JP7017345B2 - Separator for power storage device - Google Patents

Description

The present invention relates to a separator for a power storage device.

In recent years, the development of non-aqueous electrolyte batteries represented by lithium ion batteries has been actively carried out. Usually, a non-aqueous electrolyte battery is provided with a separator containing a microporous membrane between the positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the microporous.

It has been proposed to coat or place various polymers on the separator substrate in order to ensure the electrical characteristics and safety of the non-aqueous electrolyte battery and to give the separator various properties. (Patent Documents 1 and 2).

Patent Document 1 examines the safety of a battery using a separator having a breaking elongation of a certain value or more in the winding direction and the winding axis direction when the battery is crushed.
In Patent Document 2, for a battery having a sheet-shaped negative electrode collector containing copper as a main component and a sheet-shaped positive electrode current collector containing aluminum as a main component, the thickness of the positive electrode current collector is the negative electrode current collector. When the thickness is smaller than the thickness, the safety of the battery during the nail piercing test has been investigated.

Japanese Unexamined Patent Publication No. 2000-156216 Japanese Unexamined Patent Publication No. 2007-194203

Conventionally, in order to pass a collision test of a lithium ion battery including a separator in accordance with, for example, UL (Underwriters Laboratories Inc.) safety standard UL1642 and / or UL2054, the tensile strength in the width direction (TD direction) of the separator is relatively high. It tended to be low, causing the separator to break during a crash test and leak in a large short circuit area, leaving the battery in a safe state.
However, the lower the separator strength, the weaker the rigidity of the laminate composed of the separator and the electrode.

From the viewpoint of increasing the rigidity of the laminate, it is considered to apply a polymer to the separator base material. Further, the higher the temperature and the higher the pressure of the hot press of the separator base material, the higher the rigidity and the better.
However, the heat press permeability of the separator base material deteriorates as the pressing temperature and pressure increase. When the heat press air permeability deteriorates, the output characteristic, which is one of the battery performance characteristics, deteriorates.

Therefore, an object to be solved by the present invention is to provide a separator for a power storage device that can maintain the collision test safety of the power storage device using the separator and the output characteristics of the power storage device.

The present inventors have provided a cylindrical power storage device using a separator containing a porous membrane-containing substrate having a tensile strength within a specific range and a polymer present in at least one region of at least one surface of the substrate. In the crushing test, the present invention was completed by finding that the above problems can be solved when the stress is in a specific range.
That is, the present invention is as follows.
[1]
A substrate containing at least one porous membrane and
A separator for a power storage device comprising a polymer present in at least one region of at least one surface of the substrate.
The tensile strength of the base material in the width direction is 0.05 kgf / cm or more and less than 0.90 kgf / cm, and the crushing test is described in the following formula (A):
294.2N (30kgf) ≤ F _sep -F _base ≤980.7N (100kgf) ... (A)
{In the formula, F _sep is the maximum stress of the crushing test of the cylindrical power storage device using the separator for the power storage device and the electrode, and F _base is the maximum stress of the cylindrical power storage device using the base material and the electrode. Maximum stress in crush test}
Separator for power storage device that satisfies the relationship represented by.
[2]
The separator for a power storage device according to [1], wherein the press permeability increase rate of the separator is 15% or less.
[3]
The separator for a power storage device according to [1] or [2], wherein the polymer layer containing the polymer of the separator has a coating weight of 0.1 g / m ² or more and 1.0 g / m ² or less.
[4]
The separator for a power storage device according to any one of [1] to [3], wherein the polymer contains a fluororesin or an acrylic resin.
[5]
The separator for a power storage device according to [4], wherein the polymer contains the acrylic resin.
[6]
The separator for a power storage device according to any one of [1] to [5], wherein the polymer has a melting point and / or a glass transition temperature of 20 ° C. or higher.
[7]
The separator for a power storage device according to any one of [1] to [6] and the separator.
With the positive electrode
With the negative electrode
Laminated body consisting of.
[8]
A wound body in which the laminated body according to [7] is wound.
[9]
A power storage device containing the laminate according to [7] or the wound body according to [8] and an electrolytic solution.
[10]
The power storage device according to [9], wherein the positive electrode active material has a capacity density of 150 mAh / g or more.

According to the present invention, by adhering the polymer portion of the separator to the electrode, the electrode can be made to follow the operation of the separator in the collision test between the separator and the power storage device including the electrode, so that the electrode is easily broken. Safety can be ensured by suppressing heat generation or gas ejection of the device.

FIG. 1 is a photograph showing the appearance and a sample of a crushing test apparatus. FIG. 2 is a schematic diagram of a crash test (UL1642 and / or UL2054).

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

The separator for a power storage device (hereinafter referred to as "separator") according to the present embodiment includes a substrate containing at least one porous membrane and a polymer present in at least one region of at least one surface of the substrate. If desired, the separator may further include a porous layer containing an inorganic filler and a resin binder.

In the present embodiment, the separator has the following formula (A): for the crushing test.
294.2N (30kgf) ≤ F _sep -F _base ≤980.7N (100kgf) ... (A)
{In the formula, F _sep is the maximum stress of the crushing test of the cylindrical power storage device using the separator for the power storage device and the electrode, and F _base is the crushing test of the cylindrical power storage device using the base material and the electrode. Maximum stress}
Satisfy the relationship represented by.

In the formula (A), the value obtained by subtracting the F _base from the F _sep is the laminated winding body 1 obtained by laminating and winding the electrode and the separator, and the cylindrical power storage device 1 containing the electrolytic solution. And the cylindrical power storage device 2 in which the laminated winder 2 obtained by stacking the base material on the electrode instead of the separator and storing the electrolytic solution are subjected to the crushing test, respectively. It is the difference (hereinafter referred to as “stress difference”) of the maximum stress (N) between the type storage devices 1 and 2.

In the cylindrical power storage device 1 containing the laminated wound body 1 and the electrolytic solution, it is preferable to make the electrode follow the operation of the separator from the viewpoint of the safety of the device 1. For example, when a collision test of the cylindrical power storage device 1 is performed in accordance with the safety standards UL1642 and / or UL2054, if the electrode can follow the operation of the separator, the electrode is likely to break even with an impact to the extent that the separator does not break. , It is possible to suppress heat generation or gas generation of the device. From this point of view, it is possible to ensure the followability of the electrode with respect to the separator by bringing the polymer portion arranged on the separator into contact with the positive electrode active material or the negative electrode active material arranged on the electrode current collector. More preferred.

From the viewpoint of the rigidity of the laminated wound body 1 obtained by laminating and winding the electrode and the separator, it is preferable that the separator is firmly adhered to the electrode.

In the present embodiment, the structure of the separator capable of firmly adhering to the electrode and allowing the electrode to follow the operation of the separator is such that the stress difference satisfies the relationship represented by the formula (A), that is, the stress difference. Is specified by 294.2N (30kgf) or more and 980.7N (100kgf) or less.

For example, the type, thickness, texture, etc. of the polymer placed on the substrate can be selected, the polymer having high adhesive strength to the electrode active material and / or the substrate can be selected, and the adhesive or adhesive at the interface between the electrode and the separator can be selected. The stress difference can be adjusted in the range of 294.2N to 980.7N by arranging the polymer on the substrate so as to have an anchor effect. More specifically, the stress difference can be controlled by placing a suitable polymer, described below, in at least one region of at least one surface of the substrate.

From the viewpoint of the followability of the electrode to the separator and the rigidity of the laminated wound body 1, the lower limit of the stress difference is preferably 300 N or more, 350 N or more, or 400 N or more, and the upper limit of the stress difference is 900 N or less. It is preferably 850 N or less, 800 N or less, 750 N or less, or 700 N or less.

In F _sep in the formula (A), electrodes and separators are stacked and wound to form a laminated wound body 1, the laminated wound body 1 is put into a cylindrical outer body 1, and an electrolytic solution is applied to the cylindrical outer body 1. After pouring the electrolytic solution, the cylindrical exterior body 1 is heated and stored at 60 ° C. for 48 hours to stabilize the cylindrical exterior body 1 before measurement.
The winding is performed by applying a tension of 600 g to the positive electrode and the negative electrode in the direction opposite to the rotation direction of the winding shaft, and applying a tension of 250 g to the separator in the direction opposite to the rotation direction of the winding shaft.

In the F _base in the formula (A), the base material and the electrode are overlapped and wound to form the laminated wound body 2, the laminated wound body 2 is put into the cylindrical outer body 2, and the laminated winding body 2 is electrolyzed into the cylindrical outer body 2. The measurement is performed after pouring the liquid, and after pouring the electrolytic solution, the cylindrical exterior body 2 is heated and stored at 60 ° C. for 48 hours to stabilize the cylindrical exterior body 2.
The winding is performed by applying a tension of 600 g to the positive electrode and the negative electrode in the direction opposite to the rotation direction of the winding shaft, and applying a tension of 250 g to the separator in the direction opposite to the rotation direction of the winding shaft.

The electrodes used for the crushing test are a positive electrode having a composite oxide of nickel, manganese and cobalt as a positive electrode active material and a negative electrode having graphite powder as a negative electrode active material. The non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ in a mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2 so as to be 1 mol / L. It is a non-aqueous electrolyte.

The exterior body to be subjected to the crushing test is a stainless steel cylindrical battery case (exterior body) having dimensions of 18 mm in diameter and 65 mm in length.

In the present embodiment, from the viewpoint of ease of crushing test and reproducibility, the laminated wound bodies 1 and 2 are preferably formed under the same winding conditions, and the materials and dimensions of the cylindrical exterior bodies 1 and 2 are preferable. Is preferably the same, the cylindrical exterior bodies 1 and 2 preferably contain the same electrolyte, and the cylindrical power storage devices 1 and 2 are stabilized under the same heat set conditions. preferable.
Details of the crushing test will be described in Examples. It should be noted that in the present specification, it should be understood that the term "crush test" and the term "collision test" are used separately.

In the present embodiment, the tensile strength of the base material constituting the separator in the width (TD) direction is 0.05 kgf / cm or more and less than 0.90 kgf / cm, and 0.10 kgf / cm or more and 0 from the viewpoint of the collision test. It is preferably .80 kgf / cm or less. Collision test of power storage device The structure of the separator that can maintain the safety and output characteristics of the power storage device is the stress difference in the range of 294.2N to 980.7N in the crush test and 0.05kgf / cm or more and less than 0.9kgf / cm. It is specified by the tensile strength in the TD direction within the range of. The tensile strength is measured by the method described in Examples.

The separator according to this embodiment can be used for manufacturing a power storage device. Each configuration related to the separator will be described below.

[Polymer, polymer layer and adhesive layer]

A polymer is a single region of a porous membrane or at least one region of at least one surface of a porous membrane having a porous layer containing an inorganic filler and a resin binder on at least one surface (collectively referred to as a "base material"). Is placed in. The polymer placed on the substrate is preferably a thermoplastic polymer in order to adhere the separator to the electrode when applied to the electrode and to make the electrode follow the operation of the separator. As used herein, the term "thermoplastic polymer" includes a thermoplastic polymer usually used as a binder for adhering a separator and an electrode, or a polymer that develops adhesiveness by heating in an electrolytic solution. That is, the polymer layer can function as an adhesive layer between the electrode and the separator.
The layer containing the polymer (hereinafter referred to as "polymer layer") is formed on at least one side of the substrate. The polymer layer may be formed in at least a part of at least one side of the substrate.

(Thermoplastic polymer)
The thermoplastic polymer used in this embodiment is not particularly limited, but for example, the following:
Polyolefin resins such as polyethylene, polypropylene, α-polyolefin;
Fluororesin such as polyvinylidene fluoride, polytetrafluoroethylene, or copolymer containing these;
Diene-based polymers containing conjugated diene such as butadiene and isoprene as monomer units, copolymers containing these, and hydrides thereof;
Acrylic resin containing acrylic acid ester, methacrylic acid ester, etc. as a monomer unit, copolymers containing these, and hydrides thereof;
Rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate;
Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
Examples thereof include resins having a melting point and / or a glass transition temperature of 180 ° C. or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester: and mixtures thereof.

Among the thermoplastic polymers listed above, the diene polymer, the acrylic resin or the fluororesin is preferable because it is excellent in binding property, strength and flexibility to the electrode active material, and is preferably a separator base material and an electrode active material. In the crushing test of the power storage device including the separator and the electrode, acrylic resin or fluororesin is more preferable, and the temperature is relatively low, from the viewpoint of the followability of the electrode to the operation of the separator. Acrylic resins are particularly preferable from the viewpoint of exhibiting adhesion even when pressed in.

(Diene polymer)
The diene-based polymer is not particularly limited, but is a polymer containing a monomer unit obtained by polymerizing a conjugated diene monomer having two conjugated double bonds such as butadiene and isoprene.

The conjugated diene monomer is not particularly limited, but for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2 -Methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadien, 3-butyl-1,3-octadien and the like can be mentioned. These may be polymerized alone or copolymerized.

The ratio of the monomer units obtained by polymerizing the conjugated diene in the diene-based polymer is not particularly limited, but is preferably 40% by mass or more, more preferably 50% by mass, based on the mass of the total diene-based polymer, for example. Above, more preferably 60% by mass or more.

The diene-based polymer is not particularly limited, and examples thereof include homopolymers of conjugated diene such as polybutadiene and polyisoprene, and copolymers of conjugated diene and a copolymerizable monomer.

The monomer copolymerizable with the conjugated diene is not particularly limited, and examples thereof include the (meth) acrylate monomer described later and the following monomers (hereinafter, also referred to as “other monomers”).

(Other monomers)
The other monomers are not particularly limited, but are, for example, α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid and fumaric acid; styrene and chloro. Stylized monomers such as styrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl benzene; olefins such as ethylene and propylene. Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl biel ether; methyl vinyl ketone, Vinyl ketones such as ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; heterocyclic-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; acrylic acid esters such as methyl acrylate and methyl methacrylate and acrylic acid esters such as methyl methacrylate and / Or a methacrylic acid ester compound; a hydroxyalkyl group-containing compound such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; an amide-based monomer such as acrylamide, N-methylol acrylamide, and acrylamide-2-methylpropanesulfonic acid. ..
One of these may be used, or two or more thereof may be used in combination.

(Acrylic resin)
The acrylic resin is not particularly limited, but is preferably a polymer containing a monomer unit obtained by polymerizing a (meth) acrylate monomer.
In the present specification, "(meth) acrylic acid" means "acrylic acid or methacrylic acid", and "(meth) acrylate" means "acrylate or methacrylate".

The (meth) acrylate monomer is not particularly limited, and is, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t. -Butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate. Alkyl (meth) acrylates such as lauryl (meth) acrylates, n-tetradecyl (meth) acrylates and stearyl (meth) acrylates; hydroxyethyl (meth) acrylates, hydroxypropyl (meth) acrylates, hydroxybutyl (meth) acrylates and the like. Examples thereof include hydroxy group-containing (meth) acrylates; amino group-containing (meth) acrylates such as aminoethyl (meth) acrylates; and epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylates.

The ratio of the monomer units obtained by polymerizing the (meth) acrylate monomer is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60, based on the total mass of the acrylic resin. It is mass% or more.

Examples of the acrylic resin include a homopolymer of a (meth) acrylate monomer, or a copolymer of a (meth) acrylate monomer and a monomer copolymerizable with the (meth) acrylate monomer.

Examples of the monomer copolymerizable with the (meth) acrylate monomer include “other monomers” listed in the above item of diene polymer, and one or more of these may be used in combination.

(Fluororesin)
The fluororesin is not particularly limited, and examples thereof include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and a copolymerizable monomer. The fluororesin is preferable from the viewpoint of electrochemical stability.

The ratio of the monomer unit obtained by polymerizing vinylidene fluoride is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass, based on the total mass of the fluororesin. % Or more.

The monomer copolymerizable with vinylidene fluoride is not particularly limited, and for example, vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, etc. Fluorine-containing ethylenically unsaturated compounds such as fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexylvinyl ether and hydroxyethyl vinyl ether; fluorine-free diene compounds such as butadiene, isoprene and chloroprene. Can be mentioned.

Among the fluororesins, a homopolymer of vinylidene fluoride, a vinylidene fluoride / tetrafluoroethylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer and the like are preferable. More preferred fluoropolymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, the monomer composition of which is usually 30-90% by weight of vinylidene fluoride, 50-9% by weight of tetrafluoroethylene, and hexafluoro. 20 to 1% by mass of propylene.

The fluororesin may be in the form of particles. In that case, the fluororesin particles may be used alone or in combination of two or more.

(Synthesis of thermoplastic polymer)
As the monomer used in synthesizing the thermoplastic polymer, a monomer having at least one group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group and a cyano group may be used. good.

The monomer having a hydroxyl group is not particularly limited, and examples thereof include vinyl-based monomers such as pentenol.

The monomer having a carboxyl group is not particularly limited, and examples thereof include unsaturated carboxylic acids having an ethylenic double bond such as (meth) acrylic acid and itaconic acid, and vinyl-based monomers such as pentenic acid.

The monomer having an amino group is not particularly limited, and examples thereof include 2-aminoethyl methacrylate and the like.

The monomer having a sulfonic acid group is not particularly limited, but for example, vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) Alice sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-sulfonic acid ethyl, 2-. Examples thereof include acrylamide-2-methylpropanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.

The monomer having an amide group is not particularly limited, and examples thereof include acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

The monomer having a cyano group is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

The thermoplastic polymer used in the present embodiment may be used alone or in combination of two or more kinds, but it is preferable to contain two or more kinds of polymers.

(Melting point of thermoplastic polymer)
Regarding the thermal properties of the thermoplastic polymer used in this embodiment, the melting point of at least one polymer is 20 ° C. or higher from the viewpoint of the followability of the electrode to the separator in the power storage device crushing test and the adhesiveness between the separator and the electrode. It is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and particularly preferably 40 ° C. or higher. As used herein, the melting point of a polymer refers to the temperature (° C.) corresponding to the heat absorption peak associated with melting of the crystalline polymer in the DSC curve obtained by differential scanning calorimetry (DSC) of the polymer.

(Glass transition point of thermoplastic polymer)
The glass transition temperature of the thermoplastic polymer used in the present embodiment is not particularly limited, but is -50 ° C or higher, preferably 20 ° C or higher, more preferably 20 ° C to 120 ° C, still more preferably 20 ° C. It is ~ 100 ° C. When the Tg of the thermoplastic polymer is 20 ° C. or higher, the outermost surface of the separator provided with the polymer layer can be suppressed from stickiness, and the handleability tends to be improved. Further, when the Tg is 120 ° C. or lower, the adhesiveness of the separator to the electrode (electrode active material) tends to be better, and when the Tg is 20 ° C. or lower, the drying before impregnation with the electrolytic solution is performed. It is good because it develops adhesiveness even in the state.
Here, the glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may be expressed as "Tg".

Specifically, Tg is determined by the intersection of a straight line extending the baseline on the low temperature side of the DSC curve to the high temperature side and a tangent line at the inflection point of the stepwise change portion of the glass transition. More specifically, the methods described in the examples can be referred to.

Here, "glass transition" refers to a DSC in which a change in calorific value accompanying a change in the state of a polymer, which is a test piece, occurs on the endothermic side. Such a calorific value change is observed in the DSC curve as a stepped change shape or a shape in which a stepped change and a peak are combined.

"Stepped change" refers to the portion of the DSC curve from the previous baseline to the transition to a new baseline. It should be noted that the step-like change also includes a shape in which a peak and a step-like change are combined.

The "inflection point" indicates a point where the gradient of the DSC curve of the stepped change portion is maximized. It can also be expressed as a point where an upwardly convex curve changes to a downwardly convex curve in the stepped change portion.

The “peak” refers to the portion of the DSC curve from when the curve leaves the baseline until it returns to the baseline again.

"Baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs on the test piece.

In the present embodiment, at least one of the glass transition temperatures of the thermoplastic polymer used is in the range of −50 ° C. to 100 ° C., so that the stress difference described above is 294.2N to 980.7N. It becomes easier to control within the range.

In the present embodiment, the glass transition temperature (Tg) of the thermoplastic polymer can be appropriately adjusted by, for example, changing the monomer component used for producing the thermoplastic polymer and the input ratio of each monomer. That is, for each monomer used in the production of thermoplastic polymers, the Tg generally indicated for the corresponding homopolymer (eg, the Tg described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and each monomer. The Tg of the thermoplastic polymer can be roughly estimated from the blending ratio.

For example, a copolymer containing a high proportion of monomers such as styrene, methylmethacrylate, and acrylonitrile that give a polymer of Tg at about 100 ° C. can have a high Tg. For example, copolymers containing high proportions of monomers such as butadiene, which gives a polymer of Tg at about -80 ° C, n-butylacryllate and 2-ethylhexylacrylate, which give a polymer of Tg at about -50 ° C, are low. Can have Tg.

Further, in general, the Tg of the polymer is the FOX formula (the following formula (2)):
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + Wi _i / Tg _i + ... W _n / Tg _n (2)
{In the formula, Tg (K) is the glass transition temperature (Tg) of the copolymer, Tg _i (K) is the Tg of the homopolymer of each monomer _i , and Wi is the mass fraction of each monomer. Is}
It can also be estimated more. However, since the Tg obtained by the FOX formula is only an approximate value, in the present specification, unless otherwise specified, the Tg measured by the method using the above DSC is adopted as the Tg of the thermoplastic polymer.

When the polymer layer present on the substrate has at least two glass transition temperatures, it is preferable that at least one of the glass transition temperatures is present in the region of −50 ° C. to 20 ° C. As a result, the polymer layer has further excellent adhesiveness to the substrate, and as a result, the separator has excellent adhesion to the electrode, and also has the effect of exhibiting adhesiveness even in a dry state before impregnation with the electrolytic solution.

When the polymer layer present on the substrate has at least two glass transition temperatures, it is preferable that at least one of the glass transition temperatures is present in a region above 20 ° C. This has the effect of further improving the adhesiveness and handleability between the separator and the electrode. Further, in a crushing test of a power storage device including a separator and an electrode, it is preferable from the viewpoint of the followability of the electrode to the separator.

The thermoplastic polymer having at least two glass transition temperatures is not limited, but can be achieved by, for example, a polymer blending method in which two or more kinds of thermoplastic polymers are blended. In the polymer blending method, by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature, the glass transition temperature of the entire thermoplastic polymer can be controlled, and a plurality of functions can be imparted to the entire thermoplastic polymer.

In the case of the polymer blend method, the anchor effect of the polymer layer is obtained by blending two or more types of a polymer existing in a region where the glass transition temperature exceeds 20 ° C and a polymer existing in a region where the glass transition temperature is 20 ° C or less. , It is possible to achieve both the followability of the electrode to the operation of the separator, the stickiness resistance, and the applicability to the substrate. In the case of the polymer blend method, as the mixing ratio of a plurality of polymers, the ratio of the polymer existing in the region where the glass transition temperature exceeds 20 ° C. to the polymer existing in the region where the glass transition temperature is 20 ° C. or lower is 0.1. : 99.9 to 99.9: 0.1 is preferable, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably. It is from 60:40 to 90:10.

From the viewpoint of the followability of the electrode to the separator and the adhesion between the separator and the electrode, at least one polymer present on the substrate is from the viewpoint of the followability of the electrode to the separator in the crushing test of the energy storage device including the separator and the electrode. Therefore, it is preferable to have a melting point of 20 ° C. or higher or a glass transition temperature of 20 ° C. or higher, and more preferably to have both a melting point of 20 ° C. or higher and a glass transition temperature of 20 ° C. or higher.

(Forms of Granular Thermoplastic Polymers and Polymer Layers)
The thermoplastic polymer may be granular and, more particularly, particles consisting of one type of thermoplastic polymer or a mixture of a plurality of thermoplastic polymers, or may have the core-shell structure described above.
When the thermoplastic polymer is granular, "granular" refers to the contoured state of the individual polymers as measured by a scanning electron microscope (SEM). Therefore, the granular thermoplastic polymer may have, for example, a flat shape, a spherical shape, a polygonal shape, or the like.

In order to secure the adhesiveness and rigidity of the thermoplastic polymer and further improve the output of the power storage device, the area ratio of the surface of the substrate coated with the polymer after impregnating the separator with the electrolytic solution is 5% or more. It is preferably 10% or more, 15% or more, or 20% or more. This area ratio is measured by observing the outermost surface of the base material with an SEM (magnification of 30,000 times).

The coating weight of the polymer layer is preferably 0.1 g / m ² or more and 1.0 g / m ² or less, and more preferably 0.3 g / m ² or more and 0.8 g / m ² or less. When the coating weight of the polymer layer is 0.1 g / m ² or more, the adhesiveness of the polymer layer is ensured, thereby improving the rigidity of the laminate composed of the separator and the electrode. When the basis weight is 1.0 g / m ² or less, the ion permeability of the separator is ensured, thereby improving the cycle characteristics of the power storage device.

In the present embodiment, the polymer may be present on the entire surface of the base material, or may be present on the base material in a pattern such as a dot shape, a grid pattern, a linear shape, a striped shape, or a hexagonal pattern. May be good.

(Polymer coating method)
One aspect of the method for producing a separator includes a step of applying a coating liquid containing the polymer described above onto a substrate.
The method for applying the coating liquid to the polyolefin microporous film or the multilayer microporous film is not particularly limited, and for example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, and the like. Examples thereof include a dip coater method, a knife coater method, an air doctor coater method, a blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method, and an inkjet coating method. Among these, the gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom in the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

When a thermoplastic polymer is applied to a base material containing a porous membrane, if the coating liquid penetrates into the inside of the base material, the adhesive resin fills the surface and inside of the pores and the permeability decreases. It ends up. Therefore, as the medium of the coating liquid, a poor solvent of a thermoplastic polymer is preferable. When a poor solvent of a thermoplastic polymer is used as the medium of the coating liquid, the coating liquid does not enter the inside of the porous membrane, and the adhesive polymer is mainly present on the surface of the multilayer microporous membrane, so that it permeates. It is preferable from the viewpoint of suppressing deterioration of sex. Water is preferred as such a medium. The medium that can be used in combination with water is not particularly limited, and examples thereof include ethanol and methanol.

It is preferable to apply a surface treatment to the base material before coating because the coating liquid can be easily applied and the adhesiveness between the base material and the adhesive polymer is improved. The surface treatment method is not particularly limited as long as the porous structure of the multilayer microporous membrane is not significantly impaired. For example, a corona discharge treatment method, a plasma treatment method, a mechanical roughening method, a solvent treatment method, and an acid treatment method. , Ultraviolet oxidation method and the like.

The method for removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the polyolefin microporous film or the multilayer microporous film. For example, a method of fixing a polyolefin microporous film or a multilayer microporous film and drying it at a temperature below its melting point, a method of drying under reduced pressure at a low temperature, or a method of immersing the adhesive polymer in a poor solvent to solidify the adhesive polymer. At the same time, a method of extracting the solvent or the like may be used.

[Base material]
In this embodiment, the substrate comprises at least one porous membrane and the polymer is placed in at least one region of at least one surface.
The porous membrane preferably has low electron conductivity, ionic conductivity, high resistance to an organic solvent, and a fine pore size.

Examples of such a porous film include a porous film containing a polyolefin resin, a resin such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene. Examples thereof include a porous film containing the above, a woven fabric of a polyolefin-based fiber (woven cloth), a non-woven fabric of the polyolefin-based fiber, paper, and an aggregate of insulating substance particles. Among these, when a multilayer porous film, that is, a separator for a power storage device is obtained through a coating process, the coating property of the coating liquid is excellent, the film thickness of the separator is made thinner, and the activity in the power storage device such as a battery is used. From the viewpoint of increasing the material ratio and increasing the capacity per volume, a porous membrane containing a polyolefin resin (hereinafter, also referred to as “polyolefin resin porous membrane” or “polyolefin microporous membrane”) is preferable.

The polyolefin resin porous membrane will be described.
The polyolefin resin porous film is formed of a polyolefin resin composition in which the polyolefin resin accounts for 50% by mass or more and 100% by mass or less of the resin component constituting the porous film from the viewpoint of improving the shutdown performance when used as a separator for a power storage device. It is preferably a porous membrane to be formed. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

As the polyolefin resin contained in the polyolefin resin composition, for example, a homopolymer obtained by using ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like as monomers. , Copolymer, multi-stage polymer and the like. Further, these polyolefin resins may be used alone or in combination of two or more.

In the present embodiment, the microporous polyolefin membrane comprises one or more polyethylenes, i.e., one or more types of polyethylene, from the viewpoint of the shutdown characteristics of the separator and the battery safety and battery characteristics.
If desired, from the viewpoint of the shutdown property of the separator for a power storage device, the polyolefin microporous membrane may contain polypropylene, a copolymer of propylene and other monomers, and a mixture thereof, in addition to polyethylene.

Specific examples of polyethylene include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, and the like.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, and the like.
Specific examples of the copolymer include ethylene-propylene random copolymer, ethylene propylene rubber and the like.
In the present specification, the high-density polyethylene means polyethylene having a density of 0.942 to 0.970 g / cm ³ . The density of the high-density polyethylene is preferably 0.960 to 0.969 (g / cm ³ ) or 0.950 to 0.958 (g / cm ³ ) from the viewpoint of the strength of the porous film. In the present specification, the density of polyethylene means a value measured according to JIS K7112 (1999).

The polyolefin resin composition may contain any additive. Examples of the additive include polymers other than polyolefin resins; inorganic fillers; antioxidants such as phenols, phosphorus and sulfur; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers. ; Antistatic agent; Antifogging agent; Colored pigment and the like.

Since the porous membrane has a porous structure in which a large number of very small pores are gathered to form a dense communication hole, the porous membrane has excellent ionic conductivity and at the same time has good withstand voltage characteristics and high strength. It has the feature.
The porous membrane may be a single-layer membrane made of the above-mentioned material or a laminated membrane.

As a method for producing the porous film contained in the base material, a known production method can be adopted. Generally, the porous film is formed by forming a resin film by melt extrusion of the resin composition, subsequent stretching, or the like, and making the resin film porous. The porosity of the resin film is roughly classified into a dry method and a wet method. As used herein, the "dry method" refers to a stretching and opening method that does not use a solvent. By using the dry method, the pore diameter obtained is relatively small, and it tends to be easy to form a direct hole structure. The "wet method" refers to a stretching and opening method using a solvent.

As a dry method, an unstretched sheet containing incompatible particles such as inorganic particles and polyolefin is subjected to stretching and extraction to peel off the interface between different materials to form pores, a lamella opening method, and β crystal opening. There are laws, etc.

In the lamellar perforation method, an unstretched sheet having a crystalline lamellar structure is obtained by controlling the melt crystallization conditions at the time of sheet formation by melt extrusion of a resin, and the obtained unstretched sheet is stretched to cleave the lamella interface. It is a method of forming a hole.

In the β-crystal opening method, an unstretched sheet having β-crystals having a relatively low crystal density is produced during melt extrusion of polypropylene (PP), and the produced unstretched sheet is stretched to form an α having a relatively high crystal density. This is a method of transferring crystals to crystals and forming pores by the difference in crystal density between the two.

As a wet method, a pore-forming material (extract) such as a plasticizer is added to polyolefin, dispersed, and sheeted, and then the extract is extracted with a solvent to form pores, if necessary. There is a method of performing stretching before and / or after extraction.

From the viewpoint of improving the rigidity of the base material and maintaining the output characteristics of the power storage device including the separator, the porosity of the resin film is preferably carried out by a dry method, more preferably by a dry lamella opening method.

As an example, a method for producing a laminated microporous film including a microporous film porousd by a dry porous method will be described below.
[Manufacturing method of laminated microporous film]
The method for producing the laminated microporous film of this embodiment is described in the following steps:
A first resin film composed of a first resin composition having a melting point TmA and a second resin film composed of a second resin composition having a melting point TmB lower than the melting point TmA are laminated. A film forming step of forming a laminated film containing polyolefin,
A pore-opening step of opening the film by a dry method to form a microporous film, and
In this order.
The film forming step, the pore opening step, and other preferable steps will be described below.

[Film forming process]
The film forming step is a second resin composed of a first resin film having a melting point TmA and a second resin composition having a melting point TmB lower than the melting point TmA. This is a step of forming a laminated film containing polyolefin, which is laminated with a film.

As a method for forming the laminated film, a method (a); in which a laminated film in which each resin film is laminated is formed by an extrusion method using a T die or a circular die, and then the laminated film is stretched to be porous. A method in which each resin film is separately extruded using a circular die or a circular die, and then each resin film is laminated by a laminating method to form a laminated film, and then the laminated film is stretched to make it porous (a method). b); A method in which each resin film is separately extruded using a T-die or a circular die and further stretched to obtain a microporous film, and then the microporous films are bonded together (a method). c) can be mentioned.

Among these, in the method for producing a laminated microporous film of the present embodiment, the method (a) is preferable from the viewpoint of the physical characteristics required for the obtained laminated microporous film and the initial / running cost. On the other hand, although the air permeability is slightly inferior to that of the method (a), the method (c) is also preferable from the viewpoint of reducing the heat shrinkage rate of the laminated microporous film.
In the present specification, the term "resin film" refers to a resin composition formed into a film, and a microporous film can be obtained by stretching and making the resin composition porous.

In any of the production methods (a) to (c), the draw ratio after extrusion (film winding speed (unit is m / min)) / extrusion speed of the resin composition (molten resin passing through the die lip). The linear velocity in the flow direction, and the unit is m / min)) is preferably 10 to 500, more preferably 100 to 400, and further preferably 150 to 350.
The winding speed of the film is preferably 2.0 to 400 m / min, more preferably 10 to 200 m / min.

[Annealing process]
The method for producing a laminated microporous film of the present embodiment preferably includes an annealing step of subjecting the obtained laminated film to heat treatment (annealing). As a method of annealing, for example, a method of contacting a laminated film on a heating roll; a method of exposing the laminated film into a heated gas phase; a method of winding a laminated film on a core body and exposing it to a heated gas phase or a heated liquid phase. ; And a method of combining these can be mentioned. The conditions for these heat treatments are appropriately determined depending on the type of material constituting the film and the like.

The heating temperature when annealing the laminated film is preferably (TmB-30) ° C. or higher (TmB-2) ° C., more preferably (TmB-2) ° C. or lower, from the viewpoint of the balance between porosity, air permeability and heat shrinkage. TmB-15) ° C or higher (TmB-2) ° C or lower. The heating time is preferably 10 seconds to 100 hours, more preferably 1 minute to 10 hours.

[Opening process]
The pore-opening step is a step of opening a laminated film by a dry method to form a microporous film.
The opening step is not particularly limited, but is a cold stretching step of cold stretching the laminated film at least 1.05 times to 2.0 times in one direction and 1.05 times to 5.0 times the laminated film in at least one direction. It is preferable to have a heat stretching step of doubling the heat stretching. Either the cold stretching step or the hot stretching step may be performed first, but it is preferable to perform the cold stretching step and then the hot stretching step. The air permeability of the laminated microporous film thus obtained tends to be further improved.

When a laminated film in which a first microporous film and a second microporous film are laminated in advance as in the methods (a) and (b) above is formed, the first is the laminated film. It is preferable to include a cold stretching step of applying the stretching of 1 to obtain a stretched laminated film. Further, when the second microporous film and the first microporous film are separately porousd and then laminated as in the method (c) above, the first is applied to each film. It is preferable to include a cold stretching step of performing stretching to obtain a stretched laminated film.

(Cold stretching process)
When the laminated film is cold-stretched, it is preferably −20 ° C. or higher (TmB-60) ° C., more preferably 0 ° C. or higher and 50 ° C. or lower. When the stretching temperature of cold stretching is −20 ° C. or higher, there is a tendency that fracture can be further suppressed. Further, when the stretching temperature of cold stretching is (TmB-60) ° C. or lower, the porosity and the air permeability tend to be further improved. Here, the stretching temperature of cold stretching means the surface temperature of the film in the cold stretching step. The surface temperature of the film can be measured with a contact thermometer.

The stretching ratio in the cold stretching step is preferably 1.05 to 2.0 times, more preferably 1.1 to 2.0 times. The cold stretching is performed in at least one direction, but may be performed in both the extrusion direction of the film (hereinafter referred to as “MD direction”) and the width direction of the film (hereinafter referred to as “TD direction”). Preferably, uniaxial stretching is performed only in the extrusion direction of the film.

(Heat stretching process)
When heat stretching is applied to the laminated film, the stretching temperature in the heat stretching step is preferably (TmB-60) ° C. or higher (TmB-2.0) ° C., more preferably (TmB-30) ° C. or higher. It is (TmB-2.0) ° C. or lower. When the stretching temperature of the thermal stretching is (TmB-60) ° C. or higher, the fracture tends to be further suppressed. Further, when the stretching temperature of the thermal stretching is (TmB-2.0) ° C. or lower, the porosity and the air permeability tend to be further improved. Here, the stretching temperature in the thermal stretching step means the surface temperature of the film.

The stretching ratio in the heat stretching step is preferably 1.05 to 5.0 times, more preferably 1.1 to 5.0 times, and further preferably 2.0 to 5.0 times. be. The heat stretching may be performed in at least one direction and may be performed in both the MD and TD directions, but it is preferably performed in the same direction as the stretching direction of the cold stretching, and more preferably only in the same direction as the stretching direction of the cold stretching. It is to perform uniaxial stretching.

[Heat fixing process]
The method for producing a laminated microporous film of the present embodiment preferably includes a heat fixing step of heat-fixing the microporous film after the pore opening step. By performing the heat fixing step, it is possible to suppress the shrinkage of the laminated microporous film in the stretching direction due to the residual stress acting during the stretching of the pore opening step, and the delamination strength of the obtained laminated microporous film tends to be further improved. ..
The heat fixing method is not particularly limited, but for example, a method of heat shrinking to such an extent that the length of the laminated microporous film after heat fixing is reduced by 3 to 50% (hereinafter, this method is referred to as "relaxation"). Examples thereof include a method of fixing the dimensions in the stretching direction so that the dimensions do not change.
When heat-fixing the microporous membrane, the heat-fixing temperature is preferably (TmB-30) ° C. or higher (TmB-2) ° C., more preferably (TmB-15) ° C. or higher (TmB-2). ) ℃ or less. Here, the heat fixing temperature means the surface temperature of the film.

In the above-mentioned cold stretching step, hot stretching step, other stretching step, and heat fixing step, stretching is performed in one step or two or more steps in one step or two steps or more in the uniaxial direction and / or the biaxial direction by a roll, a tenter, an autograph, or the like. , A method of heat fixing can be adopted. Among these, from the viewpoint of physical properties and applications required for the laminated microporous film obtained in the present embodiment, it is preferable to perform uniaxial stretching and heat fixing in two or more stages by a roll.

[Filler porous layer]
The filler porous layer contains an inorganic filler and a resin binder.
(Inorganic filler)
The inorganic filler used for the filler porous layer is not particularly limited, but preferably has a melting point of 200 ° C. or higher, has high electrical insulation, and is electrochemically stable within the range of use of the lithium ion secondary battery. ..
The inorganic filler is not particularly limited, and is, for example, oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, ittoria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride. Ceramics; Silicon Carbide, Calcium Carbonate, Magnesium Sulfate, Aluminum Sulfate, Aluminum Hydroxide, Aluminum Hydroxide, Potassium Titanium, Tarku, Kaolinite, Decite, Nacronite, Halloysite, Pyrophyllite, Montmorillonite, Sericite, Mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, kaolin, and silica sand; glass fibers and the like can be mentioned. These may be used alone or in combination of two or more.

Among these, from the viewpoint of improving electrochemical stability and heat resistance of the separator,
Aluminum oxide compounds such as alumina and aluminum hydroxide; and aluminum silicate compounds having no ion exchange ability such as kaolinite, dekite, naphthite, halloysite, and pyrophyllite are preferable.

As the aluminum oxide compound, aluminum hydroxide oxide (AlO (OH)) is particularly preferable. As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin minerals is more preferable because it is inexpensive and easily available. As kaolin, wet kaolin and calcined kaolin formed by calcining the wet kaolin are known. In the present invention, calcined kaolin is particularly preferable. Calcined kaolin is particularly preferable in terms of electrochemical stability because water of crystallization is released during the calcining treatment and impurities are also removed.

The average particle size of the inorganic filler is preferably more than 0.01 μm and 4.0 μm or less, more preferably more than 0.2 μm and 3.5 μm or less, and more than 0.4 μm and 3.0 μm. The following is more preferable. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of suppressing heat shrinkage at high temperatures even when the thickness of the porous filler layer is thin (for example, 7 μm or less). Examples of the method for adjusting the particle size and the distribution of the inorganic filler include a method of pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, a bead mill, and a jet mill to reduce the particle size. ..

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape. A plurality of types of inorganic fillers having these shapes may be used in combination.

The ratio of the inorganic filler in the porous filler layer can be appropriately determined from the viewpoints of the binding property of the inorganic filler, the permeability of the separator, the heat resistance, and the like. The ratio of the inorganic filler in the filler porous layer is preferably 20% by mass or more and less than 100% by mass, more preferably 50% by mass or more and 99.99% by mass or less, and further preferably 80% by mass or more and 99.9% by mass. % Or less, particularly preferably 90% by mass or more and 99% by mass or less.

(Resin binder)
The type of resin binder contained in the filler porous layer is not particularly limited, but is insoluble in the electrolytic solution of the lithium ion secondary battery and is electrochemically stable in the range of use of the lithium ion secondary battery. It is preferable to use a resin binder.
Specific examples of such a resin binder include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene. -Fluorine-containing rubber such as tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid. Ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, rubbers such as polyvinyl acetate; ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxy Cellulous derivatives such as methyl cellulose; resins having a melting point and / or a glass transition temperature of 180 ° C. or higher, such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester and the like, can be mentioned.

In order to reduce the ionic resistance of the porous filler layer, it is also preferable to include a polyalkylene glycol group-containing thermoplastic polymer described later in the porous filler layer as a resin binder.

As the resin binder, it is preferable to use a resin latex binder. When a resin latex binder is used as the resin binder, the separator provided with the filler porous layer containing the binder and the inorganic filler binds the resin binder onto the porous film through the step of applying the resin binder solution onto the substrate. Compared with the separated separator, the ion permeability is less likely to decrease, and there is a tendency to provide a power storage device having high output characteristics. Further, the power storage device having the separator exhibits smooth shutdown characteristics even when the temperature rises rapidly at the time of abnormal heat generation, and tends to easily obtain high safety.

The resin latex binder is obtained by copolymerizing an aliphatic conjugated diene-based monomer, an unsaturated carboxylic acid monomer, and other monomers copolymerizable with the aliphatic conjugated diene-based monomer and the unsaturated carboxylic acid monomer from the viewpoint of improving electrochemical stability and binding property. Is preferred. The polymerization method in this case is not particularly limited, but emulsion polymerization is preferable. The method of emulsion polymerization is not particularly limited, and a known method can be used. The method for adding the monomer and other components is not particularly limited, and any of a batch addition method, a split addition method, and a continuous addition method can be adopted, and the polymerization method is one-stage polymerization or two-stage polymerization. , Or any of three or more stages of multi-step polymerization can be adopted.

The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and even more preferably 80 to 250 nm. When the average particle size of the resin binder is 50 nm or more, the separator provided with the filler porous layer containing the binder and the inorganic filler does not easily reduce the ion permeability and easily gives a storage device having high output characteristics. Further, even when the temperature rises rapidly at the time of abnormal heat generation, it is easy to obtain a power storage device showing smooth shutdown characteristics and having high safety. When the average particle size of the resin binder is 500 nm or less, good binding property is exhibited, and when a multilayer porous film is used, heat shrinkage is good, and the safety tends to be excellent.
The average particle size of the resin binder can be controlled by adjusting the polymerization time, the polymerization temperature, the raw material composition ratio, the raw material charging order, the pH, and the like.

The thickness of the porous filler layer is preferably 0.5 μm or more from the viewpoint of improving heat resistance and insulation, and preferably 50 μm or less from the viewpoint of improving the capacity and permeability of the battery. It is more preferably 10 μm or less, and further preferably 5 μm or less.
The layer density of the filler porous layer is preferably 0.5 to 3.0 g / cm ³ , and more preferably 0.7 to 2.0 cm ³ . When the layer density of the filler porous layer is 0.5 g / cm ³ or more, the heat shrinkage rate at high temperature tends to be good, and when it is 3.0 g / cm ³ or less, the air permeability tends to decrease. It is in.

As a method for forming the porous filler layer, for example, a method of applying a coating liquid containing an inorganic filler and a resin binder to at least one surface of the base material can be mentioned. The coating liquid in this case may contain a solvent, a dispersant and the like in order to improve the dispersion stability and the coatability.
The method of applying the coating liquid to the base material is not particularly limited as long as the required layer thickness and coating area can be realized. The filler raw material containing the resin binder and the polymer base material raw material may be laminated and extruded by a coextrusion method, or the base material and the filler porous membrane may be individually prepared and then bonded.

[Separator for power storage device]
By providing the polymer layer on the substrate, the separator according to the present embodiment has excellent adhesiveness to the electrode active material, and the electrode is made to follow the operation of the separator.
The thickness of the separator is preferably 2 μm or more, more preferably 3 μm or more, and preferably 100 μm or less, preferably 50 μm, from the viewpoint of ensuring the safety of the power storage device and the turnability of the separator. The following is more preferable, and 30 μm or less is further preferable. When the polymer is present on the separator substrate, the thickness obtained by measuring the separator portion in which the polymer is present is the thickness of the separator. When the polymer and the porous filler layer are present on the separator substrate, the thickness obtained by measuring the separator portion in which both the polymer and the porous filler layer are present is the thickness of the separator.

The press air permeability increase rate of the separator is preferably 15% or less, more preferably 10% or less, still more preferably 5% or less, still more preferably 3%. A press air permeability increase rate of 15% or less means that the transparency of the separator is maintained, and is therefore effective for the output characteristics or cycle characteristics of the battery including the separator. Press air permeability is measured under the harsh conditions of high temperature (eg 90 ° C.) and high pressurization (eg 1 MPa). A specific method for measuring press air permeability will be described in Examples.

The press permeability of the separator can be determined by the method of making the substrate, eg dry or wet porosity, stretching temperature or stretching ratio of the substrate precursor; and the polymer present on the substrate, eg polymer. It can be adjusted according to the area ratio or the form of existence. A base material obtained by the dry porosity method is preferable because it is easy to adjust the press air permeability increase rate of the separator containing the base material within the range of 15% or less.

The short temperature, which is an index of heat resistance of the separator, is preferably 140 ° C. or higher, more preferably 150 ° C. or higher, and even more preferably 160 ° C. or higher, from the viewpoint of safety of the power storage device.

[Power storage device]
By superimposing the separator according to the present embodiment on the electrode, a laminated body in which the separator and the electrode are laminated can be obtained.
The laminated body is excellent not only in handleability at the time of winding and rate characteristics and cycle characteristics of the power storage device, but also in adhesiveness and permeability. Therefore, the laminate can be suitably used for, for example, a battery such as a non-aqueous electrolyte secondary battery, a capacitor, and a power storage device such as a capacitor.

The method for producing the laminate is not particularly limited, but may include, for example, a step of superimposing the separator and the electrode according to the present embodiment, heating and / or pressing as necessary. Heating and / or pressing can be performed when the electrode and the separator are overlapped. The laminate can be folded in a zigzag if desired.

After stacking the electrode and the separator, the wound body obtained by winding in a circular or flat spiral shape may be heated and / or pressed. The heating and pressing steps of the laminate may be performed after the laminate is manufactured, and may be performed after the laminate is housed in the exterior and the electrolytic solution is injected into the exterior.
The laminated body can also be manufactured by laminating in the order of positive electrode / separator / negative electrode / separator in the order of a flat plate, and pressurizing and auxiliary heating if necessary.

The pressure at the time of pressurization is preferably 1 MPa to 30 MPa. The pressurization time is preferably 5 seconds to 30 minutes. The heating temperature is preferably 40 ° C to 120 ° C. The heating time is preferably 5 seconds to 30 minutes. Further, the pressurization may be performed after heating, the pressurization may be performed after pressurization, or the pressurization and heating may be performed at the same time. Among these, it is preferable to pressurize and heat at the same time.

The power storage device according to the present embodiment includes the laminate described above or the wound body in which the laminate is wound, together with the electrolytic solution, in the exterior body.

The capacity density of the positive electrode active material of the power storage device according to the present embodiment is preferably 150 mAh / g or more, more preferably 160 mAh / g or more, and 170 mAh / g from the viewpoint of high output or long life. It is more preferable that the amount is g or more, but the higher the capacity density, the more difficult it becomes to ensure the safety of the power storage device. Therefore, the present invention, which is effective for the safety of the crush test, is considered to be effective.

When the power storage device is a secondary battery, the positive electrode terminal is welded to the end of the positive electrode laminate composed of the positive electrode current collector and the positive electrode active material layer, and the negative electrode laminate composed of the negative electrode current collector and the negative electrode active material layer is welded. By welding the negative electrode terminals to the ends of the body, it is possible to charge and discharge the secondary battery including the positive electrode laminated body with terminals and the negative electrode laminated body with terminals.

When laminating in the order of positive electrode laminate with terminal / separator / negative electrode laminate with terminal / separator, the coated surface of the separator (for example, the exposed surface of the polymer layer and / or the porous filler layer described above) is the negative electrode with terminal. It is preferable to arrange it on the laminated body side. When both sides of the separator are coated, it is more preferable to arrange at least the exposed surface of the polymer layer of the separator on the negative electrode laminate side.

When a non-aqueous electrolytic solution secondary battery is manufactured using the separator according to the present embodiment, known positive electrodes, negative electrodes, and non-aqueous electrolytic solutions may be used.

The positive electrode material is not particularly limited, and examples thereof include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ .
The negative electrode material is not particularly limited, and examples thereof include carbon materials such as graphitic, non-graphitizable carbonaceous material, easy-graphitable carbonaceous material, and composite carbonaceous materials; silicon, tin, metallic lithium, various alloy materials, and the like. ..
The non-aqueous electrolytic solution is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and the like. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

Unless otherwise specified, the above-mentioned measured values of various physical properties are values measured according to the measuring method in the examples described later.

The present embodiment will be described more specifically with reference to Examples and Comparative Examples. However, the present embodiment is not limited to the following examples as long as the gist is not exceeded.
The physical properties in the examples or comparative examples were measured by the following methods, respectively. When the measurement atmosphere was not specified, the measurement was performed in the atmosphere at 23 ° C., 1 atm, and 50% relative humidity.

<Measurement method and evaluation method>
(1) Viscosity average molecular weight (Mv) of polyolefin
The ultimate viscosity [η] (dl / g) at 135 ° C. in a decalin solvent was determined according to ASTM-D4020.
The Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ^-4 Mv ^0.67
The Mv of polypropylene was calculated by the following formula.
[Η] = 1.10 × 10 ^-4 Mv ^0.80

(2) Melting point The melting point of the resin composition was measured by a method according to JIS K-7121.

(3) Thickness (μm)
A sample of MD10 mm × TD10 mm was cut out from the base material. Nine points (3 points x 3 points) are selected in a grid pattern on the sample surface, and the film thickness of each point is measured at room temperature of 23 ± 2 ° C. using a microthickening instrument (Toyo Seiki Seisakusho Co., Ltd. type KBM). did. The average value of the measured values at each of the nine points was taken as the film thickness (μm) of the base material.

(4) Metsuke (g / m ² )
A sample of 10 cm × 10 cm square was cut out and weighed with an electronic balance AEL-200 manufactured by Shimadzu Corporation. By multiplying the obtained weight by 100, the basis weight (g / m ² ) of the film per 1 m ² was calculated. The coating basis weight of the polymer layer was obtained according to the following formula.
Polymer layer coating weight (g / m ² ) = Water storage device separator weight (g / m ² ) -Base material weight (g / m ² )

(5) Press permeability of separator The separator was pressed for 5 seconds under the conditions of 90 ° C. and 1 MPa using a heat press machine with eight separators stacked. Before heat pressing with an area of 645 mm ² (circle with a diameter of 28.6 mm) using a Garley type air permeability meter (GB2 (trademark) manufactured by Toyo Seiki Co., Ltd., inner cylinder mass: 567 g) conforming to JIS P-8117. The time (seconds) through which 100 cc of air passed was measured for the separator and the heat-pressed separator, and the rate of change of these values was calculated according to the following formula and evaluated as the press air permeability increase rate (%) of the separator.
Separator press air permeability increase rate (%) = (air permeability after hot pressing (seconds) -air permeability before hot pressing (seconds)) / air permeability before hot pressing (seconds) x 100

(6) Tensile strength Tensile breaking strength was measured for a sample (shape; width 10 mm x length 100 mm) using a tensile tester manufactured by Shimadzu Corporation, Autograph AG-A type (trademark), in accordance with JIS K7127. .. In addition, the sample has a chuck spacing of 50 mm. The tensile breaking strength (MPa) is a measured value in the TD direction. The measurement was performed under the conditions of a temperature of 23 ± 2 ° C., a chuck pressure of 0.30 MPa, and a tensile speed of 200 mm / min.

(7) Glass transition temperature of thermoplastic polymer An appropriate amount of the coating liquid of the thermoplastic polymer (nonvolatile content = 38 to 42%, pH = 9.0) was taken in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. .. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DSC curve under a nitrogen atmosphere were obtained with a DSC measuring device (DSC6220 manufactured by Shimadzu Corporation). The measurement conditions were as follows.
(1st stage temperature rise program)
Start at 70 ° C, raise the temperature at a rate of 15 ° C per minute, and maintain for 5 minutes after reaching 110 ° C.
(2nd stage temperature lowering program)
The temperature is lowered from 110 ° C at a predetermined rate per minute, and maintained for a predetermined time after reaching -50 ° C.
The temperature lowering rate and the maintenance time of −50 ° C. in the second-stage temperature lowering program are as follows.
(Manufacturing Examples A1 and A2)
Temperature down rate 40 ℃ / min
Maintenance time 5 minutes (3rd stage temperature rise program)
The temperature rises from -50 ° C to 130 ° C at a rate of 15 ° C per minute. Data of DSC and DDSC were acquired at the time of this third stage temperature rise.
Then, the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve to the high temperature side) and the tangent line at the inflection point (the point where the upward convex curve changes to the downward convex curve) is glass-transitioned. The temperature (Tg) was used.

(8) Average particle size of polymer The 50% particle size (nm) of the polymer was measured as the average particle size by a light scattering method using a particle size measuring device (manufactured by LEED & NORTHRUP, trade name “MICROTRAC UPA150”).

(9) Polymer gel fraction (toluene insoluble content)
A polymer coating liquid (nonvolatile content: 38 to 42%, pH: 9.0) was dropped on a Teflon (registered trademark) plate with a dropper (diameter 5 mm or less), and dried in a hot air dryer at 130 ° C. for 30 minutes. .. After drying, about 0.5 g of the dry film was precisely weighed (a), placed in a 50 mL polyethylene container, 30 mL of toluene was poured into the container, and the mixture was shaken at room temperature for 3 hours. Then, the contents were filtered through a 325 mesh, and the toluene insoluble content remaining on the mesh was dried together with the mesh in a hot air dryer at 130 ° C. for 1 hour. The dry weight of the 325 mesh used was weighed in advance.
After volatilizing the toluene, the dry weight of the toluene insoluble matter (b) was obtained by subtracting the previously weighed dry weight of the 325 mesh from the weight of the toluene insoluble matter and the 325 mesh. The gel fraction (toluene insoluble matter) was calculated by the following formula.
Gel fraction of raw material polymer (toluene insoluble) = (b) / (a) x 100 [%]

(10) Degree of swelling of polymer with respect to electrolytic solution (degree of swelling of electrolyte solvent)
After allowing the raw material polymer or the raw material polymer dispersion to stand in an oven at 130 ° C. for 1 hour, the dried polymer is cut off to a weight of 0.5 g, and ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio). It was placed in a 50 mL vial with 10 g of the mixed solvent of. After the sample in the vial was infiltrated for 3 hours, the sample was taken out, washed with the above mixed solvent, and the weight (Wa) was measured. After allowing the sample to stand in an oven at 150 ° C. for 1 hour, the weight (Wb) was measured, and the degree of swelling of the polymer with respect to the electrolytic solution was measured by the following formula.
Swelling degree (double) of thermoplastic polymer with respect to electrolytic solution = (Wa-Wb) ÷ (Wb)

(11) Rigid crush test, collision test a. Preparation of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ , mass density 175 mAh / g) as the positive electrode active material. 90.4% by mass, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) as a conductive auxiliary material and 1.6% by mass of acetylene black powder (AB) (density 1.95 g). ( ³ , number average particle size 48 nm) was mixed at a ratio of 3.8% by mass, and vinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder was mixed at a ratio of 4.2% by mass, and these were mixed with N. -Slurries were prepared by dispersing in methylpyrrolidone (NMP). This slurry was applied to an aluminum foil having a thickness of 20 μm as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes on both sides, and then rolled using a roll press machine. The rolled product was cut into a length of 750 mm and a width of 57.0 mm to obtain a positive electrode. The amount of the positive electrode active material applied at this time was 218 g / m ² .

b. Preparation of negative electrode As negative electrode active material, graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) was added to 87.6% by mass and graphite powder B (density 2.27 g / cm ³ , number average particle diameter). 9.7% by mass (6.5 μm), 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass (diene rubber-based latex) as a binder. A slurry was prepared by dispersing (in terms of solid content) (solid content concentration 40% by mass aqueous solution) in purified water. This slurry was applied to a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes on both sides, and then rolled using a roll press machine. The rolled product was cut into a length of 800 mm and a width of 58.5 mm to obtain a negative electrode. The amount of the negative electrode active material applied at this time was 104 g / m ² .

c. Preparation of non-aqueous electrolyte solution LiPF ₆ was added to 1 mol / L in a mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2. To obtain an electrolytic solution which is a non-aqueous electrolyte.

d. Battery assembly A wound body was obtained by stacking the prepared positive electrode and negative electrode on both sides of a separator slit with a width of 60.0 mm and winding it into a cylindrical shape. For the winding operation of these members, a winding device having a diameter of about 4 mm and a winding shaft having a half-split structure was used. The two separators wound in a roll shape were pulled out, sandwiched between the half-split parts of the winding shaft, the winding shaft was rotated several times to wind, and the positive and negative electrodes were inserted between the separator and the separator and wound. .. A tension of 600 g was applied to the positive electrode and the negative electrode in the direction opposite to the rotation direction of the winding shaft. A tension of 250 g was applied to the separator in the direction opposite to the rotation direction of the winding shaft. After winding the positive electrode and the negative electrode, the separator was further wound several times and cut. The prepared wound body was inserted into a stainless steel cylindrical battery case (exterior body) having dimensions of 18 mm in diameter and 65 mm in length. Next, 5 mL of the above electrolytic solution was injected therein, the wound body was immersed in the electrolytic solution, and then the battery case was sealed to prepare a non-aqueous electrolyte secondary battery.

e. Heat treatment d. The non-aqueous electrolyte secondary battery obtained in 1 above was stored in an environment of 60 ° C. for 48 hours.

f. Initial charge / discharge e. The non-aqueous electrolyte secondary battery obtained in 1 above was charged at a constant current of 0.3 C in an environment of 25 ° C., reached 4.2 V, and then charged at a constant voltage of 4.2 V to 0.3 C. It was discharged to 3.0V with a constant current. The total of charging time at a constant current and charging time at a constant voltage was set to 8 hours. Note that 1C is a current value at which the battery is discharged in one hour.
Next, the battery was charged with a constant current of 1C, reached 4.2V, then charged with a constant voltage of 4.2V, and discharged to 3.0V with a constant current of 1C. The total of charging time at a constant current and charging time at a constant voltage was set to 3 hours. Further, the capacity when discharged with a constant current of 1C was defined as 1C discharge capacity (mAh).

g. Rigid crush test FIG. 1 is a photograph showing the appearance of the crush test device and the arrangement of samples. The procedure of the crushing test in Examples and Comparative Examples will be described below with reference to FIG.
In an environment of 25 ° C, f. 50% of the 1C discharge capacity of the non-aqueous electrolyte secondary battery obtained in 1C was charged with a constant current of 1C.
Next, in an environment of 25 ° C., the battery is placed sideways on a stainless steel installation table, and a stainless steel upper jig (R = 5 × L) is applied so that pressure is applied at right angles to the vertical axis direction of the battery. = 25 mm) is started from the upper part 10 cm away from the battery and descends at a speed of 1 cm / sec. After holding the 6 mm position for 5 seconds, the battery was returned to the start position at a speed of 5.4 mm / s. At this time, the maximum load applied to the battery was defined as the rigid stress.
The stress difference was calculated from the following formula.
Stress difference = F _sep -F _base
{In the formula, F _sep is the maximum stress (N) of the battery crushing test using the separator and the electrode, and F _base is the maximum stress (N) of the battery crushing test using the substrate and the electrode. be. }

h. Crash test FIG. 2 is a schematic diagram of a crash test according to UL Standards 1642 and / or 2054.
In UL standard 1642 and / or 2054, a round bar is placed on the sample placed on the test table so that the sample and the round bar (φ = 15.8 mm) are approximately orthogonal to each other, and 610 ± from the round bar. Observe the effect of impact on the sample by dropping a 9.1 kg (about 20 pounds) weight from a height of 25 mm onto the top surface of the round bar.
The procedure of the collision test in Examples and Comparative Examples will be described below with reference to FIG. 2 and UL Standards 1642 and 2054.
In an environment of 25 ° C, f. The non-aqueous electrolyte secondary battery obtained in 1C was charged with a constant current of 1C, reached 4.2V, and then charged with a constant voltage of 4.2V for a total of 3 hours.
Next, in an environment of 25 ° C., the battery was placed sideways on a flat surface, and a stainless steel round bar having a diameter of 15.8 mm was placed in the center of the battery so as to cross the battery. A 9.1 kg weight was dropped from a height of 61 ± 2.5 cm from a round bar placed in the center of the battery so that an impact was applied at a right angle to the vertical direction of the battery. After that, the exterior temperature of the battery was measured, and the presence or absence of gas ejection from the battery and the presence or absence of ignition of the battery were observed. The battery exterior temperature is a temperature measured by a thermocouple (K-type seal type) at a position 1 cm from the bottom side of the battery exterior.
The collision test was evaluated according to the following criteria.
○ (Good): Battery exterior temperature less than 80 ° C △ (possible): Battery exterior temperature 80 ° C or higher, no gas ejection, no ignition × (Defective): Gas ejection or ignition

(12) Output characteristics a. Fabrication of positive electrode
As the positive electrode active material, nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ , mass density 175 mAh / g) is 90.4. Mass%, graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) as conductive auxiliary material 1.6 mass% and acetylene black powder (AB) (density 1.95 g / cm ³ ) , Number average particle diameter 48 nm) at a ratio of 3.8% by mass, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass, and these are mixed with N-methylpyrrolidone. A slurry was prepared by dispersing in (NMP). This slurry was applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then rolled using a roll press machine. The amount of the positive electrode active material applied at this time was 109 g / m ² .
b. Preparation of negative electrode As negative electrode active material, graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) was added to 87.6% by mass and graphite powder B (density 2.27 g / cm ³ , number average particle diameter). 9.7% by mass (6.5 μm), 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass (diene rubber-based latex) as a binder. A slurry was prepared by dispersing (in terms of solid content) (solid content concentration 40% by mass aqueous solution) in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then rolled using a roll press machine. The amount of the negative electrode active material applied at this time was 52 g / m ² .
c. Battery assembly The separator was cut into a length of 76.0 mm and a width of 55.0 mm, the positive electrode was cut into a length of 50.0 mm and a width of 30.0 mm, and the negative electrode was cut into a length of 52.0 mm and a width of 32.0 mm.
The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode faced each other, and housed in the packaging material. A single-layer laminated battery was assembled by injecting 0.5 ml of the non-aqueous electrolytic solution into this container and sealing the container.
d. Heat treatment c. The battery assembled in 1 was surface pressed at a temperature of 90 ° C. and a pressure of 1 MPa for 5 seconds.

e. Evaluation of output characteristics d. The battery obtained in 1. is charged with a constant current of 0.3C in an environment of 25 ° C., reaches 4.2V, is charged with a constant voltage of 4.2V, and has a constant current of 0.3C. It was discharged to 0V. The total of charging time at a constant current and charging time at a constant voltage was set to 8 hours. Note that 1C is a current value at which the battery is discharged in one hour.
Next, the simple battery was charged with a constant current of 1C, reached 4.2V, then charged with a constant voltage of 4.2V, and discharged to 3.0V with a constant current of 1C. The total of charging time at a constant current and charging time at a constant voltage was set to 3 hours, and the capacity when discharged at a constant current of 1C was defined as 1C discharge capacity (mAh).
Next, the simple battery was charged with a constant current of 1C, reached 4.2V, then charged with a constant voltage of 4.2V, and discharged to 3.0V with a constant current of 2C. The total of the charging time at a constant current and the charging time at a constant voltage was set to 3 hours, and the capacity when discharged at a constant current of 2C was defined as the 2C discharge capacity (mAh).
Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated from the following formula, and this value was used as the output characteristic.
Output characteristics (%) = (2C discharge capacity / 1C discharge capacity) x 10
The obtained output characteristics were evaluated according to the following criteria.
◎ (Very good): Output characteristics are over 95% ○ (Good): Output characteristics are over 90% and 95% or less △ (Yes): Output characteristics are over 80% and 90% or less × (Defective): Output characteristics But less than 80%

<Manufacturing of base material>

[Manufacturing of dry substrate D1]
A homopolymer high-density polypropylene (a-1) having an Mv of 600,000 and a melting point of 165 ° C., having a diameter of 20 mm, L / D (L: distance (m) from the raw material supply port to the discharge port of the extruder, D. : Inner diameter (m) of extruder. The same shall apply hereinafter.) = Polypropylene having a Mv of 210,000 and a melting point of 136 ° C. (B-1) was put into a single-screw extruder set to a diameter of 20 mm, L / D = 30, and 200 ° C. under a nitrogen atmosphere via a feeder, and the lip thickness was 3.0 mm installed at the tip of the extruder. Extruded from the push T die. Immediately after that, the molten resin was blown with cold air at 25 ° C. and wound with a cast roll cooled to 95 ° C. under the conditions of a draw ratio of 200 times and a winding speed of 15 m / min, and the outer layer was polypropylene (a-1). A three-layer laminated film (D1) having the structure of the microporous film (A-1) of No. 1 and the second microporous film (B-1) having a polyethylene (b-1) inner layer was formed (co-operated). Extrusion process). The laminated film (D1) was annealed for 6 hours in a hot air circulation oven heated to 130 ° C. (annealing step).
Next, the laminated film after annealing was uniaxially stretched 1.3 times in the vertical direction at a temperature of 25 ° C. to obtain a stretched laminated film (cold stretching step). Next, the stretched laminated film was uniaxially stretched (strain rate: 0.5 / sec) at a temperature of 120 ° C. in the longitudinal direction at a magnification of 3.0 times to obtain a microporous film (heat stretching step). Then, it was heat-fixed by relaxing 0.8 times at a temperature of 130 ° C.

[Manufacturing of dry base material D2]
The base material D2 was obtained by the same method as that for the base material D1 except that the homopolymer high-density polypropylene (a-2) having an Mv of 600,000 and a melting point of 162 ° C. was used.

[Manufacturing of dry base material D3]
The base material D3 was obtained by the same method as that for the base material D1 except that the homopolymer high-density polypropylene (a-3) having an Mv of 600,000 and a melting point of 167 ° C. was used.

[Manufacturing of wet substrate T1]
19.2% by weight of ultra-high molecular weight polyethylene homopolymer having Mv of 1 million, 12.8% by weight of high-density polyethylene of homopolymer having 250,000 Mv, and 48% by weight of dioctyl phthalate (DOP). 20% by weight of fine powder silica having a primary particle size of 15 nm and a DOP oil absorption of 200 ml / 100 g was mixed and granulated. Next, it was melt-kneaded in a nitrogen atmosphere with a twin-screw extruder equipped with a T-die at the tip, extruded, rolled from both sides with a roll heated to 110 ° C., and formed into a sheet having a thickness of 110 μm. DOP and fine silica powder were extracted and removed from the molded product to prepare a fine porous membrane. Two of the microporous membranes were stacked and stretched 4.5 times in the vertical direction with a roll heated to 115 ° C., and then stretched 2.1 times in the horizontal direction at a temperature of 120 ° C. using a tenter stretching machine. Then, this stretched sheet was relaxed by about 20% in the width direction and heat-treated at 137 ° C. to obtain a base material T1 which is a polyolefin resin porous film.

[Manufacturing of wet substrate B1]
47 parts by mass of homopolymer high-density polyethylene with Mv of 700,000, 46 parts by mass of homopolymer high-density polyethylene with Mv of 300,000, and 7 parts by mass of homopolymer polypropylene with Mv of 400,000. , Dry blended using a tumbler blender. To 99 parts by mass of the obtained pure polymer mixture, add 1 part by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant, and tumbler again. A mixture such as a polymer was obtained by dry blending using a blender. After replacing the obtained mixture such as a polymer with nitrogen, it was supplied to a twin-screw extruder by a feeder under a nitrogen atmosphere. Further, 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 operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture to be extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.
Then, they were melt-kneaded while being heated to 200 ° C. in a twin-screw extruder, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll controlled to a surface temperature of 25 ° C., and the extruded product was extruded. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify.

This sheet was stretched at a temperature of 125 ° C. at a magnification of 7.0 × 7.0 times by a simultaneous biaxial stretching machine. Then, the stretched product was immersed in methylene chloride to extract and remove liquid paraffin, and then dried. Further, it was stretched twice in the lateral direction at a temperature of 125 ° C. using a tenter stretching machine.
Then, this stretched sheet was relaxed by about 20% in the width direction and heat-treated at 130 ° C. to obtain a base material B1 which is a polyolefin resin porous film.

[Manufacturing of wet substrate B2]
47.5 parts by mass of homopolymer high-density polyethylene with Mv of 700,000, 47.5 parts by mass of homopolymer high-density polyethylene with Mv of 250,000, and homopolymer polypropylene with Mv of 400,000. Was dry-blended with 5 parts by mass using a tumbler blender. To 99 wt% of the obtained pure polymer mixture, add 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane as an antioxidant, and tumbler blender again. By dry blending using the above, a mixture such as a polymer was obtained.

The obtained mixture was fed to a twin-screw extruder under a nitrogen atmosphere by a feeder. Further, 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 operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture to be extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.
Then, they were melt-kneaded while being heated to 200 ° C. in a twin-screw extruder, and the obtained melt-kneaded product was extruded through a T-die onto a cooling roll controlled to a surface temperature of 25 ° C., and the extruded product was extruded. A sheet-shaped molded product was obtained by contacting with a cooling roll and molding (casting) to cool and solidify.

This sheet was stretched at a temperature of 120 ° C. at a magnification of 7.0 × 6.4 times by a simultaneous biaxial stretching machine. Then, the stretched product was immersed in methylene chloride to extract and remove liquid paraffin, and then dried. Further, it was stretched 1.2 times in the lateral direction at a temperature of 125 ° C. using a tenter stretching machine.
Then, this stretched sheet was relaxed by about 20% in the width direction and heat-treated at 130 ° C. to obtain a base material B2 which is a polyolefin resin porous film.

Details of all the substrates obtained above are shown in Table 1 below.

<Synthesis of resin and preparation of aqueous dispersion containing the resin>
(Aqueous dispersion A1)
In a reaction vessel equipped with a synthetic stirrer, a reflux condenser, a dropping tank, and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). Notated as "KH1025" in Table 2. The same applies hereinafter.) 0.5 parts by mass and "Adecaria soap SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution, notated as "SR1025" in Table 2. The same applies hereinafter. .) 0.5 parts by mass was charged, and the internal temperature of the reaction vessel was raised to 80 ° C. Then, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (denoted as “APS (aq)” in Table 2; the same applies hereinafter) was added while maintaining the container internal temperature of 80 ° C.

On the other hand, methyl methacrylate (denoted as "MMA" in Table 2; the same applies hereinafter) 38.5 parts by mass, n-butyl acrylate (denoted as "BA" in Table 2; the same applies hereinafter) 19.6 parts by mass, 2-Ethylhexyl acrylate (denoted as "EHA" in Table 2. The same shall apply hereinafter) 31.9 parts by mass, methacrylic acid (denoted as "MAA" in Table 2. The same shall apply hereinafter) 0.1 part by mass of acrylic acid (same below). Notated as "AA" in Table 2. 0.1 parts by mass, 2-hydroxyethyl methacrylate (denoted as "HEMA" in Table 2. The same shall apply hereinafter), acrylamide ("AM" in Table 2. (Same as below.) 5 parts by mass, glycidyl methacrylate (denoted as "GMA" in Table 2. The same shall apply hereinafter) 2.8 parts by mass, "Aqualon KH1025" (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 25% aqueous solution) 3 parts by mass, "Adecaria soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) 3 parts by mass, sodium p-styrene sulfonate (denoted as "NaSS" in Table 2. The same shall apply hereinafter). 0.05 parts by mass, trimethyl propanetriacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., indicated as "A-TMPT" in Table 2. The same shall apply hereinafter) 0.7 parts by mass, γ-methacryloxypropyltrimethoxysilane ( Notated as "AcSi" in Table 2. The same applies hereinafter.) A mixture of 0.3 parts by mass, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water is mixed for 5 minutes with a homomixer. To prepare an emulsion.

The obtained emulsion was dropped from the dropping tank into the reaction vessel. The dropping was started 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of the emulsion was dropped over 150 minutes. During the dropping of the emulsion, the temperature inside the container was maintained at 80 ° C.

After the completion of dropping the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH = 9.0 using an aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an acrylic copolymer latex having a concentration of 40% by mass (raw material polymer A1). The physical properties of the obtained latex containing the raw material polymer were evaluated by the above method. The evaluation results are shown in Table 2.

(Aqueous dispersion A2)
A copolymer latex (raw material polymer A2) was obtained in the same manner as the raw material polymer (aqueous dispersion) A1 except that the compositions of the monomers and other raw materials used in Table 2 were changed. The physical properties of the obtained latex containing the raw material polymer were evaluated by the above method. The evaluation results are shown in Table 2.

Explanation of abbreviations in Table 2 MMA: Methyl methacrylate IBXA: Isobornyl acrylate BA: n-butyl EHA acrylate: 2-ethylhexyl acrylate MAA: AA methacrylate: HEMA acrylate: 2-hydroxyethyl methacrylate AM: Acrylamide GMA: Glycydyl methacrylate NaSS: P-sodium styrene sulfonate A-TMPT: Trimethylol propantriacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.)
AcSi: γ-methacryloxypropyltrimethoxysilane KH1025: Aqualon KH1025 (registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
SR1025: Adecaria Soap SR1025 (registered trademark, manufactured by ADEKA CORPORATION)
APS: Ammonium persulfate

<Example 1>
80 parts by mass of the aqueous dispersion A2 with a solid content and 20 parts by mass of the aqueous dispersion A1 with a solid content are uniformly dispersed in water to obtain a coating liquid (solid content 10% by mass) containing a thermoplastic polymer. Prepared. At this time, carboxymethyl cellulose was added as a thickener so as to be 1% by mass with respect to the coating liquid, and the viscosity of the coating liquid was adjusted to 20 mPa · s. Then, using a gravure coater, the coating liquid was applied to the entire surface of one side of the base material D1 by reverse coating. Then, the coating liquid after coating was dried at 60 ° C. to remove water. Further, the coating liquid was similarly applied to the other surface of the base material D1 and dried again in the same manner as described above. In this way, a separator having a polymer layer formed on both sides of the base material D1 was obtained.

<Examples 2 to 4, Comparative Examples 1 to 4>
A coating liquid was prepared in the same manner as in Example 1 except that the base material and the aqueous dispersion used were as shown in Table 3, respectively, and a separator was prepared and evaluated using the coating liquid. ..

The evaluation results of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 3.

Claims (9)

A substrate containing at least one porous membrane and
A separator for a power storage device comprising a polymer present in at least one region of at least one surface of the substrate.
The tensile strength of the base material in the width direction is 0.05 kgf / cm or more and less than 0.90 kgf / cm .
About the crushing test The following formula (A):
294.2N (30kgf) ≤ F _sep -F _base ≤980.7N (100kgf) ... (A)
{In the formula, F _sep is the maximum stress of the crushing test of the cylindrical power storage device using the separator for the power storage device and the electrode, and F _base is the maximum stress of the cylindrical power storage device using the base material and the electrode. Maximum stress in crush test}
Satisfy the relationship represented by
The electrode includes a positive electrode and a negative electrode, and includes a positive electrode and a negative electrode.
The positive electrode has an aluminum foil as a positive electrode current collector, nickel, manganese, and cobalt composite oxide as a positive electrode active material applied to the positive electrode current collector, and graphite powder (density 2.26 g / cm) as a conductive auxiliary material. 3. Containing acetylene black powder ( ³ , number average particle size 6.5 μm), and polyvinylidene fluoride as a binder.
The negative electrode has a copper foil as a negative electrode current collector, graphite powder (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) and graphite powder as a negative electrode active material applied to the negative electrode current collector. (Density 2.27 g / cm ³ , number average particle size 6.5 μm), and contains ammonium salt of carboxymethyl cellulose and diene rubber-based latex as a binder, and
A separator for a power storage device, wherein the polymer layer containing the polymer of the separator for the power storage device has a coating weight of 0.3 g / m ² or more and 1.0 g / m ² or less . The separator for a power storage device according to claim 1, wherein the press air permeability increase rate of the separator is 15% or less. The separator for a power storage device according to claim 1 or 2 , wherein the polymer contains a fluororesin or an acrylic resin. The separator for a power storage device according to claim 3 , wherein the polymer contains the acrylic resin. The separator for a power storage device according to any one of claims 1 to 4 , wherein the polymer has a melting point and / or a glass transition temperature of 20 ° C. or higher. The separator for a power storage device according to any one of claims 1 to 5 ,
With the positive electrode
With the negative electrode
Laminated body consisting of. A wound body in which the laminated body according to claim 6 is wound. A power storage device containing the laminate according to claim 6 or the wound body according to claim 7 and an electrolytic solution. The power storage device according to claim 8 , wherein the positive electrode active material has a capacity density of 150 mAh / g or more.

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