KR20210024953A - Separator dispersed crosslinkable resin - Google Patents

Abstract

The present invention provides a separator for power storage devices, which can ensure high safety (suppression of the internal maximum heat generation rate evaluated by a nail-piercing test and securing of the voltage drop time) by making a shutdown function and high-temperature film breakability compatible. A separator for electrical storage devices has a mass ratio in which {(A)/(B)} of the silane graft-modified polypropylene (A) to the polyethylene (B) is 2/98 to 80/20.

Description

Crosslinked resin dispersion separator {SEPARATOR DISPERSED CROSSLINKABLE RESIN}

The present invention relates to a separator (separator for power storage devices) and the like in which a silane graft-modified polypropylene as a crosslinkable resin is suitably dispersed in a predetermined polyethylene.

Microporous membranes are widely used as separators for various materials or selective permeation membranes and separators, and examples of their applications include microfiltration membranes, separators for fuel cells or condensers, functional membranes for expressing new functions by filling a functional material in a hole. And a separator for a base material and a battery. Among them, polyolefin microporous membranes are suitably used as separators for lithium ion batteries and constituent materials thereof, which are widely used in notebook personal computers, mobile phones, digital cameras, and the like.

In order to ensure battery safety, the separator is required to both activate the shutdown function and improve the rupture temperature. For example, in Patent Document 1, it is described to adjust the high-order physical properties of the polyolefin resin contained in the separator for lithium ion batteries. In addition, in Patent Document 2, by adjusting the crystallinity and the gel fraction region, heat generation due to a short circuit inside the battery is suppressed with a shutdown function, and even if a high temperature part is partially generated in the battery cell, it is not broken (170°C or higher). In the breakdown), securing the performance is described.

Japanese Patent Laid-Open No. Hei 9-216964 International Publication No. 97/44839 Japanese Patent Laid-Open No. Hei 11-144700 Japanese Patent Application Publication No. Hei 11-172036 Japanese Patent Laid-Open No. 2001-176484 Japanese Patent Publication No. 2000-319441 Japanese Patent Publication No. 2017-203145

In recent years, high output and high energy density of lithium-ion batteries for mobile device mounting or vehicle mounting are in progress. Therefore, it is desired that the separator to be used is of a high quality (for example, there are few resin aggregates in the separator). The level of safety for power storage devices is also becoming more stringent than before, and a shutdown function and high-temperature film breakability are demanded further than those assumed in Patent Documents 1 to 7.

Incidentally, in Patent Document 3, if a master batch catalyst is used in the extrusion step, the crosslinking reaction of the silane-modified polyethylene proceeds in the extruder, and there is a possibility that resin aggregates may occur in the separator. In addition, in Patent Document 4, there is a possibility that the silane crosslinking reaction cannot be sufficiently advanced, and it is difficult to obtain high-temperature rupture resistance.

In addition, the heat-resistant resin microporous membrane described in Patent Document 7 is only obtained by applying a photopolymerizable coating solution to a membrane made porous by a dry method. And in Example 5 of Patent Document 7, a low molecular weight silane coupling agent such as γ-methacryloxypropyltrimethoxysilane is added to the porous membrane. On the other hand, since the low molecular weight silane coupling agent is easy to react or bond with the plasticizer used for porosity by the wet method, if a low molecular weight silane coupling agent is used in the wet method, the low molecular weight silane coupling agent and the resin of the porous membrane are It is expected that bonding will become difficult to occur.

In addition, the battery using the separator described in Patent Documents 3 to 7 has poor cycle characteristics, and in the case of long-term use, there is a concern about a decrease in battery safety by causing an unexpected side reaction in the battery.

In view of the above problems, the present invention makes it possible to ensure high safety of the power storage device (suppression of the maximum internal heat generation rate and securing the voltage drop time, evaluated from a nail prick test) by making both a shutdown function and a high-temperature film breakable property. , It is an object of the present invention to provide a separator for power storage devices. Further, an object of the present invention is to provide a lithium ion secondary battery and a power storage device including such a separator for power storage devices, and a method of manufacturing such a separator for power storage devices.

As a result of repeated intensive examination, the inventors of the present invention have found that the above problems can be solved by using polyethylene and silane graft-modified polypropylene as a crosslinkable resin in a predetermined ratio, and the present invention has been completed. That is, the present invention is as follows.

[One]

The separator for power storage devices in which the mass ratio {(A)/(B)} of the silane graft-modified polypropylene (A) and polyethylene (B) is 2/98 to 80/20.

[2]

The separator for power storage devices according to [1], wherein the film breaking temperature measured by thermomechanical analysis (TMA) is 170 to 210°C.

[3]

The following process:

(1) silane graft-modified polypropylene (A), ultra-high molecular weight polyethylene (B), and plasticizer were extruded, cooled and solidified, and the mass ratio ((A)/(B)) of the above (A) and the above (B) was A sheet forming step of forming a sheet of 1/99 to 80/20;

(2) a stretching step of stretching the sheet to obtain a stretched product;

(3) a step of forming a porous body by extracting a plasticizer from the stretched product; And

(4) a heat treatment step of performing heat treatment on the porous body to obtain a heat treatment porous body;

The manufacturing method of the separator for power storage devices containing.

[4]

The following process:

(5) an affinity treatment step of immersing the heat-treated porous body in an organic solvent having amphiphilicity in water and an organic substance to obtain an affinity-treated porous body;

(6) a crosslinking treatment step of forming a crosslinked porous body having a silane crosslinked structure by contacting the affinity-treated porous body with a mixture of an organic metal-containing catalyst and water or immersing it in a base solution or an acid solution; And

(7) a water washing drying step of washing and drying the crosslinked porous body with water;

The manufacturing method of the separator for power storage devices according to [3], further comprising:

[5]

The following steps;

(2-A) a preparation step of preparing a laminated body or a wound body of an electrode and the separator for power storage devices described in [1] or [2], and a non-aqueous electrolyte solution;

(2-B) Injection process of injecting the non-aqueous electrolyte into the exterior body

Containing, the manufacturing method of a power storage device.

[6]

The power storage device according to [5], wherein the silane crosslinking reaction of the silane graft-modified polyolefin contained in the separator for power storage devices is initiated by bringing the separator for power storage devices into contact with the non-aqueous electrolyte during or after the injecting step. Manufacturing method.

[7]

The method for manufacturing an electrical storage device according to [5] or [6], wherein the non-aqueous electrolyte solution contains a fluorine-containing lithium salt.

[8]

The method for manufacturing a power storage device according to any one of [5] to [7], wherein the non-aqueous electrolyte solution is an acid solution or a base solution.

[9]

The following process:

(2-c) a terminal connection step of connecting a lead terminal to the electrode in the exterior body or the electrode exposed from the exterior body,

(2-D) Charging/discharging process in which at least 1 cycle of charging and discharging is performed

The method for manufacturing the power storage device according to any one of [5] to [8], further comprising:

[10]

A lithium ion secondary battery comprising a positive electrode, a negative electrode, the separator for power storage devices according to [1] or [2], and a non-aqueous electrolyte.

[11]

A power storage device comprising a positive electrode, a negative electrode, the separator for power storage devices according to [1] or [2], and a non-aqueous electrolyte.

According to the present invention, high safety of the power storage device (suppression of the maximum internal heat generation rate evaluated by a nail-prick test and securing the voltage drop time) of the power storage device is ensured by making the shutdown function of the power storage device separator and the high-temperature rupture resistance compatible. It is possible to provide a separator for power storage devices that can be used. Further, according to the present invention, it is possible to provide a lithium ion secondary battery and a power storage device including such a separator for power storage devices, and a method of manufacturing such a separator for power storage devices.

Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described, but the present invention is not limited only to the present embodiment. The present invention can be variously modified without departing from the gist of the present invention. In the present specification, "to" means that the numerical values at both ends thereof are included as an upper limit value and a lower limit value, unless otherwise specified. In addition, in this specification, the upper limit value and the lower limit value of a numerical range can be combined arbitrarily.

<Power storage device>

The separator for power storage devices (hereinafter, simply referred to as "separator" in some cases) according to the present embodiment is used for power storage devices. The power storage device includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. Examples of these types of power storage devices include lithium batteries, lithium secondary batteries, lithium ion secondary batteries, sodium secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, calcium secondary batteries, calcium ion secondary batteries, and aluminum. Secondary batteries, aluminum ion secondary batteries, nickel hydride batteries, nickel cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, lithium sulfur batteries, lithium air batteries, and zinc air batteries. Among them, from the viewpoint of practicality, a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a nickel hydride battery, and a lithium ion capacitor are preferable, and a lithium battery and a lithium ion secondary battery are more preferable.

<Lithium ion secondary battery>

Lithium ion secondary batteries, for example, use lithium transition metal oxides such as lithium cobalt oxide and lithium cobalt complex oxide as the positive electrode, carbon materials such as graphite and graphite as the negative electrode, and a storage battery using a non-aqueous electrolyte to be.

Examples of the non-aqueous solvent constituting the non-aqueous electrolyte solution include ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or a mixed solvent thereof. Examples of the electrolyte constituting the non-aqueous electrolyte include fluorine-containing lithium salts (LiPF ₆ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiSO ₃ CF _3, etc.) or LiBC ₄ O ₈ . A separator is disposed between the electrodes so that the movement between the electrodes of lithium (Li) is possible and contact between the electrodes is avoided.

<Separator>

(Polyolefin microporous membrane)

The separator according to the present embodiment includes a polyolefin microporous film according to the present embodiment (hereinafter, simply referred to as "microporous film" in some cases).

The microporous membrane contains (A) silane graft-modified polypropylene and (B) polyethylene. In addition, the mass ratio {(A)/(B)} of the silane graft-modified polypropylene and polyethylene is 2/98 to 80/20. In other words, based on 100% of the total mass of the silane graft-modified polypropylene and polyethylene, the mass ratio of the silane graft-modified polypropylene is 2 to 80% by mass, and the mass ratio of the polyethylene is 20 to 98% by mass. Thereby, it is possible to realize a high-quality separator (for example, there are few resin aggregates in the separator), and by including such a separator, high safety of the power storage device (evaluated from a nailing test, suppression of the internal maximum heat generation rate) And the voltage drop time) can be secured.

In this regard, in the microporous membrane, by constructing a silane crosslinked structure (gelling structure) with a silane graft-modified polypropylene, high-temperature rupture resistance can be expressed. This is a result of suitably connecting polypropylenes dispersed in polyethylene with a silane crosslinked structure, the morphology of the entire film changes, exceeding the melting point of polyethylene (for example, about 130°C to 140°C), and polypropylene It is estimated that this is because the film shape can still be maintained even around or exceeding the melting point of (for example, about 170°C). Therefore, from the viewpoint of securing high-temperature rupture resistance, the mass ratio of the silane graft-modified polypropylene is preferably 2.5% by mass or more, more preferably 3% by mass, based on 100% of the total mass of the silane graft-modified polypropylene and polyethylene. That's it. In other words, the mass ratio of polyethylene is preferably 97.5% by mass or less, and more preferably 97% by mass or less.

On the other hand, in the microporous membrane, by including polyethylene, it becomes possible to perform heat fixation at high temperature while suppressing clogging of pores in the resulting microporous membrane. Therefore, from the viewpoint of forming a dense and uniform porous structure, the mass ratio of polyethylene is preferably 20.5% by mass or more, more preferably 21% by mass or more, based on 100% of the total mass of the silane graft-modified polypropylene and polyethylene. to be. In other words, the mass ratio of the silane graft-modified polypropylene is preferably 98.5% by mass or less, and more preferably 98% by mass or less.

The total weight average molecular weight of the microporous membrane is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

Based on the total 100% by mass of the microporous membrane, the total mass of the silane graft-modified polypropylene and polyethylene is preferably 50% by mass or more, more preferably 65% by mass from the viewpoint of reliably exerting the effect of the present invention. It is mass% or more, more preferably 80 mass% or more, and particularly preferably 95 mass% or more.

The microporous membrane includes an organic metal-containing catalyst (dehydration condensation catalyst); Plasticizer; Metal soaps such as calcium stearate or zinc stearate; Ultraviolet absorbers; Light stabilizer; Antistatic agent; Anti-fog agents; Colored pigments; You may contain known additives, such as.

((A) Silane Graft Modified Polypropylene)

The silane graft-modified polypropylene has a structure in which a main chain is polypropylene, and an alkoxysilyl group is grafted to the main chain. It is estimated that the alkoxysilyl group is converted to a silanol group through a hydrolysis reaction with water and causes a crosslinking reaction to form a siloxane bond (see the following formula; change from a T0 structure to a T1 structure, a T2 structure, or a T3 structure. The rate to do is arbitrary). Although it does not specifically limit as an alkoxide substituted with an alkoxysilyl group, For example, methoxide, ethoxide, butoxide, etc. are mentioned. For example, in the following formula, R is methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, and the like.

In the silane graft-modified polypropylene, the main chain and the graft are connected by covalent bonds. Although it does not specifically limit as a structure which forms such a covalent bond, For example, alkyl, ether, glycol, ester, etc. are mentioned. In the step before performing the crosslinking reaction in the silane graft-modified polypropylene, the ratio of silicon to carbon (Si/C) is preferably 0.2 to 1.8%, more preferably 0.5 to 1.7%.

Preferred silane graft-modified polypropylene has a density of 0.82 to 0.96 g/cm 3 and a melt flow rate (MFR) of 0.5 to 25 g/min at 230°C.

The polypropylene constituting the silane graft-modified polypropylene may be composed of one type of single propylene, or may be composed of two or more types of propylene. Two or more types of silane graft-modified polypropylenes composed of different propylenes may be used in combination.

Further, as the polypropylene constituting the silane graft-modified polypropylene, it is preferably a propylene homopolymer.

Considering the manufacturing process of the separator according to the present embodiment, in the silane graft-modified polypropylene, in the previous step of the crosslinking treatment process described later, the unit containing silanol is 10% as a modified amount with respect to all ethylene units of the main chain. It is less than or equal to, Preferably it is 5% or less, More preferably, it is 2% or less. Preferred silane graft-modified polypropylene has a density of 0.90 to 0.96 g/cm 3 and a melt flow rate (MFR) of 0.2 to 5 g/min at 190°C.

The above-described crosslinking reaction is promoted using an organometallic-containing catalyst. In the present specification, a master batch resin obtained by adding an organometallic-containing catalyst in advance to a resin containing a silane graft-modified polypropylene before the sheet forming process (for example, a step of a kneading process performed as needed) It is called.

((B) polyethylene)

As polyethylene, a single type of polyethylene may be used, or two or more types of polyethylene may be used in combination.

As polyethylene, it is preferably a homopolymer of ethylene. However, if it is 50 mass% or less or 45 mass% or less with respect to the total mass of ethylene which comprises polyethylene, a monomer (other monomer) other than ethylene may be contained. As another monomer mentioned here, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, norbornene, etc. are mentioned.

(Arbitrary layer)

The microporous membrane itself may be used as a separator, and one having a functional layer on at least one side thereof may be used as a separator. Examples of the functional layer include, but are not limited to, an inorganic porous layer containing inorganic particles and a binder, an adhesive layer containing a thermoplastic polymer, and the like.

<Thermal Mechanical Analysis (TMA)>

From the viewpoint of reliably securing the high-temperature rupture resistance of the separator and reliably securing the safety of the power storage device, the separator preferably has a rupture temperature of 170 to 210°C as measured by TMA. As described above, in the present embodiment, as a result of the silane crosslinked polypropylene being suitably dispersed in polyethylene, the morphology of the entire film is changed to reach a temperature (170 to 210° C.) near or exceeding the melting point of polyethylene. The film shape can be maintained.

In general, when the power storage device heats up due to an unexpected runaway reaction, the separator fuses at a low temperature (for example, 150°C or less), and the movement of Li ions early, and discharges in or outside the power storage device accompanying it Is stopped. Thereafter, the entire power storage device is cooled by standing-cooling by outside air or a refrigerant of the power storage device, thereby preventing the non-aqueous electrolyte from igniting or decomposing and exothermic reaction of the electrolyte, and is expected to ensure safety. However, even if the runaway reaction generated in the power storage device is not stopped by the fuse and heat generation continues, the separator according to the present embodiment can suppress the fusion breakdown to a high temperature such as 170 to 210°C, and thus Thus, the safety of the power storage device can be ensured.

The film breaking temperature measured by TMA can be obtained by the method described in Examples, and can be controlled by changing the composition of the microporous film or the like.

<Separator characteristics>

Hereinafter, although it is a characteristic of a microporous membrane, when a microporous membrane itself is used as a separator, the characteristic of the microporous membrane is analyzed as a characteristic of a separator.

The porosity of the microporous membrane is preferably 20% or more, more preferably 30% or more, and still more preferably 32% or more or 35% or more. When the porosity is 20% or more, the followability to rapid movement of lithium (Li) ions tends to be further improved. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and still more preferably 50% or less. When the porosity is 90% or less, the film strength is more improved and the self-discharge tends to be more suppressed. This porosity can be measured by the method described in Examples, and can be controlled by changing the draw ratio of the microporous membrane or the like.

The air permeability of the microporous membrane is preferably 1 sec/100 cm 3 or more, more preferably 50 sec/100 cm 3 or more, still more preferably 55 sec/100 cm 3 or more, even more preferably 70 sec/100 cm 3 or more, 90 sec/100 It is not less than cm 3. When the air permeability is 1 sec/100 cm 3 or more, the balance between the film thickness, the porosity, and the average pore diameter tends to be further improved. Further, the air permeability is preferably 400 sec/100 cm 3 or less, more preferably 300 sec/100 cm 3 or less, and still more preferably 270 sec/100 cm 3 or less. When the air permeability is 400 sec/100 cm 3 or less, the ion permeability tends to be further improved. This air permeability can be measured by the method described in Examples, and can be controlled by changing the stretching temperature and/or stretching ratio of the microporous membrane.

The thickness of the microporous membrane is preferably 1.0 µm or more, more preferably 2.0 µm or more, still more preferably 3.0 µm or more, 4.0 µm or more, or 4.5 µm or more. When the film thickness is 1.0 µm or more, the film strength tends to be further improved. On the other hand, the film thickness is preferably 500 µm or less, more preferably 100 µm or less, still more preferably 80 µm or less, 22 µm or less, or 19 µm or less. When the film thickness is 500 µm or less, the ion permeability tends to be further improved. This film thickness can be measured by the method described in Examples, and can be controlled by changing the draw ratio of the microporous film or the like.

When a microporous membrane is used as a separator for a lithium ion secondary battery or a constituent material thereof, the film thickness of the microporous membrane is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, even more preferably 18 μm Hereinafter, it is particularly preferably 16 µm or less. When this film thickness is 25 µm or less, the permeability tends to be further improved. In this case, the lower limit of the film thickness may be 1.0 µm or more, 3.0 µm or more, 3.5 µm or more, or 4.0 µm or more.

<Method of manufacturing separator>

The separator manufacturing method is the following steps:

(1) sheet forming process;

(2) drawing process;

(3) Porous body formation step; And

(4) heat treatment process;

Includes. The separator manufacturing method may include a kneading step before the sheet forming step (1) and/or a winding step after the heat treatment step (4) as desired.

(Kneading process)

The kneading process is a process of kneading a polyolefin composition containing silane graft-modified polypropylene and ultra high molecular weight polyethylene (UHMWPE) to obtain a kneaded product. The polyolefin composition includes an organic metal-containing catalyst; Plasticizer; Metal soaps such as calcium stearate or zinc stearate; Ultraviolet absorbers; Light stabilizer; Antistatic agent; Anti-fog agents; Colored pigments; You may contain known additives, such as.

((1) sheet forming process (extrusion process))

The sheet forming step is a step of extruding a mixture of the obtained kneaded product and a plasticizer (that is, a mixture of silane graft-modified polypropylene, UHMWPE, and a plasticizer), cooling and solidifying, and forming a sheet. For extruding the mixture, a known extruder is used. Although it does not specifically limit as a method of molding, For example, a method of melt-kneading and extruding a melt solidified by compression cooling is mentioned. Examples of the cooling method include a method of directly contacting a cooling medium such as cold air or cooling water, and a method of contacting a roll or press machine cooled with a refrigerant. Among them, a method of bringing into contact with a roll or press machine cooled with a refrigerant is preferable from the viewpoint of excellent film thickness controllability.

The mass ratio {(A)/(B)} of (A) silane graft-modified polypropylene and (B) UHMWPE in the sheet is 2/98 to 80/20. Thereby, it is possible to realize a high-quality separator (for example, there are few resin aggregates in the separator), and by including such a separator, high safety of the power storage device (evaluated from a nailing test, suppression of the internal maximum heat generation rate) And the voltage drop time) can be secured.

Here, UHMWPE means polyethylene whose weight average molecular weight is 100,000 or more. Two or more types of UHMWPE having different weight average molecular weights may be used in combination.

As UHMWPE, it is preferably a homopolymer of ethylene. However, if it is 50 mass% or less or 45 mass% or less with respect to the total mass of ethylene which comprises UHMWPE, a monomer (other monomer) other than ethylene may be contained. As another monomer mentioned here, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, norbornene, etc. are mentioned.

From the viewpoint of securing a low-temperature shutdown of 150°C or less, and suppressing thermal runaway at the time of destruction of an electrical storage device while having a film resistance at 170 to 210°C to improve safety, in the sheet forming process, silane graft modification It is preferred that the polypropylene is not the master batch resin.

Although it does not specifically limit as a plasticizer, For example, the organic compound which can form a polyolefin and a uniform solution at a temperature below a boiling point is mentioned. More specifically, decalin, xylene, dioctylphthalate, dibutylphthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil, etc. have. Among these, paraffin oil and dioctylphthalate are preferable. Plasticizers may be used alone or in combination of two or more. The proportion of the plasticizer is not particularly limited, but is preferably 20% by mass or more from the viewpoint of the porosity of the microporous membrane to be obtained with respect to the total 100% by mass of the silane graft-modified polypropylene and UHMWPE, and 90% by mass from the viewpoint of the viscosity at the time of melt-kneading. % Or less is preferable.

((2) stretching process)

The stretching step is a step of stretching the sheet obtained in the sheet forming step described above to obtain a stretched product. As the stretching method of the sheet, MD uniaxial stretching by a roll stretching machine, TD uniaxial stretching by a tenter, sequential biaxial stretching by a combination of a roll stretching machine and a tenter, or a tenter and a tenter, simultaneous biaxial tenter or inflation molding. Simultaneous biaxial stretching etc. are mentioned. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferable. In other words, MD refers to the machine direction of the membrane, and TD refers to the width direction, that is, the direction perpendicular to the MD.

The surface magnification of the total is preferably 8 times or more, more preferably 15 times or more, still more preferably 20 times or more, or 30 from the viewpoint of the uniformity of the film thickness, the tensile elongation and the balance between the porosity and the average pore diameter. It's more than twice as long. When the total surface magnification is 8 times or more, it tends to be easy to obtain those having high strength and good thickness distribution. In addition, this surface magnification may be 250 times or less from the viewpoint of preventing breakage or the like.

((3) Porous body formation process (extraction process))

The porous body formation step is a step of forming a porous body by extracting a plasticizer from the stretched product obtained in the stretching step described above. Although it does not specifically limit as a method for extracting a plasticizer, For example, a method of immersing a stretched product in an extraction solvent, a method of showering an extraction solvent in a stretched product, etc. are mentioned. Although it does not specifically limit as an extraction solvent, For example, it is a poor solvent with respect to a polyolefin, and it is a good solvent with respect to a plasticizer, and it is preferable that a boiling point is lower than the melting point of a polyolefin. Although it does not specifically limit as such an extraction solvent, For example, Hydrocarbons, such as n-hexane and cyclohexane; Halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbon type; Alcohols such as ethanol and isopropanol; Ketones such as acetone and 2-butanone; Alkaline water, etc. are mentioned. The extraction solvent may be used alone or in combination of two or more.

((4) heat treatment process)

The heat treatment step is a step for obtaining a heat-treated porous body by performing heat treatment on the porous body obtained in the porous body forming step described above. Although it does not specifically limit as a method of heat treatment, For example, a heat fixation method which performs extending|stretching and relaxation operation etc. using a tenter or a roll drawing machine is mentioned. The relaxation operation refers to a reduction operation performed in MD and/or TD at a predetermined temperature and relaxation rate. The relaxation rate is a value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation; Or a value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the film before the operation; Alternatively, when both MD and TD are relaxed, it is a value obtained by multiplying the relaxation rate of MD and the relaxation rate of TD.

Incidentally, in the first manufacturing method, from the viewpoint of obtaining a heat-treated porous body suitable for an affinity treatment step and a crosslinking treatment step after that, it is preferable to stretch and relax the porous body with TD.

<1st manufacturing method>

Hereinafter, a first manufacturing method for manufacturing an electrical storage device will be described.

First, the manufacturing method of a separator used for an electrical storage device is, in addition to the above-described steps (1) to (4), further the following steps:

(5) affinity treatment process;

(6) crosslinking treatment step; And

(7) Water washing drying process

It is preferable to include and, if desired, a winding step may be included after the step (7).

((5) affinity treatment process)

The affinity treatment step is a step of obtaining an affinity-treated porous body by immersing the heat-treated porous body obtained in the above-described heat treatment step in an organic solvent having amphiphilicity in water and organic substances. Specifically, in order to improve the wettability between water and polyolefin, it is a step of immersing the heat-treated porous body in an organic solvent having an amphiphilicity in water and an organic substance to obtain an affinity-treated porous body. In the present embodiment, an organic solvent having amphiphilicity is disposed inside the affinity-treated porous body (affinity-treated porous body), so that the affinity with the liquid can be increased. Thereby, for example, in the case of a crosslinking treatment step, the affinity with the material or catalyst that accelerates the crosslinking reaction may also be increased in some cases. The organic solvent used is not particularly limited, and examples thereof include alcohols, acetone, ethylene carbonate, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. In addition, the method of immersion is not particularly limited, and examples thereof include a method of immersing the heat-treated porous body in an organic solvent, a method of showering an organic solvent in the heat-treated porous body, and the like.

((6) crosslinking treatment process)

In the crosslinking treatment step, the affinity treated porous body obtained in the above affinity treatment step is brought into contact with a mixture of an organic metal-containing catalyst and water, or immersed in a base solution or an acid solution, thereby crosslinking treatment having a silane crosslinking structure. It is a process of forming a porous body. That is, the crosslinking treatment step is a step of causing a silane dehydration condensation reaction (crosslinking reaction) to a siloxane bond with an alkoxysilyl group contained in the obtained affinity treated porous body.

In general molded articles such as hot water pipes, the Sn-based catalyst is often introduced into the extruder during the extrusion process. On the other hand, in the manufacturing process of the separator for power storage devices, when silane crosslinking is promoted in the extruder during the sheet forming step, the gelled portion causes production defects, and it becomes difficult to stretch the silane crosslinked polyolefin in the subsequent stretching step. Therefore, in the first manufacturing method, a silane crosslinking treatment is performed after the stretching step, the heat treatment step, and the affinity treatment step. The heat resistance, shape retention, and rupture resistance of the separator are ensured by the silane crosslinked structure thus obtained.

The metal of the organic metal-containing catalyst may be, for example, at least one selected from the group consisting of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, and lead, among which tin and zinc Or palladium is preferable, and tin or zinc is more preferable. The organic tin complex usable as a catalyst may be, for example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltindioctate, stannous acetate, stannous caprylate, or the like.

The base solution has a pH of more than 7, and may contain, for example, alkali metal hydroxides, alkaline earth metal hydroxides, carbonates of alkali metals, phosphates of alkali metals, ammonia, amine compounds, and the like. Among these, alkali metal hydroxides or alkaline earth metal hydroxides are preferable, alkali metal hydroxides are more preferable, and sodium hydroxide is still more preferable from the viewpoint of safety of the electrical storage device and silane crosslinkability.

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

The crosslinking treatment step is preferably performed by immersing the affinity-treated porous body in a base solution or an acid solution from the viewpoint of suppressing a thermal runaway reaction at the time of destruction of the electrical storage device and improving safety.

When the affinity-treated porous body is immersed in a base solution, from the viewpoint of further improving safety, the temperature of the base solution is preferably 20°C to 100°C, and/or the pH of the base solution is preferably 8 to 14. The reagent used for pH adjustment is not particularly limited, and examples thereof include alkali metal hydroxides and alkaline earth metal hydroxides. From the same viewpoint, it is preferable that the aqueous alkali solution does not contain amine compounds such as ethylamine, dibutylamine, hexylamine, and pyridine.

When the affinity-treated porous body is immersed in an acid solution, it is not desired to be bound by theory, but the acid prevents the formation of Si-O bonds of the silane cross-linked polyolefin rather than cleaving the Si-O bond of the silane cross-linked polyolefin. It is believed to act to promote catalytically.

When the affinity-treated porous body is brought into contact with a mixture of an organometallic-containing catalyst and water, from the viewpoint of securing safety by controlling the amorphous portion of the affinity-treated porous body, scandium, vanadium, copper, zinc, and It is preferable to adjust the content of zirconium, palladium, gallium, tin, titanium, iron, nickel, or lead in a range of 0.10 ppm or more and 200 ppm or less in terms of total atoms. In particular, it is more preferable that the content of zinc or tin in the microporous membrane is adjusted within the range of 0.10 ppm or more and 200 ppm or less in terms of atoms. The content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, or lead in the microporous membrane can be adjusted by, for example, a washing and drying process described later. With the metal content in such a limited range, decomposition of the crosslinked structure in the film can be suppressed, thereby making it easier to ensure safety, and there is a tendency for the battery cycle characteristics to exhibit good performance. When the separator contains an excessive amount of metal, eluted ions penetrate into the positive electrode, change the structure of the metal cluster storing Li, create electrical defect points in the entire positive electrode, and possibly deteriorate the cycle performance.

((7) water washing drying process)

The water washing drying step is a step of washing and drying the crosslinked porous body obtained in the crosslinking treatment step described above. Preferred conditions for the washing and drying step are that the water temperature is 20 to 100°C and/or the pH of the washing water is 6 to 8. For example, after replacing the inside of the crosslinked porous body with water having a pH of 6 to 8 at a temperature of 20 to 100°C, it can be dried. The drying method is not particularly limited, but examples thereof include conveyance in a heating roll, spraying of hot air, or heat drying using an infrared heater. By passing through the water washing drying process, a microporous membrane is obtained.

(Winding process)

The winding process is a process of slitting the microporous membrane obtained in the water washing drying process described above as needed, and winding it with a predetermined core. As described above, the microporous membrane itself may be used as a separator, or one having a functional layer on at least one side thereof may be used as a separator.

In other words, when the winding step is performed after the heat treatment step, the winding step is handled as a step of slitting the heat-treated porous body obtained in the heat treatment step as necessary and winding it to a predetermined core.

A method of manufacturing an electrical storage device using the separator includes, for example, the following steps;

(1-A) a step of laminating and/or winding a positive electrode, a separator obtained by the first manufacturing method, and a negative electrode to obtain a laminated body or a wound body;

(1-b) the step of putting the laminated body or the wound body into the exterior body;

(1-C) the process of injecting a non-aqueous electrolyte into the exterior body; And

(1-D) a step of connecting a lead terminal to the positive electrode and the negative electrode;

It may include. In steps (1-a) to (1-d), except for using the above-described separator, it can be performed by a method known in the art. In addition, in steps (1-a) to (1-D), the electrodes and non-aqueous electrolytes described above can be used, and known positive electrodes, negative electrodes, non-aqueous electrolytes, exterior bodies and charge/discharge solutions in the present technical field You can also use the device.

<2nd manufacturing method>

Hereinafter, a second manufacturing method for manufacturing an electrical storage device will be described.

First, in the second manufacturing method, a heat-treated porous body obtained through the above steps (1) to (4) can be prepared, and this can be used as a separator.

A method of manufacturing an electrical storage device using such a separator includes the following steps;

(2-a) a preparation step of preparing a laminated body of an electrode and a separator or an exterior body containing a wound body, and a non-aqueous electrolyte solution,

(2-b) an injection process of injecting a non-aqueous electrolyte into the exterior body, and

(2-C) a terminal connection step of connecting a lead terminal to an electrode in the exterior body or an electrode exposed from the exterior body, as desired, and

(2-D) Charging/discharging process in which at least 1 cycle of charging and discharging is performed as desired

Includes. In steps (2-a) to (2-d), except for using a separator (a heat-treated porous body obtained through the above-described steps (1) to (4)), the method known in the art Can be done by In addition, in steps (2-a) to (2-D), the electrodes and non-aqueous electrolytes described above can be used, and known positive electrodes, negative electrodes, non-aqueous electrolytes, exterior bodies and charging/discharging devices in the present technical field You can also use

In the second manufacturing method, it is preferable to initiate a silane crosslinking reaction of the silane graft-modified polypropylene by bringing the separator and the nonaqueous electrolyte into contact during the step (2-b) or after the step (2-b). In addition, from the viewpoint of reliably performing the silane crosslinking reaction of the separator, it is preferable to perform the (2-c) process and the (2-d) process. It is thought that a substance exerting a catalytic action on the silane crosslinking reaction is generated in the non-aqueous electrolyte solution or on the electrode surface by the charge/discharge cycle, whereby the silane crosslinking reaction is achieved.

Although not wishing to be bound by theory, it is assumed that the silane graft part is converted to silanol with a little moisture contained in the power storage device (moisture contained in the electrode, separator, non-aqueous electrolyte, etc.), undergoes crosslinking reaction, and changes into siloxane bonds. Has become. In addition, when the non-aqueous electrolyte (or electrolyte in the non-aqueous electrolyte) contacts the electrode, substances that catalyze the silane crosslinking reaction are generated in the non-aqueous electrolyte or on the surface of the electrode, and they penetrate into the non-aqueous electrolyte, and the silane graft portion is present. It is thought that the crosslinking reaction of the separator-containing laminated body or the wound body is uniformly promoted by uniformly swelling and diffusing to the amorphous part in the polyolefin. The substance exerting a catalytic action on the silane crosslinking reaction may be in the form of an acid solution (for example, an inorganic acid or organic acid having a pH <7), a basic solution (for example, an alkaline solution having a pH>7) or a film, When the electrolyte contains LiPF ₆ , _{it may be hydrogen fluoride (HF) generated by reacting LiPF 6} with moisture or a fluorine-containing organic material derived from HF. Here, the HF or fluorine-containing organic substance corresponds to the species generated in the battery according to the present embodiment.

As the non-aqueous electrolyte, the above-described non-aqueous electrolyte can be used as a non-aqueous electrolyte that can be used for a lithium ion secondary battery. For example, LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ or LiSO ₃ CF ₃ This is desirable.

A power storage device assembly kit can be provided by using a separator (the heat treatment porous body obtained through the above-described (1) process to (4) process). The power storage device assembly kit, for example, has two elements:

(2-a) a positive electrode, a separator obtained by the second manufacturing method, and an exterior body housing a laminated body or a wound body of the negative electrode; And

(2-b) a container for storing a non-aqueous electrolyte solution;

Includes. When using the power storage device assembly kit, a silane crosslinking reaction is performed on the spot by contacting the laminated body or wound body of the urea (2-a) and the non-aqueous electrolyte solution of the urea (2-b) in the exterior body, A power storage device that supports both outputs can be formed.

From the viewpoint of accelerating the crosslinking reaction of the separator, the power storage device assembly kit includes, as an accessory (or urea (2-c)), a catalyst for crosslinking an alkoxysilyl group to a siloxane bond, for example, the above-described organometallic catalyst and A separate container for storing a mixture of water, an acid solution, or a base solution may be provided.

A power storage device may be manufactured using the power storage device assembly kit described above. As a manufacturing method of an electrical storage device using an electrical storage device assembly kit, for example, the following steps:

(2-A) a step of preparing the power storage device assembly kit described above;

(2-B) Initiating the silane crosslinking reaction of the silane graft-modified polyolefin by contacting the separator in the electrical storage device assembly kit (i.e., the heat-treated porous body obtained through the above-described steps (1) to (4)) and a non-aqueous electrolyte. fair;

(2-C) as desired, a step of connecting a lead terminal to the positive electrode and the negative electrode in the power storage device assembly kit;

(2-D) a step of charging and discharging at least one cycle as desired;

It may include. In the (2-A) process to the (2-D) process, the positive electrode, the negative electrode, the non-aqueous electrolyte and the exterior body can be used as described above or known in the present technical field. From the viewpoint of reliably performing the silane crosslinking reaction of the separator, it is preferable to perform the (2-C) process and the (2-D) process.

In the second production method, when contacted with a non-aqueous electrolytic solution, the silane graft-modified polyolefin is crosslinked. For this reason, while being suitable for the manufacturing process of a conventional power storage device, a silane crosslinking reaction occurs after manufacture of a power storage device, and the safety of a power storage device can be improved.

<Example>

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples. Physical properties in Examples were measured by the following method.

(1) weight average molecular weight

Using Waters' ALC/GPC 150C type (trademark), standard polystyrene was measured under the following conditions, and a calibration curve was created. Further, for each of the following polymers, the chromatogram was measured under the same conditions, and the weight average molecular weight of each polymer was calculated by the following method based on the calibration curve.

Column: Tosoh _{Corporation GMH 6} -HT (trademark) 2 + GMH ₆ -HTL (trademark) 2

Mobile phase: o-dichlorobenzene

Detector: differential refractometer

Flow rate: 1.0ml/min

Column temperature: 140°C

Sample concentration: 0.1wt%

(Weight average molecular weight)

By multiplying each molecular weight component in the obtained calibration curve by 0.43 (polyethylene Q factor/polystyrene Q factor = 17.7/41.3), a molecular weight distribution curve in terms of polyethylene was obtained, and the weight average molecular weight was calculated.

(Weight average molecular weight of resin composition)

The Q factor value of the polyolefin having the largest mass fraction was used, and the weight average molecular weight was calculated in the same manner as in the case of polyethylene other than that.

(2) Melt flow rate (MFR) (g/10min)

The weight of the resin extruded for 10 minutes was determined as the MFR value under the conditions of 230° C. and a weight of 2.16 kg using a Toyo Seiki melt flow rate meter (Melt Index Corporation F-F01).

(3) Film thickness (㎛)

The film thickness of the microporous membrane was measured at a room temperature of 23±2°C and a relative humidity of 60% using a Toyo Seiki micro-thickness measuring instrument, KBM (trademark). Specifically, the film thickness of five points was measured at approximately equal intervals over the entire width of the TD, and their average value was obtained.

(4) Porosity (%)

A sample having a size of 10 cm x 10 cm was cut out from the microporous membrane, its volume (cm 3) and mass (g) were calculated, and the porosity was calculated using the following equation from them and the density (g/cm 3 ). For the density of the mixed composition, a value calculated and calculated from the respective densities and mixing ratios of the raw materials used was used.

Porosity (%) = (volume-mass/density of mixed composition)/volume×100

(5) Air permeability and air permeability increase (sec/100 cm3)

In accordance with JIS P-8117 (2009), the air permeability of the microporous membrane was measured with a Gurley type air permeability meter manufactured by Toyo Seiki Co., Ltd., G-B2 (trademark).

(6) Quantification of resin aggregates in separator

Among the separators, when the separators obtained in Examples and Comparative Examples described later are observed with a transmission optical microscope, the resin aggregate has an area of 100 µm in length x 100 µm in width and is defined as a region through which light is not transmitted. In observation with a transmission optical microscope, the number of resin aggregates per 1000 m 2 of separator area was measured.

(7) Breaking temperature measured by TMA (℃)

Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Seisakusho, the environmental temperature is changed over 25 to 250°C, and the temperature at the moment when the load is fully opened is the TMA rupture temperature (the rupture temperature measured by TMA). Decide.

Specifically, when measuring MD, microporous membranes of TD 3 mm and MD 13 mm were collected, both ends of the MD were chucked on a dedicated probe, and an initial 1.0 g load was applied to 10 mm between the chuck, and the furnace on which the test piece was mounted. Was heated, and the temperature at which the load was expressed as 0 g was taken as the TMA rupture temperature. When measuring TD, a microporous membrane having a TD of 13 mm and an MD of 3 mm is collected, and the same operation as above is performed.

(8) Battery breakdown safety test (sticking test)

The battery breakdown safety test is a test in which an iron nail is typed into a battery charged to 4.5V at a rate of 20 mm/sec, penetrated, and causes an internal short circuit. In this test, the phenomena at the time of internal short-circuit can be clarified by measuring the time change behavior of the voltage drop of the battery due to the internal short circuit and the behavior of the battery surface temperature increase due to the internal short circuit. In addition, the battery may rapidly generate heat due to insufficient shutdown function of the separator or rupture at a low temperature during an internal short circuit, and the non-aqueous electrolyte ignites, resulting in smoke and/or explosion of the battery. There is.

(Production of batteries used in battery destruction safety tests)

a. Production of positive poles

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

b. Production of negatives

A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of an ammonium salt of carboxymethylcellulose as a binder, and 1.7% by mass of styrene-butadiene copolymer latex as a binder. This slurry was applied with a die coater on one side of a 12 µm-thick copper foil to be a negative electrode current collector, dried at 120° C. for 3 minutes, and then compression-molded with a roll press. 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 was 1.35 g/cm 3.

c. Preparation of non-aqueous electrolyte

In a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio), LiPF ₆ was dissolved as a solute to a concentration of 1.0 mol/L to prepare.

d. Battery assembly

The separator was cut out with a TD of 60 mm and an MD of 1000 mm, and the separator was folded 99, and the positive electrode and the negative electrode were alternately overlapped between the separators (12 positive electrodes and 13 negative electrodes). In other words, a product having an area of 30 mm×50 mm for the positive electrode and 32 mm×52 mm for the negative electrode was used. After the 99-folded laminate was put in a Lamy bag, the non-aqueous electrolyte solution obtained in c. above was injected and sealed. After leaving at room temperature for 1 day, charging the battery voltage to 4.2V at a current value of 3mA (0.5C) in an atmosphere of 25℃, and maintaining 4.2V after reaching the current value, and starting to lower the current value from 3mA. For 6 hours, the initial charging after battery production was performed. Subsequently, it was discharged from a current value of 3 mA (0.5 C) to a battery voltage of 3.0 V.

(Maximum heating rate)

After penetrating the iron nail with the obtained battery, the battery surface temperature was determined as the maximum heat generation rate from the temperature change graph measured over 300 seconds using a thermocouple, when the temperature increase change was greatest per 1 sec.

(Voltage drop time)

After passing an iron nail through the obtained battery, the time required for the voltage drop from 4.5V to 3V was determined as the voltage drop time (3V drop time).

(9) Evaluation of cycle characteristics and manufacturing method of the battery

A. of the method of manufacturing a battery used in the above item "(8) Battery destruction safety test". In the same manner as in c. to c., except for the assembling, a battery for evaluating cycle characteristics was produced by the following d.

Charging and discharging of the obtained battery was performed 100 cycles in an atmosphere at 60°C. Charging is a method of charging the battery voltage to 4.2V at a current value of 6.0mA (1.0C) and maintaining 4.2V after reaching the current value to start lowering the current value from 6.0mA, and charged for a total of 3 hours. Discharge was discharged from a current value of 6.0 mA (1.0 C) to a battery voltage of 3.0 V. From the 100th cycle discharge capacity and the 1st cycle discharge capacity, the capacity retention rate was calculated. When the capacity retention rate was high, it was evaluated as having good cycle characteristics.

d. Battery assembly

The separator was cut into a circular shape having a diameter of 18 mm and a positive electrode and a negative electrode having a diameter of 16 mm, and the positive electrode, the separator, and the negative electrode were sequentially stacked so that the active material surfaces of the positive electrode and the negative electrode face each other, and stored in a stainless steel container with a lid. The container and the lid were insulated, the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. Into this container, the non-aqueous electrolyte solution obtained in c. of the above item "(8) Battery destruction safety test" was injected and sealed. After leaving at room temperature for 1 day, charging the battery voltage up to 4.2V at a current value of 3mA (0.5C) in an atmosphere of 25℃, and maintaining 4.2V after reaching it, and starting to lower the current value from 3mA. For 6 hours, the initial charging after battery production was performed. Subsequently, it was discharged from a current value of 3 mA (0.5 C) to a battery voltage of 3.0 V.

(10) extrusion stability

During the extrusion process, the state of the extruded polyolefin composition was observed and evaluated according to the following criteria.

○ (Good): The fluctuation of the current value of the extruder is within ±0.5A from the average value of 300 seconds.

× (defect): The fluctuation of the current value of the extruder exceeds ±0.5A at the average value of 300 seconds.

[Example 1]

<The manufacturing method of silane graft-modified polypropylene>

The raw material polyolefin used for the silane graft-modified polypropylene has a viscosity average molecular weight (Mv) of 100,000 or more and 1 million or less, a weight average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number average molecular weight of 10,000 or more. Further, it may be 150,000 or less, and may be propylene or butene copolymerized α-olefin. While melt-kneading the raw material polyolefin with an extruder, an organic peroxide (di-t-butyl peroxide) is added, a radical is generated in the α-olefin polymer chain, and then a trimethoxy alkoxide substituted vinylsilane is injected, and an addition reaction As a result, an alkoxysilyl group is introduced into the α-olefin polymer to form a silane graft structure.

In addition, in order to simultaneously 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 the chain-chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heated and dried at 80°C for 2 days to remove moisture or unreacted trimethoxy alkoxide-substituted vinylsilane. In other words, the residual concentration in the pellets of unreacted trimethoxy alkoxide substituted vinylsilane is about 1500 ppm or less.

The silane graft-modified polyolefin obtained by the above-described manufacturing method is shown below or in Table 1 as "silane graft-modified polypropylene".

<Production of microporous membrane (single layer)>

Polyethylene (UHMWPE) of a homopolymer having a weight average molecular weight of 1,000,000 and the above-described silane graft-modified polypropylene were added to polyethylene: silane graft-modified polypropylene = 95:5 (% by mass), and pentaerythritol-tetrakis as an antioxidant -[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added at 1% by mass, followed by dry blending using a tumbler blender to obtain a mixture. The obtained mixture was fed by a feeder in a nitrogen atmosphere with a twin screw extruder. Further, liquid paraffin (kinetic viscosity at 37.78° C. 7.59×10 ⁻⁵ m 2 /s) was injected into the extruder cylinder by a plunger pump.

The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and the pump were adjusted so that the ratio of the amount of liquid paraffin occupied in the extruded polyolefin composition was 70% by mass (that is, the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 230°C, a screw rotation speed of 240 rpm, and a discharge amount of 18 kg/h.

Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled at a surface temperature of 25°C via a T-die, thereby obtaining a gel sheet (sheet) having a raw film thickness of 1300 µm.

(Stretching process)

Next, the gel sheet was guided by a simultaneous biaxial tenter stretching machine, and biaxial stretching was performed to obtain a stretched product. The set stretching conditions were MD magnification 7.0 times, TD magnification 6.0 times (that is, 7×6 times), and biaxial stretching temperature of 124°C.

(Porous body formation process)

Subsequently, the stretched gel sheet was guided into a dichloromethane bath, sufficiently immersed in dichloromethane to extract and remove liquid paraffin, and then dichloromethane was dried and removed to obtain a porous body.

(Heat treatment process)

Next, in order to perform heat fixation, the porous body was guided by a TD tenter, heat fixation was performed at a heat setting temperature of 131°C and a draw ratio of 1.8 times, and then relaxation operation was performed to a TD of 1.7 times. Thereby, a heat-treated porous body was obtained.

(Affinity treatment process)

Subsequently, the heat-treated porous body was guided into an ethanol bath (affinity treatment tank) and stayed while being immersed for 60 seconds to perform affinity treatment of the heat-treated porous body to obtain an affinity-treated porous body.

(Crosslinking treatment process)

Subsequently, the affinity-treated porous body was guided into a 25% aqueous caustic soda solution (crosslinking treatment tank) and immersed for 60 seconds to stay therein, and the affinity-treated porous body was crosslinked to obtain a crosslinked porous body.

(Water washing drying process)

Subsequently, the crosslinked porous body was guided into water (water washing treatment tank) and stayed while being immersed for 60 seconds, and the crosslinked porous body was washed with water. This was guided to a conveyance dryer, and dried at 120° C. for 60 seconds to obtain a microporous membrane.

Then, about the obtained microporous membrane, the edge part was cut|disconnected, and it wound up as a mother roll 1,100 mm in width and 5,000 m in length.

[Examples 2 to 5 and Comparative Examples 1 to 3]

A microporous membrane was produced by the same method as in Example 1, except that the conditions were changed as described in Table 1.

The evaluation was performed using the microporous membrane obtained in the above-described Examples and Comparative Examples. Table 1 shows the evaluation results.

In other words, the silane graft-modified polypropylene (A) in Example 1 uses polypropylene having a viscosity average molecular weight of 20,000 as a raw material, and has a density of 0.91 g, obtained by a modification reaction with a trimethoxy alkoxide substituted vinylsilane. /Cm 3, and a melt flow rate (MFR) of 18.0 g/min at 230°C is a silane graft-modified polypropylene.

In Table 1, "resin composition" represents a mass ratio of the silane graft-modified polypropylene (A) and polyethylene (UHMWPE) (B) to 100% by mass in total.

In addition, the "system|system|group" represents the method of a silane crosslinking reaction, and is classified according to the method by alkali treatment or acid treatment in the table.

In addition, the "timing of the crosslinking reaction" means that the silane crosslinking reaction was performed by the above-described (6) crosslinking treatment step, or was performed by the (2-d) step in the second manufacturing method described above (in particular, This indicates whether it was performed at the time of charging and discharging in the first cycle of the power storage device).

In addition, "reagent" represents a reagent used in the above-described (6) crosslinking treatment step, excluding Example 5 and Comparative Example 3. Incidentally, in Example 4, a 10% hydrochloric acid solution was used as a reagent in place of the 25% caustic soda aqueous solution in Example 1.

In addition, "temperature" represents the temperature during the process indicated in the timing of the crosslinking reaction.

In addition, "the pH of the crosslinking treatment tank" and "the pH of the water washing treatment tank" indicate the pH in each tank, and for example, "7 to 12" means that the pH is distributed with a width in the vicinity of the inlet to the outlet of the tank. Indicates that.

Claims (11)

The separator for power storage devices in which the mass ratio {(A)/(B)} of the silane graft-modified polypropylene (A) and polyethylene (B) is 2/98 to 80/20. The separator for an electrical storage device according to claim 1, wherein the film breaking temperature measured by thermo-mechanical analysis (TMA) is 170 to 210°C. The following process:
(1) Silane graft-modified polypropylene (A), ultra-high molecular weight polyethylene (B), and plasticizer were extruded, cooled and solidified, and the mass ratio ((A)/(B)) of the above (A) and the above (B) was A sheet forming step of forming a sheet of 1/99 to 80/20;
(2) a stretching step of stretching the sheet to obtain a stretched product;
(3) a step of forming a porous body by extracting a plasticizer from the stretched product; And
(4) a heat treatment step of performing heat treatment on the porous body to obtain a heat treatment porous body;
The manufacturing method of the separator for power storage devices containing. The process according to claim 3, wherein:
(5) an affinity treatment step of immersing the heat-treated porous body in an organic solvent having amphiphilicity in water and an organic substance to obtain an affinity-treated porous body;
(6) a crosslinking treatment step of contacting the affinity-treated porous body with a mixture of an organic metal-containing catalyst and water or immersing it in a base solution or an acid solution to form a crosslinked porous body having a silane crosslinked structure; And
(7) a water washing drying step of washing and drying the crosslinked porous body with water;
The manufacturing method of the separator for power storage devices which further contains. The following steps;
(2-A) a preparation step of preparing a laminated body or a wound body of an electrode and the separator for power storage devices according to claim 1 or 2, and a non-aqueous electrolyte solution;
(2-B) Injection process of injecting the non-aqueous electrolyte into the exterior body
Containing, the manufacturing method of a power storage device. The power storage according to claim 5, wherein the silane crosslinking reaction of the silane graft-modified polyolefin contained in the separator for power storage devices is initiated by bringing the separator for power storage devices into contact with the nonaqueous electrolyte during or after the injection step. Device manufacturing method. The method for manufacturing a power storage device according to claim 5, wherein the non-aqueous electrolyte solution contains a fluorine-containing lithium salt. The method for manufacturing a power storage device according to claim 5, wherein the non-aqueous electrolytic solution is an acid solution or a base solution. The process according to claim 5, wherein:
(2-C) a terminal connection step of connecting a lead terminal to the electrode in the exterior body or the electrode exposed from the exterior body,
(2-D) Charging/discharging process in which at least 1 cycle of charging and discharging is performed
The method of manufacturing an electrical storage device further comprising a. A lithium ion secondary battery comprising a positive electrode, a negative electrode, the separator for power storage devices according to claim 1 or 2, and a non-aqueous electrolyte. A power storage device comprising a positive electrode, a negative electrode, the separator for power storage devices according to claim 1 or 2, and a non-aqueous electrolyte.