JP2018170281A - Separator for power storage device, power storage device, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a power storage device excellent in both adhesion to an electrode and oxidation resistance.SOLUTION: A separator for a power storage device includes: a substrate; and a layer containing a thermoplastic polymer formed at least partially on at least one surface of the substrate. The thermoplastic polymer contains a copolymer having as monomer units an aromatic vinyl compound monomer and (meth) acrylic acid ester monomer.SELECTED DRAWING: None

Description

  The present invention relates to an electricity storage device separator, an electricity storage device, and a lithium ion secondary battery.

  In recent years, development of nonaqueous electrolyte batteries centering on lithium ion batteries has been actively conducted. Usually, in a nonaqueous electrolyte battery, a microporous membrane (separator) is provided between positive and negative electrodes. Such a 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 micropores.

  In order to improve the cycle characteristics and safety of the nonaqueous electrolyte battery, improvement of the separator has been studied. In recent years, as portable devices become smaller and thinner, power storage devices such as lithium ion secondary batteries are also required to be smaller and thinner. On the other hand, in order to be able to carry for a long time, the capacity is increased by improving the volume energy density.

  Conventional separators have a characteristic that the battery reaction is quickly stopped if the separator is abnormally heated (fuse characteristics), preventing the dangerous situation where the cathode and anode materials react directly by maintaining the shape even at high temperatures. Performance related to safety such as performance (short characteristics) is required. In addition to these, recently, separators are also required to have improved adhesion to electrodes from the viewpoints of uniform charge / discharge current and suppression of lithium dendrite.

  By improving the close contact between the separator and the battery electrode, non-uniform charge / discharge current is less likely to occur, and lithium dendrite is less likely to precipitate, resulting in longer charge / discharge cycle life. Become.

  Under such circumstances, as an attempt to give the separator an adhesive property, for example, in Patent Document 1, a porous material having pores is intended to improve the adhesive property, scratch resistance and wear resistance. A microporous membrane comprising a substrate and a coating layer formed on at least one region selected from the group consisting of a substrate surface and a part of pores present in the substrate, wherein the coating layer is styrene- Microporous membranes containing butadiene have been proposed. Patent Document 2 is a polymer for bonding a positive electrode and a negative electrode of a lithium ion secondary battery and a separator disposed between them, and suppresses thermal contraction of the separator without deteriorating battery characteristics. The positive electrode and the negative electrode of a lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, with the intention of providing a polymer for a lithium ion secondary battery that can use a thinner separator A polymer for adhering a separator disposed therebetween, (A) a monomer unit having cationic polymerizability, (B) a monomer unit imparting affinity for the electrolytic solution, and (C) the electrolysis A monomer unit that imparts poor solubility to a liquid, and (D) a monomer unit containing an anionic and nonionic hydrophilic group. It is a polymer obtained by radical polymerization by emulsion polymerization or suspension polymerization, and its elution rate to a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) [EC: DEC = 5: 5 (weight ratio)] is 10 wt. %, A polymer for a lithium ion secondary battery is proposed. Furthermore, in Patent Document 3, the electrode / separator is sufficiently used to manufacture a battery having sufficient adhesion between the electrodes / separator, excellent swelling property by the electrolyte, low internal resistance, and high rate characteristics. In order to provide a porous film carrying a crosslinkable polymer for a separator that can be used, and a method for producing a battery using such a crosslinkable polymer-supported porous film, a plurality of cationically polymerizable functional groups in the molecule A crosslinkable polymer-supported porous film for a battery separator in which a crosslinkable polymer having a group and an oxyalkylene group having a specific structure in the side chain is supported on a porous film has been proposed.

International Publication No. 2006/062349 JP 2006-278235 A JP 2008-311126 A

  However, when the present inventors examined conventional separators including those described in Patent Documents 1 to 3, the technique described in Patent Document 1 has sufficient oxidation resistance of the coat layer. It became clear that it was not. In addition, since the separators described in Patent Documents 2 and 3 are highly swellable with respect to the electrolytic solution, the separator is further synonymous with the electrode (in this specification, synonymous with “adhesion”). It turns out that there is room for improvement.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a separator for an electricity storage device, an electricity storage device, and a lithium ion secondary battery that are excellent in adhesion to an electrode and excellent in oxidation resistance. To do.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that the above-mentioned problems can be solved if the separator for an electricity storage device has a specific polymer on at least a part of at least one side of the substrate. The present invention has been completed.

That is, the present invention is as follows.
[1] A separator for an electricity storage device comprising: a base material; and a layer containing a thermoplastic polymer formed on at least a part of at least one surface of the base material,
The separator for electrical storage devices in which the said thermoplastic polymer contains the copolymer which has an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as a monomer unit.
[2] The above-mentioned separator for an electricity storage device, wherein the (meth) acrylic acid ester monomer contains a hydrocarbon ester of (meth) acrylic acid.
[3] The copolymer has a ratio of the infrared absorption peak intensity at a wavelength of 1720cm ^-1 ~1750cm ^-1 for infrared absorption peak intensity at a wavelength of the 740cm ^-1 ~770cm ^-1 is in 1 to 18 The said separator for electrical storage devices.
[4] The above separator for an electricity storage device, wherein the degree of swelling of the copolymer with respect to a mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is 0.5 to 6.0 times.
[5] The copolymer further comprises at least one monomer selected from the group consisting of a monomer having a chain alkyl group having 4 or more carbon atoms and a monomer having a cycloalkyl group. The said separator for electrical storage devices which has as a monomer unit.
[6] The above separator for an electricity storage device, wherein the copolymer includes a copolymer produced by emulsion polymerization.
[7] An electricity storage device comprising the above electricity storage device separator.
[8] A lithium ion secondary battery provided with the separator for an electricity storage device.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices which was excellent in the adhesiveness with an electrode and was excellent also in oxidation resistance, an electrical storage device, and a lithium ion secondary battery can be provided.

(A)-(E) are schematic diagrams which show the planar shape of the layer containing the thermoplastic polymer with which the separator of this invention is provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto, “(Meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.

  The copolymer according to this embodiment is a copolymer having an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as monomer units. The separator for an electricity storage device of this embodiment includes a base material and a layer containing a thermoplastic polymer (hereinafter referred to as “polymer layer”) formed on at least a part of at least one surface of the base material. The thermoplastic polymer contains a copolymer having an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as monomer units. Here, the “aromatic vinyl compound” is a compound having an aromatic ring and a vinyl group in the molecule, and may have other groups and atoms. In the present specification, the “ethylenically unsaturated monomer” means a monomer having one or more ethylenically unsaturated bonds in the molecule.

  Although it does not specifically limit as an aromatic vinyl compound monomer, For example, styrene, vinyl toluene, and alpha methyl styrene are mentioned. Among these, styrene is preferable from the viewpoint of more effectively and reliably achieving the effects of the present invention. These are used singly or in combination of two or more.

The (meth) acrylic acid ester monomer is particularly used for enhancing oxidation resistance, and is not particularly limited, but preferably has one ethylenically unsaturated bond. For example, in the following formula (1) And the compounds represented.
^{_{CH 2 = CR 1 -COO-R}} 2 (1)
In Formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² represents a monovalent hydrocarbon group that may have a substituent and may have a hetero atom in the chain. . That is, the (meth) acrylic acid ester monomer preferably contains a hydrocarbon ester of (meth) acrylic acid. Examples of the monovalent hydrocarbon group include a linear alkyl group, a cycloalkyl group, and an aryl group, which may be linear or branched. In addition, examples of the substituent include a hydroxyl group and a phenyl group, and examples of the hetero atom include an oxygen atom. A (meth) acrylic acid ester monomer is used individually by 1 type or in combination of 2 or more types.

More specifically, the chain alkyl group which is one kind of R ² is a chain alkyl group having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group, n-butyl. And a chain alkyl group having 4 or more carbon atoms, such as a group, isobutyl group, t-butyl group, n-hexyl group, 2-ethylhexyl group and lauryl group. The aryl group is a type of R ^2, for example, include a phenyl group.
Specific examples of the (meth) acrylic acid ester monomer having R ² include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, and n-hexyl. Chain alkyl such as acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate (Meth) acrylate, phenyl acrylate and phenyl methacrylate having a group Include (meth) acrylate having an aromatic ring is.

Among these, from the viewpoint of improving adhesion to the electrode (electrode active material), a monomer having a chain alkyl group having 4 or more carbon atoms, more specifically, R ² has 4 carbon atoms. The (meth) acrylic acid ester monomer which is the above chain alkyl group is preferable. More specifically, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate are 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 14, for example, but 7 is preferable. These (meth) acrylic acid ester monomers (b5) are used singly or in combination of two or more.

The (meth) acrylic acid ester monomer may be a monomer having a cycloalkyl group as R ² instead of or in addition to the monomer having a chain alkyl group having 4 or more carbon atoms. It is preferable to include. This also further improves the adhesion with the electrode.
More specifically, examples of such a monomer having a cycloalkyl group include cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, adamantyl acrylate and adamantyl methacrylate. 4-8 are preferable, as for the number of the carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6 and 7 are more preferable, and 6 is especially preferable. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a tertiary butyl group. Among these, cyclohexyl acrylate and cyclohexyl methacrylate are preferable in that the polymerization stability at the time of preparing the copolymer is good. These are used singly or in combination of two or more.

  In addition, from the viewpoint of improving the polymerization stability of the copolymer, the (meth) acrylic acid ester monomer may include a (meth) acrylic acid ester monomer having a hydroxyl group as a substituent. A (meth) acrylic acid ester monomer having an oxygen atom in the chain may be included. Examples of such monomers include hydroxyalkyl (meth) acrylates such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate, polyethylene glycol acrylate and polyethylene glycol methacrylate. These are used singly or in combination of two or more. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferred. By using hydroxyethyl acrylate and / or hydroxyethyl methacrylate, the polymerization stability of the copolymer tends to be improved.

  Further, the copolymer may contain, for example, benzyl acrylate and benzyl methacrylate as a (meth) acrylic acid ester monomer having a phenyl group as a substituent.

  Further, the copolymer according to this embodiment includes a crosslinkable monomer as a (meth) acrylic acid ester monomer instead of or in addition to the above, preferably in addition to the above. It is preferable. The crosslinkable monomer is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a single monomer having a functional group that gives a self-crosslinking structure during or after polymerization. The body is mentioned. These are used singly or in combination of two or more.

  Examples of the monomer having two or more radically polymerizable double bonds include polyfunctional (meth) acrylate, and this is preferable from the viewpoint that better electrolytic solution resistance can be achieved even with a small amount. .

The polyfunctional (meth) acrylate may be a bifunctional (meth) acrylate, a trifunctional (meth) acrylate, or a tetrafunctional (meth) acrylate. For example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, poly Oxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, And pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Of these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferable from the same viewpoint as described above.
Examples of the (meth) acrylic acid ester having a hydrolyzable silyl group include γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxy. And propyltriethoxysilane. These are used singly or in combination of two or more.

  Among the crosslinkable monomers, polyfunctional (meth) acrylate is particularly preferable in that there is little variation in the degree of crosslinking.

  Further, the copolymer according to this embodiment may further have a monomer other than the above as a monomer unit in order to improve various qualities and physical properties. As such a monomer, for example, other than the above, a monomer having a cycloalkyl group, a monomer having a hydroxyl group, a crosslinkable monomer, a monomer having a carboxyl group, and an amide group Monomers and monomers having a cyano group can be mentioned. These are used singly or in combination of two or more. Moreover, the monomer which concerns on this embodiment may belong to two or more types simultaneously among each said monomer.

  From the viewpoint of improving cushioning properties in the swollen state, the copolymer preferably has a monomer having a carboxyl group as a monomer unit. As the monomer having a carboxyl group, an ethylenically unsaturated monomer having a carboxyl group is preferable. Examples of the ethylenically unsaturated monomer having a carboxyl group include monocarboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester and fumaric acid half ester, and And dicarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid. These are used singly or in combination of two or more. Among these, from the same viewpoint, acrylic acid, methacrylic acid and itaconic acid are preferable, and acrylic acid and methacrylic acid are more preferable.

  Moreover, it is preferable that a copolymer has a monomer which has an amide group as a monomer unit from a viewpoint of an adhesive improvement with an electrode (electrode active material). From the same viewpoint, the monomer having an amide group is preferably an ethylenically unsaturated monomer having an amide group, and such a monomer is not particularly limited, and examples thereof include acrylamide and methacrylamide. N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic acid amide and maleimide. These are used singly or in combination of two or more. Of these, acrylamide and methacrylamide are preferable. By using acrylamide and / or methacrylamide, the adhesion of the separator to the electrode (electrode active material) tends to be further improved.

  As the monomer having a hydroxyl group, an ethylenically unsaturated monomer having a hydroxyl group is preferable.

  Further, from the viewpoint of setting an insoluble content in the electrolytic solution to an appropriate amount, the copolymer preferably has a crosslinkable monomer as a monomer unit. The crosslinkable monomer is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a single monomer having a functional group that gives a self-crosslinking structure during or after polymerization. The body is mentioned. These are used singly or in combination of two or more.

  Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene. Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, an ethylenically unsaturated monomer having an epoxy group, an ethylenic monomer having a methylol group, and an alkoxymethyl group. And an ethylenically unsaturated monomer having a hydrolyzable silyl group. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an epoxy group include allyl glycidyl ether. Examples of the ethylenically unsaturated monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. Examples of the ethylenically unsaturated monomer having an alkoxymethyl group include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, and N-butoxymethyl methacrylamide. Examples of the ethylenically unsaturated monomer having a hydrolyzable silyl group include vinyl silane. These are used singly or in combination of two or more.

  As the monomer having a cyano group, an ethylenically unsaturated monomer having a cyano group is preferable, and specific examples include acrylonitrile and methacrylonitrile.

  The content of the aromatic vinyl compound monomer in the copolymer is preferably 5 to 95% by mass with respect to 100% by mass of the copolymer. The lower limit is more preferably 10% by mass, still more preferably 25% by mass, and particularly preferably 40% by mass. A content ratio of the aromatic vinyl compound monomer of 5% by mass or more is preferable because rate characteristics are improved. On the other hand, a more preferable upper limit value is 85% by mass, and a more preferable upper limit value is 75% by mass. It is preferable from the point of adhesiveness with the electrode (electrode active material) of a separator that the content rate of an aromatic vinyl compound monomer is 95 mass% or less.

  The content ratio of the (meth) acrylic acid ester monomer in the copolymer is preferably 5 to 95% by mass with respect to 100% by mass of the copolymer. The lower limit is more preferably 15% by mass, still more preferably 20% by mass, and particularly preferably 30% by mass. When the content ratio of the (meth) acrylic acid ester monomer is 5% by mass or more, it is preferable in terms of binding property to the base material and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, a still more preferred upper limit is 80% by mass, and a particularly preferred upper limit is 60% by mass. It is preferable for the content ratio of the (meth) acrylic acid ester monomer to be 95% by mass or less since the adhesion to the substrate is improved.

  When the copolymer has a hydrocarbon ester of (meth) acrylic acid as a monomer unit, the content is preferably 3 to 92% by mass with respect to 100% by mass of the copolymer, and more Preferably it is 10-90 mass%, More preferably, it is 15-75 mass%, Most preferably, it is 25-55 mass%. The content of this monomer is preferably 3% by mass or more from the viewpoint of improving oxidation resistance, and it is preferably 92% by mass or less because the binding property with the substrate is improved.

  When the copolymer has a monomer having a carboxyl group as a monomer unit, the content of the ethylenically unsaturated monomer having a carboxyl group in the copolymer is 100% by mass of the copolymer. Preferably, it is 0.1-5 mass%. When the content of the ethylenically unsaturated monomer having a carboxyl group is 0.1% by mass or more, the separator tends to improve cushioning properties in a swollen state, and when the content is 5% by mass or less, polymerization is performed. The stability tends to be good.

  When the copolymer has a monomer having an amide group as a monomer unit, the content of the ethylenically unsaturated monomer having an amide group in the copolymer is based on 100% by mass of the copolymer. Preferably, it is 0.1-5 mass%. When the content ratio of the ethylenically unsaturated monomer having an amide group is 0.1% by mass or more, the adhesion with the electrode (electrode active material) tends to be further improved, and is 5% by mass or less. In addition, the polymerization stability in preparing the copolymer tends to be further improved.

  When the copolymer has a monomer having a hydroxyl group as a monomer unit, the content ratio of the ethylenically unsaturated monomer having a hydroxyl group in the copolymer is based on 100% by mass of the copolymer. Preferably, it is 0.1-5 mass%. When the content ratio of the ethylenically unsaturated monomer having a hydroxyl group is within the above range, the polymerization stability when preparing the copolymer tends to be further improved.

  When the copolymer has a crosslinkable monomer as a monomer unit, the content of the crosslinkable monomer in the copolymer is preferably 0.01 to 10% with respect to 100% by mass of the copolymer. It is mass%, More preferably, it is 0.1-5 mass%, More preferably, it is 0.1-3 mass%. When the content of the crosslinkable monomer is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when the content is 10% by mass or less, a decrease in cushioning property in the swollen state can be further suppressed.

  The glass transition temperature (hereinafter also referred to as “Tg”) of the copolymer is not particularly limited, but may be −50 ° C. or higher, preferably 20 ° C. or higher, more preferably 20 ° C. to 120 ° C. It is 20 degreeC, More preferably, it is 20 to 100 degreeC. When the Tg of the copolymer is 20 ° C. or higher, sticking of the outermost surface of the separator including the polymer layer containing the copolymer can be suppressed, and the handling property 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.

  Further, the copolymer has at least two glass transition temperatures, at least one of the glass transition temperatures is present in a region below 20 ° C., and at least one of the glass transition temperatures is 20 ° C. It is preferable to exist in the above region. When at least one of the glass transition temperatures of the copolymer is present in a region below 20 ° C., when the substrate is a microporous film, it has excellent adhesion to the microporous film, and as a result, the separator and the electrode There exists a tendency to show | play the effect of being further excellent in adhesiveness. From the same viewpoint, at least one of the glass transition temperatures of the copolymer is more preferably present in the region of 15 ° C. or lower, more preferably in the region of −30 ° C. or higher and 15 ° C. or lower. The glass transition temperature existing in the region below 20 ° C. is a region of −30 ° C. or more and 15 ° C. or less from the viewpoint of further maintaining the handling property while further improving the adhesion between the copolymer and the microporous film. It is preferable that it exists only in.

  Furthermore, when at least one of the glass transition temperatures of the copolymer is present in the region of 20 ° C. or higher, there is a tendency that the adhesion between the separator and the electrode and the handling property are further improved. From the same viewpoint, at least one of the glass transition temperatures of the copolymer is more preferably present in the region of 20 ° C. or higher and 120 ° C. or lower, and more preferably in the region of 50 ° C. or higher and 120 ° C. or lower. When the glass transition temperature exists in the above range, it is possible to impart better handling properties. Furthermore, it is possible to further improve the adhesion between the electrode and the separator that are manifested by pressurization during battery production. The glass transition temperature existing in the region of 20 ° C. or higher is in the region of 20 ° C. or higher and 120 ° C. or lower from the viewpoint of further maintaining the handleability while further improving the adhesion between the copolymer and the microporous membrane. Is preferably present only.

  Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is determined by the intersection of a straight line obtained by extending the base line on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepped change portion of the glass transition.

  “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change.

  Further, the “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece.

In the present embodiment, the glass transition temperature of the copolymer or thermoplastic polymer (hereinafter referred to as “copolymer or the like”), that is, Tg is, for example, the type of monomer used to produce the copolymer or the like and each monomer. It can adjust suitably by changing the compounding ratio. The Tg of a copolymer or the like is the Tg of the homopolymer generally indicated for each monomer used in the production of the copolymer or thermoplastic polymer (e.g., described in "A WILEY-INTERSCIENCE PUBLICATION") And roughly from the blending ratio of the monomers. For example, a copolymer containing a high ratio of monomers such as styrene, methyl methacrylate, and acrylonitrile that give a polymer having a Tg of about 100 ° C. has a high Tg. Further, for example, a copolymer containing a high ratio of monomers such as butadiene which gives a polymer having a Tg of about -80 ° C, and n-butyl acrylate and 2-ethylhexyl acrylate which give a Tg polymer of about -50 ° C. Etc. have a low Tg.
The Tg of the polymer can be estimated from the FOX formula (the following formula (2)). In addition, what was measured by the method using said DSC is employ | adopted as glass transition temperature, such as a copolymer.
1 / Tg = W1 / Tg1 + W2 / Tg2 +... + Wi / Tgi +... Wn / Tgn (2)
Here, in the formula (2), Tg (K) represents the Tg of the copolymer, Tgi (K) represents the Tg of the homopolymer of each monomer i, and Wi represents the mass fraction of each monomer. .

Copolymer has according to the present embodiment, the ratio of infrared absorption peak intensity at a wavelength of 1720cm ^-1 ~1750cm ^-1 for infrared absorption peak intensity at a wavelength of 740cm ^-1 ~770cm ^-1 is in 1 to 18 Preferably there is. The ratio of the infrared absorption peak intensity is more preferably 2 to 15 when the copolymer has an aromatic vinyl compound monomer and a (meth) acrylate monomer as monomer units. Preferably, it is 5-10. In addition, it is thought that the former peak is derived from the aromatic ring of the aromatic vinyl compound monomer, and the latter peak is derived from the (meth) acryloyl group of the (meth) acrylic acid ester monomer. Therefore, when the total of the aromatic vinyl compound monomer and the (meth) acrylic acid ester monomer is 100% by mass, the thermoplastic polymer may contain about 5% by mass to the aromatic vinyl compound monomer. Since it contains 50 mass%, it is preferable from a viewpoint of the balance of the adhesiveness to an electrode, and handling property. The ratio of the infrared absorption peak intensity can be determined from the infrared absorption analysis described in the following examples.

  In the separator of the present embodiment, the degree of swelling of the copolymer with respect to the mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is preferably 0.5 to 6.0 times or less, and 1.0 times. It is more preferable that it is -5.0 times. When the degree of swelling is 6.0 times or less, the ionic resistance of the separator can be more effectively and reliably suppressed, thereby further improving the reliability of the electricity storage device and improving the rate characteristics. At the same time, the film strength can be further increased. In addition, when a polymer layer contains 2 or more types of copolymers, a swelling degree is taken as the weighted average of the swelling degree of each copolymer.

  The copolymer is obtained, for example, by a usual emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-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 in an aqueous medium as a basic composition component, each of the above monomers. A copolymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the monomer composition to be supplied is made constant throughout the entire polymerization process, or the morphological composition change of the particles of the resin dispersion to be produced is changed sequentially or continuously in the polymerization process. Various methods can be used as necessary, such as a method of giving When the copolymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate copolymer dispersed in the water.

  The surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfone. Anionic interfaces such as acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene disty Phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactants. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

  Examples of the anionic surfactant in the reactive surfactant include an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group or a sulfate ester group and a salt thereof, and a sulfonic acid group, or A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is an ammonium salt or an alkali metal salt thereof is preferable. Specifically, for example, alkylallylsulfosuccinate (for example, Eleminol (trademark) JS-20 manufactured by Sanyo Chemical Co., Ltd., Latemuru (trademark; manufactured by Kao Corporation), S-120, S-180A, S- 180), polyoxyethylene alkylpropenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark; the same shall apply hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1- [ (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, ADEKA Corporation soap (trademark; the same shall apply hereinafter) SE-10N manufactured by ADEKA Corporation), ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (eg, Aquaron KH-10 manufactured by Ichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), α- [2-[(allyloxy)- 1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adeka Soap SR-10 manufactured by ADEKA Corporation), polyoxyethylene polyoxybutylene (3-methyl-3- Butenyl) ether sulfate (for example, LATEMUL PD-104 manufactured by Kao Corporation) may be mentioned.

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10)), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) A Le (for example, Kao Corp. LATEMUL PD-420.) And the like.

  Among the above-mentioned various surfactants, reactive surfactants are preferable, anionic reactive surfactants are more preferable, and reactive surfactants having a sulfonic acid group are more preferable. 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. Surfactant is used individually by 1 type or in combination of 2 or more types.

  The radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition with heat or a reducing substance, and any of inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used. Examples of the water-soluble polymerization initiator include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of the peroxide include hydrogen peroxide, t- Examples thereof include butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis (N-hydroxyethylisobutyramide), 2 And 2-azobis (2-amidinopropane) dichloride and 4,4-azobis (4-cyanopentanoic acid). Examples of the redox system of the peroxide-reducing agent include sodium peroxide and sodium peroxide. Sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate Um, sodium hydroxymethanesulfinic acid, L- ascorbic acid, and its salts, cuprous salts, and include those that combine one or more reducing agents such as ferrous salts.

  The radical polymerization initiator is preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. A radical polymerization initiator is used individually by 1 type or in combination of 2 or more types.

  A monomer composition containing an ethylenically unsaturated monomer (A) having a cycloalkyl group and another monomer (B) is emulsion-polymerized, and the polymer particles are in a solvent (water). When forming a dispersed dispersion, the solid content of the obtained dispersion is preferably 30% by mass to 70% by mass.

  The dispersion is preferably adjusted to have a pH in the range of 5 to 12 in order to maintain long-term dispersion stability. For pH adjustment, amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol are preferably used, and pH is more preferably adjusted with ammonia (water) or sodium hydroxide.

  The aqueous dispersion of this embodiment includes a copolymer obtained by copolymerizing the monomer composition containing the specific monomer as particles (copolymer particles) dispersed in water. In addition to water and the copolymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, and the like.

  The average particle size of the copolymer particles is preferably 50 to 750 nm, more preferably 100 to 400 nm, and still more preferably 130 to 180 nm. It is preferable that the average particle size of the copolymer particles be 50 nm or more because the air permeability of a separator including a polymer layer and a base material described later supporting the layer can be maintained better. Moreover, it is preferable from the viewpoint of ensuring the dispersion stability of the aqueous dispersion that the average particle diameter of the copolymer particles is 750 nm or less. The average particle diameter of the copolymer particles can be measured according to the method described in the following examples.

  In addition, it can confirm by pyrolysis gas chromatography that a copolymer has an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as a monomer unit. More specifically, the homopolymer of each of the above monomers is measured by pyrolysis gas chromatography, and the retention time of the pyrolyzate is determined in advance. Next, when the copolymer is measured under the same conditions by pyrolysis gas chromatography and has a peak of pyrolyzate at the same retention time, it has the above monomer as the copolymer monomer unit. Can be estimated. Moreover, it is also possible to obtain | require the ratio of each monomer in a copolymer monomer unit by making the homopolymer of each monomer of the above into an internal standard.

Since the separator of this embodiment has a polymer layer on at least a part of at least one surface of the base material, the electrode and the separator can be bonded through a hot pressing process. That is, the polymer layer can function as an adhesive layer.
The thermoplastic polymer preferably contains 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more, based on the total amount of the copolymer. In addition to the copolymer, the thermoplastic polymer may contain other components to the extent that the solution to the problem of the present invention is not impaired.

  The substrate used in the present embodiment may itself be one that has been conventionally used as a separator. The base material is preferably a porous film having a fine pore size, having no electron conductivity, ionic conductivity, high resistance to organic solvents. As such a porous membrane, for example, a polyolefin-based (for example, polyethylene, polypropylene, polybutene and polyvinyl chloride), and a microporous membrane containing a resin such as a mixture or copolymer thereof as a main component, polyethylene terephthalate, Microporous membrane containing resin such as polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, woven polyolefin fiber (woven fabric) ), Polyolefin fiber nonwoven fabric, paper, and aggregates of insulating substance particles. Among these, when a polymer layer is obtained through a coating process, the coating solution is excellent in coating property, the separator film thickness is made thinner, and the active material ratio in an electricity storage device such as a battery is increased to increase the volume per volume. From the viewpoint of increasing the capacity, a polyolefin microporous film containing a polyolefin-based resin as a main component is preferable. Here, “include as a main component” means to contain more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more. More preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass.

  The thickness of a base material becomes like this. Preferably it is 0.5-40 micrometers, More preferably, it is 1-30 micrometers, More preferably, it is 1-10 micrometers. When the thickness of the base material is within this range, the resistance by the separator in the electricity storage device such as a battery becomes smaller, and when the polymer layer is obtained through the coating process, it is applied to the base material. Workability at the time is further improved.

  In the present embodiment, examples of the polyolefin-based resin used as the base material include homopolymers such as polyethylene and polypropylene, copolymers, and mixtures thereof. Examples of the polyethylene include low density, medium density, and high density polyethylene, and high density polyethylene is preferable from the viewpoint of piercing strength and mechanical strength. These polyethylenes may be used in combination of two or more for the purpose of imparting flexibility. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Philips catalysts, and metallocene catalysts. From the viewpoint of achieving both high mechanical strength and high permeability, the viscosity average molecular weight of polyethylene is preferably 100,000 or more and 12 million or less, more preferably 200,000 or more and 3 million or less.

The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135 ° C. using decalin as a solvent based on ASTM-D4020 by the following formula.
Polyethylene: [η] = 6.77 × 10 ⁻⁴ Mv ^0.67 (Chiang formula)
Polypropylene: [η] = 1.10 × 10 ⁻⁴ Mv ^0.80

  Examples of polypropylene include homopolymers, random copolymers, and block copolymers, and one kind or a mixture of two or more kinds can be used. The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts. Moreover, there is no restriction | limiting in particular also in the stereoregularity of a polypropylene, Any of isotactic, syndiotactic, and atactic may be sufficient. However, it is preferable to use isotactic polypropylene because it is inexpensive. Furthermore, an appropriate amount of polyolefins other than polyethylene and polypropylene, and additives such as antioxidants and nucleating agents may be added to the base material within the range not impairing the effects of the present invention.

  A method for producing a base material containing a polyolefin-based resin as a main component may be a known one. Examples of the manufacturing method include a dry manufacturing method and a wet manufacturing method. In the dry production method, for example, a film is first formed by melt extrusion of a polyolefin-based resin such as polypropylene or polyethylene. Thereafter, the film is annealed at a low temperature to grow a crystal domain, and in this state, the film is stretched to extend the amorphous region, thereby forming a microporous film as a substrate. In the wet manufacturing method, for example, first, a hydrocarbon solvent or other low molecular weight material and a polyolefin-based resin such as polypropylene or polyethylene are mixed, and then formed into a film shape. Next, the film in which the solvent and low-molecular material have gathered in the amorphous phase and have started to form the island phase is removed using another solvent that easily volatilizes the solvent and low-molecular material, so that A porous film is formed.

  The method for producing a nonwoven fabric or paper as a substrate may be a known one. The production method includes, for example, a chemical bond method in which a web is dipped in a binder and dried to bond fibers; a thermal bond method in which hot-melt fibers are mixed into the web and the fibers are partially melted to bond fibers. A needle punch method in which a needle having a stab is repeatedly stabbed into the web and mechanically entangled with the fiber; a high-pressure water flow is entangled between the fibers by jetting a high-pressure water stream from the nozzle through the net (screen).

  The base material used in the present embodiment may contain a filler (inorganic filler or organic filler) or a fiber compound for the purpose of controlling strength, hardness, and thermal shrinkage. In addition, when the base material is a laminate of non-conductive particles and a porous membrane layer containing a binder, the adhesion is improved, or the surface tension with the electrolyte is lowered to improve the liquid impregnation property. For this purpose, the substrate surface may be coated with a low molecular compound or a polymer compound in advance, or may be subjected to electromagnetic radiation treatment such as ultraviolet rays or plasma treatment such as corona discharge / plasma gas. In particular, it contains polar groups such as a carboxylic acid group, a hydroxyl group, and a sulfonic acid group from the viewpoint that the impregnation property of the electrolytic solution is high and the adhesion to the porous membrane layer containing the non-conductive particles and the binder is easily obtained. It is preferable to coat with a polymer compound.

  The base material used in the present embodiment may have a multilayer structure in which the above-mentioned base materials are stacked for the purpose of increasing the tear strength and the puncture strength. Specific examples include a laminated film of a polyethylene microporous film and a polypropylene microporous film, and a laminated film of a nonwoven fabric and a polyolefin microporous film.

  The air permeability of the substrate is not particularly limited, but is preferably 10 sec / 100 cc or more, more preferably 50 sec / 100 cc or more, preferably 1000 sec / 100 cc or less, more preferably 500 sec from the viewpoint of enhancing the performance of the electricity storage device. / 100 cc or less. The air permeability is preferably 10 sec / 100 cc or more from the viewpoint of further suppressing self-discharge of the electricity storage device. On the other hand, setting it to 1000 sec / 100 cc or less is preferable from the viewpoint of obtaining even better charge / discharge characteristics.

  Further, from the same viewpoint, the porosity of the base material is preferably 20% or more, more preferably 35% or more, preferably 90% or less, from the viewpoint of improving the mechanical strength while enhancing the performance of the electricity storage device. Preferably it is 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing excellent permeability of the separator. On the other hand, it is preferable to set it as 90% or less from a viewpoint of ensuring the outstanding puncture strength.

  Further, the puncture strength of the substrate is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2000 g / 20 μm or less, from the viewpoint of improving reliability as a separator and suppressing thermal shrinkage. More preferably, it is 1000 g / 20 μm or less. It is preferable that the puncture strength is 200 g / 20 μm or more from the viewpoint of further suppressing film breakage due to the dropped active material or the like during battery winding. Moreover, it is also preferable from the viewpoint of further suppressing the fear of short-circuiting due to the expansion and contraction of the electrode accompanying charging and discharging. On the other hand, it is preferable to set it as 2000 g / 20 micrometers or less from a viewpoint which can reduce the width | variety shrinkage by the orientation relaxation at the time of a heating.

  These air permeability, porosity, and puncture strength are measured according to the methods described in Examples.

(Amount of polymer layer supported on substrate)
Loading amount to the substrate of the polymer layer in the present embodiment is preferably from 0.05 g / m ² or more 1.50 g / m ² or less in terms of solid content, more preferably 0.07 g / m ² or more 1.00 g / m ² Or less, more preferably 0.10 g / m ² or more and 0.70 g / m ² or less. To the carrying amount to the substrate of the layer with 0.05 g / m ² or more 1.50 g / m ² or less, the separator obtained, while further improving the adhesion between the polymer layer and the substrate, group It is preferable from the viewpoint of further suppressing the deterioration of the cycle characteristics (permeability) caused by closing the pores of the material.

  The amount of the polymer layer supported on the substrate can be adjusted, for example, by changing the concentration of the thermoplastic polymer or copolymer in the coating solution or the coating amount of the thermoplastic polymer solution. However, the method for adjusting the carrying amount is not limited to the above.

(Surface coverage)
In the present embodiment, the polymer layer is preferably present on the surface of the substrate with a surface coverage of 80% or less, more preferably 50% or less, and still more preferably with respect to the surface area per surface of the substrate. It is present on the surface of the substrate with a surface coverage of 45% or less, particularly preferably 40% or less. Moreover, it is preferable that a polymer layer exists on the surface of a base material with the surface coverage of 5% or more. It is preferable that the surface coverage of the polymer layer is 80% or less from the viewpoint of further suppressing clogging of the pores of the base material by the thermoplastic polymer (for example, the copolymer) and further improving the permeability of the separator. . On the other hand, setting the surface coverage to 5% or more is preferable from the viewpoint of further improving the adhesion to the electrode.

  The surface coverage of the polymer layer in the present embodiment is, for example, the thermoplastic polymer or copolymer concentration in the coating liquid applied to the substrate, the coating amount of the coating liquid, the coating method, and the coating in the separator manufacturing method described later. It can be adjusted by changing the conditions. However, the method for adjusting the surface coverage is not limited thereto. Moreover, the surface coverage of the polymer layer in this embodiment is measured according to the method as described in the following Example.

(Average thickness of polymer layer)
The average thickness of the polymer layer in the separator of the present embodiment is not particularly limited, but is preferably 2.0 μm or less, more preferably 1.0 μm or less, and further preferably 0.5 μm or less. Setting the average thickness of the polymer layer to 2.0 μm or less suppresses the decrease in permeability due to the polymer layer and also has an effect of adhering the polymer layers to each other or the polymer layer and the substrate when the separator is stored as a roll. From the standpoint of suppression. The average thickness of the polymer layer in the present embodiment is adjusted, for example, by changing the thermoplastic polymer or copolymer concentration in the coating liquid applied to the substrate, the coating amount of the coating liquid, the coating method, and the coating conditions. Can do. However, the adjustment method of the average thickness of a polymer layer is not limited to them.

(Presence form of polymer layer on substrate)
The presence form (pattern) on the base material of the polymer layer in the present embodiment is not particularly limited, and may exist over the entire surface of the base material, or, for example, the planar shape shown in black in FIG. You may have. That is, the polymer layer has, for example, a dot shape (for example, FIG. 1A), a lattice shape (for example, FIG. 1B), a linear shape (for example, FIG. 1C), a stripe shape (for example, FIG. 1 (D)), a tortoiseshell pattern (for example, (E) in FIG. 1), and the like may exist.

  In these, it is preferable that a polymer layer exists in the dot form on the at least single side | surface of a base material from a viewpoint of ensuring permeability | transmittance and a further improving uniform adhesiveness with an electrode. “Dot-like” indicates a state of a sea-island structure in which a polymer layer is present in an island shape on a substrate and a portion where the polymer layer is not present is a sea shape. Although the polymer layer may exist independently in the form of islands, a part of it may form a continuous surface, but the polymer layer is continuous in most parts, and most of the base material is polymer. It does not include the case where it is covered with a layer (when the sea of the sea-island structure is a polymer layer).

  When the polymer layer exists independently in an island shape, the distance between the island dots (the distance between the ends of the adjacent island dots) is 5 μm to 500 μm. It is preferable from the point of coexistence. The size of the dot (the longest diameter of one dot; the longest diameter) is not particularly limited, but is preferably 20 μm or more and 1000 μm or less on average, more preferably 30 μm or more and 800 μm or less, and further preferably 50 μm or more and 500 μm or less. is there. Setting the average major axis of the dots of the polymer layer to 20 μm or more and 1000 μm or less is preferable from the viewpoint of securing the adhesion to the electrode.

  The average major axis of the dots of the polymer layer can be adjusted, for example, by changing the copolymer or thermoplastic polymer concentration of the coating liquid, the coating amount of the coating liquid, the coating method, and the coating conditions. However, the method of adjusting the average major axis of the dots of the polymer layer is not limited to them.

  Moreover, in this embodiment, it is preferable that the thermoplastic polymer has at least two glass transition temperatures. Thereby, the balance of the adhesiveness to an electrode and handling property can be made compatible more favorably.

  In this embodiment, it is preferable that at least one of the glass transition temperatures of the thermoplastic polymer to be used exists in a region below 20 ° C. Thereby, it is further excellent in adhesiveness with a base material, As a result, there exists an effect that a separator is more excellent in adhesiveness with an electrode. From the same viewpoint, it is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer to be used exists in a region of 15 ° C. or lower, and more preferably in a region of −30 ° C. or higher and 15 ° C. or lower. The glass transition temperature existing in the region below 20 ° C is present only in the region of -30 ° C or higher and 15 ° C or lower from the viewpoint of further improving the adhesion between the thermoplastic polymer and the base material while maintaining the handling property better. It is preferable.

  In this embodiment, it is preferable that at least one of the glass transition temperatures of the thermoplastic polymer to be used exists in a region of 20 ° C. or higher. Thereby, there exists an effect that it is further excellent in the adhesiveness and handling property of a separator and an electrode. Moreover, it is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer to be used exists in the region of 20 ° C. or higher and 120 ° C. or lower, and further preferably 50 ° C. or higher and 120 ° C. or lower. When the glass transition temperature exists in the above range, it is possible to impart better handling properties. Furthermore, it is possible to further improve the adhesion between the electrode and the separator that are manifested by pressurization during battery production. The glass transition temperature that exists in the region of 20 ° C or higher exists only in the region of 20 ° C or higher and 120 ° C or lower in order to further improve the adhesion between the thermoplastic polymer and the base material while maintaining better handling properties. It is preferable that it exists only in the region of 50 ° C. or higher and 120 ° C. or lower.

  The thermoplastic polymer having at least two glass transition temperatures can be achieved by, for example, a method of blending two or more kinds of thermoplastic polymers or a method using a thermoplastic polymer having a core-shell structure, but is limited to these methods. Not. The core-shell structure is a polymer having a dual structure in which the polymer belonging to the central portion and the polymer belonging to the outer shell portion have different compositions.

  In particular, the polymer blend and the core-shell structure can control the glass transition temperature of the entire thermoplastic polymer by combining a polymer having a high glass transition temperature and a polymer having a low glass transition temperature. Moreover, a plurality of functions can be imparted to the entire thermoplastic polymer. For example, in the case of blending, the polymer having a glass transition temperature of 20 ° C. or more and the polymer having a glass transition temperature of less than 20 ° C. are blended in two or more types to prevent stickiness. And the paintability to the base material can be more satisfactorily achieved. As a mixing ratio in the case of blending, a ratio of a polymer existing in a region having a glass transition temperature of 20 ° C. or higher and a polymer existing in a region having a glass transition temperature lower than 20 ° C. is 0.1: 99.9 to 99.99. The range is preferably 9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably 60:40 to 90:10. It is. In the case of the core-shell structure, it is possible to adjust the adhesion and compatibility with other materials such as polyolefin microporous membrane by changing the type of outer shell polymer. By changing the type of polymer belonging to the central part, for example, hot press It can adjust to the polymer which improved the adhesiveness to a later electrode. Further, 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 less, and further preferably -30 ° C or more and 15 ° C or less. 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 separator in this embodiment has a short temperature which is an index of heat resistance, preferably 150 ° C. or higher, and more preferably 160 ° C. or higher. Setting the short circuit temperature to 150 ° C. or higher is preferable from the viewpoint of the safety of the electricity storage device. The short temperature is measured by the method described in Japanese Patent No. 4733232.

  Moreover, it is preferable that the separator in this embodiment is 50% or more of adhesiveness with the electrode measured by the method mentioned later.

(Method for manufacturing separator for thermoplastic polymer-carrying power storage device)
In the present embodiment, the method for supporting the thermoplastic polymer containing the copolymer on at least one surface (one surface) of the substrate is not particularly limited. For example, there is a method in which a coating liquid containing a thermoplastic polymer is applied to at least one surface of a substrate, and then a solvent or a dispersion medium of the coating liquid is removed as necessary.

  The solvent or dispersion medium contained in the coating solution is not particularly limited, but water is preferable. When the coating solution is applied to the substrate, if the coating solution gets into the substrate, the thermoplastic polymer containing the copolymer closes the surface and the inside of the pores of the substrate and the permeability is lowered. It becomes easy to do. In this regard, when water is used as the solvent or dispersion medium of the coating solution, it becomes difficult for the coating solution to enter the substrate, and the thermoplastic polymer including the copolymer is mainly present on the outer surface of the substrate. Since it becomes easy, the fall of permeability can be controlled more effectively, and is preferred. Examples of the solvent or dispersion medium that can be used in combination with water include ethanol and methanol.

  The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. For example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll Examples include a coater method, a kiss coater method, 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, and a spray coating method.

  In the present embodiment, it is preferable to perform a surface treatment on the surface of the base material prior to the application of the coating liquid because the coating liquid can be more easily applied and the adhesion between the base material and the thermoplastic polymer is improved. The surface treatment method is not particularly limited as long as the structure of the substrate (for example, the porous structure of the polyolefin microporous membrane) is not significantly impaired. For example, the corona discharge treatment method, the plasma treatment method, the mechanical surface roughening. Method, solvent treatment method, acid treatment method, and ultraviolet oxidation method.

  In the present embodiment, when the solvent is removed from the coating solution applied to the substrate, there is no particular limitation as long as it is a method that does not adversely affect the substrate. For example, when using a polyolefin microporous membrane as a substrate, a method of drying at a temperature below the melting point while fixing the substrate, a method of drying at a low temperature under reduced pressure, a copolymer immersed in a poor solvent for the copolymer And a method of extracting the solvent at the same time as coagulating.

  Further, when the copolymer contains copolymer particles and the substrate is a polyolefin microporous membrane, the glass transition is performed for the purpose of improving the adhesion between the copolymer particles and the polyolefin microporous membrane as the substrate. Copolymer particles having a temperature (Tg) of 20 ° C. or lower can be mixed and used. The copolymer particles having a Tg of 20 ° C. or less are preferably contained in an amount of 5 to 50% by mass with respect to the total amount of the copolymer particles. The degree of swelling of the copolymer having a Tg of 20 ° C. or less is not particularly limited, but is preferably 10.0 times or less from the viewpoint of more effectively expressing the adhesiveness.

[Separator for electricity storage devices]
Although an electrical storage device provided with the electrical storage device separator of this embodiment is not specifically limited, For example, batteries, such as a nonaqueous electrolyte secondary battery, a capacitor, and a capacitor are mentioned. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable. Since the separator for an electricity storage device of the present embodiment includes a polymer layer on a substrate, the separator has excellent handling properties when wound, adhesion with an electrode active material, and permeability.

  The separator of this embodiment is not particularly limited, but when the layer side containing the thermoplastic polymer, measured by the following method, is pressed on the aluminum foil of the positive electrode current collector at 80 ° C. and a pressure of 10 MPa for 2 minutes. The peel strength (hereinafter, also referred to as “heat peel strength”) is preferably 4 mN / mm or more in either condition 1 or condition 2. A separator having a heat peel strength in the above range is preferable in terms of excellent adhesion between the electrode and the separator when applied to an electricity storage device described later.

(Condition 1)
As an adherend, a positive electrode current collector (aluminum foil manufactured by Fuji Process Paper Co., Ltd., thickness: 20 μm) is cut into 30 mm × 150 mm. On the other hand, a separator (size: width 20 mm, length 100 mm) is immersed in an electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate are mixed at a ratio (volume ratio) of 2: 3 and sufficiently wetted. Pull up after. Next, after the separator sufficiently wetted with the current collector was superposed from the polymer layer side, they were put on two Teflon (registered trademark) sheets (Naflon PTFE sheet TOMBO-No. 9000 manufactured by Nichias Corp.) Name)). A laminate obtained by pressing for 2 minutes under conditions of 80 ° C. and 10 MPa is used as a sample for a heat peel strength test (condition 1). The 90 ° peel strength between the separator of the obtained test sample and the current collector was measured using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. at a tensile speed of 50 mm / min. To do.

(Condition 2)
A positive electrode current collector (aluminum foil manufactured by Fuji Process Paper Co., Ltd., thickness: 20 μm) is cut to 30 mm × 150 mm as an adherend, and a separator (size: width 20 mm, length 100 mm) is polymerized on the current collector. After overlapping from the layer side, they are sandwiched between two Teflon (registered trademark) sheets (Naflon PTFE sheet TOMBO-No. 9000 (product name) manufactured by NICHIAS Corporation). A laminate obtained by pressing for 2 minutes at 80 ° C. and 10 MPa is used as a sample for a heat peel strength test (condition 2). The 90 ° peel strength between the separator of the obtained test sample and the current collector was measured using a force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. at a tensile speed of 50 mm / min. To do.

  Further, after the separator of the present embodiment was sufficiently immersed in a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio), the same measurement as above was performed in the same manner as above, and the sample was measured in the same manner as described above. It is also preferable that the peel strength obtained is 4 mN / mm or more.

  In addition, the separator in the present embodiment is measured in accordance with the method described in the examples described later, two sheets are stacked, and 90 ° after pressurizing for 3 minutes at a temperature of 25 ° C. and a pressure of 5 MPa in the stacking direction. The peel strength (hereinafter also referred to as “room temperature peel strength”) is preferably 40 mN / mm or less, and more preferably 20 mN / mm or less. Thereby, the effect that a separator is further excellent in blocking resistance and the handling property becomes more favorable is acquired.

  Surprisingly, the present inventors have found that the adhesiveness when the separator of this embodiment is heated and pressed to the electrode is further improved by having the room temperature peel strength and the heat peel strength within the above ranges. . The reason why such an effect is obtained is not clear, but that the room temperature peel strength is within the above range is that the layer containing the thermoplastic polymer of the separator of this embodiment has a high glass transition temperature on the outermost surface side. It is considered that a large amount of thermoplastic resin is present and that a large amount of thermoplastic resin having a low glass transition temperature is present on the substrate side. That is, the stickiness is further suppressed by the presence of many thermoplastic resins having a high glass transition temperature on the outermost surface side of the layer containing the thermoplastic polymer, and the thermoplastic resin having a high glass transition temperature is in close contact with the electrode. It is considered that a separator having low stickiness and excellent adhesion to the electrode was obtained as a result. On the other hand, the presence of many thermoplastic resins having a low glass transition temperature on the substrate side of the layer containing the thermoplastic polymer improves the adhesion between the substrate and the thermoplastic resin. As a result, the substrate and the thermoplastic resin are improved. It is considered that a separator having excellent adhesion to the electrode was obtained as a result.

[Laminate]
The laminate according to this embodiment is a laminate of the separator and the electrode. The separator of this embodiment can be used as a laminate by adhering to an electrode. Here, “adhesion” means that the peel strength between the separator and the electrode is preferably 4 mN / mm or more, more preferably 6 mN / mm or more, and further preferably 8 mN / mm or more.

  The laminate is excellent in handling property at the time of winding and rate characteristics of the electricity storage device, and further excellent in adhesion and permeability between the thermoplastic polymer and the substrate. Therefore, the use of the laminate is not particularly limited, but for example, it is suitably used for batteries such as non-aqueous electrolyte secondary batteries, power storage devices such as capacitors and capacitors, and the like.

  As an electrode used for the laminated body of this embodiment, the thing as described in the item of the electrical storage device mentioned later can be used.

  The method for producing a laminate using the separator of the present embodiment is not particularly limited. For example, the separator and the electrode of the present embodiment can be stacked and heated and / or pressed as necessary. . The heating and / or pressing can be performed when the electrode and the separator are stacked. Moreover, it can also manufacture by heating and / or pressing with respect to the wound body obtained by winding an electrode and a separator in a circular shape or a flat spiral shape.

  Moreover, a laminated body can also be manufactured by laminating | stacking in the shape of a flat plate in order of a positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator, and heating and / or pressing as needed.

  More specifically, the separator of this embodiment is produced as a vertically long 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). It can be manufactured by stacking in the order of -separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and heating and / or pressing as necessary.

  As temperature at the time of the said heating, 40-120 degreeC is preferable. The heating time is preferably 5 seconds to 30 minutes. As a pressure at the time of the said press, 1-30 Mpa is preferable. The pressing time is preferably 5 seconds to 30 minutes. Moreover, the order of heating and pressing may be performed after heating, or may be performed after pressing, or may be performed simultaneously. Among these, it is preferable to perform pressing and heating simultaneously.

[Power storage device]
The separator of this embodiment can be used for separators and substances in batteries, capacitors, capacitors and the like. In particular, when used as a separator for a non-aqueous electrolyte battery, it is possible to impart adhesion to electrodes and excellent battery performance. The electricity storage device of this embodiment includes an electricity storage device separator, and other configurations may be the same as those conventionally known. Although an electrical storage device is not specifically limited, For example, batteries, such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor are mentioned. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, a battery is preferable, a non-aqueous electrolyte secondary battery is more preferable, and a lithium ion secondary battery is still more preferable. Hereinafter, a suitable aspect in the case where the electricity storage device is a non-aqueous electrolyte secondary battery will be described.

  The non-aqueous electrolyte secondary battery including the separator according to this embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte in addition to the separator. A positive electrode, a negative electrode, and a nonaqueous electrolyte solution are not specifically limited, A well-known thing can be used.

As the cathode material (cathode active material) is not particularly limited, for example, LiCoO _2, LiNiO _2, spinel-type LiMnO _4, lithium-containing composite oxides such as olivine type LiFePO ₄ and the like. The negative electrode material is not particularly limited, and examples thereof include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials. . Each of the positive electrode and the negative electrode may include a current collector. Examples of the positive electrode current collector include an aluminum foil, and examples of the negative electrode current collector include a copper foil.

The non-aqueous electrolyte is not particularly limited, but an electrolyte obtained by dissolving an electrolyte in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Can be mentioned. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

  Although the electrical storage device of this embodiment is not specifically limited, For example, it manufactures as follows. That is, the separator of this embodiment is produced as a vertically long 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). Next, the separator is stacked together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. Next, the laminate is wound into a cylindrical or flat spiral shape to obtain a wound body. And the electrical storage device is obtained by accommodating the said wound body in a battery can, and also inject | pouring electrolyte solution. In addition, the electricity storage device of this embodiment is obtained by laminating a positive electrode, a separator, a negative electrode, a separator, a positive electrode, or a negative electrode, a separator, a positive electrode, a separator, and a negative electrode in the order of a flat plate, and then in a bag-shaped film. It can also be manufactured through a process of housing and laminating and injecting an electrolytic solution therein. Moreover, it can also manufacture using what wound the above-mentioned laminated body in the shape of a circle or a flat spiral as said wound body. In addition, the electricity storage device is formed by laminating a flat plate in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, or the above laminate with a bag-like film, and injecting an electrolyte solution. It can also be manufactured through a process and optionally a process of heating and / or pressing. The step of performing the heating and / or pressing can be performed before and / or after the step of injecting the electrolytic solution.

  The various parameters described above are values measured according to the measurement methods in the examples described later unless otherwise specified.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example. The measurement methods and evaluation methods for various physical properties used in the following synthesis examples, production examples, examples and comparative examples are as follows.

[Measuring method]
(1) Solid content About 1 g of the obtained aqueous dispersion of the copolymer was precisely weighed on an aluminum dish, and the mass of the aqueous dispersion weighed at this time was defined as (a) g. It was dried for 1 hour with a hot air dryer at 130 ° C., and the dry mass of the dried copolymer was (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Average particle diameter of copolymer particles Using a light-scattering particle diameter measuring apparatus (LEED & NORTH UP, trade name “MICROTRAC UPA150”), 50% particle diameter (nm) was measured and used as the average particle diameter. .

(3) Weight of base material (polyolefin microporous film) A 10 cm × 10 cm square sample was cut from the base material, and mass was measured using an electronic balance AEL-200 (trade name) manufactured by Shimadzu Corporation. Is multiplied by the resulting mass 100 was calculated 1 m ² per layer of basis weight (g / m ²⁾ in.

(4) Porosity of Substrate (Polyolefin Microporous Membrane) A 10 cm × 10 cm square sample was cut from the substrate, its volume (cm ³ ) and mass (g) were determined, and the membrane density was 0.95 (g / cm ³ ) Calculated using the following formula.
Porosity = (1−mass / volume / 0.95) × 100

(5) Air Permeability of Substrate (Polyolefin Microporous Membrane) Air permeation resistance measured by Gurley type air permeability meter, G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. according to JIS P-8117 Was the air permeability.

(6) Puncture strength of substrate (polyolefin microporous membrane) Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, the substrate was fixed with a sample holder having a diameter of 11.3 mm. Next, by performing a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec using a needle having a radius of curvature of 0.5 mm at the center of the fixed substrate. The puncture strength (g) was obtained as the maximum puncture load.

(7) Average pore size of substrate (polyolefin microporous membrane) It is known that the fluid inside the capillary follows the Knudsen flow when the fluid mean free path is larger than the capillary pore size, and the Poiseuille flow when it is small. Yes. Therefore, it was assumed that the air flow in the air permeability measurement of the base material follows the Knudsen flow, and the water flow in the base material permeability measurement follows the Poiseuille flow.

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)), From the air molecular velocity ν (m / sec), water viscosity η (Pa · sec), standard pressure P _s (= 101325 Pa), porosity ε (%), and film thickness L (μm), the following equation is used. Asked.
d = 2ν × (R _liq / R _gas ) × (16η / 3Ps) × 10 ⁶
Here, R _gas was calculated | required from the air permeability (second) using the following formula.
R _gas = 0.0001 / (air permeability × (6.424 × 10 ⁻⁴ ) × (0.01276 × 101325))
R _liq was determined from the water permeability (cm ³ / (cm ² · sec · Pa)) using the following formula.
R _liq = water permeability / 100

The water permeability was determined as follows. A base material previously immersed in ethanol is set in a stainless steel liquid-permeable cell having a diameter of 41 mm, and after the ethanol of the base material is washed with water, water is permeated through the base material with a differential pressure of about 50000 Pa, From the water permeability (cm ³ ) when 120 seconds passed, the water permeability per unit time, unit pressure, and unit area was calculated and used as the water permeability.

Ν is a gas constant R (= 8.314), an absolute temperature T (K), a circumference π, and an average molecular weight M of air (= 2.896 × 10 ⁻² kg / mol), using the following formula. Asked.
ν = ((8R × T) / (π × M)) ^1/2

(8) Average thickness of polymer layer The average thickness of the polymer layer was measured by observing the cross section of the separator using a scanning electron microscope (SEM) “Model S-4800, manufactured by HITACHI”. More specifically, the separator was cut out to about 1.5 mm × 2.0 mm and dyed with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then cleaved with a hammer. Next, the sample was subjected to osmium vapor deposition and observed at an acceleration voltage of 1.0 kV and 30000 times, and the average thickness of the polymer layer was calculated. The outermost surface area where the porous structure of the cross section of the substrate (polyolefin microporous film) was not visible in the SEM image was defined as the polymer layer area.

(9) Glass transition temperature of copolymer An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing a copolymer is placed in an aluminum dish and heated with a hot air dryer at 130 ° C. Dried for minutes. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measuring apparatus (manufactured by Shimadzu Corporation, model number: DSC6220). The measurement conditions were as follows.
(First stage temperature rise program)
Starting at 70 ° C., the temperature was increased at a rate of 15 ° C. per minute. After reaching 110 ° C., the temperature was maintained for 5 minutes.
(Second stage temperature drop program)
The temperature was lowered from 110 ° C. at a rate of 30 ° C. per minute. After reaching −50 ° C., the temperature was maintained for 4 minutes.
(Third-stage temperature rising program)
The temperature was raised from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data were acquired during the third stage of temperature increase.
The intersection of the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg).

(10) Infrared absorption analysis of copolymer The measurement was performed as follows using an infrared absorption analyzer (product name “FTS-60A / 896 UMA300”) manufactured by BIO RAD. The copolymer aqueous dispersion was vacuum dried at 60 ° C. for 24 hours to obtain a white measurement sample. This was ground in an agate mortar. Similarly, KBr was prepared and pulverized in an agate mortar. After adding 0.5 mg of a measurement sample to 100 mg of KBr and thoroughly mixing the measurement sample and KBr in an agate mortar, a tablet was prepared, and the measurement was performed using the tablet as a sample. In addition, the background was measured before the measurement.
Measurement mode: Microscopic transmission method Detector: MCT
Beam splitter: KBr (potassium bromide)
Scan speed: 20 kHz
Integration count: 64 times Resolution: 4 cm ^-1
Measurement wavelength: 4000 to 700 cm ⁻¹
From the obtained infrared absorption spectrum, an infrared absorption peak intensity at a wavelength most infrared absorption intensity is greater in the wavelength range of ^{740cm -1 ~770cm -1 (A (Ar} )), 1720cm -1 ~1750cm -1 Infrared absorption peak intensity (A (Ac)) at a wavelength having the largest infrared absorption intensity in the wavelength range of 720 cm ^{−1 to} 770 cm ⁻¹ and an infrared absorption peak intensity at a wavelength of 720 cm ^{−1 to} 1750 cm The intensity ratio (A (Ac) / A (Ar)) with the infrared absorption peak at a wavelength of ⁻¹ was calculated.

(11) Swelling degree of copolymer with respect to electrolyte solution The aqueous dispersion containing the copolymer was allowed to stand in an oven at 130 ° C. for 1 hour and dried. The copolymer film obtained by drying was cut to 0.5 g. The cut sample is put in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio), and the mixed solvent is infiltrated for 1 day. And the mass (Wa: g) was measured. Thereafter, the sample was allowed to stand in an oven at 150 ° C. for 1 hour, the mass was measured (Wb: g), and the degree of swelling of the copolymer with respect to the electrolytic solution was calculated from the following formula.
Swelling degree of copolymer to electrolyte (times) = (Wa−Wb) ÷ (Wb)

(12) Amount of polymer layer supported on base material For each of the base material (polyolefin microporous membrane) and the separator, the total mass of three samples cut into 10 cm x 10 cm was measured, and the polymer layer in the sample was calculated according to the following formula. The loading amount (solid content) of was measured.
Polymer layer loading (g / m ² ) = [(total mass of 3 separators) − (total mass of 3 substrates)] ÷ 3 × 100

[Evaluation method]
(13) Adhesiveness between separator and electrode The adhesion between the separator and the electrode was evaluated by the following procedure.
(Preparation of positive electrode)
92.2% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.3% by mass of flake graphite and acetylene black as a conductive material, and 3.2% by mass of polyvinylidene fluoride (PVDF) as a binder A slurry was prepared by dispersing in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector with a die coater, dried at 130 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material coating amount of the positive electrode was 250 g / m ² , and the active material bulk density was 3.00 g / cm ³ .

(Preparation of negative electrode)
A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of an aqueous dispersion of styrene-butadiene copolymer as a binder in purified water. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press. At this time, the active material application amount of the negative electrode was set to 106 g / m ² , and the active material bulk density was set to 1.35 g / cm ³ .

(Adhesion test between separator and electrode)
The positive electrode obtained by the above method was cut into a width of 17 mm and a length of 50 mm. On the other hand, a separator (size: width 20 mm, length 100 mm) is immersed in an electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd.) in which ethylene carbonate and diethyl carbonate are mixed at a ratio (volume ratio) of 2: 3 and sufficiently wetted. Raised after. Next, a separator sufficiently wetted with the electrode was stacked on the surface on the polymer layer side. The obtained laminate was put in an aluminum zipped bag and pressed at 80 ° C. and 10 MPa for 2 minutes to obtain a laminate of electrodes and separators. Thereafter, the laminate was removed from the bag and used as a sample for adhesion test. The 90 ° peel strength between the base material of the obtained test sample and the electrode was measured at a tensile speed of 50 mm / min using force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. . Based on the peel strength value, the following evaluation criteria were used.
<Evaluation criteria>
6mN / mm or more ... ◎
4mN / mm or more, less than 6mN / mm ... ○
Less than 4 mN / mm ... ×
(Separator adhesion test)
An aluminum foil (manufactured by Fuji Paper Co., Ltd., thickness: 20 μm) is cut into 20 mm × 100 mm, and the surface of the polymer layer side of the separator of this embodiment is superimposed on the aluminum foil, and then two pieces of Teflon (registered trademark) are used. ) Sheet (Naflon (trademark) PTFE sheet TOMBO-No. 9000) manufactured by NICHIAS Corporation and pressed in the laminating direction at 80 ° C. and a pressure of 10 MPa for 2 minutes. In the sample thus obtained, the peel strength between the aluminum foil and the separator was measured at a tensile speed of 50 mm / min using force gauge ZP5N and MX2-500N manufactured by Imada Corporation. Based on the peel strength value, the following evaluation criteria were used.
<Evaluation criteria>
4mN / mm or more ... ○
Less than 4 mN / mm ... ×

(14) Handling properties of separator (blocking resistance; room temperature peel strength test)
Two separators cut to 20 mm × 100 mm were prepared, overlapped, and sandwiched between two Teflon (registered trademark) sheets (Naflon (trademark) PTFE sheet TOMBO-No. 9000 manufactured by NICHIAS Corporation). . The obtained sample was pressed for 2 minutes under the conditions of a temperature of 25 ° C. and a pressure of 10 MPa. The 90 ° peel strength between the separators in the sample after pressing was measured at a tensile speed of 50 mm / min using Force Gauge ZP5N and MX2-500N manufactured by Imada Corporation. Based on the peel strength value, the following evaluation criteria were used.
<Evaluation criteria>
40 mN / mm or less ... ○
More than 40mN / mm ... ×

(15) Evaluation of oxidation resistance The oxidation resistance was evaluated by observing the blackening of the separator surface after the trickle test using the NC cell. Specifically, the separator coated with the aqueous dispersion was 18 mmφ, and the positive electrode and the negative electrode prepared in the above “(13) Adhesion between separator and electrode” were cut into a 16 mmφ circle (disc), and the positive electrode and the negative electrode After stacking the positive electrode, the separator, and the negative electrode in this order so that the active material surfaces face each other, they were housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was placed in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. The electrolyte was poured into this container and sealed, and left in that state at room temperature for 1 day to obtain a battery. The electrolyte used was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1/2 (volume ratio). . Next, in an atmosphere of 25 ° C., the battery voltage was charged to 4.2 V at a current value of 6 mA (1.0 C), and the current value started to be reduced from 6 mA so as to maintain 4.2 V. Charged for hours. Next, the battery was discharged to a battery voltage of 3.0 V at a current value of 6 mA (1.0 C). Next, in a 60 ° C. atmosphere, the battery voltage is charged to 4.2 V at a current value of 6 mA (1.0 C), and the current value starts to be reduced from 6 mA so that 4.2 V is maintained. Charged for hours. Next, the battery was stored for 4 days in an atmosphere of 60 ° C. while being charged so as to maintain 4.2 V, and then discharged to a battery voltage of 3.0 V at a current value of 6 mA (1.0 C). The separator was taken out from the battery, and ultrasonic cleaning was performed for 15 minutes in dimethoxyethane, ethanol, and 1N hydrochloric acid in order to remove deposits. Then, it dried in the air, the black discoloration condition of the aqueous dispersion application part of the positive electrode contact surface side of a separator was observed visually, and oxidation resistance was evaluated. The case where the ratio of the color change to black was 5% or less per area was evaluated as ◎, the case where it was 10% or less as ◯, and the case where it exceeded 10% as x.

(16) Rate characteristics A separator is 18 mmφ, and the positive electrode and the negative electrode prepared in the above “(13) Adhesiveness between separator and electrode” are cut into a 16 mmφ circle (disc), and the active material surfaces of the positive electrode and the negative electrode are The positive electrode, the separator, and the negative electrode were stacked in this order so as to face each other, and then housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was placed in contact with the negative electrode copper foil and the lid in contact with the positive electrode aluminum foil. The electrolyte solution was poured into the container and sealed, and left in that state at room temperature for 1 day. The electrolyte used was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1/2 (volume ratio). . Thereafter, the battery is charged at a current value of 2 mA (0.3 C) in a 25 ° C. atmosphere until the battery voltage reaches 4.2 V. After reaching the voltage, 4.2 V is maintained as it is, and the current value is 3 mA. The first charge after battery preparation was performed for a total of 8 hours by the method of starting to squeeze from. Subsequently, the battery was discharged at a current value of 6 mA (1 C) until the battery voltage reached 3.0 V (constant current discharge), and the discharge capacity was measured. Then, after charging in the same manner as described above, the battery was discharged (constant current discharge) at a current value of 12 mA (2C) until the battery voltage reached 3.0 V, and the discharge capacity was measured.
The ratio of the discharge capacity of the latter (2C) to the discharge capacity of the former (1C) is defined as a capacity maintenance ratio (%), and when the capacity maintenance ratio is 90% or more, ◎, and when the capacity maintenance ratio is 70% or more and less than 90% The rate characteristics were evaluated with x being less than 70%.

[Synthesis Example 1]
(Water dispersion A1)
In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier 2.0 parts by mass and “Adekaria soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, “SR1025” in the table, the same applies hereinafter) 0 And 5 parts by mass were charged. Next, the temperature inside the reaction vessel was raised to 80 ° C., and while maintaining the temperature at 80 ° C., a 2% aqueous solution of ammonium persulfate (indicated as “APS (aq) in the table, the same shall apply hereinafter)” 7.5. Part by mass was added. Five minutes after the completion of the addition of the ammonium persulfate aqueous solution, the emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes. The emulsified liquid is an aromatic vinyl compound monomer (in the table, expressed as “Ar vinyl compound monomer”), and 78 parts by mass of styrene (in the table, expressed as “St”; the same applies hereinafter), As a (meth) acrylic acid ester monomer, 20 parts by mass of methyl methacrylate (in the table, expressed as “MMA”, the same applies hereinafter), acrylic acid (in the table, expressed as “AA”, the same applies hereinafter) 1.0 mass Parts, methacrylic acid (in the table, expressed as “MAA”, the same applies hereinafter), 1.0 part by mass, trimethylolpropane triacrylate (A-TMPT, trade name of Shin-Nakamura Chemical Co., Ltd., in the table, “A- “TMPT”. The same applies hereinafter.) 1.0 part by mass, γ-methacryloxypropyltrimethoxysilane (in the table, indicated as “AcSi”, the same applies hereinafter) 0.5 part by mass, “Aqualon KH1025” (registered) as an emulsifier Trademark 25% aqueous solution) 2.0 mass parts manufactured by Dai-ichi Kogyo Seiyaku Co., 2% aqueous solution 7.5 parts by weight of ammonium persulfate, and mixtures of ion-exchanged water 52 parts by mass was prepared by mixing for 5 minutes by a homomixer.
After completion of dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature. The obtained emulsion was adjusted to pH = 9.0 with an aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an aqueous dispersion having a concentration of 40% (aqueous dispersion A1). About the copolymer in obtained aqueous dispersion A1, Tg, average particle diameter, ratio of infrared absorption peak intensity, and the swelling degree with respect to electrolyte solution were measured by the said method. The obtained results are shown in Table 1.

[Synthesis Examples 2 to 10]
(Water dispersions A2 to A10)
Except having changed the kind and compounding ratio of a raw material as shown in Table 1, it carried out similarly to the synthesis example 1, and obtained water dispersion A2-A10. In addition, "BA" in the table | surface means butyl acrylate. To do. About the copolymer in obtained water dispersion A2-A10, the ratio of Tg, a particle diameter, infrared absorption peak intensity, and the swelling degree with respect to electrolyte solution were measured with the said method. The obtained results are shown in Table 1. In the table, the composition of raw materials is based on mass.

[Production Example 1]
(Manufacture of base material B1-1)
Mv is 700,000, 45 parts by mass of homopolymer high-density polyethylene, Mv is 300,000, homopolymer high-density polyethylene is 45 parts by mass, and Mv is 400,000. 10 parts by mass of a mixture of a homopolymer having 150,000 and polypropylene (mass ratio = 4: 3) was dry blended using a tumbler blender. 1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture. The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 −5 m ² / s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass, that is, 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 controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling. The sheet was stretched by a simultaneous biaxial stretching machine at a magnification of 7 × 6.4 and a temperature of 112 ° C., then immersed in methylene chloride, extracted by removing liquid paraffin and dried, and then a temperature of 130 by a tenter stretching machine. The film was stretched 2 times in the transverse direction at ° C. Thereafter, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a base material B1-1.

About the obtained base material B1-1, various physical properties were measured by the said method. The results are shown in Table 2.
[Manufacture of base material B2-1]
96.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm), acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film forming temperature 0 ° C. or less) 4.0 parts by mass, and polycarboxylic acid 1.0 parts by mass of an aqueous ammonium solution (San Nopco SN Dispersant 5468) is uniformly dispersed in 100 parts by mass of water to prepare a coating solution, and is applied to the surface of the base material B1-1 using a micro gravure coater. did. Water was removed by drying at 60 ° C., and a porous layer was formed to a thickness of 2 μm to obtain a polyolefin microporous membrane B2-1. Base material B2-1 which is the obtained polyolefin microporous film was evaluated by the above method in the same manner as base material B1-1. The obtained results are shown in Table 2.

[Example 1]
An aqueous dispersion A1 having a solid content of 80 parts by mass and an aqueous dispersion A7 having a solid content of 20 parts by mass are uniformly dispersed in water to obtain a coating liquid containing a thermoplastic polymer (solid content of 30% by mass). Prepared. Subsequently, the coating liquid was apply | coated so that the polymer layer might become a dot form using the micro gravure coater on the single side | surface of base material B1. Then, the coating liquid after application | coating was dried at 60 degreeC, and water was removed. Furthermore, the coating solution was similarly applied to the other surface of the substrate B1, and dried again in the same manner as described above. In this way, the separator which formed the polymer layer on both surfaces of base material B1 was obtained.
About the obtained separator, handling property, adhesiveness, oxidation resistance, and a rate characteristic were evaluated by the said method. The obtained results are shown in Table 3.

[Comparative Example 1]
A separator was obtained in the same manner as in Example 1 except that styrene butadiene polymer (grade name: L1571, particle size: 200 nm, glass transition temperature: 0 ° C.) manufactured by Asahi Kasei Chemicals Corporation was used as the coating solution. About the obtained separator, handling property, adhesiveness, oxidation resistance, and a rate characteristic were evaluated by the said method. The obtained results are shown in Table 3.

[Examples 2 to 9, Comparative Examples 2 to 4]
Coating solution in the same manner as in Example 1 except that the type and mixing ratio (% by mass) of the aqueous dispersion, the pattern of the polymer layer, and the solid content (part by mass) in the coating solution were changed as shown in Table 3. A separator was prepared. Table 3 shows various physical properties and evaluation / test results of the separator obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the separator which is excellent also in the outstanding adhesiveness with an electrode (electrode active material) and also oxidation resistance can be provided. Therefore, the present invention is useful as a separator for an electricity storage device such as a battery such as a non-aqueous electrolyte secondary battery, a capacitor, and a capacitor, and has industrial applicability in these fields.

That is, the present invention is as follows.
[1] A separator for an electricity storage device, comprising: a substrate composed of a microporous polyolefin membrane ; and a layer containing a thermoplastic polymer that adheres to an electrode formed on at least a part of at least one surface of the substrate. ,
The thermoplastic polymer has at least two glass transition temperatures;
At least one of the glass transition temperatures is in a region below 20 ° C .;
At least one of the glass transition temperatures is present in a region of 20 ° C. or higher,
The glass transition temperature of the thermoplastic polymer present in the 20 ° C. or more regions, viewed contains a copolymer having an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as a monomer unit,
The copolymer has, as a monomer unit, one or more selected from the group consisting of a monomer having an amide group, a monomer having an epoxy group, and a monomer having a hydroxyl group,
The separator for electrical storage devices in which the layer containing the said thermoplastic polymer exists in 5 to 80% with respect to the surface per surface of the said base material .
[2] The above-mentioned separator for an electricity storage device, wherein the thermoplastic polymer existing in a region where the glass transition temperature is less than 20 ° C. includes a copolymer having a (meth) acrylic acid ester monomer as a monomer unit.
[3] The mixing ratio of the thermoplastic polymer present in a region where the glass transition temperature is less than 20 ° C. and the thermoplastic polymer present in a region where the glass transition temperature is 20 ° C. or higher is 50:50 to 50% by mass. The above separator for an electricity storage device, which is 5:95.
[4] The above separator for an electricity storage device, wherein the peel strength of at least one of the following (1) and (2) is 4 mN / mm or more.
(1) The above-mentioned electricity storage wetted with an electrolytic solution obtained by mixing ethylene foil and diethyl carbonate at a ratio (volume ratio) of 2: 3 to aluminum foil (aluminum foil manufactured by Fuji Process Paper Co., Ltd., thickness: 20 μm). The device separator is overlapped from the thermoplastic polymer-containing layer side, pressed in the overlapping direction at 80 ° C. and a pressure of 10 MPa for 2 minutes, the aluminum foil and the electricity storage device separator, 90 ° peel strength when peeled at a tensile rate of 50 mm / min.
(2) A direction in which the separator for an electricity storage device is overlapped on an aluminum foil (aluminum foil manufactured by Fuji Processed Paper Co., Ltd., thickness: 20 μm) from the layer containing the thermoplastic polymer, and the layers are overlapped. 90 ° peel strength when the aluminum foil and the electricity storage device separator were peeled at a tensile rate of 50 mm / min after pressing at 80 ° C. and a pressure of 10 MPa for 2 minutes.
[5] The above-mentioned separator for an electricity storage device, wherein the following (3) peel strength is 40 mN / mm or less.
(3) After pressurizing a sample comprising two stacked 20 mm × 100 mm separators and two PTFE sheets sandwiching the separators at a temperature of 25 ° C. and a pressure of 10 MPa for 2 minutes, 90 ° peel strength when the separators in the sample are peeled at a tensile speed of 50 mm / min.
[ 6 ] The above separator for an electricity storage device, wherein the (meth) acrylic acid ester monomer contains a hydrocarbon ester of (meth) acrylic acid.
[7] The copolymer has a ratio of the infrared absorption peak intensity at a wavelength of 1720cm ^-1 ~1750cm ^-1 for infrared absorption peak intensity at a wavelength of the 740cm ^-1 ~770cm ^-1 is in 1 to 18 The said separator for electrical storage devices.
[ 8 ] The above separator for an electricity storage device, wherein the degree of swelling of the copolymer with respect to a mixed solvent of ethylene carbonate and diethyl carbonate (mass ratio 2: 3) is 0.5 times to 6.0 times.
[ 9 ] The copolymer further comprises at least one monomer selected from the group consisting of a monomer having a chain alkyl group having 4 or more carbon atoms and a monomer having a cycloalkyl group. The said separator for electrical storage devices which has as a monomer unit.

Claims (8)

A separator for an electricity storage device comprising: a base material; and a layer containing a thermoplastic polymer formed on at least a part of at least one surface of the base material,
The separator for electrical storage devices in which the said thermoplastic polymer contains the copolymer which has an aromatic vinyl compound monomer and a (meth) acrylic acid ester monomer as a monomer unit.   The separator for an electricity storage device according to claim 1, wherein the (meth) acrylic acid ester monomer includes a hydrocarbon ester of (meth) acrylic acid. Included in the copolymer, the ratio of infrared absorption peak intensity at a wavelength of 1720cm ^-1 ~1750cm ^-1 for infrared absorption peak intensity at 740cm ^-1 ~770cm ^-1 wavelength, 1 to 18, claim 1 Or 2 is a separator for an electricity storage device.   The swelling degree of the said copolymer with respect to the mixed solvent (mass ratio 2: 3) of ethylene carbonate and diethyl carbonate is 0.5 time-6.0 time, Any one of Claims 1-3. Electric storage device separator.   The copolymer has one or more monomers selected from the group consisting of a monomer having a chain alkyl group having 4 or more carbon atoms and a monomer having a cycloalkyl group as a monomer unit. The separator for electrical storage devices of any one of Claims 1-4 which has.   The separator for an electricity storage device according to any one of claims 1 to 5, wherein the copolymer includes a copolymer produced by emulsion polymerization.   An electrical storage device provided with the separator for electrical storage devices of any one of Claims 1-6.   A lithium ion secondary battery provided with the separator for electrical storage devices of any one of Claims 1-6.

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