the active material applied to the positive electrode was adjusted to be 250 g/m 2 , and the bulk density of the active material was adjusted to be 3.00 g/cm 3 .

b. production of negative electrode

96.9 mass % of artificial graphite as a negative electrode active material, and 1.4 mass % of ammonium salt of carboxymethyl cellulose and 1.7 mass % of styrene-butadiene copolymer latex as a binder were disperse|distributed in purified water, and the slurry was prepared. This slurry was apply|coated with the die coater on the single side|surface of 12 micrometers-thick copper foil used as a negative electrode collector, and after drying at 120 degreeC for 3 minutes, it compression-molded with a roll press machine. At this time, the amount of the active material applied to the negative electrode was adjusted to be 106 g/m 2 , and the bulk density of the active material to be 1.35 g/cm 3 .

c. Preparation of non-aqueous electrolyte

In a mixed solvent of ethylene carbonate:ethylmethylcarbonate=1:2 (volume ratio), LiPF ₆ as a solute was dissolved so as to have a concentration of 1.0 mol/L to prepare an electrolyte-containing electrolyte solution.

d. Lamination and measurement

The positive electrode, the separator, and the negative electrode to which the electric wire for resistance measurement was adhere|attached with the conductive silver paste behind the aluminum foil were cut out so that it might become a circular shape with a diameter of 200 mm, and it overlapped and obtained the laminated body. The electrolytic solution containing the electrolyte of c. was added to the obtained laminate, and the whole was dyed. The laminate is sandwiched in the center with a circular aluminum heater having a diameter of 600 mm, and the aluminum heater is pressed at 0.5 Mpa from the top and bottom with a hydraulic jack to complete the measurement. The resistance (Ω) between the electrodes is measured while heating the laminate with an aluminum heater under the condition of a temperature increase rate of 2°C/min. In all of the fuses of the separator, the resistance between the electrodes increases, and the temperature at which the resistance first exceeds 1000 Ω is the fuse temperature (shutdown temperature). Further, heating is continued and the temperature at which the resistance drops to 1000 Ω or less is referred to as the meltdown temperature (film breaking temperature).

[Heat Shrinkage]

In the measurement of the heat shrinkage rate, the microporous membrane after crosslinking was cut out into a rectangle with a side of 5 cm, marked at 9 places with an interval of 2 cm, and surrounded with paper. After the marked sample was heat-treated at 130° C. for 1 hour, and then cooled to room temperature, the length in the MD direction was measured at each of three locations to determine the shrinkage.

<Method for producing silane graft-modified polyolefin>

The raw material polyolefin used for the silane graft-modified polyolefin has a viscosity average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight (Mn) of 1 10,000 or more and 150,000 or less polyethylene or polypropylene. While melt-kneading the raw material polyolefin with an extruder, an organic peroxide (di-t-butyl peroxide) is added, radicals are generated in the polymer chain, and then trimethoxy alkoxide-substituted vinylsilane is injected, followed by an addition reaction. , an alkoxysilyl group is introduced to form a silane graft structure. At the same time, in order to adjust the radical concentration in the system, an antioxidant (pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]) is added in an appropriate amount, Suppresses chain reaction (gelation) in α-olefin. After cooling the obtained silane-grafted polyolefin molten resin in water and performing pellet processing, it heat-dries at 80 degreeC for 2 days, and removes water|moisture content or unreacted trimethoxy alkoxide-substituted vinylsilane. Incidentally, the residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets is from about 1000 ppm to about 1500 ppm.

The silane graft-modified polyolefin obtained by the above production method is shown as "silane-modified polyethylene (PE)" or "silane-modified polypropylene (PP)" in the following Examples and Tables 2 or 3.

[Example 1]

<Production of microporous membrane>

After dry blending a high molecular weight polyethylene resin (PE, MFR = 0.2, density = 0.96 g/cm 3 ) and the silane-modified polyethylene in a mass ratio of PE: silane-modified polyethylene = 80: 20 (mass %), 2.5 inches of Melted with an extruder and fed to a T die using a gear pump. The temperature of the die was set at 210°C, and the molten polymer was cooled by suction air, and then wound up on a roll.

Similarly, a polypropylene resin (PP, MFR = 0.83, density = 0.91 g/cm 3 ) was melted with a 2.5 inch extruder, and supplied using a T-die and a gear pump. The temperature of the die was set at 230°C, and the molten polymer was cooled by suction air, and then wound up on a roll.

The PP and PE precursors (raw films) wound on the rolls each had a thickness of 5 µm. Then, PP and PE precursors were bound to be PP/PE/PP, and a raw film having a PP/PE/PP three-layer structure was obtained. The raw film having this three-layer structure was annealed at 125°C for 20 minutes. Subsequently, the annealed film was cold stretched in the MD direction at room temperature to 12%, then hot stretched in the MD direction at 115°C to 158%, and relaxed to 113% at 125°C to form a microporous film. After the opening of the stretching, the physical properties of the microporous membrane were measured. The MFR of the microporous membrane was peeled off after stretching PP and PE, and measured for each layer. The results are shown in Table 2.

[Examples 2 to 9]

A microporous membrane was obtained in the same manner as in Example 1 except that the raw material was changed as shown in Table 2, and the obtained microporous membrane was evaluated.

[Example 10]

<Production of microporous membrane>

After dry blending a high molecular weight polyethylene resin (PE, MFR = 0.38, density = 0.96 g/cm 3 ) and the silane-modified polyethylene at a mass ratio of PE: silane-modified polyethylene = 80: 20 (mass %), 2.5 inches of It was melted with an extruder, and a polypropylene resin (PP, MFR=0.83, density=0.91 g/cm 3 ) was further melted with a 2.5 inch extruder, and fed using a T-die and a gear pump. The temperature of the die was set at 230°C, and the molten polymer was extruded to be PP/PE/PP, cooled by suction air, and then wound up on a roll. In this way, a PP/PE/PP precursor (raw film) having a three-layer structure with a thickness of 15 µm was obtained. This raw film was annealed at 125°C for 20 minutes. Subsequently, the annealed film was cold stretched in the MD direction at room temperature to 12%, then hot stretched in the MD direction at 115°C to 158%, and relaxed to 113% at 125°C to form a microporous film. After the above stretching openings, physical properties of the microporous membrane were measured. The MFR of the microporous membrane was peeled off after stretching PP and PE, and measured for each layer. The results are shown in Table 2.

[Example 11]

A microporous membrane was obtained in the same manner as in Example 10 except that it was extruded to be PE/PP/PE, and the obtained microporous membrane was evaluated.

[Example 12]

The microporous membrane was obtained by the method similar to Example 10 except having extruded so that it might become PE/PE/PP and produced the raw film of a two-layer structure, and the obtained microporous membrane was evaluated.

[Example 13]

A high molecular weight polyethylene resin (PE, MFR = 0.38, density = 0.96 g/cm 3 ) was melted with a 2.5 inch extruder and fed to a T die using a gear pump. The temperature of the die was set at 210°C, and the molten polymer was cooled by suction air, and then wound up on a roll.

Similarly, after dry blending the polypropylene resin (PP, MFR = 0.83, density = 0.91 g/cm 3 ) and the silane-modified polypropylene at a mass ratio of PP: silane-modified polypropylene = 80: 20 (mass %), Melted with a 2.5 inch extruder and fed to a T die using a gear pump. The temperature of the die was set at 230°C, and the molten polymer was cooled by suction air, and then wound up on a roll.

The PP and PE precursors (raw films) wound on the rolls each had a thickness of 5 µm. Then, PP and PE precursors were bound to be PP/PE/PP, and a raw film having a PP/PE/PP three-layer structure was obtained. The raw film having this three-layer structure was annealed at 125°C for 20 minutes. Subsequently, the annealed film was cold stretched in the MD direction at room temperature to 12%, then hot stretched in the MD direction at 115°C to 158%, and relaxed to 113% at 125°C to form a microporous film. After the opening of the stretching, the physical properties of the microporous membrane were measured. The MFR of the microporous membrane was peeled off after stretching PP and PE, and measured for each layer. The results are shown in Table 3.

[Examples 14 to 20]

A microporous membrane was obtained in the same manner as in Example 13 except that the raw material was changed as shown in Table 3, and the obtained microporous membrane was evaluated.

[Example 21]

A microporous membrane was obtained in the same manner as in Example 13 except that it was bound to be PE/PP/PE, and the obtained microporous membrane was evaluated.

[Comparative Examples 1 to 3]

A microporous membrane was obtained in the same manner as in Example 1 except that the raw material was changed as shown in Table 4 without using the silane-modified polyolefin, and the obtained microporous membrane was evaluated.

[Comparative Example 4]

A microporous membrane was obtained in the same manner as in Example 10 except that the raw material was changed as shown in Table 4 without using the silane-modified polyolefin, and the obtained microporous membrane was evaluated.

Claims (9)

A microporous film for electrical storage devices having a laminated structure and comprising polyolefin in at least one layer of the laminated structure, the microporous film comprising:
The said polyolefin has 1 type, or 2 or more types of functional groups,
After storage in the power storage device, (1) the functional groups are subjected to a condensation reaction, (2) the functional group reacts with a chemical substance inside the power storage device, or (3) the functional group reacts with a different type of functional group to crosslink structure is formed, and
Ratio of the orientation ratio of the width direction (TD) to the machine direction (MD) when at least one layer of the laminated structure contains polypropylene, and the layer containing the polypropylene is measured as a single layer by wide-angle X-ray scattering MD/TD satisfies 1.3 or more, The microporous film for electrical storage devices characterized by the above-mentioned. The microporous film for electrical storage devices according to claim 1, wherein the crosslinked structure is formed by (1) a condensation reaction between the functional groups. The microporous film for a power storage device according to claim 1, wherein the crosslinked structure is formed by (2) the functional group reacts with a chemical substance inside the power storage device. The microporous membrane for electrical storage devices according to claim 1 or 3, wherein the chemical substance is any one of an electrolyte, an electrolyte solution, an electrode active material, an additive, or a decomposition product thereof contained in the electrical storage device. The microporous membrane for electrical storage devices according to claim 1, wherein the crosslinked structure is formed by (3) reacting the functional group with a different type of functional group. 6. The method according to any one of claims 1 to 3 and 5, wherein the at least one layer comprising the polyolefin has the following formula (I):
R _E'X =E' _Z /E' _Z0 (I)
{wherein, E' _Z is, after at least one reaction of (1) to (3) of the microporous membrane for the electrical storage device proceeds in the electrical storage device, the storage measured in a temperature range of 160°C to 300°C is the modulus of elasticity, and also
E' _Z0 is the storage elastic modulus measured in a temperature range of 160°C to 300°C before the microporous membrane for the electrical storage device is embedded in the electrical storage device, and the measurement conditions of the storage elastic modulus that are _{E' Z} or E' _{Z0 are} , is defined by the following structures (i) to (iv).
(i) dynamic viscoelasticity measurement under the following conditions:
・Atmosphere: nitrogen
・Used measuring device: RSA-G2 (manufactured by TA Instruments)
・Sample film thickness: in the range of 5 µm to 50 µm (measured with one sheet regardless of the film thickness of the sample)
・Measurement temperature range: -50 to 300°C
·Temperature increase rate: 10℃/min
・Measurement frequency: 1Hz
Deformation mode: sine wave tension mode (Linear tension)
·Initial value of static tensile load: 0.5N
・Initial gap distance (at 25℃): 25mm
Auto strain adjustment: Enabled (Range: amplitude value 0.05 to 25%, sinusoidal load 0.02 to 5N)
was done in
(ii) The static tensile load refers to an intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillation 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 0.2%. At that time, the distance between the gaps and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 20%. Vibration stress was measured. Incidentally, when the sine wave load was 0.02 N or less, the amplitude value was amplified so that the sine wave load was within 5 N and the amount of increase in the amplitude value was within 25%, and the vibration stress was measured.
(iv) the relation between the obtained sine wave load and the amplitude value, and the following formula:
σ ^* =σ ₀ Exp[i(ωt+δ)],
ε ^* =ε ₀ Exp(iωt),
σ ^* =E ^* ε ^*
E ^* =E'+iE''
(where, σ ^* : vibrational stress, ε ^* : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E ^* : complex elastic modulus, E': storage modulus , E'': loss modulus
Vibration stress: sinusoidal load/initial cross-sectional area
Static tensile load: the load at the minimum of the vibration stress in each period (minimum of the inter-gap distance in each period)
Sine wave load: difference between measured vibration stress and static tensile load)
Calculate the storage modulus from
The mixed storage elastic modulus ratio ( _RE'x ) defined by is 1.2 to 20 times, the microporous membrane for electrical storage devices. A microporous film for electrical storage devices having a laminated structure and comprising polyolefin in at least one layer of the laminated structure, the microporous film comprising:
The polyolefin has an amorphous portion crosslinked structure in which an amorphous portion is crosslinked, and
Ratio of the orientation ratio of the width direction (TD) to the machine direction (MD) when at least one layer of the laminated structure contains polypropylene, and the layer containing the polypropylene is measured as a single layer by wide-angle X-ray scattering MD/TD satisfies 1.3 or more, The microporous film for electrical storage devices characterized by the above-mentioned. The microporous membrane for electrical storage devices according to claim 7, wherein the amorphous portion is selectively crosslinked. According to claim 7 or 8, wherein the at least one layer comprising the polyolefin, the formula (II):
R _E'mix =E'/E' ₀ (II)
{wherein, E' is the storage elastic modulus measured at 160°C to 300°C when the microporous membrane for electrical storage device has the amorphous part crosslinked structure, and
E' ₀ is the storage elastic modulus measured at 160 ° C. to 300 ° C. of the microporous film for electrical storage devices that does not have an amorphous part crosslinked structure, and the measurement conditions for the storage elastic modulus of _{E' or E' 0 are the following configuration (i)} to (iv).
(i) dynamic viscoelasticity measurement under the following conditions:
・Atmosphere: nitrogen
・Used measuring device: RSA-G2 (manufactured by TA Instruments)
・Sample film thickness: in the range of 5 µm to 50 µm (measured with one sheet regardless of the film thickness of the sample)
・Measurement temperature range: -50 to 300°C
·Temperature increase rate: 10℃/min
・Measurement frequency: 1Hz
Deformation mode: sine wave tension mode (linear tension)
·Initial value of static tensile load: 0.5N
・Initial gap distance (at 25℃): 25mm
Automatic strain adjustment: available (Range: amplitude value 0.05 to 25%, sine wave load 0.02 to 5N)
was done in
(ii) The static tensile load refers to an intermediate value between the maximum stress and the minimum stress in each periodic motion, and the sinusoidal load refers to an oscillation 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 0.2%. At that time, the distance between the gaps and the static tensile load are varied so that the difference between the static tensile load and the sinusoidal load is within 20%. Vibration stress was measured. Incidentally, when the sine wave load was 0.02 N or less, the amplitude value was amplified so that the sine wave load was within 5 N and the amount of increase in the amplitude value was within 25%, and the vibration stress was measured.
(iv) the relationship between the obtained sine wave load and the amplitude value, and the formula:
σ ^* =σ ₀ Exp[i(ωt+δ)],
ε ^* =ε ₀ Exp(iωt),
σ ^* =E ^* ε ^*
E ^* =E'+iE''
(where, σ ^* : vibrational stress, ε ^* : strain, i: imaginary unit, ω: angular frequency, t: time, δ: phase difference between vibrational stress and strain, E ^* : complex elastic 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 in each cycle (minimum point of the inter-gap distance in each cycle)
Sine wave load: difference between measured vibration stress and static tensile load)
Calculate the storage modulus from
The mixed storage elastic modulus ratio ( _RE'mix ) defined by is 1.2 to 20 times, the microporous membrane for electrical storage devices.

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