JP6893402B2 - 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.

In addition to the electrical characteristics and safety of the non-aqueous electrolyte battery, the separator is also required to have improved adhesiveness to the electrode from the viewpoint of uniform charging / discharging current and suppression of lithium dendrite. In order to give the separator adhesiveness, coating of various polymers on the separator base material has been proposed (Patent Documents 1 to 9).

In Patent Document 1, an adhesive polymer having a core-shell type structure and the degree of swelling thereof are studied.

In Patent Document 2, the shape variation and the particle size variation of the polymer particles contained in the polymer coating liquid are studied.

Regarding the selection of the adhesive polymer, Patent Document 3 describes the combined use of the acrylic polymer having a sulfonic acid group and the acrylic polymer having an epoxy group, and Patent Document 9 describes styrene-butadiene rubber as the adhesive polymer. Has been done.

Regarding the thermal properties of the adhesive polymer, Patent Document 4 examines the glass transition temperature of the thermoplastic polymer placed on the substrate, and Patent Document 5 examines the glass transition temperature of the polymer having a glass transition temperature of 10 ° C. to 100 ° C. Particles have been proposed, and Patent Document 7 proposes an adhesive polymer that exhibits adhesiveness at a temperature lower than the melting point of the polymer forming the separator substrate.

Regarding the location of the adhesive polymer on the substrate, Patent Document 6 proposes to evenly distribute the binder polymer within the range of 1% to 80% of the substrate surface, and Patent Document 8 states. It has been proposed to partially place the gel polymer on the substrate.

JP-A-2015-28843 International Publication No. 2012/020737 International Publication No. 2012/043729 International Publication No. 2014/017651 International Publication No. 2013/151144 International Publication No. 2003/012896 Japanese Unexamined Patent Publication No. 2011-0231186 Special Table 2006-525624 Japanese Patent Publication No. 2008-521964

However, when the adhesive layer is formed on the base material using the adhesive polymer described in Patent Documents 1 to 9, the adhesive force is secured at the interface between the base material and the electrode in the power storage device, but in the electrolytic solution. Since the rigidity of the adhesive layer in the above is insufficient, the rigidity of the laminate of the separator and the electrode or the wound laminate may not be increased, and the power storage device may be deformed.

Therefore, an object to be solved by the present invention is to provide a separator for a power storage device capable of suppressing deformation of a laminate of a separator and an electrode or a wound laminate in a power storage device.

｛式中、Ｓｉは、ボロノイ多角形の面積の実測値であり、ｍは、ボロノイ多角形の面積の実測値の平均値であり、かつｎは、ボロノイ多角形の総数である｝
によって定義される分散（σ^２）が、０．０１以上０．７以下である、［９］に記載の蓄電デバイス用セパレータ。
［１１］
前記分散（σ^２）は、９５視野について算出された値の平均値である、［１０］に記載の蓄電デバイス用セパレータ。
［１２］
前記ポリマーを含む塗工液を、５％〜７０％の前記基材に対する塗工面積割合、０．０５ｇ／ｍ^２〜１．０ｇ／ｍ^２の塗工目付、及び０．１μｍ〜３μｍの塗工厚みの条件下で、前記基材の前記少なくとも１つの面に塗工する工程を含む、［１］〜［８］のいずれか１項に記載の蓄電デバイス用セパレータの製造方法。 The present inventors have found that the above problems can be solved by allowing a polymer having rigidity even in an electrolytic solution to be present on a separator substrate, and have completed the present invention.
That is, the present invention is as follows.
[1]
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;
The following formula (f):
Fsep _max −Fbase _max ≧ 10 (f)
{In the formula, Fsep _max is a load (N) for maintaining the pushing speed of the indenter with respect to the laminated wound body 1 of the electrode and the separator for the power storage device and the storage body 1 in which the electrolytic solution is stored at 50 mm / min. Is the maximum value when plotted over time, and Fbase _max is the pushing speed of the indenter with respect to the laminated wound body 2 of the base material and the electrode and the storage body 2 in which the electrolytic solution is stored by 50 mm. This is the maximum value when the load (N) for maintaining at / min is plotted over time}
The separator for the power storage device that satisfies the relationship represented by.
[2]
The separator for a power storage device according to [1], wherein the electrode is a positive electrode or a negative electrode.
[3]
The separator for a power storage device according to [2], which satisfies the relationship represented by the above formula (f) regardless of whether the electrode is the positive electrode or the negative electrode.
[4]
The indenter is pushed into the storage body 1 or the storage body 2 from a direction perpendicular to the winding direction of the laminated winding body 1 or the laminated winding body 2, any of [1] to [3]. The separator for a power storage device according to item 1.
[5]
The separator for a power storage device according to any one of [1] to [4], wherein the size and material of the storage body 1 are the same as the size and material of the storage body 2.
[6]
Any one of [1] to [5], wherein the area ratio of the surface of the base material coated with the polymer after impregnating the separator for a power storage device with the electrolytic solution is 5% to 80%. Separator for power storage device according to the section.
[7]
When the aluminum foil is pressed on the outermost surface of the power storage device separator where the polymer is present for 3 minutes under the conditions of a temperature of 25 ° C. and a pressure of 5 MPa, the power storage device separator and the aluminum foil are pressed. The separator for a power storage device according to any one of [1] to [6], wherein the peel strength between the two is 8 N / m (8 gf / cm) or less.
[8]
When the aluminum foil is pressed on the outermost surface of the power storage device separator where the polymer is present for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa, the power storage device separator and the aluminum foil are pressed. The separator for a power storage device according to any one of [1] to [7], wherein the peel strength between the two is 9.8 N / m (10 gf / cm) or more.
[9]
The separator for a power storage device according to any one of [1] to [8], wherein the polymer is a granular thermoplastic polymer.
[10]
Using the area (Si) of the Voronoi polygon obtained by performing Voronoi division of the granular thermoplastic polymer, the following formula:

{In the equation, Si is the measured value of the area of the Voronoi polygon, m is the average value of the measured values of the area of the Voronoi polygon, and n is the total number of Voronoi polygons}
The separator for a power storage device according to [9], wherein the variance (σ ^{2) defined by is 0.01 or more and 0.7 or less.}
[11]
The separator for a power storage device according to [10], wherein the variance (σ ² ) is an average value of values calculated for 95 visual fields.
[12]
The coating liquid containing the polymer, coating area ratio with respect to the substrate of ^{5% ~70%, 0.05g / m} 2 ~1.0g / m 2 of coating basis weight, and 0.1μm~3μm coating The method for producing a separator for a power storage device according to any one of [1] to [8], which comprises a step of coating the at least one surface of the base material under the condition of the working thickness.

According to the present invention, since the rigidity of the adhesive portion of the power storage device separator is ensured, the rigidity of the power storage device can be improved and the deformation of the power storage device can be suppressed.

FIG. 1 shows an example of a photograph in which the surface of the polymer layer is observed. FIG. 2 shows an example of the result of automatically identifying the thermoplastic polymer included in the observation field of FIG. 1 using image processing software. FIG. 3 shows an example of the result of obtaining a Voronoi polygon by performing Voronoi division on a plurality of particles identified in FIG. FIG. 4 shows an example of the result of automatically calculating the area of the Voronoi polygon obtained in FIG. 3 using image processing software. FIG. 5 shows an example of a method of setting one compartment consisting of 19 fields of view out of 95 fields of view for observing thermoplastic polymer particles arranged on a separator. FIG. 6 shows an example of a method of setting 5 compartments including 95 fields of view for observing thermoplastic polymer particles arranged on a separator. 7A to 7E are schematic views showing a planar shape of a polymer layer formed on at least one surface of a base material in the separator according to the embodiment of the present invention.

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 energy storage device separator (hereinafter referred to as "separator") according to the present embodiment includes a base material containing at least one porous membrane and a polymer present in at least one region of at least one surface of the base material. 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 (f): for a three-point bending test.
Fsep _max −Fbase _max ≧ 10 (f)
{In the formula, Fsep _max applies a load (N) over time to maintain the indenter pushing speed at 50 mm / min with respect to the laminated wound body 1 of the electrode and the separator and the storage body 1 in which the electrolytic solution is stored. It is a maximum value when plotted, and Fbase _max is a load for maintaining the pushing speed of the indenter against the laminated wound body 2 of the base material and the electrode and the storage body 2 in which the electrolytic solution is stored at 50 mm / min. This is the maximum value when (N) is plotted over time}
Satisfy the relationship represented by.

_{The values obtained by subtracting Fbase max} from Fsep _max in the formula (f) are the laminated wound body 1 obtained by laminating and winding the electrodes and the separator, and the accommodating body 1 containing the electrolytic solution. A storage body 1 in the case where a laminated winding body 2 obtained by stacking a base material on an electrode instead of a separator and a storage body 2 containing an electrolytic solution are subjected to a three-point bending test, respectively. It is the difference between the strength (N) of the above and the strength (N) of the housing body 2 (hereinafter referred to as “rigidity difference”).

Based on the configuration of the accommodating body 1 containing the laminated wound body 1 and the electrolytic solution or the accommodating body 2 containing the laminated wound body 2 and the electrolytic solution, the power storage device is modeled by the accommodating body 1 or 2, and thus described above. The higher the rigidity difference defined in, the higher the rigidity of the power storage device provided with the separator. When the rigidity difference is 10 N or more, even if a shear stress is applied between the separator and the electrode in the electrolytic solution, the power storage device has sufficient rigidity to suppress the deformation of the power storage device or the interface peeling between the separator and the electrode. Has. From the viewpoint of the rigidity of the power storage device, the higher the rigidity difference is, the more preferable it is, and the upper limit value of the rigidity difference is not limited because it is determined according to the design of the power storage device.

On the other hand, when the difference in rigidity is less than 10 N for both the positive and negative electrodes, the power storage device provided with the separator cannot withstand the shear stress applied between the separator and the electrode in the electrolytic solution, and the power storage device is deformed and the separator base material and the electrode are deformed. Aggregate fracture of the polymer portion existing between the two, or interface peeling between the separator and the electrode occurs.

Therefore, when the rigidity difference is 10 N or more, (i) generation of lithium dendrite and wrinkles or delamination of the wound body in the electrolytic solution are suppressed, thereby suppressing an increase in the thickness of the power storage device over time. Therefore, the cycle characteristics of the power storage device are improved, and / or even if the coverage area of the separator base material surface coated with the polymer (ii) is small, rapid charging / discharging of the power storage device can be achieved. The rate characteristics of the power storage device are improved. From the viewpoints of (i) and (ii), the rigidity difference is more preferably 12 N or more, and further preferably 14 N or more.

The difference in rigidity is controlled to 10 N or more by achieving both adhesiveness and rigidity of the polymer present in at least one region of at least one surface of the separator base material in the electrolytic solution. Therefore, the strength (N) of the housing body 1 formed by using the separator having the polymer in at least one region of at least one surface of the base material is the strength (N) of the housing body 2 formed by using the base material instead of the separator. It is preferably 10 N or more larger than the strength (N) of the above, more preferably 12 N or more, and preferably 14 N or more.

_{For Fsep max} in the formula (f), preferably, the electrodes and the separator are laminated and wound to form the laminated wound body 1, the laminated wound body 1 is put into the accommodating body 1, and the electrolytic solution is put into the accommodating body 1. It is measured after pouring, and more preferably, it is measured after heat-pressing the housing 1 after pouring the electrolytic solution.

_{The Fbase max} in the formula (f) is preferably formed by stacking the base material and the electrode and winding them to form the laminated wound body 2, put the laminated wound body 2 in the accommodating body 2, and put the electrolytic solution in the accommodating body 2. Is measured after pouring, and more preferably, the accommodating body 2 is heat-pressed after pouring the electrolytic solution.

From the viewpoint of ease and accuracy of the three-point bending test, the indenter is pushed into the accommodating body not from the direction perpendicular to the end face of the laminated wound body but from the direction perpendicular to the longitudinal direction of the laminated wound body. It is preferable that the indenter is pushed into the accommodating body from a direction perpendicular to the winding direction of the laminated wound body, and is pushed so that the tip of the indenter can approach the center of the laminated wound body in the accommodating body. Is even more preferable.

In the three-point bending test, the electrodes used are electrode current collectors such as aluminum foil and copper foil as long as the housing can be subjected to the three-point bending test; a positive electrode having a positive electrode active material on the positive electrode current collector. ; And a negative electrode having a negative electrode active material on the negative electrode current collector may be used. From the viewpoints of (i) and (ii) above, the electrode is preferably a positive electrode or a negative electrode, and regardless of whether the electrode is a positive electrode or a negative electrode, the rigidity difference is more preferably 10 N or more.

The housing to be subjected to the three-point bending test may be a pouch-shaped case obtained by laminating a plurality of polymer films, for example, polypropylene films, and one or more metal sheets, for example, aluminum sheets.

The dimensions of the housing body to be subjected to the three-point bending test are arbitrary as long as the laminated wound body obtained by laminating and winding the electrode and the separator or the base material and the electrolytic solution can be stored. May have the form and dimensions of. Since both ends of the storage body are fixed during the 3-point bending test, the dimensions of the storage body are preferably close to the dimensions of the laminated wound body, and the laminated wound body is from the indenter pushing direction during the 3-point bending test. It is preferable that the laminated wound body is arranged in the storage body so that the center or the center of gravity of the laminated wound body coincides with the center or the center of gravity of the storage body when the storage body is observed.

In the present embodiment, both the accommodating body 1 for accommodating the laminated wound body 1 of the electrode and the separator and the accommodating body 2 for accommodating the laminated wound body 2 of the electrode and the base material have arbitrary dimensions and materials. However, from the viewpoint of ease and accuracy of the three-point bending test, it is preferable that the dimensions and materials of the housing body 1 are the same as the dimensions and materials of the housing body 2.
From the viewpoint of ease and accuracy of the three-point bending test, it is preferable that the electrolytic solution used for forming the accommodating body 1 and the electrolytic solution used for forming the accommodating body 2 are the same.
From the viewpoint of ease and accuracy of the three-point bending test, it is preferable that the heat press conditions of the storage body 1 and the heat press conditions of the storage body 2 are the same.
The method and conditions of the three-point bending test will be described in Examples.

Separators can be used in the manufacture of power storage devices. Each configuration related to the separator will be described below.

[Polymer, polymer layer and adhesive layer]

The polymer is located in at least one region of at least one surface of the porous membrane or a porous membrane having a porous layer containing an inorganic filler and a resin binder on at least one surface (collectively referred to as "base material"). Will be done. The polymer is preferably a thermoplastic polymer. As used herein, the term "thermoplastic polymer" is a thermoplastic polymer usually used as a binder for adhering a separator and an electrode, or is gelled by hot pressing in an electrolytic solution to exhibit adhesiveness. It shall contain the polymer to be used.
The layer containing the polymer (hereinafter referred to as "polymer layer") is formed on at least one side of the base material. The polymer layer may be formed in at least a part of a region on at least one side of the base material.
The polymer layer can be bonded to the electrode and the separator by undergoing a heat pressing process. That is, the polymer layer can function as an adhesive layer between the electrode and the separator.

In order to improve the rigidity of the power storage device by controlling the rigidity difference measured by the three-point bending test to 10 N or more, the adhesiveness of the polymer layer at the interface between the electrode and the separator and the rigidity of the polymer layer in the electrolytic solution It is required to achieve both.

In order to ensure the adhesiveness of the polymer layer at the interface between the electrode and the separator, it is preferable that the polymer layer formed on the substrate has an adhesive or anchoring effect.
Further, in order to improve the rigidity of the adhesive layer in the electrolytic solution, at least one of the following 1 to 3 is required:
1. 1. Use a polymer with high rigidity in the electrolyte;
2. The polymer layer forms a continuous layer; and 3. An adhesive layer containing a mixture of an inorganic filler and a polymer is formed.

[1. Use a polymer with high rigidity in the electrolyte]
The polymer having high rigidity in the electrolytic solution may be a thermoplastic polymer as long as the difference in rigidity can be controlled to 10 N or more. Specific examples of the thermoplastic polymer include the following 1) to 4).
1) Conjugated diene polymer,
2) Acrylic polymer,
3) Polyvinyl alcohol-based resin, and 4) Fluororesin.

The above 1) conjugated diene polymer is a polymer containing a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, and substituted linear chain. Conjugated pentadienes, substitutions, side chain conjugated hexadiene and the like can be mentioned, and these may be used alone or in combination of two or more.
Further, the conjugated diene polymer may contain a (meth) acrylic compound or another monomer described later as a monomer unit. Specifically, for example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride and the like.

The above 2) acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The (meth) acrylic compound refers to at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester.
Examples of such a compound include a compound represented by the following formula (P1).
CH ₂ = CR ^Y1- COO- ^RY2 (P1)
In the formula (P1), ^RY1 represents a hydrogen atom or a methyl group, and ^RY2 represents a hydrogen atom or a monovalent hydrocarbon group. When ^RY2 is a monovalent hydrocarbon group, it may have a substituent and may have a heteroatom in the chain. Examples of the monovalent hydrocarbon group include a chain alkyl group which may be linear or branched, a cycloalkyl group, and an aryl group. Examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include a halogen atom and an oxygen atom. The (meth) acrylic compound may be used alone or in combination of two or more.
Examples of such (meth) acrylic compounds include (meth) acrylic acid, chain alkyl (meth) acrylate, cycloalkyl (meth) acrylate, (meth) acrylate having a hydroxyl group, and phenyl group-containing (meth) acrylate. Can be mentioned.

^{More specifically, as a chain alkyl group which is a kind of RY2} , a methyl group, an ethyl group, an n-propyl group, and a chain alkyl group having 1 to 3 carbon atoms, which are isopropyl groups; n- Examples thereof include chain alkyl groups having 4 or more carbon atoms, such as a butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group, and a lauryl group. Further, ^{as an aryl group which is one kind of RY2} , for example, a phenyl group can be mentioned.
Specific examples of such a ^{(meth) acrylic acid ester monomer having RY2} include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, and the like. Chain alkyl groups such as 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate. Has (meth) acrylate;
Examples thereof include (meth) acrylates having an aromatic ring, such as phenyl (meth) acrylate and benzyl (meth) acrylate.

Among these, from the viewpoint of improving the adhesion to the electrode (electrode active material), and by appropriately separating the solubility parameter (SP value) of the electrolytic solution and the SP value of the polymer, excessive swelling in the electrolytic solution can be prevented. From the viewpoint of suppressing and balancing rigidity and resistance, a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, ^RY2 is a chain alkyl group having 4 or more carbon atoms. A (meth) acrylic acid ester monomer is preferable. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferable. The upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms is not particularly limited, and may be, for example, 14, but 7 is preferable. These (meth) acrylic acid ester monomers are used alone or in combination of two or more.

(Meth) acrylic acid ester monomer, in place of the monomers the carbon atoms having 4 or more chain alkyl group, or in addition, it is also preferred to include a monomer having a cycloalkyl group as R ^Y2. Due to the presence of the high cycloalkyl group, excessive swelling in the electrolytic solution can be suppressed, which also further improves the adhesion to the electrode.
More specific examples of the monomer having such a cycloalkyl group include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and adamantyl (meth) acrylate. The number of carbon atoms constituting the alicyclic of the cycloalkyl group is preferably 4 to 8, more preferably 6 and 7, and particularly preferably 6. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferable in that the polymerization stability at the time of preparing the acrylic polymer is good. These may be used alone or in combination of two or more.

Further, the acrylic polymer preferably contains a crosslinkable monomer as the (meth) acrylic acid ester monomer in place of or in addition to the above-mentioned one, preferably in addition to the above-mentioned one. The crosslinkable monomer is not particularly limited, and examples thereof include a monomer having two or more radically polymerizable double bonds, a monomer having a functional group that gives a self-crosslinking structure during or after polymerization, and the like. These may be used alone or in combination of two or more.
Examples of the monomer having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. The polyfunctional (meth) acrylate may be at least one selected from the group consisting of bifunctional (meth) acrylate, trifunctional (meth) acrylate, and tetrafunctional (meth) acrylate. Specifically, for example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol. Examples thereof include dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferable from the same viewpoint as described above.

Examples of the monomer having a functional group that gives a self-crosslinking structure during or after the polymerization include a monomer having an epoxy group, a monomer having a methylol group, a monomer having an alkoxymethyl group, and a monomer having a hydrolyzable silyl group. Be done. As the monomer having an epoxy group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specifically, for example, glycidyl (meth) acrylate, 2,3-epoxycyclohexyl (meth) acrylate, and 3,4-epoxide. Cyclohexyl (meth) acrylate, allyl glycidyl ether and the like can be mentioned.
Examples of the monomer having a methylol group include N-methylolacrylamide, N-methylolmethacrylamide, dimethylolacrylamide, and dimethylolmethacrylamide.
As the monomer having an alkoxymethyl group, an ethylenically unsaturated monomer having an alkoxymethyl group is preferable, and specifically, for example, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, N- Butoxymethylmethacrylamide and the like can be mentioned.
Examples of the monomer having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxy. Examples include silane.
These may be used alone or in combination of two or more.

Further, the above-mentioned acrylic polymer may further have a monomer other than the above as a monomer unit in order to improve various qualities and physical properties. Examples of such a monomer include a monomer having a carboxyl group (excluding (meth) acrylic acid), a monomer having an amide group, a monomer having a cyano group, a monomer having a hydroxyl group, an aromatic vinyl monomer, and the like. Can be mentioned.
Furthermore, various vinyl-based monomers having functional groups such as a sulfonic acid group and a phosphoric acid group, and vinyl acetate, vinyl propionate, vinyl versaticate, vinylpyrrolidone, methylvinyl ketone, butadiene, ethylene, propylene, vinyl chloride, and chloride Vinyl chloride and the like can also be used as needed.
These may be used alone or in combination of two or more. Further, the other monomer may belong to two or more of the above-mentioned monomers at the same time.

Examples of the monomer having an amide group include (meth) acrylamide and the like.
As the monomer having a cyano group, an ethylenically unsaturated monomer having a cyano group is preferable, and specific examples thereof include (meth) acrylonitrile.
Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate and the like.

Examples of the aromatic vinyl monomer include styrene, vinyltoluene, α-methylstyrene and the like. Styrene is preferred.

The acrylic polymer is obtained, for example, by a usual emulsion polymerization method. The method of emulsion polymerization is not particularly limited, and a conventionally known method can be used.

For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary as basic composition components in an aqueous medium, a monomer composition containing each of the above-mentioned monomers can be used. An acrylic polymer can be obtained by polymerization. In the case of polymerization, a method of making the composition of the supplied monomer composition constant in the entire polymerization process, a method of giving a morphological composition change of the particles of the resin dispersion produced by sequentially or continuously changing the composition in the polymerization process, etc. , Various methods are available as needed.

Surfactants are compounds having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Various surfactants include non-reactive surfactants and reactive surfactants, preferably reactive surfactants, more preferably anionic reactive surfactants, and even more preferably sulfonic acids. It is a reactive surfactant having a group.
The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the monomer composition. The surfactant may be used alone or in combination of two or more.

The radical polymerization initiator is one that radically decomposes with a heat or a reducing substance to initiate addition polymerization of the monomer, and either an inorganic initiator or an organic initiator can be used. Further, as the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used.
The radical polymerization initiator can be preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. The radical polymerization initiator may be used alone or in combination of two or more.

Examples of the above 3) polyvinyl alcohol-based resin include polyvinyl alcohol and polyvinyl acetate.

4) Examples of the fluororesin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer and the like. Can be mentioned.

A polymer having high rigidity in an electrolytic solution is a polymer that can be dissolved or dispersed in a solvent (hereinafter referred to as "solvent-based polymer") but can be dissolved or dispersed in water (hereinafter referred to as "aqueous polymer"). May be good.
As the solvent-based polymer, among the above-mentioned thermoplastic polymers, a polymer having solubility in an organic solvent and / or a polymer having dispersibility in an organic solvent may be used.
The aqueous polymer may be in the form of an aqueous dispersion (hereinafter referred to as "latex") containing water and a granular polymer dispersed in water, or the polymer itself may have a site having a high affinity for water. ..
Among them, an aqueous polymer is preferable, and a latex is more preferable, from the viewpoint of the coatability of the polymer or the electrical characteristics of the power storage device. Latex can be formed, for example, when the thermoplastic polymer is obtained by emulsion polymerization.

As the polymer in the latex, it is preferable to use at least one selected from the group consisting of an acrylic polymer, a fluororesin and a styrene-butadiene rubber.

When the aqueous polymer contains an acrylic polymer, it has been described in 2) above in order to suppress the swelling of the aqueous polymer in the electrolytic solution, that is, to appropriately reduce the degree of swelling of the aqueous polymer with respect to the electrolytic solution. Among the (meth) acrylic compounds, it is preferable to use a monomer having an SP value that is appropriately different from the solubility parameter (SP value) of the electrolytic solution.

The SP value of the electrolytic solution is arbitrarily determined according to the desired storage device design.
For example, the electrolyte for a non-aqueous electrolyte secondary battery generally contains one or more carbonates as the non-aqueous solvent. Examples of the carbonate include ethylene carbonate (EC, SP value derived by the Hildebrand SP value (hereinafter referred to as “Hildebrand SP value”): 14.7), propylene carbonate (PC, Hildebrand SP value: 13.3). ), Dimethyl carbonate (DMC, Hildebrand SP value: 9.9), diethyl carbonate (DEC, Hildebrand SP value: 8.8), methyl ethyl carbonate (MEC) and the like.
The SP value of a mixture of two or more carbonates is the sum of _{the product (SP n} V _n ) of the SP value of each component and the volume ratio of each component. For example, the Hildebrand SP value of a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume / DEC volume = 2/3) is 11.6.

In order to improve the rigidity of the acrylic polymer in the electrolytic solution, the amount of the functional group having the SP value equal to or close to the SP value of the functional group of the electrolytic solution component is reduced in the (meth) acrylic compound. It is also preferable.

The monomer described above preferably has an appropriate degree of swelling in the electrolytic solution. If the degree of swelling of the monomer is too low, the affinity with the electrolytic solution deteriorates, and the battery characteristics also deteriorate. On the other hand, if the degree of swelling of the monomer is too high, the polymer cannot maintain its strength in the electrolytic solution, so that the rigidity of the polymer in the electrolytic solution decreases.

The thermoplastic polymer contains a monomer in which the difference between the Hildebrand SP value of the electrolytic solution and the Hildebrand SP value of the monomer (hereinafter referred to as “SP value difference”) is in the range of 0.5 to 4.0. Is preferable. When the SP value difference is 0.5 or more, the affinity between the electrolytic solution and the polymer is maintained appropriately, so that the polymer swells appropriately in the electrolytic solution and the rigidity of the polymer can be suppressed from decreasing. it can. On the other hand, when the SP value difference is 4.0 or less, the affinity between the electrolytic solution and the polymer becomes good, and the battery characteristics become good. The SP value difference is more preferably 1.0 to 3.5, further preferably 1.5 to 3.2, and particularly preferably 1.8 to 3.0.

The amount of the monomer having an SP value difference in the range of 0.5 to 4.0 is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, based on 100 parts by mass of the polymer containing the monomer as a constituent unit. , More preferably 60 parts by mass or more.
The amount of the monomer having an SP value difference in the range of 1.8 to 3.0 is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, based on 100 parts by mass of the polymer containing the monomer as a constituent unit. , More preferably 50 parts by mass or more.
By adjusting the amount of monomer whose SP value difference is in the range of 0.5 to 4.0 or 1.8 to 3.0 to the above mass ratio, the rigidity in the electrolytic solution can be maintained and the battery characteristics can be maintained. Can be compatible with each other.
On the other hand, the smaller the amount of the monomer having the SP value difference in the vicinity of 0 is, the more preferably 20 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by mass of the polymer containing the monomer having the SP value difference in the vicinity of 0 as a constituent unit. It is preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less.

In order to improve the rigidity of the acrylic polymer in the electrolytic solution, it is also preferable to adjust the degree of cross-linking of the acrylic polymer to an appropriate range. Since the strength of the acrylic polymer may decrease if the degree of cross-linking is excessively increased, the gel fraction of the acrylic polymer is preferably 85% to 99%, more preferably 90% to 97%. preferable.

When the aqueous polymer contains a fluororesin, among the fluororesins described in 4) above, polyvinylidene fluoride or a copolymer containing vinylidene fluoride and hexafluoropropylene as a copolymerization component is preferable, and vinylidene fluoride-hexafluoro. More preferred are propylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers and the like.
In order to improve the rigidity of the fluororesin in the electrolytic solution, the copolymerization ratio of hexafluoropropylene in the fluororesin is preferably in the range of 0.5 mol% to 15 mol%, for example, 1 More preferably, it is in the range of mol% to 10 mol%. It is also preferable to increase the molecular weight of the fluororesin, and the weight average molecular weight (Mw) of the fluororesin is preferably 100,000 or more, more preferably 300,000 or more, still more preferably 500,000 or more. The higher the crystallinity of the fluororesin, the more preferable it is, more preferably 15% or more, still more preferably 20% or more, and particularly preferably 25% or more.

When the aqueous polymer contains styrene-butadiene rubber, it is preferable to adjust the degree of cross-linking of the styrene-butadiene rubber to an appropriate range in order to improve the rigidity of the styrene-butadiene rubber in the electrolytic solution. If the degree of cross-linking is excessively increased, the strength of the styrene-butadiene rubber may decrease. Therefore, the gel fraction of the styrene-butadiene rubber is preferably 90% to 99%, preferably 95% to 98%. Is more preferable.

When a thermoplastic polymer is used as a polymer having high rigidity in an electrolytic solution, the glass transition temperature (hereinafter, also referred to as “Tg”) of the thermoplastic polymer is not particularly limited, but may be −50 ° C. or higher. It is preferably 20 ° C. or higher, more preferably 20 ° C. to 120 ° C., and even more preferably 20 ° C. to 100 ° C. When the Tg of the thermoplastic polymer is 20 ° C. or higher, stickiness of the outermost surface of the separator provided with the polymer layer can be suppressed, and the handleability tends to be improved. Further, when Tg is 120 ° C. or lower, the adhesion of the separator to the electrode (electrode active material) tends to be better.

Here, the glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it 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.
Further, "glass transition" refers to a DSC in which a change in calorific value accompanying a change in the state of a polymer as a test piece occurs on the endothermic side. Such a change in calorific value is observed as a shape of a stepwise change in the DSC curve. The “step-like change” refers to the portion of the DSC curve until the curve departs from the previous baseline on the low temperature side and shifts to a new baseline on the high temperature side. In addition, the combination of the step-like change and the peak is also included in the step-like change.
Further, the "inflection point" indicates a point where the gradient of the stepwise change portion of the DSC curve is maximized. Further, in the stepped change portion, when the upper side is the heat generating side, it can be expressed as a point where the upwardly convex curve changes to the downwardly convex curve. The “peak” refers to the portion of the DSC curve from when the curve leaves the baseline on the low temperature side to when it returns to the same baseline. “Baseline” refers to the DSC curve in the temperature range where no transition or reaction occurs on the test piece.

The Tg of the thermoplastic polymer can be appropriately adjusted by, for example, changing the type of the monomer used for producing the thermoplastic polymer and the compounding ratio of each monomer. The Tg of the thermoplastic polymer is based on the Tg of the homopolymer generally shown for each monomer used in its production (eg, described in the "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the mixing ratio of the monomers. It can be roughly estimated. For example, a thermoplastic polymer containing a high proportion of monomers such as styrene, methylmethacrylate, and acrylonitrile that give a polymer of Tg at about 100 ° C. has a high Tg. Further, for example, a thermoplastic polymer containing a high ratio of monomers such as butadiene giving a polymer of Tg at about -80 ° C, n-butylacryllate giving a polymer of Tg at about -50 ° C, and 2-ethylhexylacryllate. Has a low Tg.
Further, the Tg of the polymer can be estimated from the FOX formula (the following formula (2)). As the glass transition temperature of the thermoplastic polymer, the one measured by the method using the DSC is adopted.
1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + Wi / Tgi + ... Wn / Tgn (2)
{In the formula, Tg (K) indicates the Tg of the copolymer, Tgi (K) indicates the Tg of the homopolymer of each monomer i, and Wi indicates the mass fraction of each monomer}.

Further, it is preferable that the thermoplastic polymer-containing layer formed on the substrate has at least two glass transition temperatures. As a result, it is possible to better balance the adhesiveness to the electrode and the handleability.

When the thermoplastic polymer-containing layer has at least two glass transition temperatures, it is preferable that at least one of the glass transition temperatures is present in a region of less than 20 ° C. As a result, the adhesion to the base material is further improved. As a result, the separator has an effect of being more excellent in adhesion to the electrode. From the same viewpoint, it is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer used is in the region of 15 ° C. or lower. More preferably, it is present in a region of −30 ° C. or higher and 15 ° C. or lower. The glass transition temperature existing in the region of less than 20 ° C. exists only in the region of -30 ° C. or higher and 15 ° C. or lower from the viewpoint of improving the adhesion between the thermoplastic polymer and the substrate and maintaining the handleability even better. Is preferable.

When the thermoplastic polymer has at least two glass transition temperatures, it is preferable that at least one of the glass transition temperatures is present in a region of 20 ° C. or higher. This has the effect of further improving the adhesiveness and handleability between the separator and the electrode. Further, it is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer used is in the region of 20 ° C. or higher and 120 ° C. or lower. More preferably, it is 50 ° C. or higher and 120 ° C. or lower. When the glass transition temperature exists in the above range, better handleability can be imparted. Further, the adhesion between the electrode and the separator, which is developed by pressurization during battery production, can be further enhanced. The glass transition temperature existing in the region of 20 ° C. or higher exists only in the region of 20 ° C. or higher and 120 ° C. or lower from the viewpoint of further improving the adhesion between the thermoplastic polymer and the substrate and maintaining the handleability even better. It is more preferable that the substance is present only in the region of 50 ° C. or higher and 120 ° C. or lower.

The fact that the thermoplastic polymer has at least two glass transition temperatures can be achieved by, for example, a method of blending two or more kinds of thermoplastic polymers, a method of using a thermoplastic polymer having a core-shell structure, and the like. However, it is not limited to these methods. The core-shell structure is a polymer in the form of a double structure in which a polymer belonging to the central portion and a polymer belonging to the outer shell portion have different compositions.
In particular, in polymer blends and core-shell structures, the glass transition temperature of the entire thermoplastic polymer can be controlled by combining a polymer with a high glass transition temperature and a polymer having a low glass transition temperature. In addition, a plurality of functions can be imparted to the entire thermoplastic polymer.

For example, in the case of blending, stickiness resistance is obtained by blending two or more types of a polymer having a glass transition temperature of 20 ° C. or higher and a polymer having a glass transition temperature of less than 20 ° C. And the applicability to the base material can be better compatible with each other. As for the mixing ratio when blending, the ratio of the polymer existing in the region where the glass transition temperature is 20 ° C. or higher and the polymer existing in the region where the glass transition temperature is lower than 20 ° C. is 0.1: 99.9 to 99. It is preferably in the range of .9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably 60:40 to 90: It is 10.

In the case of the core-shell structure, the adhesiveness and compatibility with other materials (for example, polyolefin microporous membrane) can be adjusted by changing the type of outer shell polymer. Further, by changing the type of the polymer belonging to the central portion, it is possible to adjust the polymer to have improved adhesion to the electrode after hot pressing, for example. Alternatively, the viscoelasticity can be controlled by combining a highly viscous polymer and a highly elastic polymer.
The glass transition temperature of the shell of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably less than 20 ° C, more preferably 15 ° C or lower, and even more preferably −30 ° C or higher and 15 ° C or lower. The glass transition temperature of the core of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20 ° C. or higher, more preferably 20 ° C. or higher and 120 ° C. or lower, and further preferably 50 ° C. or higher and 120 ° C. or lower.

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 ensure the adhesiveness and rigidity of the thermoplastic polymer in the electrolytic solution and further improve the cycle characteristics or rate characteristics of the power storage device, the base material coated with the polymer after the separator is impregnated in the electrolytic solution. The area ratio of the surface is preferably 100% or less, 80% or less, 70% or less, 60% or less, or 50% or less, and the area ratio is 5% or more, 10% or more, 15% or more, or It is preferably 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).

FIG. 7 is a schematic view showing the planar shape of the polymer layer existing on at least one surface of the base material in the separator. The polymer layer on the substrate may have, for example, a planar shape shown in black in FIG. The polymer layer exists in a planar shape such as a dot shape (FIG. 7A), a grid pattern (FIG. 7B), a linear shape (FIG. 7C), a striped shape (FIG. 7D), and a hexagonal pattern (FIG. 7E). May be good.

A Voronoi polygon obtained by performing Voronoi division on a granular thermoplastic polymer (hereinafter, also referred to as "thermoplastic polymer particles") arranged on a separator base material in order to improve high temperature storage characteristics in addition to the rigidity of the power storage device. dispersion of the area of _{(s i)} (σ ²⁾ is preferably at 0.01 to 0.7.

Voronoi division refers to dividing a plurality of points (mother points) arranged at arbitrary positions in a certain metric space into regions according to which mother point another point in the same space is close to. .. The diagram including the region thus obtained is called a Voronoi diagram. Generally, in the Voronoi diagram, the boundary line of a plurality of regions becomes a part of the bisector of each mother point, and each region forms a polygon (Voronoi polygon).

｛式中、ｓ_ｉは、ボロノイ多角形の面積の実測値であり、ｍは、ボロノイ多角形の面積の実測値の平均値であり、かつｎは、ボロノイ多角形の総数である｝
により算出される値である。観察視野においてボロノイ分割を行なった時に、閉じられていない領域は、上記式の計算対象としないものとする。閉じられていない領域としては、例えば、観察視野の境界に粒子が存在し、その粒子の全体が観察されていない時に、その粒子に対してボロノイ分割を行なうことによって得られる領域が挙げられる。
従って、セパレータ表面の少なくとも一部の領域を撮影して得られた画像において、その画像の端に位置する粒子については、その粒子全体が観察されているか否かを確認することが好ましい。 When observing the surface of the separator in a specific field of view, one thermoplastic polymer particle is regarded as one circle having an average diameter (l) in the field of view. Then, a vertical bisector is drawn between the plurality of adjacent thermoplastic polymer particles, and the polygon surrounded by the vertical bisector for each particle is referred to as a "Voronoi polygon".
Voronoi A distributed polygonal area ^{_{(s i) (σ 2)}} , the following formula:

{Wherein, s _i is the measured value of the area of the Voronoi polygon, m is an average value of the measured values of the area of the Voronoi polygon, and n is the total number of Voronoi polygons}
It is a value calculated by. When the Voronoi division is performed in the observation field of view, the unclosed area is not included in the calculation target of the above equation. Examples of the unclosed region include a region obtained by performing Voronoi division on the particles when the particles are present at the boundary of the observation field of view and the entire particles are not observed.
Therefore, in an image obtained by photographing at least a part of the surface of the separator, it is preferable to confirm whether or not the entire particles of the particles located at the edges of the image are observed.

In the present embodiment, dispersion of the Voronoi polygon area (s ^_i) (σ ^₂₎ is indicative of the level of variation in the arrangement of the granular thermoplastic polymer on the substrate. This dispersion (σ ² ) is considered to represent the distribution or agglomeration state of the granular thermoplastic polymer on the coated surface. When Voronoi dispersion polygonal area (s ^_i) (σ ^₂₎ is 0.01 or more, it can be evaluated that the thermoplastic polymer of the particulate is placed on the surface of the separator moderately agglomerated. Therefore, in this case, the adhesiveness between the electrode and the separator tends to be sufficient. When this dispersion (σ ² ) is 0.7 or less, it can be evaluated that the granular thermoplastic polymer is not excessively agglomerated on the separator surface. Therefore, in this case, the ion resistance on the surface of the separator is made uniform, lithium ions are not concentrated in a specific region of the surface, and the generation of metallic lithium is suppressed, so that the high temperature storage characteristics of the power storage device tend to be excellent. It is in. The value of this dispersion (σ ² ) is preferably 0.01 or more and 0.6 or less, more preferably 0.01 or more and 0.5 or less, and 0.1 or more and 0.4 or less. Is more preferable, and 0.1 or more and 0.35 or less is particularly preferable.

The average particle size of the granular thermoplastic polymer is preferably 10 nm to 2,000 nm, more preferably 50 nm to 1,500 nm, still more preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, and particularly preferably 150. It is ~ 800 nm, most preferably 200 ~ 750 nm. Setting the average particle size to 10 nm or more ensures that the dimensions of the granular thermoplastic polymer do not enter the pores of the base material when the granular thermoplastic polymer is applied to the base material containing at least the porous membrane. Means to be done. Therefore, in this case, it is preferable from the viewpoint of improving the adhesiveness between the electrode and the separator and the cycle characteristics of the power storage device. Further, when the average particle size is 2,000 nm or less, an amount of granular thermoplastic polymer necessary for achieving both the adhesiveness between the electrode and the separator and the cycle characteristics of the power storage device is applied onto the base material. It is preferable from the viewpoint of construction. The average particle size of the granular thermoplastic polymer can be measured according to the method described in the following Examples.

In order to know the area density of the thermoplastic polymer particles and the dispersion (σ ² _{) of the area (s i} ) of the Voronoi polygon obtained by performing Voronoi division on the thermoplastic polymer particles, the surface of the separator is observed. The observation means is appropriately selected according to the size or distribution state of the thermoplastic polymer particles coated on the separator, and any method can be adopted. For example, an electron microscope, an atomic force microscope, an optical microscope, a differential interference microscope, and the like can be used. Among these, when dealing with the distributed state of dispersed particles as in the present embodiment, it is preferable to use an electron microscope or an atomic force microscope.

An average observation field of view of the polymer layer coated on the separator surface should be ensured within the observation field of view. In addition, the projected area in the observation field of view should be appropriately adjusted so that the average distribution state of the dispersed particles can be grasped. For example, the number of dispersed particles used for calculation is preferably about 80 to 200 particles / field of view. This observation field of view can be obtained by observing the polymer layer with a preset observation means and magnification. For example, FIG. 1 is an example of a photograph in which the surface of a polymer layer is observed with a scanning electron microscope as an observation means and a magnification of 10,000 times. FIG. 1 clearly captures a state in which thermoplastic polymer particles having a particle diameter of about 500 nm are dispersed and present on the surface of the polymer layer. By capturing the state in which the thermoplastic polymer particles are dispersed on the surface of the polymer layer in this way, the dispersed state of the thermoplastic polymer particles can be analyzed by Voronoi partitioning.

In the observation using a scanning electron microscope, an appropriate magnification is set for the analysis by Voronoi division according to the particle size of the thermoplastic polymer particles. Specifically, the number of thermoplastic polymer particles observed in one field of view is preferably set to a magnification of 40 to 300, more preferably 60 to 240, and even more preferably 80 to 200. .. This makes it possible to appropriately perform the analysis by Voronoi division. For example, if the particle size is about 500 nm, it is appropriate to set the magnification to 10,000 times, and if the particle size is about 200 nm, the magnification is set to about 30,000 times for analysis by Voronoi division. Appropriate.

The thermoplastic polymer particles contained in the observation field obtained by the above observation method are specified. For example, the thermoplastic polymer particles are identified from the observation field with the naked eye or using image processing software. FIG. 2 is an example showing the result of automatically identifying the thermoplastic polymer particles included in the observation field of FIG. 1 using image processing software. By identifying the thermoplastic polymer particles in a preset method and magnification observation field, the total number of particles, the diameter of each particle, and the projected area of each particle are calculated (see also FIG. 3 below). In that case, it is preferable to specify only the particles whose whole is included in the observation field of view.

The Voronoi division defined above can be performed on the thermoplastic polymer particles identified in a particular field of view on the surface of the separator. Specifically, the surface of the coating film after the surface of the separator is coated with the thermoplastic polymer is photographed to obtain an image. The Voronoi polygon can be drawn by regarding the thermoplastic polymer particles identified in the obtained image as circles having an average diameter (l) and performing Voronoi partitioning. For example, the Voronoi polygon may be drawn manually or using image processing software. Then, the area of the drawn Voronoi polygon is calculated.

For example, FIG. 3 is an example of the result of obtaining a Voronoi polygon by performing Voronoi division on a plurality of thermoplastic polymer particles identified in FIG. Among the Voronoi polygons shown in FIG. 3, the number and area of the Voronoi polygons corresponding to the closed area are automatically calculated by using image processing software, and the result is shown in FIG.

The above-mentioned observation method and image processing method determine the projected area in the observation field, and obtain the total number of thermoplastic polymer particles in the field, the projected area, and the area of the Voronoi polygon. Then, according to the above definition, can be calculated for the thermoplastic polymer particles in the visual field, the area density, and Voronoi dispersion polygonal area (s _i) a (sigma ^2).
However, the distribution of the thermoplastic polymer particles may change depending on the observation field of view. Therefore, as the area density and the variance (σ ² ), it is preferable to adopt the average value of the values calculated for each of the plurality of observation fields. The number of visual fields is preferably 3 or more.

Particularly preferably, the average value of the values calculated for the 95 visual fields determined as follows is adopted.
i) Each measurement field of view: image taken with a scanning electron microscope ii) How to set the field of view:
a) Set the field of view of the starting point,
b) Nine visual fields consisting of regions sequentially adjacent to the starting point visual field in the horizontal direction, nine visual fields consisting of regions sequentially adjacent in the vertical direction, and the starting point visual field 19 Set the field of view,
c) The area defined by the 19 visual fields is set as the starting point section, and the area is set as the starting point.
d) Four sections consisting of regions sequentially adjacent to the starting point section in the uniaxial direction at intervals of 10 mm are set.
e) For each of the four compartments, 19 visual fields are set at positions similar to the 19 visual fields in the origin compartment, and f) a total of 95 visual fields (19 visual fields x 5) in the four compartments and the origin compartment. Section) is set as the measurement field of view.

Each measurement field of view is preferably an image taken by setting the magnification so that the number of thermoplastic polymer particles observed in one field of view is 80 to 200.

Hereinafter, a preferable setting method of the 95 visual fields in the present embodiment will be described with reference to the drawings.
i) As the captured image, as described above, it is preferable to use an image captured by a scanning electron microscope having a magnification of 10,000 times. For example, it is an image shown in FIG. FIG. 5 is a diagram showing a part of an image of thermoplastic polymer particles on a substrate as a model, taken with a scanning electron microscope having a magnification of 10,000 times.
In the image of FIG. 5, first, the field of view (10) of the starting point is set. Since one field of view is composed of images taken by a scanning electron microscope with a magnification of 10,000 times, the scale of the one field of view is about 10 μm × 10 μm, and a field of view suitable for boronoy division evaluation based on thermoplastic polymer particles can be obtained. Configure. Next, nine visual fields (1 to 9) that are sequentially adjacent to the visual field (10) of the starting point in the lateral direction (X-axis direction) are set. Each of these fields of view (1 to 9) is composed of captured images having the same magnification as the field of view (10) of the starting point, and is sequentially set in one direction with one side in common with an adjacent region. Next, nine visual fields (11 to 19) that are sequentially adjacent to the visual field (10) of the starting point in the vertical direction are set. Each of these visual fields (11 to 19) is composed of the same region as the visual field (10) of the starting point, and is sequentially set in one direction with one side in common with the adjacent region.

Subsequently, the region defined by the 19 visual fields is set as the starting point section (I). Since the starting point section (I) is composed of a square region having two sides, the upper side of the fields of view 1 to 10 in FIG. 5 and the right side of the fields of view 10 to 19, the scale of one section is about 100 μm × 100 μm. The dispersion calculated from the 19 fields of view constituting the section (I) can be evaluated as a value more accurately representing the state of the separator surface, which corresponds to an image captured by a scanning electron microscope having a magnification of 1,000 times.
In this embodiment, in order to further accurately evaluate the state of the separator surface, five sections equivalent to the above one section are provided and the evaluation is performed. Specifically, refer to FIG. FIG. 6 is an overall image of the thermoplastic polymer particles on the substrate shown in FIG. In FIG. 6, four compartments (II to V) sequentially adjacent to the starting point compartment (I) in the uniaxial direction at intervals of 10 mm are set. Each of these four compartments consists of the same region as the origin compartment (I).
Next, for each of these four compartments (II to V), 19 visual fields are set at positions similar to the 19 visual fields in the starting point compartment (I). Then, a total of 95 visual fields (19 visual fields × 5 compartments) in the four compartments (II to V) and the visual field (I) of the starting point are set as observation visual fields of the thermoplastic polymer particles on the substrate.

The above observation of the separator surface is preferably performed on a region of the separator surface that is not involved in ion conduction. For example, it is possible to observe a separator that has just been manufactured and has not yet been incorporated into the power storage element. When the power storage element is in use or after use, it is also possible to observe the so-called "ear" portion of the separator (the region near the outer edge of the separator and not involved in ion conduction). , Which is a preferred embodiment in the present embodiment.
As can be understood from the above evaluation method, when the 95 field of view is the observation target, the separator piece having a length of about 40 mm is the measurement target, so that the dispersed state of the thermoplastic polymer on the separator surface can be accurately evaluated.

The fact that the thermoplastic polymer particles can be divided into Voronoi as described above means that the thermoplastic polymer particles exist as single-layer particles in the polymer layer formed on the substrate without substantially overlapping. It shows that there is. For example, when the thermoplastic polymers are overlapped in multiple layers in the polymer layer, the Voronoi division cannot be performed because the concept of the area occupied by a single particle does not hold.
The separator in the present embodiment is arranged so that the thermoplastic polymer particles in the polymer layer formed on the substrate do not substantially overlap, and then the area density and dispersion (σ ² ) described above. However, it is preferable that each is adjusted within the above range.

The means for adjusting the area density and dispersion (σ ² ) of the thermoplastic polymer within the above range is not limited, but for example, the thermoplastic polymer content and coating in the coating liquid to be applied to the base material. It can be adjusted by changing the coating amount of the working liquid, the coating method and the coating conditions. More specifically, the viscosity of the thermoplastic polymer solution is adjusted to be high, and the surface to be coated of the porous film is coated while applying a shearing force, whereby the thermoplastic polymer is dispersed and arranged in the above range. be able to.

The form (pattern) of the polymer layer on the substrate is not particularly limited, but it is preferable that the thermoplastic polymer particles are dispersed with each other over the entire surface of the substrate so as to satisfy the above dispersion. .. The thermoplastic polymer particles may form clusters in a part of the regions, but it is necessary that the particles are dispersed to such an extent that the above dispersion range is satisfied as a whole. Further, the polymer particles may be stacked in a part of the region, but it is necessary that the polymer particles are dispersed to such an extent that the above dispersion range is satisfied as a whole.

When the polymer layer is present in a pattern on the substrate, the area density and dispersion (σ ² ) are preferably evaluated using images taken of the region where the polymer layer is present, respectively.

[2. Polymer layer forms a continuous layer]
"The polymer layer forms a continuous layer" means that one or more interfaces are not formed in the polymer layer itself. When the polymer on the base material forms a continuous layer, the rigidity of the adhesive layer itself composed of the continuous layer is increased, so that the rigidity of the power storage device is also easily increased.

Examples of the polymer for forming the continuous layer include polyethylene oxide (PEO), polyacrylic nitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyether urethane (PEU), and polyethyl acrylate. (PEA), PVDF-hexafluoropropylene (HFP) copolymer, or a combination thereof and the like can be mentioned.

In order to form the polymer layer as a continuous layer, it is preferable to dissolve the polymer in a good solvent to obtain a coating liquid, and then apply the coating liquid to the base material. At this time, in order to ensure the permeability of the separator, the ratio of the coating area of the polymer layer to the substrate may be adjusted, or the polymer layer formed by coating may be made porous by using solvent phase separation or the like. More preferred.

In order to adjust the ratio of the coating area of the polymer layer to the base material to such an extent that the permeability of the separator is ensured, it is preferable to disperse or dissolve the polymer in a volatile solvent such as acetone to obtain a coating liquid. In that case, the polymer concentration in the coating liquid is preferably less than 30% by mass, more preferably less than 15% by mass, and even more preferably less than 10% by mass. After the coating liquid is applied to the substrate to form the polymer layer, it is preferable that the volatile solvent such as acetone is removed from the polymer layer by drying.

When the polymer layer on the substrate is made porous by solvent phase separation or the like, the permeability of the separator can be ensured even if the coating area ratio of the coating liquid containing the polymer is 100%. Specifically, the polymer is dissolved in a good solvent to prepare a coating liquid. This coating liquid is applied onto the substrate and immersed in a suitable coagulating liquid. This causes the polymer to solidify while inducing a phase separation phenomenon. In this solidification step, the polymer layer (continuous layer) has a porous structure. Then, the coagulant is removed by washing with water and dried.

As the coating liquid, for example, a good solvent that dissolves a polyvinylidene fluoride-based resin may be used. As a good solvent, for example, a polar amide solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, or dimethylformamide can be preferably used. From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation with the polar amide solvent in addition to the above-mentioned good solvent. Examples of the phase separating agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol and the like. The phase separator is preferably added within a range in which an appropriate viscosity can be ensured for coating. As the solvent, from the viewpoint of forming an appropriate porous structure, it is preferable to use a mixed solvent of 60% by weight or more of a good solvent and 40% by weight or less of a phase separating agent.

As the coagulating liquid, water, a mixed solvent of water and a good solvent, or a mixed solvent of water, a good solvent and a phase separation agent can be used. In particular, a mixed solvent of water, a good solvent and a phase separation agent is preferable.

In order to form the polymer layer as a continuous layer, it is also preferable to make the adhesive layer a continuous layer by using a film-forming auxiliary. Specifically, by incorporating a film-forming auxiliary into latex, the adhesive layer formed of latex can form a continuous layer. Examples of the film-forming auxiliary include glycol-based compounds and acetate-based compounds.

In order to form a continuous layer using an aqueous polymer, it is also preferable to use a plurality of aqueous polymers that are easily fused to each other. By using a plurality of aqueous polymers that are easily fused to each other, the motility of the surface of the continuous layer can be enhanced, and the degree of swelling of the continuous layer with respect to the electrolytic solution can be adjusted within an appropriate range.

[3. Form an adhesive layer containing a mixture of inorganic filler and polymer]
By applying a mixture of an inorganic filler and a polymer as a binder for an inorganic filler to a base material, a composite of the inorganic filler and the polymer can be formed in a coating layer (adhesive layer) formed on the base material. it can. The composite of the inorganic filler and the polymer improves the rigidity of the adhesive layer.

As the binder for the inorganic filler, the polymer described in 1 or 2 above may be used. If desired, the coating liquid may further contain a dispersant, water, an organic solvent and the like.

The inorganic filler is not particularly limited, but preferably has high heat resistance and electrical insulation, and is electrochemically stable within the range of use of the lithium ion secondary battery.
Examples of the inorganic filler include aluminum compounds, magnesium compounds, and other compounds.
Examples of the aluminum compound include aluminum oxide, aluminum silicate, aluminum hydroxide, aluminum hydroxide oxide, sodium aluminate, aluminum sulfate, aluminum phosphate, hydrotalcite and the like.
Examples of the magnesium compound include magnesium sulfate and magnesium hydroxide.
Other compounds include, for example, oxide-based ceramics, nitride-based ceramics, clay minerals, silicon carbide, calcium carbonate, barium titanate, asbestos, zeolites, calcium silicate, magnesium silicate, diatomaceous soil, silica sand, etc. Examples include glass fiber. Examples of the oxide-based ceramics include silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide and the like. Examples of the nitride-based ceramics include silicon nitride, titanium nitride, and boron nitride. Examples of clay minerals include talc, montmorillonite, sericite, mica, amesite, bentonite and the like.
These may be used alone or in combination of two or more.

Among the above, from the viewpoint of electrochemical stability and heat resistance, one or more selected from the group consisting of aluminum oxide, aluminum hydroxide oxide, and aluminum silicate is preferable. Specific examples of aluminum oxide include alumina and the like. Specific examples of aluminum hydroxide oxide include boehmite and the like. Specific examples of aluminum silicate include kaolinite, decite, nacrite, halloysite, pyrophyllite and the like.

As the aluminum oxide, alumina is more preferable from the viewpoint of electrochemical stability. By adopting particles containing alumina as a main component as the inorganic filler constituting the porous layer, it is possible to realize a very lightweight porous layer while maintaining high permeability. Further, even when the porous layer thickness is thinner, heat shrinkage of the porous membrane at high temperature is suppressed, and excellent heat resistance tends to be exhibited. Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be preferably used. Of these, α-alumina is most preferable because it is thermally and chemically stable.

As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit due to the generation of lithium dendrite. By adopting particles containing boehmite as a main component as the inorganic filler constituting the porous layer, a very lightweight porous layer can be realized while maintaining high permeability. Further, even when the porous layer thickness is thinner, heat shrinkage of the porous membrane at high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite, which can reduce ionic impurities that adversely affect the characteristics of the power storage device, is more preferable.

Among aluminum silicates, kaolinite (hereinafter, also referred to as kaolin), which is mainly composed of kaolin minerals, is preferable from the viewpoint of light weight and air permeability. Kaolin includes wet kaolin and calcined kaolin obtained by calcining the wet kaolin. Of these, calcined kaolin is particularly preferable in terms of electrochemical stability because it releases impurities in addition to releasing water of crystallization during the calcining treatment. By adopting particles containing calcined kaolin as a main component as the inorganic filler constituting the porous layer, a very lightweight porous layer can be realized while maintaining high permeability. Further, even when the porous layer thickness is thinner, heat shrinkage of the porous membrane at high temperature is suppressed, and excellent heat resistance tends to be exhibited.

The average particle size of the inorganic filler is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.2 μm or more and 5.0 μm or less, and further preferably 0.4 μm or more and 3.0 μm or less. preferable. Adjusting the average particle size of the inorganic filler within the above range is preferable from the viewpoint of increasing the air permeability and suppressing heat shrinkage at high temperatures.

The particle size distribution of the inorganic filler is preferably as follows. The minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 7 μm or less. The maximum particle size / average particle size ratio is preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less. Adjusting the particle size distribution of the inorganic filler within the above range is preferable from the viewpoint of suppressing heat shrinkage at high temperatures. The particle size distribution of the inorganic filler may further have one or more particle size peaks between the maximum particle size and the minimum particle size. As a method of adjusting the particle size distribution of the inorganic filler, for example, a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill or the like to adjust the particle size distribution to a desired size, or blending fillers having a plurality of particle size distributions after adjustment. The method of doing this can be mentioned.

Examples of the shape of the inorganic filler include a plate shape, a scale shape, a polyhedron, a needle shape, a columnar shape, a spherical shape, a spindle shape, and a lump shape. A plurality of types of inorganic fillers having the above shape may be used in combination. Among these, from the viewpoint of improving permeability, one or more shapes selected from the group consisting of plate-like, scaly-like, and polyhedron are preferable.

From the viewpoint of rigidity, it is preferable that the aspect ratio of the inorganic filler is small. Specifically, the aspect ratio of the inorganic filler is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. The aspect ratio can be calculated from the major axis / minor axis by measuring the major axis and the minor axis of the particles from an SEM image or the like. When five or more particles are confirmed in the SEM image, the aspect ratio may be the average value of the major axis / minor axis calculated for the five particles.

The weight ratio of the inorganic filler to the polymer in the coating liquid can be arbitrarily determined according to the rigidity and battery characteristics required for the power storage device, but the inorganic filler: polymer = 95: 5 to 20:80 is used. It is preferable, more preferably 90:10 to 30:70, and even more preferably 85: 15 to 40:60.

When the inorganic filler and the polymer are composited, the filler-rich portion in the adhesive layer allows ionic components such as lithium ions to pass through more easily than the binder-rich portion, so that the area ratio of the substrate surface covered with the coating liquid is 100. Even when it is%, the rigidity of the power storage device and the electrical characteristics can be compatible with each other.

The thickness of the adhesive layer containing the mixture of the inorganic filler and the polymer is not limited, but may be 0.1 μm to 10 μm from the viewpoint of achieving both adhesiveness and rigidity of the adhesive layer in the electrolytic solution. It is preferably 0.5 μm to 8 μm.

[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 coating conditions of the coating liquid containing the polymer, the coating area ratio to the substrate of the polymer is preferably from 5% to 70%, the coating basis weight of the polymer, 0.05 g / m ² to 1 It is preferably 0.0 g / m ² and / or the coating thickness of the polymer is preferably 0.1 μm to 3 μm. When applying a coating liquid containing a granular thermoplastic polymer that can be subjected to the Voronoi division described above, the coating thickness is preferably 0.1 μm to 0.8 μm.

The method of 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, etc. 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 of 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 base material, the adhesive resin fills the surface and inside of the pores, resulting in reduced permeability. It ends up. Therefore, as the medium of the coating liquid, a poor solvent of the 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 of 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.

[Perforated layer containing inorganic filler and resin binder]
The separator may further include a porous layer containing an inorganic filler and a resin binder. The position where the separator is provided with the filler porous layer may be one side or both sides of the base material.

In order to form the porous layer, the inorganic filler described in 3 above may be used.

The ratio of the inorganic filler in the porous filler layer can be appropriately determined from the viewpoint of the binding property of the inorganic filler, the permeability of the separator, the heat resistance, etc., but is 50% by mass or more and less than 100% by mass. It is preferable, more preferably 70% by mass or more and 99.99% by mass or less, further preferably 80% by mass or more and 99.9% by mass or less, and particularly preferably 90% by mass or more and 99% by mass or less.

The type of resin binder is not particularly limited, but when the separator includes a porous filler layer, it is insoluble in the electrolyte of the lithium ion secondary battery and is electrochemical within the range of use of the lithium ion secondary battery. It is preferable to use a resin binder that is stable.

Specific examples of the resin binder include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers and ethylene-tetrafluoroethylene copolymers. Fluororesin-containing rubbers such as 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; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, poly Examples thereof include resins having a melting point and / or a glass transition temperature of 180 ° C. or higher, such as etherimide, polyamideimide, polyamide, and polyester.

As the resin binder, a resin latex binder is preferable. When a resin latex binder is used, when a filler porous layer containing an inorganic filler and a binder is laminated on at least one side of the base material, a part or all of the resin binder is dissolved in a solvent, and then the obtained solution is used. Compared with the case where the resin binder is laminated on at least one side of the base material and the resin binder is bound to the porous film by dipping in a poor solvent or removing the solvent by drying, the ion permeability is less likely to decrease and high output characteristics can be obtained. It tends to be easy. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics and tends to provide high safety.

The resin latex binder is obtained by emulsion polymerization of an aliphatic conjugated diene-based monomer, an unsaturated carboxylic acid monomer, and other monomers copolymerizable with these, from the viewpoint of improving electrochemical stability and binding property. Is preferred. The method of emulsion polymerization is not particularly limited, and a conventionally known method can be used. The method of 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 one-stage polymerization, two-stage polymerization, or multi-stage polymerization can be adopted. Any of these 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, when the filler porous layer containing the inorganic filler and the binder is laminated on at least one surface of the polyolefin porous membrane, the ion permeability is less likely to decrease and high output characteristics can be easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics and is easy to obtain 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 formed, heat shrinkage is good and 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 1 μm or more from the viewpoint of improving heat resistance and insulating properties, and preferably 50 μm or less from the viewpoint of improving the capacity and permeability of the battery.

Layer density of the filler porous layer is preferably from 0.5 to 2.0 g / cm ^3, more preferably 0.7~1.5cm ^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 2.0 g / cm ³ or less, the air permeability tends to decrease. It is in.

Examples of the method for forming the porous filler layer include a method in which a coating liquid containing an inorganic filler and a resin binder is applied to at least one surface of the base material to form the porous filler layer. The coating liquid may further contain a solvent, a dispersant and the like in order to stabilize the dispersion and improve the coatability. The method of applying the coating liquid to the base material is not particularly limited as long as the required layer thickness or coating area can be realized.

[Base material]
The at least one porous membrane contained in the base material is not particularly limited, and may be, for example, a polyolefin microporous membrane formed from a polyolefin resin composition containing polyolefin.

In the present embodiment, the content of the polyolefin resin in the polyolefin microporous membrane is not particularly limited, but is based on the total mass of all the components constituting the porous membrane from the viewpoint of shutdown performance when used as a separator base material. It is preferably 50% or more and 100% or less, more preferably 60% or more and 100% or less, and further preferably 70% or more and 100% or less.

The polyolefin resin is not particularly limited, but may be a polyolefin resin used for ordinary extrusion, injection, inflation, blow molding, etc., and ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers such as 1-octene and copolymers, multistage polymers and the like can be used. Moreover, these polyolefins can also be used alone or in mixture.

Typical examples of polyolefin resins are low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, ethylene propylene. Examples include rubber. When a polyolefin microporous membrane is used as a separator base material, a resin containing high-density polyethylene as a main component is preferable because it has a low melting point and high strength.

In order to improve the heat resistance of the polyolefin microporous film, it is more preferable to use a porous film composed of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.

The three-dimensional structure of polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, from the viewpoint of achieving both heat resistance and a good shutdown function. It is more preferably 4 to 10% by mass.

Polyolefin resins other than polypropylene include, but are not limited to, homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene. Be done. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, ethylene-propylene random copolymer and the like.

From the viewpoint of shutdown characteristics in which the pores of the polyolefin microporous film are closed by thermal melting, as a polyolefin resin other than polypropylene, polyethylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and ultra high molecular weight polyethylene is used. Is preferably used. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having ^{a density of 0.93 g / cm 3 or more measured according to JIS K 7112.}

The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and further preferably 100,000 or more. Less than 1 million. When the viscosity average molecular weight is 30,000 or more, the melt tension during melt molding is increased, the moldability is improved, and the polymer tends to be entangled with each other to increase the strength, which is preferable. On the other hand, when the viscosity average molecular weight is 12 million or less, it becomes easy to uniformly melt-knead, and the formability of the sheet, particularly the thickness stability tends to be excellent, which is preferable. Further, when the viscosity average molecular weight is less than 1,000,000, the pores are easily closed when the temperature rises, and a good shutdown function tends to be obtained, which is preferable.

For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000 and having a viscosity average molecular weight of less than 1 million is used. You may use it.

The polyolefin microporous membrane may contain any additive. The additive is not particularly limited, and is, for example, a polymer other than polyolefin; inorganic particles; antioxidants such as phenol-based, phosphorus-based, and sulfur-based; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; Examples thereof include light stabilizers; antistatic agents; antifogging agents; coloring pigments and the like.

The puncture strength of the polyolefin microporous membrane is not particularly limited, but is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2000 g / 20 μm or less, and more preferably 1000 g / 20 μm or less. The puncture strength of 200 g / 20 μm or more is preferable from the viewpoint of suppressing the film rupture due to the active material or the like that has fallen off during battery winding, and from the viewpoint of suppressing the concern of short circuit due to expansion and contraction of the electrode due to charging and discharging. .. On the other hand, the puncture strength of 2000 g / 20 μm or less is preferable from the viewpoint of reducing the width shrinkage due to the relaxation of orientation during heating.

The puncture strength can be adjusted by adjusting the stretching ratio and / or the stretching temperature of the microporous polyolefin membrane. The puncture strength is measured by the method described in the examples.

The porosity of the polyolefin microporous membrane is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, and preferably 80% or less. A porosity of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, a porosity of 90% or less is preferable from the viewpoint of ensuring puncture strength. The porosity can be adjusted by changing the draw ratio of the polyolefin microporous membrane. Porosity is measured by the method described in the Examples.

The film thickness of the polyolefin microporous membrane is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less. It is preferable that the film thickness is 2 μm or more from the viewpoint of improving the mechanical strength. On the other hand, it is preferable that the film thickness is 100 μm or less because the occupied volume of the separator in the battery is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.

The air permeability of the polyolefin microporous membrane is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, preferably 1000 seconds / 100 cc or less, and more preferably 500 seconds / 100 cc or less. It is preferable that the air permeability is 10 seconds / 100 cc or more from the viewpoint of suppressing self-discharge of the power storage device. On the other hand, it is preferable that the air permeability is 1000 seconds / 100 cc or less from the viewpoint of obtaining good charge / discharge characteristics. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the polyolefin microporous membrane. The air permeability is measured by the method described in the examples.

The average pore size of the polyolefin microporous membrane is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. It is preferable that the average pore diameter is 0.15 μm or less from the viewpoint of suppressing the self-discharge of the power storage device and suppressing the decrease in capacity when the separator for the power storage device is used. The average pore size can be adjusted by changing the draw ratio when producing the microporous polyolefin membrane.

From the viewpoint of safety of the power storage device, the short temperature, which is an index of the heat resistance of the polyolefin microporous membrane, is preferably 140 ° C. or higher, more preferably 150 ° C. or higher, and further preferably 160 ° C. or higher.

The method for producing the microporous polyolefin membrane is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to form a sheet, stretched in some cases, and then made porous by extracting the plasticizer, or a polyolefin resin composition is melt-kneaded and highly drawn. A method of extruding by ratio and then peeling the polyolefin crystal interface by heat treatment and stretching to make it porous. A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and molded on a sheet, and then stretched to form a polyolefin and an inorganic filler. Examples thereof include a method of making the polyolefin resin composition porous by peeling off the interface with the polyolefin, and a method of immersing the polyolefin resin composition in a poor solvent for the polyolefin to solidify the polyolefin and at the same time removing the solvent to make the polyolefin porous.

[Separator for power storage device]
Since the separator is provided with a polymer layer on the base material, it has excellent adhesion to the electrode active material.

When the aluminum foil is pressed on the outermost surface of the separator in which the polymer is present on the separator substrate for 3 minutes under the conditions of a temperature of 25 ° C. and a pressure of 5 MPa, the peeling strength between the separator and the aluminum foil ( Hereinafter, it is also referred to as “normal temperature peeling strength”), which is preferably 8 N / m (8 gf / cm) or less, more preferably 7 gf / cm or less, and further preferably 6 gf / cm or less.

Since the aluminum foil is used as an electrode current collector, the adhesiveness and blocking resistance of the separator at room temperature to the electrode can be easily confirmed by measuring the peel strength at room temperature. When the normal temperature peeling strength exceeds 8 gf / cm, the stickiness of the separator is observed, and the slit property or the winding property of the separator is impaired.

When the aluminum foil is pressed against the outermost surface of the separator in which the polymer is present on the separator substrate for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa, the peeling strength between the separator and the aluminum foil is obtained. (Hereinafter also referred to as "heat peeling strength") is preferably 9.8 N / m (10 gf / cm) or more, more preferably 15 gf / cm or more, and further preferably 20 gf / cm or more. ..

Since the aluminum foil is used as an electrode current collector, the adhesiveness of the separator to the electrode during heating can be easily confirmed by measuring the heat peeling strength. If the heat peeling strength is less than 10 gf / cm, peeling of the electrode and the separator is observed during the assembly process or use of the power storage device, which causes the performance of the power storage device to deteriorate.

The normal temperature peel strength and the heat peel strength are measured by the method described in Examples.

The thickness of the separator is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, and more preferably 50 μm or less from the viewpoint of ensuring the rigidity of the power storage device and the strength of the separator. It is preferable, and more preferably 30 μm or less. When the polymer is present on the separator base material, the thickness obtained by measuring the separator portion in which the polymer is present is the thickness of the separator.

The air permeability of the separator is preferably equal to or higher than the air permeability of the base material containing at least one porous membrane in order to obtain good charge / discharge characteristics of the power storage device. The air permeability of the separator is adjusted by the stretching temperature or stretching ratio when producing a polyolefin microporous film as a base material, the area ratio of the polymer present on the base material, the existence form, and the like.

From the viewpoint of safety of the power storage device, the short temperature, which is an index of the 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.

[Power storage device]
By adhering the separator according to the present embodiment to the electrode, a laminated body in which the separator and the electrode are laminated can be obtained.

The laminate 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 transparency. 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 stacking the separator and the electrode according to the present embodiment and heating and / or pressing as necessary. Heating and / or pressing can be performed when the electrodes and separators are overlapped. 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.

A vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be prepared and superposed on the electrode.

The laminate can also be produced by laminating the positive electrode-separator-negative electrode-separator or the negative electrode-separator-positive 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 perform pressurization and heating at the same time.

When the power storage device is a secondary battery, the laminated body is wound in a circular or flat spiral shape to obtain a wound body, and the wound body is stored in a storage body such as a can or a pouch type case, and further. A secondary battery can be obtained by injecting an electrolytic solution and, if desired, further heating and / or pressing.

When a non-aqueous electrolyte secondary battery is manufactured using the separator according to the present embodiment, known positive electrodes, negative electrodes, and non-aqueous electrolyte 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 graphite, non-graphitizable carbon, easily graphitized carbon, and composite carbon; 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, ethyl methyl carbonate and the like. Examples of the electrolyte include lithium salts such as _{LiClO 4} , LiBF ₄ , and LiPF _6.

In the present embodiment, the rigidity of the power storage device can be improved by improving the adhesiveness and rigidity of the adhesive portion of the separator in the electrolytic solution. Therefore, the separator according to the present embodiment is used for a laminate type or pouch type power storage device formed by further performing heat pressing after putting the wound laminate and the electrolytic solution in the accommodating body. Is preferable.

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.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the examples. The methods for measuring and evaluating various physical properties used in the following production examples, examples, and comparative examples are as follows. Unless otherwise specified, various measurements and evaluations were carried out under the conditions of room temperature of 23 ° C., 1 atm and relative humidity of 50%.

<Measurement method and evaluation method>
(1) Glass transition temperature of the raw material polymer An appropriate amount of the raw material polymer aqueous dispersion (nonvolatile content: 38 to 42%, pH: 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130 ° C. for 30 minutes. Approximately 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve were obtained in a DSC measuring device (DSC6220 manufactured by Shimadzu Corporation) in a nitrogen atmosphere. The measurement conditions were as follows.
(1st stage temperature rise program)
The temperature was started at 70 ° C., the temperature was raised at a rate of 15 ° C. per minute, and after reaching 110 ° C., the temperature was maintained at that temperature for 5 minutes.
(2nd stage temperature lowering program)
The temperature was lowered from 110 ° C. to 40 ° C. per minute, and after reaching −50 ° C., the temperature was maintained at that temperature for 5 minutes.
(3rd stage temperature rise program)
The temperature was raised from −50 ° C. to 130 ° C. at a rate of 15 ° C. per minute. Data of DSC and DDSC were obtained at the time of raising the temperature in the third stage.
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 the glass transition temperature (the glass transition temperature). It was calculated as Tg).

(2) Average particle size of the raw material polymer The 50% particle size (nm) of the raw material 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”).

(3) Gel fraction of raw material polymer (toluene insoluble content)
A raw polymer coating liquid (nonvolatile content: 38 to 42%, pH: 9.0) is 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. did. 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 matter 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 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 dry product 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 [%]

(4) Degree of swelling of the raw material polymer with respect to the electrolytic solution (degree of swelling of the electrolyte solvent)
The raw material polymer or the raw material polymer dispersion was allowed to stand in an oven at 130 ° C. for 1 hour, and then the dried polymer was cut to a weight of 0.5 g, and ethylene carbonate: ethylmethyl carbonate = 1: 2 (volume ratio). ) Was placed in a 50 mL vial with 10 g of the mixed solvent. 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.
The degree of swelling of the thermoplastic polymer with respect to the electrolytic solution (times) = (Wa-Wb) ÷ (Wb)

(5) Strength of Raw Material Polymer after Impregnation with Electrolyte The raw material polymer was dried at 60 ° C. overnight to obtain a dried polymer product. After impregnating 1.0 g of the dried polymer product with 10 ml of the electrolytic solution for 24 hours, the strength of the raw material polymer after the impregnated with the electrolytic solution was evaluated based on the following evaluation criteria.
<Evaluation criteria>
S: Maintains the shape (does not cut) even when pushed with tweezers.
A: If you push it in with tweezers, it will eventually cut.
B: It cuts the moment you push in the tweezers.
C: The polymer itself is not self-supporting and difficult to grasp with tweezers.

(6) Weight average molecular weight (hereinafter, also referred to as "Mw")
By gel permeation chromatography (GPC), the weight average molecular weight of the polymer was calculated as a polystyrene-equivalent value using the calibration curve of the polystyrene standard sample.

(7) Viscosity average molecular weight (hereinafter, also referred to as "Mv")
Based on ASRM-D4020, the ultimate viscosity [η] of the decalin solvent at 135 ° C. was determined, and the Mv of polyethylene was calculated by the following formula.
[Η] = 0.00068 × Mv ^0.67
Further, the Mv of polypropylene was calculated by the following formula.
[Η] = 1.10 × Mv ^0.80

(8) Grain of base material (polyolefin microporous membrane) A sample of 10 cm × 10 cm square was cut out from the polyolefin microporous membrane, and the weight was measured with an electronic balance AEL-200 manufactured by Shimadzu Corporation. Is multiplied by the obtained weight 100 at 1 m ² per layer of basis weight (g / ^{m 2)} was calculated.

(9) Film thickness (μm) of polyolefin microporous membrane
A 10 cm x 10 cm square sample is cut from a polyolefin microporous membrane, 9 points (3 points x 3 points) are selected in a grid pattern, and a room temperature of 23 ± 2 is used using a microthickening instrument (Toyo Seiki Seisakusho type KBM). The film thickness was measured at ° C. The average value of the obtained measured values at 9 points was calculated as the film thickness of the polyolefin microporous film.

(10) Porosity (%) of polyolefin microporous membrane
A 10 cm × 10 cm square sample is cut from a polyolefin microporous film, the volume (cm ³ ) and mass (g) of ^{the sample are determined, and the film density is regarded as 0.95 (g / cm 3} ), and the pores are pored using the following equation. The rate was calculated.
Porosity = (1-mass / volume / 0.95) x 100

(11) Air permeability of polyolefin microporous membrane (seconds / 100cc)
^{In accordance with JIS P-8117, an area of 645 mm 2} (circle with a diameter of 28.6 mm) using a Garley type air permeability meter GB2 (trademark, inner cylinder mass: 567 g) manufactured by Toyo Seiki Seisakusho Co., Ltd. The time (seconds) through which 100 cc of air passed was measured as the air permeability (seconds / 100 cc) for the polyolefin microporous membrane having.

(12) Puncture strength of polyolefin microporous membrane (g)
A microporous polyolefin membrane was fixed with a sample holder having an opening diameter of 11.3 mm using a handy compression tester KES-G5 (trademark) manufactured by Katou Tech. Next, the central portion of the fixed polyolefin microporous membrane is subjected to a puncture test under the conditions of a needle tip with a radius of curvature of 0.5 mm, a puncture speed of 2 mm / sec, and a temperature of 25 ° C. (G) was obtained.

(13) Average pore size (μm) of polyolefin microporous membrane
Since it is known that the fluid inside the capillary follows the Knudsen flow when the mean free path of the fluid is larger than the pore size of the capillary and the Poiseuil flow when it is smaller, the air in the permeability measurement of the polyolefin microporous film is known. It is assumed that the flow of water follows the flow of Knudsen, and the flow of water in measuring the permeability of the microporous polyolefin membrane follows the flow of Poiseuille.
The average pore diameter d (μm) is the air permeation rate constant R _gas (m ³ / (m ² · sec · Pa)), the water permeation rate constant R _liq (m ³ / (m ² · sec · Pa)), Obtained from the molecular rate ν (m / sec) of air, viscosity η (Pa · sec) of water, standard pressure Ps (= 101325 Pa), pore ratio ε (%), and film thickness L (μm) using the following equation. It was.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
Here, R _gas was obtained from the air permeability obtained in (9) above using the following equation.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ^-4 ) × (0.01276 × 101325))
Further, R _liq was obtained from the water permeability (cm ³ / (cm ² · sec · Pa)) by using the following equation.
R _liq = water permeability / 100
For the water permeability, a polyolefin microporous membrane previously soaked in ethanol is set in a stainless steel liquid-permeable cell having a diameter of 41 mm, the membrane ethanol is washed with water, and then water is applied at a differential pressure of about 50,000 Pa. The amount of water permeation (cm ³ ) after 120 seconds of permeation was measured to calculate the amount of water permeation per unit time, unit pressure, and unit area.
Further, ν is derived from the gas constant R (= 8.314), the absolute temperature T (K), the pi, and the average molecular weight M of air (= 2.896 × 10 ^-2 kg / mol) using the following equation. I was asked.
ν = ((8R × T) / (π × M)) ^1/2

(14) Adhesion of substrate or separator to electrodes (simple adhesion test)
A base material or separator and a positive current collector (aluminum foil manufactured by Fuji Kako Paper Co., Ltd., thickness: 20 μm) as an adherend were cut into 30 mm × 150 mm, respectively, and laminated to obtain a laminate, and then the laminate was obtained. A sample was obtained by sandwiching it between Teflon (registered trademark) sheets (Nachias Corporation Naflon (trademark) PTFE sheet TOMBO-No. 9000). Each of the obtained samples was pressed in the stacking direction for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa to obtain a test press.

The peel strength between the base material or separator of each test press obtained and the positive electrode current collector was determined according to JIS K6854-2 using the Autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. The tension was measured at a tensile speed of 200 mm / min. Based on the value of the peel strength, the adhesiveness with the electrode was evaluated according to the following evaluation criteria.
<Evaluation criteria>
A (good): 9.8 N / m (10 gf / cm) or more B (allowable): 5 N / m or more and less than 9.8 N / m C (bad): less than 5 N / m

(15) Handling property of base material or separator (blocking resistance)
A test press was obtained in the same manner as in (12) above, except that the press was performed for 3 minutes under the conditions of a temperature of 25 ° C. and a pressure of 5 MPa. The peel strength between the base material or separator of the test press and the positive electrode current collector is 200 mm at a tensile speed according to JIS K6854-2 using the Autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. Measured at / min. The handleability was evaluated according to the following evaluation criteria based on the value of the peel strength.
<Evaluation criteria>
A (good): less than 8N / m (8gf / cm) B (allowable): 8N / m or more and less than 12N / m C (bad): 12N / m or more

(16) Peeling Strength Test of Inorganic Filler Coating Layer in Electrolyte The polyolefin microporous film coated with the inorganic filler layer was cut out to a size of 76 mm × 26 mm to prepare a sample, and the sample before ultrasonic treatment was prepared. The mass (D) was weighed. This sample was placed in a 50 mL vial containing 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (volume ratio) at 25 ° C., and placed in an ultrasonic cleaner (model US-102 manufactured by SND Co., Ltd.). Was used for 10 minutes of ultrasonic treatment at an oscillation frequency of 38 kHz. Then, the sample was cut out, washed with ethanol, dried at room temperature, and the mass (E) of the sample after sonication was weighed.
The microporous polyolefin membrane used as the base material was cut out to a size of 76 mm × 26 mm, and the mass (F) of the cut out microporous polyolefin membrane was weighed.
The residual ratio of the porous layer in the electrolytic solution after the ultrasonic treatment was calculated from the following formula.
Residual rate (%) = {(EF) / (DF)} x 100

(17) Adhesive strength between the raw material polymer and the base material (bonding property to the base material)
A tape (manufactured by 3M) having a width of 12 mm and a length of 100 mm was attached to the raw material polymer coating layer of the separator. The force at which the tape was peeled from the sample at a speed of 50 mm / min was measured using a 90 ° peel strength measuring device (manufactured by IMADA, product name IP-5N). Based on the obtained measurement results, the adhesive strength was evaluated according to the following evaluation criteria.
A (good): 59N / m (6gf / mm) or more B (allowable): 40N / m or more and less than 59N / m C (bad): less than 40N / m

(18) Observation method of polymer layer (Voronoi division)
i) Evaluation using three fields of view Using a scanning electron microscope S-4800 (manufactured by Hitachi High-Technologies Corporation), the surface of the polymer layer on the separator is 3 at a magnification of 10,000 or 30,000 depending on the particle size of the polymer particles. I took a picture with one field of view. These three area density of particulate thermoplastic polymer included in the visual field, Voronoi variance (sigma ^2), and the projected area (c _i) and Voronoi polygon area polygon area (s _i) (s _i) the ratio _{(c i} / _s i) with, respectively, as a mean value of the three-field. Here, the dispersion of the area density, Voronoi polygon area ^{_{(s i) (σ 2)}} , and the ratio _{(c i} / _s i), the image processing software "A picture kun" (registered trademark; manufactured by Asahi Kasei Engineering Corporation ) Was used to calculate automatically. Moreover, when the Voronoi division was performed in the observation field of view, the unclosed region was not included in the calculation of the area of the Voronoi polygon.

ii) Evaluation using 95 visual fields Using a scanning electron microscope S-4800 (manufactured by Hitachi High-Technologies Corporation), a photograph of the surface of the polymer layer on the separator at a magnification of 10,000 or 30,000 depending on the particle size of the polymer particles. I took a picture. Using the obtained images, 5 sections and 95 fields of view were set as shown in FIGS. 5 and 6. These 95 pieces of area density of granular thermoplastic polymer included in the visual field, the area density of the Voronoi polygons, dispersion of the area of the Voronoi polygon ^{_{(s i) (σ 2)}} , and the projected area (c _i) Voronoi the ratio of the polygon area _{(s i) (c i /} s i), in the same manner as in the above i), was obtained as an average of each 95 field.

(19) Rate characteristics a. Preparation of positive electrode 90.4% by mass of nickel-manganese-cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ^{3) as the positive electrode active material,} As a conductive auxiliary material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) Particle size 48 nm) was mixed at a ratio of 3.8% by mass, and polyvinylidene 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-methylpyrrolidone (NMP). A slurry was prepared by dispersing in the mixture. This slurry is applied to one side of an aluminum foil (thickness 20 μm) which is a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then compression molded using a roll press machine. A positive electrode was prepared. The amount of the positive electrode active material coated at this time was 109 g / m ² .

b. Graphite powder A as prepared negative active material of the negative electrode (density 2.23 g / cm ^3, number average particle diameter 12.7 [mu] m) 87.6% by weight and graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) was 9.7% by mass, and 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 of diene rubber-based latex as a binder. A slurry was prepared by dispersing (in terms of solid content) (an aqueous solution having a solid content concentration of 40% by mass) in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm to be a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression-molded with a roll press to prepare a negative electrode. The amount of the negative electrode active material coated at this time was 5.2 g / m ² .

c. _{Preparation of non-aqueous electrolyte solution A non-aqueous electrolyte solution is prepared by dissolving LiPF 6} as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) so as to have a concentration of 1.0 mol / L. Prepared.

d. Battery assembly A separator or a microporous polyolefin membrane (base material itself) was cut out into a circle of 24 mmφ, and a positive electrode and a negative electrode were cut out into a circle of 16 mmφ, respectively. The negative electrode, the separator (or the base material), and the positive electrode were stacked in this order and pressed or heat-pressed so that the positive electrode and the active material surface of the negative electrode faced each other, and housed in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolytic solution into this container and sealing the container.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in step 1 at 25 ° C. with a current value of 3 mA (about 0.5 C) to a battery voltage of 4.2 V, the current value is started to be throttled from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was carried out for a total of about 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V, for a total of about 3 Charged for hours. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 12 mA (about 2.0 C) was defined as a 2 C discharge capacity (mAh).
Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) x 100
<Evaluation criteria for rate characteristics (%)>
S (Remarkably good): Rate characteristic of more than 90% A (Good): Rate characteristic of more than 85% and 90% or less B (Allowable): Rate characteristic of more than 80% and 85% or less C (Bad): Rate of 80% or less Characteristic

(20) Cycle characteristics Cycle characteristics were evaluated using the simple batteries assembled as in (17) a to d above, except that the separators obtained in Examples and Comparative Examples were used.
The above battery is constantly charged to a voltage of 4.2 V with a current value of 1 / 3C, then charged with a constant voltage of 4.2 V for 8 hours, and then discharged to a final voltage of 3.0 V with a current of 1 / 3C. Was done. Next, after a constant current charge to a voltage of 4.2 V with a current value of 1 C, a constant voltage charge of 4.2 V was performed for 3 hours, and then discharged to a final voltage of 3.0 V with a current of 1 C. Finally, after constant current charging to 4.2 V with a current value of 1 C, constant voltage charging of 4.2 V was performed for 3 hours to prepare for pretreatment. Note that 1C represents a current value that discharges the reference capacity of the battery in one hour.
The pretreated battery was discharged to a discharge end voltage of 3 V with a discharge current of 1 A under the condition of a temperature of 25 ° C., and then charged to a charge end voltage of 4.2 V with a charge current of 1 A. Charging and discharging were repeated with this as one cycle. Then, using the capacity retention rate after 200 cycles with respect to the initial capacity (capacity in the first cycle), the cycle characteristics were evaluated according to the following criteria.
<Evaluation criteria for cycle characteristics>
S (Remarkably good): Capacity retention rate of 90% or more and 100% or less A (Good): Capacity retention rate of 85% or more and less than 90% B (Allowable): Capacity retention rate of 80% or more and less than 85% C (Defective) : Capacity retention rate of 70% or more and less than 80% D (significantly defective): Capacity retention rate of less than 70%

(21) High-temperature storage characteristics In addition to using the separators obtained in Examples and Comparative Examples, the high-temperature storage specific evaluation was performed using the simple batteries assembled as in (17) a to d above.
A method in which the above battery is charged to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C) under 25 ° C., and after reaching the battery voltage of 4.2 V is maintained and the current value is started to be throttled from 3 mA. The battery was charged for a total of 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V with a current value of 3 mA.
Next, in a 25 ° C atmosphere, the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and after reaching 4.2 V, the current value is started to be throttled from 6 mA. It was charged for 3 hours. Then, the discharge capacity when discharged to a battery voltage of 3.0 V with a current value of 6 mA was defined as A (mAh).
Next, in a 25 ° C atmosphere, the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and after reaching 4.2 V, the current value is started to be throttled from 6 mA. It was charged for 3 hours. The cells kept in a charged state were held in an atmosphere of 60 ° C. for 7 days. After that, the cell was taken out and discharged to a battery voltage of 3.0 V at a current value of 6 mA under an atmosphere of 25 ° C. Next, in a 25 ° C atmosphere, the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and after reaching 4.2 V, the current value is started to be throttled from 6 mA. It was charged for 3 hours. Further, the discharge capacity when discharged to a battery voltage of 3.0 V with a current value of 6 mA was defined as B (mAh).
Then, using the ratio of B to A, the high temperature storage characteristics were evaluated according to the following criteria.
<Evaluation criteria for high temperature storage characteristics>
A (good): The ratio of the discharge capacity B to the discharge capacity A is 70% or more.
B (allowable): The ratio of the discharge capacity B to the discharge capacity A is less than 70%.

(22) 3-point bending strength test (cell rigidity difference)
(22-1) Difference in rigidity when using a positive electrode (22-1a) Preparation of the first press body Aluminum laminate (manufactured by Showa Denko Packaging Co., Ltd .: St ON25 / AL40 / OPP40) is cut to a width of 60 mm and a length of 80 mm. Then, the three sides were sealed with a heat sealer to obtain a storage body.
Positive electrode (manufactured by enertech, positive electrode material: LiCoO ₂ , conductive aid: acetylene black, binder: PVDF, LiCoO ₂ / acetylene black / PVDF (weight ratio) = 95/2/3, L / W: 36 mg / cm on both sides ^2. Density: 3.9 g / cc, thickness of Al current collector: 15 μm, thickness of positive electrode after pressing: 107 μm) and separators prepared in Examples or Comparative Examples are 30 mm wide and 30 mm long, respectively. It was cut to 180 mm, and the cut positive electrode and separator were overlapped to obtain a first laminate.
The first laminated body was wound so as to have a length of about 27 mm and a width of 30 mm under the condition of three turns, to obtain a first wound body.
The first wound body is put into the container prepared above, and as an electrolytic solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume / DEC volume = 2/3, LiPF ₆ concentration: 1 M). , 0.5 ml of Hildebrand SP value as a mixture = 11.6) was added, sealed with a heat sealer, and allowed to stand for 12 hours to obtain a first pressed body.
The first pressed body was pressed for 30 minutes under the conditions of a temperature of 80 ° C. and a pressure of 1 MPa to obtain a first pressed body. The first wound body in the first pressed body had dimensions of 30 mm × 27 mm.

(22-1b) Preparation of second press body Positive electrode (manufactured by polyolefin, positive electrode material: LiCoO ₂ , conductive aid: acetylene black, binder: PVDF, LiCoO ₂ / acetylene black / PVDF (weight ratio) = 95/2 / 3, L / W: 36 mg / cm ² on both sides, density: 3.9 g / cc, thickness of Al current collector: 15 μm, thickness of positive electrode after pressing: 107 μm), used in Examples or Comparative Examples. The above (21-1a) was obtained except that the polyolefin microporous film was cut to a width of 30 mm and a length of 180 mm, respectively, and the cut positive electrode and the polyolefin microporous film were laminated to obtain a second laminate. ), A second pressed body was obtained. The second wound body in the second pressed body had dimensions of 30 mm × 27 mm.

(22-1c) Rigidity difference between the first press body and the second press body With the digital force gauge "DS2-50N" (product name, manufactured by Imada Co., Ltd.) equipped with a piercing jig (A type A-4). A pedestal having two support bases was attached to an electric measurement stand "MX2-500N" (product name, manufactured by Imada Co., Ltd.).
The distance between the two supports was adjusted to 15 mm.
The 27 mm side of the wound body is arranged in the direction parallel to the direction connecting the two supports, and the first pressed body and the second pressed body are pierced with respect to the winding direction of the wound body. It was set on two supports so that the direction was vertical and the tip of the piercing jig and the center of the winding body could be in contact with each other.
The individually set first press body and second press body were subjected to a three-point bending strength test at a pushing speed of 50 mm / min, and the following formula:
Rigidity difference = F _{first press body max} −F _{second press body max}
{In the formula, the F _{first press body max} is the maximum when the load (N) required to maintain the pushing speed of the piercing jig with respect to the first press body at 50 mm / min is plotted over time. The value and F _{second press body max} are when the load (N) required to maintain the pushing speed of the piercing jig with respect to the second press body at 50 mm / min is plotted over time. Maximum value}
The difference in rigidity between the first press body and the second press body was calculated.

(22-2) Difference in rigidity when using a negative electrode Negative electrode (manufactured by enertech, negative electrode material: graphite, conductive auxiliary agent: acetylene black, binder: SB latex, graphite / acetylene black / SB latex (weight ratio) = 95 / 2/3, L / W: 18 mg / cm ² on both sides, density: 1.5 g / cc, thickness of Cu current collector: 10 μm, thickness of negative electrode after pressing: 140 μm) The rigidity difference was calculated in the same manner as in 21-1).

<Manufacturing of raw material polymer>
[Manufacturing of raw material polymers (low Tg) 1A, 2A and 4A with low glass transition temperature, and raw material polymers (high Tg) 1B, 2B and 4B to 6B with high glass transition temperature]
In a reaction vessel equipped with a stirrer, a reflux cooler, a dropping tank and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution) 0.5 parts by mass and 0.5 parts by mass of "Adecaria Soap SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., 25% by mass aqueous solution) were added to raise the internal temperature of the reaction vessel to 80 ° C. While maintaining the temperature of 80 ° C., 7.5 parts by mass of ammonium persulfate (2% by mass aqueous solution) was added.

Five minutes after the addition of the ammonium persulfate aqueous solution, the monomer and other raw materials used in the “Emulsified solution” column of Table 1 were mixed for 5 minutes with a homomixer and added dropwise to the reaction vessel of the emulsion prepared. The whole amount was added dropwise over 150 minutes.

After 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. By adding an aqueous ammonium hydroxide solution (25% by mass aqueous solution) to the obtained emulsion to adjust the pH to 9.0, a latex containing 40% by mass of the raw material polymer was obtained.

[Providing low Tg raw material polymer 3A, high Tg raw material polymer 3B, and raw material polymer 7]
SB latex A (Tg: -8 ° C., particle size: 300 nm, toluene insoluble content: 96%, swelling degree: 1.2 times) shown in Table 1, SB latex B (Tg: 33 ° C., particle size: 300 nm, Toluene insoluble content: 95%, swelling degree: 1.4 times), and aqueous PVDF (Mw: 500,000, HPF ratio: 3 mol%) were prepared, and low Tg raw material polymer 3A and high Tg raw material polymer 3B, respectively. It was also used as a raw material polymer 7.

The physical properties of the raw material polymers 1A to 4A, 1B to 6B and 7 were evaluated by the above method. The evaluation results are shown in Table 1.

Description of abbreviations in Table 1 MMA: Methyl methacrylate CHMA: Cyclohexyl methacrylate IBXA: Isobornyl acrylate BMA: Butyl methacrylate BA: n-butyl EHA acrylate: 2-ethylhexyl acrylate MAA: AA methacrylate: HEMA acrylate: 2-Hydroxyethyl methacrylate AM: acrylamide GMA: Glycydyl methacrylate NaSS: Sodium p-styrene sulfonate A-TMPT: Trimethylol propantriacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.)
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 SB: Styrene-butadiene copolymer PVDF: Polyvinylidene fluoride HEP: Hexafluoropropylene

<Manufacturing of base material>
[Manufacturing Example B1]
(Manufacturing of base material B1-1)
Homopolymer high-density polyethylene with Mv of 700,000 was added to 45 parts by mass.
Homopolymer high-density polyethylene with Mv of 300,000 was added to 45 parts by mass.
With 5 parts by mass of polypropylene of homopolymer having Mv of 400,000,
Dry blended using a tumbler blender.

To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane was added as an antioxidant, and the tumbler blender was used again. The mixture was obtained by dry blending using.

The resulting mixture was fed to a twin-screw extruder in 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 extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll whose surface temperature is controlled to 80 ° C., and the extruded product is 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 112 ° C. at a magnification of 7 × 6.4 times by a simultaneous biaxial stretching machine. Then, the stretched product was immersed in methylene chloride to extract and remove liquid paraffin, dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.

Then, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a base material B1-1 which is a porous polyolefin resin film.

(Manufacturing of base material B1-2)
B1-B1-except that the thickness of the melt-kneaded product coming out of the T-die was adjusted so that the temperature of the simultaneous biaxial stretching machine was 110 ° C, the temperature of the tenter stretching machine was 132 ° C, and the stretching ratio was 2.1 times. Substrate B1-2 was prepared by the same method as in 1.

[Manufacturing Example B2]
(Manufacturing of base material B2-1)
Aluminum hydroxide (average particle size 1.0 μm) 96.0 parts by mass, acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C or less) 4.0 parts by mass, and polycarboxylic acid An aqueous ammonium solution (SN Dispersant 5468 manufactured by Sannopco Co., Ltd.) was uniformly dispersed in 100 parts by mass of water to prepare a coating liquid. Subsequently, the coating liquid was applied to the surface of the polyolefin resin porous film (base material B1-1) using a gravure coater. Then, it is dried at 60 ° C. to remove water, and aluminum hydroxide (a porous layer of an inorganic filler) is formed on a polyolefin resin porous membrane (base material B1-1) with a thickness of 2 μm. I got 1.

(Manufacturing of base material B2-2)
Except for using the raw material polymer 4A (low swelling degree and high strength) shown in Table 1 instead of acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C or less). Is a base material B2-2 in which aluminum hydroxide (a porous layer of an inorganic filler) is formed on a polyolefin resin porous membrane (base material B1-1) with a thickness of 2 μm in the same manner as in the production of the base material B2-1. Obtained.

Various physical properties of each of the obtained substrates were measured by the above method. The measurement results are shown in Table 2.

(Manufacturing of base material B2-3)
Aluminum hydroxide (multi-worked layer of inorganic filler) 2 μm is formed on the microporous polyolefin resin film on the other side of the base material B2-2 in the same manner as the base material B2-2, and both sides of the base material B1-1 are formed. A base material B2-3 in which an aluminum hydroxide layer was formed in an amount of 2 μm each was obtained.

<Examples I-1 to I-17, Examples I-19 to I-20, Comparative Examples I-1 to I-3>
Separators for power storage devices were prepared according to the combination of the polyolefin microporous membrane and the raw material polymer shown in Table 3 or 4. Specifically, the raw material polymer shown in Table 3 or 4 was uniformly dispersed in water at the concentration shown in Table 3 or 4, to prepare a coating liquid containing the raw material polymer. Next, the coating liquid is applied to one surface of the polyolefin microporous film shown in Table 3 or 4 under the coating conditions shown in Table 3 or 4, and dried at 60 ° C. to prepare the coating liquid. The water was removed. Further, the other side of the polyolefin microporous film was similarly coated with the coating liquid and dried again to prepare a separator for a power storage device having a thermoplastic polymer on both sides of the polyolefin microporous film.

<Example I-18>
20 parts by mass of the raw material polymer 2A and 80 parts by mass of the raw material polymer 2B were mixed in water to obtain a polymer mixture having a polymer concentration of 10% by mass.
An aqueous solution of ammonium polycarboxylic acid (SN Dispersant 5468 manufactured by San Nopco Ltd.) was prepared by dispersing 80 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm, aspect ratio 3.5) and 20 parts by mass of a polymer mixture in water. Further addition was obtained to obtain a polymer coating solution containing an inorganic filler.
A polymer coating solution containing an inorganic filler was applied to both sides of the polyolefin microporous film B1-1 using a gravure coater under the conditions of a coating area ratio of 100% and a coating thickness of 2 μm, and dried at 60 ° C. , Example I-18 separators were obtained.

The physical characteristics and evaluation results of the separators obtained in Examples I-1 to I-20 and Comparative Examples I-1 to I-3 are shown in Table 3 or 4.

From the comparison between Examples and Comparative Examples shown in Tables 3 and 4, the separators of Comparative Examples I-1 to I-3 have a small difference in cell rigidity even though they have good adhesiveness to the electrodes. It can be seen that the cycle characteristics are poor.

<Examples II-1 to II-3, Comparative Examples II-1 to II-3>
Separators for power storage devices were prepared according to the combination of the polyolefin microporous membrane and the raw material polymer shown in Table 5. Specifically, the raw material polymer shown in Table 5 was uniformly dispersed in water at the concentration shown in Table 5 to prepare a coating liquid containing the raw material polymer. Next, the coating liquid was applied to one surface of the polyolefin microporous film shown in Table 5 under the coating conditions shown in Table 5, and dried at 60 ° C. to remove water from the coating liquid. .. Further, the other side of the polyolefin microporous film was similarly coated with the coating liquid and dried again to prepare a separator for a power storage device having a thermoplastic polymer on both sides of the polyolefin microporous film.
The produced separator for a power storage device was measured and evaluated for its physical properties according to the above method, and particularly evaluated by Voronoi division. Table 5 shows the physical properties and evaluation results.

From the comparison of Examples II-1 to II-3 shown in Table 5, the dispersion (σ ² _{) of the area (s i} ) of the Voronoi polygon obtained by performing the Voronoi division of the adhesive layer is approximately 0.7 or less. It can be seen that, in addition to a good difference in cell rigidity, good high-temperature storage characteristics can also be obtained.

Claims (7)

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;
The following formula (f):
Fsep _max −Fbase _max ≧ 10 (f)
{In the formula, Fsep _max is a load (N) for maintaining the pushing speed of the indenter with respect to the laminated wound body 1 of the electrode and the separator for the power storage device and the storage body 1 in which the electrolytic solution is stored at 50 mm / min. Is the maximum value when plotted over time, and Fbase _max is the pushing speed of the indenter with respect to the laminated wound body 2 of the base material and the electrode and the storage body 2 in which the electrolytic solution is stored by 50 mm. This is the maximum value when the load (N) for maintaining at / min is plotted over time}
Satisfy the relationship represented by
The electrode is a positive electrode or a negative electrode, and is
The positive electrode is a positive electrode material: LiCoO ₂ , a conductive auxiliary agent: acetylene black, a binder: PVDF, LiCoO ₂ / acetylene black / PVDF (weight ratio) = 95/2/3, L / W (grain) : 36 mg / on both sides. cm ² , density: 3.9 g / cc, thickness of Al current collector: 15 μm, thickness of positive electrode after pressing: 107 μm.
The negative electrode is a negative electrode material: graphite, a conductive auxiliary agent: acetylene black, a binder: a latex of a styrene-butadiene copolymer, a latex of a graphite / acetylene black / styrene-butadiene copolymer (weight ratio) = 95/2/3, L / W. (Grain) : 18 mg / cm ² on both sides, density: 1.5 g / cc, thickness of Cu current collector: 10 μm, thickness of negative electrode after pressing: 140 μm.
The laminated wound body 1 and the laminated wound body 2 are wound so as to have a length of 27 mm and a width of 30 mm under the condition of three turns.
The electrolytic solution is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC volume / DEC volume = 2/3, LiPF ₆ concentration: 1M).
The storage body 1 and the storage body 2 were pressed under the conditions of a temperature of 80 ° C. and a pressure of 1 MPa.
The indenter is pushed into the storage body 1 or the storage body 2 from a direction perpendicular to the winding direction of the laminated winding body 1 or the laminated winding body 2.
The dimensions and materials of the storage body 1 are the same as the dimensions and materials of the storage body 2.
The polymer forms an adhesive layer mixed with the inorganic filler, and the adhesive layer containing the mixture of the inorganic filler and the polymer is formed on the outermost surface of the separator, and the mixing ratio of the inorganic filler and the polymer is high. The mass is 85:15 to 40:60 ,
The aspect ratio of the inorganic filler is 5.0 or less.
The base material is a polyolefin microporous film, and the polymer is one or two of 1) conjugated diene polymer, 2) acrylic polymer, 3) polyvinyl alcohol resin, and 4) fluororesin. Separator for power storage device including the above. The separator for a power storage device according to claim 1, wherein the electrode satisfies the relationship represented by the above formula (f) regardless of whether the electrode is the positive electrode or the negative electrode. The power storage device according to claim 1 or 2, wherein after impregnating the electrolytic solution with the power storage device separator, the area ratio of the surface of the base material coated with the polymer is 5% to 80%. Separator. When the aluminum foil is pressed on the outermost surface of the power storage device separator where the polymer is present for 3 minutes under the conditions of a temperature of 25 ° C. and a pressure of 5 MPa, the power storage device separator and the aluminum foil are pressed. The separator for a power storage device according to any one of claims 1 to 3, wherein the peel strength between the two is 8 N / m (8 gf / cm) or less. When the aluminum foil is pressed on the outermost surface of the power storage device separator where the polymer is present for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa, the power storage device separator and the aluminum foil are pressed. The separator for a power storage device according to any one of claims 1 to 4, wherein the peel strength between the two is 9.8 N / m (10 gf / cm) or more. The separator for a power storage device according to any one of claims 1 to 5, wherein the polymer is a granular thermoplastic polymer. The coating liquid containing the polymer, coating area ratio with respect to the substrate of ^{5% ~70%, 0.05g / m} 2 ~1.0g / m 2 of coating basis weight, and 0.1μm~3μm coating The method for producing a separator for a power storage device according to any one of claims 1 to 6, which comprises a step of coating the at least one surface of the base material under the condition of the working thickness.

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