JP2020061312A - Trace metal cross-linked separator - Google Patents

Abstract

An object of the present invention is not only to secure long-term stability, shutdown function and high temperature membrane rupture property of a separator, but also to secure long-term cycle characteristics of an electricity storage device. A separator for an electricity storage device including a microporous film containing a silane-grafted modified polyolefin and an ultra-high molecular weight polyolefin includes scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead. Is contained in a total amount of 0.10 ppm or more and 200 ppm or less in terms of atoms. [Selection diagram] Figure 1

Description

  The present invention relates to a power storage device separator.

  Microporous membranes are widely used as separation or selective permeation separation membranes for various substances, and separators.Examples of their applications include microfiltration membranes, fuel cell separators, condenser separators, or functional materials. Examples of the base material include a base material of a functional film for filling the inside of the resin to exhibit a new function, a battery separator, and the like. Among them, the polyolefin microporous film is preferably used as a lithium ion battery separator that is widely used in notebook personal computers, mobile phones, digital cameras and the like. Among them, in order to ensure battery safety, the separator is required to have both the activation of the shutdown function and the improvement of the film rupture temperature. For example, Patent Document 1 describes that the higher-order physical properties of a polyolefin resin, which is an essential component of a lithium ion battery separator, are adjusted. Further, as shown in Patent Document 2, the separator suppresses heat generation due to a short circuit inside the battery with a shutdown function in a specific crystallinity and gel fraction region, while a high temperature part is partially generated in the battery cell. It is known that the safety of the battery can be ensured by having the property of not rupturing the membrane (breakdown at 170 ° C. or higher). Regarding Patent Documents 1 and 2, more specifically, it has been experimentally found that high-temperature film rupture properties can be exhibited by constructing a silane cross-linked portion (gelation structure) in a polyolefin separator. Furthermore, in recent years, the mounting of lithium-ion batteries on electric vehicles has advanced, and with the increase in battery area, overwhelmingly long-term stability and overwhelmingly large number of cycles compared to conventional mobile devices. Good cycle characteristics are required.

JP, 9-216964, A International Publication No. 97/44839 JP, 11-144700, A JP, 11-172036, A JP 2001-176484 A JP 2000-319441 A JP, 2017-203145, A

  In recent years, while high output and high energy density of lithium-ion secondary batteries for mobile device installations or in-vehicle use have been advanced, miniaturization of battery cells and stable cycle discharge / charge performance during long-term use are required. . Therefore, a thin film (for example, 15 μm or less) with high quality (for example, uniform physical properties and no resin aggregates) is required as a separator to be used. Furthermore, in addition to the above performance, the level of battery safety has become stricter than before, and as described in Patent Documents 1 and 2, a shutdown function and a high temperature film rupture property are required. Development of a resin composition for a separator capable of stable production and a manufacturing method is expected. Further, it is expected that the separator does not deteriorate even after long-term use, the shutdown function and the high-temperature film rupture property are compatible, and good battery cycle characteristics are secured for a long period of time.

  For example, in the method described in Patent Document 3, a crosslinking catalyst masterbatch is used during the extrusion step to promote the crosslinking reaction of the silane-modified polyethylene in the extruder, but resin agglomerates are also observed and the physical properties of the separator are uniform. Reduce sex. In contrast to this method, the methods described in Patent Documents 4, 5, and 6 are provided with a plasticizer extraction step or a silane gel crosslinking step, control the gel fraction of the resin film, and convert the uncrosslinked resin into hot water. Measures are taken by passing through molding and then dehydrating. Further, Patent Document 7 discloses that by adjusting the gel fraction of a polyolefin microporous film, the storage elastic modulus, the maximum shrinkage rate by thermomechanical analysis (TMA), and the amount of radicals measured by the electron spin resonance method, low heat It has been proposed to provide a heat resistant resin microporous membrane having excellent shrinkability, low fluidity and meltdown resistance.

  However, the method described in Patent Document 4 cannot sufficiently advance the silane cross-linking reaction, and it is difficult to obtain high-temperature film rupture resistance. In the plasticizer extraction step described in Patent Documents 3 and 4, since the tin (II) -based crosslinking catalyst is used, the crosslinking reaction can proceed, but there is a concern that the crosslinking catalyst may remain afterwards.

  The heat-resistant resin microporous film described in Patent Document 7 is merely obtained by applying a photopolymerizable coating liquid to a dry and porous film. Further, in Example 5 of Patent Document 7, a low molecular weight silane coupling agent such as γ-methacryloxypropyltrimethoxysilane is added to the porous membrane, but if the low molecular weight silane coupling agent is used in the wet porosification method, Since the low molecular weight silane coupling agent easily reacts with or binds to the plasticizer for porosity, it is expected that it does not bind to the resin of the porous membrane.

  Further, the batteries using the separators described in Patent Documents 3 to 7 have poor cycle characteristics, and when used for a long period of time, an unexpected side reaction is induced in the battery, which may reduce battery safety. . Further, in order to obtain the shutdown function and the high temperature membrane rupture property, as described above, there is a problem in the silane cross-linking method, and at the same time, it is necessary to construct the most important porous body structure for the separator only with the silane-grafted polyolefin. Since this is not possible, development of a resin mixture composition is also essential.

  In view of the above problems, an object of the present invention is not only to ensure long-term stability, shutdown function and high temperature film rupture property of a separator, but also to ensure long-term cycle characteristics of an electricity storage device.

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by controlling the amount of specific atoms contained in an electricity storage device separator, and complete the present invention. Came to.
That is, the present invention is as follows.
[1]
A separator for an electricity storage device including a microporous film containing a silane-grafted modified polyolefin and an ultra-high molecular weight polyolefin, wherein scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead is converted into atoms. A separator for an electricity storage device containing 0.10 ppm or more and 200 ppm or less in total.
[2]
A separator for an electricity storage device, which includes a microporous film containing a silane-grafted modified polyolefin and an ultra-high molecular weight polyolefin, and contains 0.10 ppm or more and 200 ppm or less in total of zinc or tin in terms of atoms.

  According to the present invention, it is possible to obtain a separator for an electricity storage device including a microporous film having long-term stability, a shutdown function, and a high-temperature film rupture property, and also stability and long-term cycle test of an electricity storage device including the separator. It is possible to ensure safety.

FIG. 1 is a TMA graph of the separator obtained in Example 1. FIG. 2 is a heat generation graph during a nail puncture safety test of a battery using the separator obtained in Example 1. FIG. 3 is a voltage drop graph at the time of a nail puncture safety test of a battery using the separator obtained in Example 1.

  Hereinafter, modes for carrying out the present invention (hereinafter, abbreviated as “this embodiment”) will be described in detail. The present invention is not limited to the embodiments described below, and various modifications can be made within the scope of the invention.

[Power storage device]
The separator according to the present embodiment can be used in a power storage device. The electricity storage device includes a positive electrode, a negative electrode, the separator according to the present embodiment arranged between the positive and negative electrodes, and optionally an electrolytic solution. As the electricity storage device, specifically, 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. , Calcium ion secondary battery, aluminum secondary battery, aluminum ion secondary battery, nickel hydrogen battery, nickel cadmium battery, electric double layer capacitor, lithium ion capacitor, redox flow battery, lithium sulfur battery, lithium air battery, zinc air battery And so on. Among these, from the viewpoint of practicality, a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a nickel hydrogen battery, or a lithium ion capacitor is preferable, and a lithium battery or a lithium ion secondary battery is more preferable.

[Lithium-ion secondary battery]
A lithium-ion secondary battery is a storage battery that uses a lithium transition metal oxide such as lithium cobalt oxide or a lithium cobalt composite oxide as a positive electrode, a carbon material such as graphite or graphite as a negative electrode, and an electrolyte solution as an electrolytic solution. Can be The electrolytic solution may be ethylene carbonate (PC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) or a mixed solvent thereof, and the electrolyte is LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ). ₂ , lithium (F) -containing lithium salts such as LiSO ₃ CF ₃ , and electrolytes such as LiBC ₄ O ₈ (LiBOB) are preferable.
During charge / discharge of the lithium-ion secondary battery, ionized lithium reciprocates between the electrodes. In addition, since the ionized lithium needs to move between the electrodes at a relatively high speed while suppressing contact between the electrodes, a lithium ion battery separator between the electrodes (hereinafter, also simply referred to as “separator”) The part called is used.

[Method for manufacturing electricity storage device]
The method of manufacturing an electricity storage device includes the following steps;
(A) a step of stacking and / or winding a positive electrode, a separator for an electricity storage device manufactured by the method according to the present embodiment, and a negative electrode to obtain a stacked body or a wound body;
(A) Step of putting the laminated body or the wound body in the outer casing;
(C) a step of pouring an electrolytic solution into the outer package; and (D) a step of connecting a lead terminal to the positive electrode and the negative electrode;
including. Steps (a) to (d) can be performed by a method known in the technical field, except that the separator for an electricity storage device manufactured by the method according to the present embodiment is used, and the step (a) In (a) to (d), a positive electrode, a negative electrode, an electrolytic solution, and an outer package known in the technical field can be used.

The electrolytic solution used in the step (c) is preferably an acidic solution and / or a basic solution from the viewpoint of accelerating the crosslinking reaction of the electricity storage device separator contained in the outer package, and the electrolyte is LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiSO ₃ CF _{3 and} other fluorine (F) -containing lithium salts, and electrolytes such as LiBC ₄ O ₈ (LiBOB) are preferable.

(Separator)
Since a separator containing a polyolefin resin such as polyethylene (PE) needs insulation and lithium ion permeability, it is generally a paper, a polyolefin non-woven fabric or a resin micro-porous material which is an insulating material having a porous structure. It is formed from a film or the like. Particularly, in a lithium ion battery, a polyolefin microporous membrane that is capable of constructing a dense and uniform porous structure and oxidation-reduction resistance deterioration of a separator is excellent.

The microporous film included in the separator according to the present embodiment contains a silane-grafted modified polyolefin and an ultrahigh molecular weight polyolefin. Further, the separator according to the present embodiment is within a range of 0.10 ppm or more and 200 ppm or less in terms of the total amount of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in terms of atoms. Including. Conventionally, from the viewpoint of viscoelasticity, it was considered preferable that elements such as germanium, tin, lead, and Pd do not exist in the microporous film that constitutes the separator. It was found that long-term cycle stability and safety can be secured by allowing Sn, Zn, Pd, or the like to exist in the microporous membrane. From the viewpoint of further improving long-term cycle stability and safety, the content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the separator is the total in atomic conversion. The amount is preferably within the range of 0.35 to 190.90 ppm or 0.75 to 180.90 ppm.
The content of zinc or tin in the separator according to another embodiment of the present invention is within the range of 0.10 ppm or more and 200 ppm or less in terms of total amount in terms of atom from the viewpoint of improving long-term cycle stability and safety. It is preferable that the total amount in terms of atom is within the range of 0.10 to 190.10 ppm or 0.20 to 180.10 ppm.
The content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the separator is adjusted by, for example, a water washing / drying step in the method for producing a microporous film described below. You can

  The siloxane bond cross-linking part in which a plurality of silane grafts are bonded to each other is hydrofluoric acid (HF) generated by an electrolyte decomposed in an electricity storage device or an electrolytic solution (ethylene carbonate, etc.) generated by HF when used for a long period of time. ) Or an additive is secondarily decomposed by an organic radical to undergo nucleophilic substitution, an open bond reaction of the cross-linking portion proceeds, an alkoxide is generated, and the degree of cross-linking decreases. Further, the decomposition of the electrolytic solution is promoted starting from an alkoxide or the like, a chain oligomer reaction of the electrolytic solution occurs, and clogging inside the separator is significantly induced, so that the cycle characteristics tend to be significantly deteriorated. However, in the present embodiment, the separator containing the transition metal species ions in a limited amount plays a role of a catalyst in this siloxane bond, suppresses the open bond of the siloxane bond, and has a crosslinking degree of the separator even during long-term use. It is possible to suppress the deterioration of the film and maintain both good shutdown characteristics and film rupture characteristics. Therefore, when a limited amount of transition metal species ions is contained in the separator as in the present embodiment, the cycle performance of the electricity storage device is not deteriorated over a long period of time.

[Characteristics of microporous membrane]
The following characteristics of the microporous film are for the case where the electricity storage device separator is a flat film, but when the electricity storage device separator is a laminate, it is measured after removing layers other than the microporous membrane from the laminate. be able to.

  The porosity of the polyolefin microporous film used in the present embodiment is preferably 20% or more, more preferably 30% or more, and further preferably 32% or more or 35% or more. When the porosity of the microporous membrane is 20% or more, the followability to rapid movement of lithium ions tends 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 further suppressed. The porosity of the microporous membrane can be measured by the method described in Examples.

  The air permeability of the microporous membrane is preferably 1 second or more, more preferably 50 seconds or more, further preferably 55 seconds or more, further preferably 70 seconds or more, 90 seconds or more, or 110 seconds or more. is there. When the air permeability of the microporous membrane is 1 second or more, the balance among the film thickness, the porosity, and the average pore diameter tends to be further improved. The air permeability of the microporous membrane is preferably 400 seconds or less, more preferably 300 seconds or less, and further preferably 270 seconds or less. When the air permeability of the microporous membrane is 400 seconds or less, the ion permeability tends to be further improved. The air permeability of the microporous membrane can be measured by the method described in Examples.

The tensile strength of the microporous film is preferably 1000 kgf / cm ² or more, and more preferably 1050 kgf / cm ² or more, in both MD and TD (directions orthogonal to MD, film width direction), respectively. It is preferably 1100 kgf / cm ² or more. When the tensile strength is 1000 kgf / cm ² or more, breakage during slitting or winding of the power storage device is more suppressed, or short circuit due to foreign matter in the power storage device tends to be further suppressed. On the other hand, the tensile strength of the microporous membrane is preferably 5000 kgf / cm ² or less, more preferably 4500 kgf / cm ² or less, and further preferably 4000 kgf / cm ² or less. When the tensile strength of the microporous membrane is 5000 kgf / cm ² or less, the microporous membrane relaxes early during the heating test, the contraction force is weakened, and as a result, the safety tends to increase.

  The film thickness of the microporous film 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 5.5 μm or more. When the film thickness of the microporous film is 1.0 μm or more, the film strength tends to be further improved. The film thickness of the microporous film is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less, 22 μm or less or 19 μm or less. When the film thickness of the microporous film is 500 μm or less, the ion permeability tends to be further improved. The film thickness of the microporous film can be measured by the method described in the examples.

  When the microporous film is a separator used in a relatively high capacity lithium ion secondary battery in recent years, the film thickness of the microporous film is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less. , More preferably 18 μm or less, particularly preferably 16 μm or less. In this case, when the thickness of the microporous film is 25 μm or less, the permeability tends to be further improved. In this case, the lower limit of the film thickness of the microporous film may be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more.

  From the viewpoint of the long-term stability of the electricity storage device separator and the long-term cycle stability and safety of the electricity storage device, the microporous membrane preferably has a melting film rupture temperature of 180 ° C. to 220 ° C. during thermomechanical analysis (TMA) measurement. C., more preferably 180 to 200.degree. Further, a separator including a microporous film having a melting film rupture temperature measured by TMA of 180 ° C to 220 ° C is also an embodiment of the present invention.

[Method for producing microporous membrane]
The microporous membrane according to the present embodiment has, for example, the following steps:
(1) Sheet forming step;
(2) Stretching step;
(3) Porous body forming step;
(4) Heat treatment step;
(5) Affinity treatment step;
It can be produced by a method including (6) a crosslinking treatment step; and (7) a water washing and drying step.
If desired, the method for producing a microporous membrane may include a kneading step before the sheet forming step (1) and / or a winding step after the water washing / drying step (7).

[Kneading process]
The kneading step is a step of kneading the silane-grafted modified polyolefin and the other polyolefin to obtain a kneaded product.

(Polyolefin)
The polyolefin used in the kneading step is not particularly limited, but for example, a homopolymer of ethylene or propylene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and Examples thereof include copolymers formed from at least two monomers selected from the group consisting of norbornene. Among these, high-density polyethylene (homopolymer) and low-density polyethylene are preferable, and high-density polyethylene (from high-density polyethylene Homopolymer) is more preferred. The polyolefins may be used alone or in combination of two or more.

  Ultra high molecular weight polyethylene (UHMWPE) is preferably used in combination with the silane-grafted modified polyolefin during the kneading step. It is generally known that the ultrahigh molecular weight polyethylene (UHMWPE) has a weight average molecular weight of 1,000,000 or more.

  In the kneading step, a polyolefin composition containing a polyolefin having a weight average molecular weight of less than 1,000,000 (preferably 40% by mass or more, and more preferably 80% by mass or more based on the total polyolefin) is used. It is preferable to use. By using the polyolefin having a weight average molecular weight of less than 1,000,000, the shrinkage of the polymer is relaxed early in the heating test of the electricity storage device, and the safety tends to be maintained particularly in the heating safety test. It should be noted that the case where a polyolefin having a weight average molecular weight of less than 1,000,000 is used is compared with the case where a polyolefin having a weight average molecular weight of 1,000,000 or more is used, the elastic modulus in the thickness direction of the obtained microporous membrane tends to be small. Therefore, it is possible to obtain a microporous film in which irregularities of the core are relatively easily transferred.

The weight average molecular weight of the entire microporous membrane is preferably 100,000 or more and 1,200,000 or less, more preferably 150,000 or more and 800,000 or less.
The polyolefin composition used in the kneading step includes a dehydration condensation catalyst, a plasticizer, metal soaps such as calcium stearate and zinc stearate, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and a coloring pigment. Known additives may be contained.

(Silane graft modified polyolefin)
The silane-grafted modified polyolefin has a main chain of polyolefin and has a structure in which alkoxysilyl is grafted to the main chain. The alkoxide substituted with the alkoxysilyl is not particularly limited, and examples thereof include methoxide, ethoxide, butoxide and the like. Further, the main chain and the graft are connected by a covalent bond, and examples thereof include structures such as alkyl, ether, glycol and ester. Considering the manufacturing process of the separator according to the present embodiment, in the silane-grafted modified polyolefin, the ratio of silicon to carbon (Si / C) is 0.2 to 1. It is preferably 8%, and more preferably 0.5 to 1.7%.

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

(Dehydration condensation catalyst)
The alkoxyl group forms a siloxane bond through a hydrolysis reaction with water. However, since the reaction rate is slow, in many cases, an organometallic catalyst can be used to accelerate the condensation reaction. The metal of the organometallic-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. Organometallic-containing catalysts are mentioned in particular as di-butyltin-di-laurate, di-butyltin-di-acetate, di-butyltin-di-octoate and the like, such as Weij et al. (FW van. Der. Weij: Macromol. Chem. , 181, 2541, 1980.), it is known that the reaction rate can be overwhelmingly promoted by the reaction mechanism, but in recent years, copper has been used in order to avoid damage to the environment and human health due to organotin. Alternatively, it is known that the Lewis function of a titanium chelate complex can be used to promote a reaction of forming a siloxane bond between alkoxysilyl groups, like an organotin complex, by combining with an organic base.

(Masterbatch resin)
It is known that the dehydration condensation catalyst also functions as a catalyst for a siloxane bond forming reaction of an alkoxysilyl group-containing resin. In this specification, a compound obtained by previously adding the dehydration condensation catalyst (organic metal-containing catalyst) to an alkoxysilyl group-containing resin or another kneading resin in a continuous process having a resin kneading step using an extruder, and compounding Called batch resin.

(Plasticizer)
The plasticizer is not particularly limited, and examples thereof include an organic compound capable of forming a uniform solution with polyolefin at a temperature equal to or lower than the boiling point. More specific examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil and the like. Among these, paraffin oil and dioctyl phthalate are preferable. The plasticizers may be used alone or in combination of two or more.
The proportion of the plasticizer is not particularly limited, but from the viewpoint of the porosity of the obtained microporous membrane, the polyolefin and the silane-grafted polyolefin are preferably 20% by mass or more based on the total mass, if necessary, and the viscosity at the time of melt kneading From the viewpoint, 90% by mass or less is preferable.

[Sheet molding process (extrusion process)]
The sheet forming step is a step of extruding the obtained kneaded product or a mixture of a silane-grafted modified polyolefin, an ultrahigh molecular weight polyolefin and a plasticizer, cooling and solidifying the mixture, and forming the sheet to obtain a sheet. The sheet forming method is not particularly limited, and examples thereof include a method in which a melt-kneaded and extruded melt is solidified by compression cooling. Examples of the cooling method include a method of directly contacting a cooling medium such as cold air or cooling water, a method of contacting with a roll or a press machine cooled with a refrigerant, and a method of contacting with a roll or a press machine cooled with a refrigerant. It is preferable because the film thickness controllability is excellent.

  From the viewpoint of the resin agglomerates in the separator or the maximum internal heat generation rate, in the sheet forming step, the mass ratio of the silane-grafted modified polyolefin and the ultrahigh molecular weight polyethylene (mass of silane graft modified polyolefin / mass of ultrahigh molecular weight polyethylene) is 0. It is preferably 05 / 0.95 to 0.40 / 0.60, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

Silane grafting is performed in the sheet forming step from the viewpoint of suppressing the thermal runaway at the time of destruction of the electricity storage device and improving safety while having a low temperature shutdown property of 150 ° C. or less and a film rupture resistance at a high temperature of 180 to 220 ° C. It is preferable that the modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst that crosslinks the silane-grafted modified polyolefin before the sheet molding step.
Further, when the silane-grafted modified polyolefin used in the sheet forming step is a masterbatch resin, by a washing and drying step described later, scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron. , The content of nickel or lead is preferably controlled within the range of 0.10 ppm or more and 200 ppm or less in terms of atomic total, and the content of zinc or tin is 0.10 ppm or more and 200 ppm or less in terms of total atomic conversion. More preferably, it is controlled within the range.

[Stretching process]
The stretching step is a step of extracting a plasticizer or an inorganic material from the obtained sheet, if necessary, and further stretching the sheet in a uniaxial or more direction. 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 roll stretching machine and a tenter, or a combination of a tenter and a tenter, simultaneous biaxial tenter or simultaneous biaxial stretching by inflation molding. Axial stretching and the like can be mentioned. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferable.
The total areal magnification is preferably 8 times or more, more preferably 15 times or more, and further preferably 20 times or more, from the viewpoint of uniformity of film thickness, balance of tensile elongation, porosity and average pore diameter. Or 30 times or more. When the total surface magnification is 8 times or more, it tends to be easy to obtain a product having high strength and good thickness distribution. Further, this surface magnification may be 250 times or less from the viewpoint of prevention of breakage and the like.

[Porous body forming step (extraction step)]
The porous body forming step is a step of extracting the plasticizer from the stretched material after the stretching step to make the stretched material porous.
The method of extracting the plasticizer is not particularly limited, and examples thereof include a method of immersing the stretched product in an extraction solvent and a method of showering the stretched product with the extraction solvent. The extraction solvent is not particularly limited, but is preferably a poor solvent for the polyolefin, a good solvent for the plasticizer or the inorganic material, and a boiling point lower than the melting point of the polyolefin. The extraction solvent is not particularly limited, but examples thereof include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane and fluorocarbons; ethanol and isopropanol. Alcohols; ketones such as acetone and 2-butanone; alkaline water. The extraction solvent may be used alone or in combination of two or more.

[Heat treatment step]
The heat treatment step is a step of obtaining a microporous membrane by further extracting the plasticizer from the sheet after the stretching step and further performing heat treatment after the stretching step.
The heat treatment method is not particularly limited, and examples thereof include a heat setting method of performing stretching and relaxation operations using a tenter or a roll stretching machine. The relaxation operation refers to a reduction operation performed in the machine direction (MD) and / or the width direction (TD) of the film at a predetermined temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation, or the value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the membrane before the operation, or MD and TD. When both are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate.
In the present embodiment, from the viewpoint of obtaining a heat-treated porous body suitable for the affinity treatment step and the crosslinking treatment step, it is preferable to perform stretching and relaxation on the TD of the porous body.

[Affinity treatment process]
The affinity treatment step is a step of immersing the microporous film obtained in the heat treatment step in an organic solvent having amphipathicity to water and an organic substance in order to improve wettability between water and the polyolefin. An amphipathic organic solvent is placed inside the affinity-treated porous body to increase the affinity with the liquid, and also with the material or catalyst that accelerates the crosslinking reaction during the crosslinking treatment step, for example. May increase.
The organic solvent used is not particularly limited, but examples thereof include alcohols, acetone, ethylene carbonate, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. Examples of the immersion method include a method of immersing the heat-treated porous body in an organic solvent and a method of showering the heat-treated porous body with the organic solvent.

[Crosslinking process]
The crosslinking treatment step is a step of reacting (crosslinking reaction) an alkoxysilyl group contained in the microporous membrane obtained in the affinity treatment step into a siloxane bond.
In the crosslinking treatment step, the affinity-treated porous body is brought into contact with a mixture of an organometallic catalyst and water or immersed in a base solution or an acid solution, and a silane dehydration condensation reaction is performed to form an oligosiloxane bond.
In general molded products such as hot water pipes, the Sn-based catalyst is charged into the extruder during the extrusion process, whereas in the manufacturing process of separators for electricity storage devices, silane crosslinking is promoted in the extruder during the sheet molding process. Then, the gelled portion causes production failure, and it becomes difficult to stretch the silane-crosslinked polyolefin in the stretching step which is a subsequent step. Therefore, it is preferable to perform a silane cross-linking treatment after the stretching step, the heat treatment step and the affinity treatment step to ensure the heat resistance, shape retention and film rupture resistance of the separator by the silane cross-linking portion.

The metal of the organometallic 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, zinc , Or palladium is preferable, and tin or zinc is more preferable. The organotin complex that can be used as a catalyst may be, for example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous caprylate and the like.
The base solution has a pH of more than 7, and may contain, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, 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 further preferable, from the viewpoints of safety of the electricity storage device and silane crosslinkability.
The acid solution has a pH of less than 7 and may include, for example, an inorganic acid, an organic acid and the like. 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 thermal runaway reaction when the electricity storage device is destroyed and improving safety.

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

  While not wishing to be bound by theory when immersing the affinity-treated porous body in an acid solution, the acid does not break the Si-O bond of the silane-crosslinked polyolefin, but rather the Si-of the silane-crosslinked polyolefin. It is speculated that it acts to catalytically promote the formation of O-bonds.

  When the affinity-treated porous body is contacted with the mixture of the organometallic catalyst and water, the final portion is controlled from the viewpoint of controlling the amorphous portion of the microporous membrane to ensure long-term cycle stability and safety. The content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the microporous film obtained in 1. is in the range of 0.10 ppm or more and 200 ppm or less in terms of atomic total amount. It is preferable to adjust so that the content of zinc or tin in the microporous membrane is in the range of 0.10 ppm or more and 200 ppm or less in terms of atomic total. The content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, or lead in the microporous film can be adjusted by, for example, a washing / drying step described later. It has been found that the metal content in such a limited range suppresses the decomposition of the crosslinked structure of the porous membrane, ensures safety, and at the same time exhibits good battery cycle characteristics. When an excessive amount of metal is contained in the electricity storage device separator, the eluted ions penetrate into the positive electrode and change the structure of the metal cluster that stores Li, resulting in electrical defects in the entire positive electrode and improving cycle performance. It was revealed by the present inventor that the aggravation was worse.

[Washing and drying process]
The washing and drying step is a step of washing and drying the microporous membrane obtained in the crosslinking treatment step. Preferable conditions for the water washing and drying step are a water temperature of 20 to 100 ° C. and / or a pH of the washing water of 6 to 8. For example, after the inside of the microporous membrane is replaced 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 it may be carried by a heating roll, blown with hot air, or heated and dried using an infrared heater.

[Winding process]
The winding step is a step of slitting the obtained microporous membrane as needed and winding it into a predetermined core.

  The separator obtained by the method including the various steps described above can be used for an electricity storage device, particularly for a lithium battery or a lithium ion secondary battery.

  Next, the present embodiment will be described more specifically with reference to examples and comparative examples, but the present embodiment is not limited to the following examples as long as the gist thereof is not exceeded. The physical properties in the examples were measured by the following methods.

(1) Weight average molecular weight Using ALC / GPC 150C type (trademark) manufactured by Waters, standard polystyrene was measured under the following conditions to prepare a calibration curve. Further, the chromatogram of each of the following polymers 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 GMH ₆ -HT (trademark) 2 + GMH ₆ -HTL (trademark) 2 Mobile phase: o-dichlorobenzene Detector: Differential refractometer Flow rate: 1.0 ml / min
Column temperature: 140 ℃
Sample concentration: 0.1wt%
(Weight average molecular weight of polyethylene)
The molecular weight distribution curve in terms of polyethylene was obtained by multiplying each molecular weight component in the obtained calibration curve by 0.43 (polyethylene Q factor / polystyrene Q factor = 17.7 / 41.3) It was calculated.
(Weight average molecular weight of resin composition)
The weight average molecular weight was calculated in the same manner as for polyethylene except that the Q factor value of the polyolefin having the largest mass fraction was used.

(2) Viscosity average molecular weight (Mv)
Based on ASTM-D4020, the intrinsic viscosity [η] at 135 ° C in the decalin solvent was determined. The Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67

(3) Melt mass flow rate (MFR) (g / 10min)
Using a melt mass flow rate measuring instrument (melt index F-F01) manufactured by Toyo Seiki, the weight of the resin extruded in 10 minutes under the conditions of 190 ° C. and a weight of 2.16 kg was determined as the MFR value.

(4) Film thickness (μm)
The film thickness of the microporous film was measured at a room temperature of 23 ± 2 ° C. and a relative humidity of 60% by using KBM (trademark), a micro thickness gauge manufactured by Toyo Seiki. Specifically, the film thickness at 5 points was measured at substantially equal intervals over the entire width in the TD direction, and the average value thereof was obtained.

(5) Porosity (%)
A 10 cm × 10 cm square sample was cut from the microporous membrane, its volume (cm ³ ) and mass (g) were determined, and the porosity was calculated from these and the density (g / cm ³ ) using the following formula. As the density of the mixed composition, a value calculated by calculating the density of each raw material used and the mixing ratio was used.
Porosity (%) = (volume−mass / density of mixed composition) / volume × 100

(6) Air permeability (sec / 100 cm ³ )
According to JIS P-8117 (2009), the air permeability of the sample was measured by G-B2 (trademark), a Gurley type air permeability meter manufactured by Toyo Seiki Co., Ltd.

(7) Quantification of Resin Aggregate in Separator The resin agglomerate in the separator is 100 μm in length when the separator obtained through the film forming steps of Examples and Comparative Examples described later is observed with a transmission optical microscope. It is defined as a region having a lateral area of 100 μm or more and not transmitting light. In observation with a transmission optical microscope, the number of resin aggregates per 1000 m ^{2 of} separator area was measured.

(8) Battery Breakage Safety Test The battery breakage safety test is a test in which an iron nail is driven into a battery charged to 4.5 V at a speed of 20 mm / sec and penetrated to cause an internal short circuit. In this test, the phenomenon 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 temperature rise behavior of the battery surface due to the internal short circuit. In addition, when the internal short circuit occurs, due to the insufficient shutdown function of the separator and the film rupture at low temperature, abrupt heat generation of the battery may occur. is there.

(Preparation of batteries used for battery destruction safety test)
a. Preparation of Positive Electrode Lithium cobalt composite oxide LiCoO ₂ as a positive electrode active material is 92.2% by mass, flaky graphite and acetylene black are respectively 2.3% by mass as conductive materials, and polyvinylidene fluoride (PVDF) as a binder. A slurry was prepared by dispersing 2% by mass in N-methylpyrrolidone (NMP). This slurry was applied on one surface of an aluminum foil having a thickness of 20 μm to be a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression-molded with a roll press. At this time, the amount of active material applied to the positive electrode was adjusted to 250 g / m ² , and the active material bulk density was adjusted to 3.00 g / cm ³ .

b. Production of Negative Electrode 96.9% by mass of artificial graphite as an anode active material, 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of styrene-butadiene copolymer latex as a binder were dispersed in purified water to form a slurry. Prepared. This slurry was applied on one surface of a copper foil having a thickness of 12 μm to be a negative electrode current collector by a die coater, dried at 120 ° C. for 3 minutes, and compression-molded by a roll press. At this time, the amount of active material applied to the negative electrode was adjusted to 106 g / m ² , and the active material bulk density was adjusted to 1.35 g / cm ³ .

c. Preparation of Non-Aqueous Electrolyte Solution LiPF ₆ was dissolved as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / L for preparation.

d. Battery assembly A separator is cut out in a width (TD) direction of 60 mm and a length (MD) direction of 1000 mm, and the separator is folded in 99 times, and the positive electrode and the negative electrode are alternately stacked between the separators (12 positive electrodes and 13 negative electrodes). . The positive electrode had an area of 30 mm × 50 mm, and the negative electrode had an area of 32 mm × 52 mm. After putting the 99-folded laminate in a laminating bag, the above c. The non-aqueous electrolytic solution obtained in (1) was injected and the vessel was sealed. After leaving it at room temperature for 1 day, charge it to a battery voltage of 4.2V at a current value of 3mA (0.5C) in an atmosphere of 25 ° C, and after reaching it, squeeze the current value from 3mA so as to maintain 4.2V. By the method of starting, the first charge after battery preparation was performed for a total of 6 hours. Subsequently, the battery was discharged to a battery voltage of 3.0 V with a current value of 3 mA (0.5 C).

(Maximum heat generation rate)
After piercing the obtained battery with an iron nail, the battery surface temperature was measured using a thermocouple over a temperature change graph of 300 seconds. It was defined as the heat generation rate.

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

(9) Cycle characteristics evaluation and battery manufacturing method thereof A. of battery manufacturing method used in the above item “(8) Battery breakdown safety test”. ~ C. Same procedure as above, but with the following d. A battery for cycle characteristic evaluation was produced by.
d. Battery Assembly A separator having a diameter of 18 mm and a positive electrode and a negative electrode having a diameter of 16 mm were cut out in a circular shape, and the positive electrode, the separator, and the negative electrode were stacked in this order so that the surfaces of the positive electrode and the negative electrode face each other, and they were housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. In the container, c. Of the above item “(8) Battery destruction safety test”. The nonaqueous electrolytic solution obtained in (3) was injected and sealed. After leaving it at room temperature for 1 day, charge it to a battery voltage of 4.2V at a current value of 3mA (0.5C) in an atmosphere of 25 ° C, and after reaching it, squeeze the current value from 3mA so as to maintain 4.2V. By the method of starting, the first charge after battery preparation was performed for a total of 6 hours. Subsequently, the battery was discharged to a battery voltage of 3.0 V with a current value of 3 mA (0.5 C).

  Charging / discharging of the obtained battery was performed 600 cycles in an atmosphere of 60 ° C. Charging is performed by charging the battery with a current value of 6.0 mA (1.0 C) to a battery voltage of 4.2 V, and then holding the battery voltage at 4.2 V and starting to squeeze the current value from 6.0 mA for a total of 3 hours. Charged The battery was discharged to a battery voltage of 3.0 V at a current value of 6.0 mA (1.0 C). The capacity retention rate was calculated from the discharge capacity at the 600th cycle and the discharge capacity at the first cycle. When the capacity retention rate was high, it was evaluated as having good cycle characteristics.

(10) TMA membrane rupture temperature After disassembling the battery used for 600 cycles in the above cycle test, only the separator (microporous membrane) was taken out, and a separator treated in the order of ethanol, acetone, and vacuum drying was used as a sample. Then, the TMA film rupture temperature of the separator is measured to evaluate the separator film rupture characteristics during long-term use. The environmental temperature is changed from 25 ° C. to 250 ° C. using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, and the temperature at the moment when the load is completely released is defined as the TMA film rupture temperature.
Specifically, when measuring the MD direction, a microporous film having a TD direction of 5 mm and an MD direction of 50 mm is sampled, and both ends in the MD direction are chucked with a dedicated probe, and the chuck distance is set to 30 mm and the initial 1.0 g. The temperature was raised by heating the furnace equipped with the test piece, and the temperature at which the load was 0 g was taken as the TMA film rupture temperature.
When measuring the TD direction, a microporous membrane having a TD direction of 50 mm and an MD direction of 5 mm is collected and the same operation as above is performed.

(11) Extrusion Stability The state of the extruded polyolefin composition was observed during the extrusion step and evaluated according to the following criteria.
◯ (Good): The fluctuation of the current value of the extruder is within ± 0.5 A at the average value of 300 seconds.
Poor (poor): The variation in the current value of the extruder exceeds ± 0.5 A at an average value of 300 seconds.

(12) Metal Content The mass ratio of Sn atom, Zn atom, Ti atom, Cu atom, Fe atom, Ni atom and the like contained in the sample was measured using an inductively coupled plasma (ICP) emission spectrometer.

[Manufacturing method of silane-grafted modified polyolefin]
The raw material polyolefin used for the silane-grafted modified polyolefin 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. It may be 150,000 or less, and may be propylene or butene copolymerized α-olefin. While melt-kneading the raw material polyethylene with an extruder, add organic peroxide (di-t-butyl peroxide) to generate radicals in the polymer chain of α-olefin, and then inject trimethoxyalkoxide-substituted vinylsilane. Then, an alkoxysilyl group is introduced into the α-olefin polymer by an addition reaction to form a silane graft structure. At the same time, in order to adjust the radical concentration in the system, an appropriate amount of antioxidant (pentaerythritol tetrakis [3- (3,5-di-tetra-butyl-4-hydroxyphenyl) propionate]) is added, and α-olefin is added. Suppress chain reaction (gelation) inside. The obtained silane-grafted polyolefin molten resin is cooled in water, pelletized, and then dried by heating at 80 ° C. for 2 days to remove water or unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellet is about 10 to 1500 ppm.
The silane-grafted modified polyethylene obtained by the above production method is shown as "silane-modified polyethylene (B)" in Tables 1 to 3.

[Example of film formation]
(Sheet molding process)
A homopolymer polyethylene having a weight average molecular weight of 2,000,000 (ultra high molecular weight polyethylene (A)) of 79.2% by mass, and a polyolefin having a viscosity average molecular weight of 20,000 as a raw material, and a modification reaction with a trimethoxyalkoxide-substituted vinylsilane. Silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR of 0.4 g / min obtained in 19.8% by mass (the resin compositions of (A) and (B) are 0.8 and 0.2, respectively) By adding 1 mass% of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant and dry blending using a tumbler blender, A mixture was obtained. The obtained mixture was fed to a twin-screw extruder under a nitrogen atmosphere by a feeder. Liquid paraffin (kinematic 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 the liquid paraffin are melt-kneaded in the extruder, and the feeder and the pump are adjusted so that the ratio of the amount of the liquid paraffin in the extruded polyolefin composition is 70% (that is, the polymer concentration is 30% by mass). Was adjusted. The melt-kneading conditions were a set temperature of 230 ° C., a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h.
Then, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25 ° C., and cast to obtain a gel sheet (sheet-shaped molded product) having an original film thickness of 1400 μm.
(Stretching process)
Next, the gel sheet was introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 6.0 times (that is, 7 × 6 times), and a biaxial stretching temperature of 125 ° C.
(Porous body forming step)
Next, the stretched gel sheet was introduced into a methylethylketone tank and sufficiently immersed in methylethylketone to extract and remove liquid paraffin, and then the methylethylketone was dried and removed to obtain a porous body.
(Heat treatment process)
Next, the porous body was introduced into a TD tenter to perform heat setting (HS), and HS was performed at a heat setting temperature of 125 ° C. and a draw ratio of 1.8 times, and then a relaxation operation of 0.5 times in the TD direction (ie, , HS relaxation rate was 0.5 times).
(Affinity processing step)
Further, the heat-treated porous body was introduced into an ethanol bath (affinity treatment tank) and dipped for 60 seconds to be retained, and the affinity treatment of the heat-treated porous body was performed to obtain an affinity-treated porous body.
(Crosslinking process)
Further, the affinity-treated porous body was introduced into a 25% caustic soda aqueous solution (cross-linking treatment tank) and allowed to stay for 60 seconds while being retained, and the affinity-treated porous body was cross-linked to obtain a cross-linked treated porous body.
(Washing and drying process)
Further, the crosslinked porous body was introduced into water (water washing treatment tank), dipped for 60 seconds and retained therein, and the crosslinked porous body was washed with water. This was introduced into a conveyor dryer and dried at 120 ° C. for 60 seconds to obtain a microporous membrane.
After that, the obtained microporous membrane was cut at its end and wound as a mother roll having a width of 1,100 mm and a length of 5,000 m.

[Examples 1 to 11, Comparative Examples 1 to 5]
As described in Tables 1 to 3, the same operations as those in the above-mentioned film forming examples were performed except that the amount ratio of the components A and B and the crosslinking method / conditions were changed to obtain the fine amounts shown in Tables 1 to 3. A porous film was obtained. Various evaluations were performed on the obtained microporous membrane according to the above evaluation methods, and the evaluation results are also shown in Tables 1 to 3.
For the separator obtained in Example 1, a TMA graph (Fig. 1), a heat generation graph (Fig. 2) and a voltage drop graph (Fig. 3) during a battery nail puncture safety test were prepared.

  The term "timing of crosslinking reaction" in Tables 1 to 3 means that the silane crosslinking reaction is (1) sheet forming step, (2) stretching step, (3) porous body forming step, (4) heat treatment, which are described above. It shows that it was performed in any one of the process, (5) affinity treatment process, (6) cross-linking treatment process, and (7) water washing and drying process.

  The term "resin composition" in Tables 1 to 3 indicates the ratio to the total amount of silane-grafted modified polyolefin and ultrahigh molecular weight polyethylene.

  The term “method” in Tables 1 to 3 indicates the method of the silane crosslinking reaction, and is classified into the method using alkali treatment, acid treatment, hot water treatment, or dehydration condensation catalyst.

The term "timing of crosslinking reaction" in Tables 1 to 3 means that the silane crosslinking reaction is (1) sheet forming step, (2) stretching step, (3) porous body forming step, (4) heat treatment, which are described above. It shows that it was performed in any one of the process, (5) affinity treatment process, (6) cross-linking treatment process, and (7) water washing and drying process.
In Example 4, a 10% hydrochloric acid solution was used instead of the 25% caustic soda aqueous solution, and in Comparative Example 2, 2.5 kg / m was used instead of dipping in the 25% caustic soda aqueous solution in the crosslinking treatment step in the film forming example. It was carried out using ² steam treatment tanks. Furthermore, in Comparative Examples 3 and 4, the crosslinking reaction was performed at the timings shown in Table 3, and the crosslinking treatment step was omitted.
In addition, in Example 11, the washing time was changed from 60 seconds to 10 minutes as compared with the above-mentioned production example, and the amount of metal ions was adjusted.

  The term "reagent" in Tables 1 to 3 indicates a reagent used in the crosslinking treatment step in the film forming example.

  The term "temperature" in Tables 1 to 3 indicates the temperature in the process described in the timing of the crosslinking reaction.

  The terms "pH of cross-linking treatment tank" and "pH of water-washing treatment tank" in Tables 1 to 3 indicate pH in each tank. For example, "7 to 12" means that the pH is near the tank entrance to near the exit. Indicates that the distribution is wide.

“Silane-modified polyethylene (B)” in Tables 1 to 3 is a silane-modified polyethylene having a density of 0.95 g / cm ³ and a melt flow rate (MFR) at 190 ° C. of 0.4 g / min. is there.

Claims (2)

  A separator for an electricity storage device including a microporous film containing a silane-grafted modified polyolefin and an ultra-high molecular weight polyolefin, wherein scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead is converted into atoms. A separator for an electricity storage device containing 0.10 ppm or more and 200 ppm or less in total.   A separator for an electricity storage device, which includes a microporous film containing a silane-grafted modified polyolefin and an ultra-high molecular weight polyolefin, and contains 0.10 ppm or more and 200 ppm or less in total of zinc or tin in terms of atoms.

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