Binder composition for heat-resistant layer of non-aqueous secondary battery, slurry composition for heat-resistant layer of non-aqueous secondary battery, heat-resistant layer for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

The present invention provides a binder composition for a heat-resistant layer of a non-aqueous secondary battery, which contains a particulate polymer. The above particulate polymer contains monomer units containing an acidic group in a content ratio of 1% by mass or more and 5% by mass or less, and contains monomer units containing a cyano group in a content ratio of 4.5% by mass or more and 25% by mass or less.

Description

Technical Field

[0001] The present invention relates to a binder composition for a heat-resistant layer of a non-aqueous secondary battery, a slurry composition for a heat-resistant layer of a non-aqueous secondary battery, a heat-resistant layer for a non-aqueous secondary battery, and a non-aqueous secondary battery Background Art

[0002] Non-aqueous secondary batteries such as lithium-ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") have characteristics such as being small, light, having a high energy density, and being capable of repeated charging and discharging, and have been used in a wide range of applications. Further, a secondary battery generally has battery components such as electrodes (a positive electrode and a negative electrode) and a separator that separates the positive electrode and the negative electrode. Moreover, heretofore, as such battery components, battery parts having a heat-resistant layer as a protective layer for improving heat resistance have been used

[0003] Here, as a heat-resistant layer of a secondary battery, a heat-resistant layer formed by binding non-conductive particles with a binder can be cited. Such a heat-resistant layer is generally formed by the following method: preparing a slurry composition (hereinafter, referred to as "slurry composition for heat-resistant layer of non-aqueous secondary battery", and sometimes simply referred to as "slurry composition for heat-resistant layer") in which non-conductive particles and a binder are dissolved or dispersed in a dispersion medium such as water, and applying the slurry composition for heat-resistant layer to a substrate such as a separator substrate or an electrode substrate and drying it

[0004] Moreover, in recent years, in order to further improve the performance of secondary batteries, attempts have been made to improve the binder composition for forming a heat-resistant layer (for example, refer to Patent Document 1).

[0005] Patent Document 1 discloses a binder composition for a porous film of a non-aqueous secondary battery containing a sulfosuccinate and / or its salt and water. In this binder composition for a porous film of a non-aqueous secondary battery, the surface acid amount of the particulate polymer is within a specified range, and the ratio of the acid amount L in the liquid phase in the binder composition to the above surface acid amount is also within a specified range. More specifically, Patent Document 1 describes that the particulate polymer preferably contains 0.1 mass% or more and 3 mass% or less of acid group-containing monomer units, and may further contain (meth)acrylonitrile monomer units. The binder composition of Patent Document 1 is a composition that can form a porous film, that is, a heat-resistant layer, which can exhibit heat resistance, together with non-conductive particles. Further, according to the binder composition of Patent Document 1, a porous film with a small water content can be formed

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: International Publication No. 2018 / 180472 Summary of the Invention

[0009] Problems to be Solved by the Invention The present invention.

[0010] However, in recent years, there has been a demand for further improving the performance of secondary batteries. For the above-described conventional binder compositions, there is still room for improvement in terms of improving the adhesion between the heat-resistant layer formed with the binder composition and the substrate (e.g., spacer substrate or electrode substrate) on which the heat-resistant layer is formed. More specifically, it is required that the binder composition can improve the peel strength of the resulting heat-resistant layer and the adhesion between the heat-resistant layer and the substrate.

[0011] Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery heat-resistant layer, which can prepare a slurry composition for a non-aqueous secondary battery heat-resistant layer that can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength.

[0012] In addition, an object of the present invention is also to provide a slurry composition for a non-aqueous secondary battery heat-resistant layer, which can form a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength.

[0013] Furthermore, an object of the present invention is to provide a heat-resistant layer for a non-aqueous secondary battery having a sufficiently high peel strength, and a non-aqueous secondary battery having the heat-resistant layer.

[0014] Means for Solving the Problems

[0015] The present inventors conducted in-depth research for the purpose of solving the above problems. As a result, the present inventors found that when a binder composition containing a particulate polymer in which the content ratio of the monomer unit containing an acidic group is 1% by mass or more and 5% by mass or less and the content ratio of the monomer unit containing a cyano group is 4.5% by mass or more and 25% by mass or less is used, a heat-resistant layer having a sufficiently high peel strength can be formed, thereby completing the present invention.

[0016] That is, an object of the present invention is to advantageously solve the above problems. The binder composition for a non-aqueous secondary battery heat-resistant layer of the present invention is characterized by containing a particulate polymer, the particulate polymer containing a monomer unit containing an acidic group and a monomer unit containing a cyano group, the content ratio of the monomer unit containing an acidic group in the particulate polymer being 1% by mass or more and 5% by mass or less, and the content ratio of the monomer unit containing a cyano group being 4.5% by mass or more and 25% by mass or less. In this way, according to the binder composition containing a particulate polymer in which the content ratio of the monomer unit containing an acidic group is 1% by mass or more and 5% by mass or less and the content ratio of the monomer unit containing a cyano group is 4.5% by mass or more and 25% by mass or less, a slurry composition that can form a heat-resistant layer having a sufficiently high peel strength can be prepared.

[0017] In addition, the meaning of "a polymer contains monomer units" is "the polymer obtained from the monomer contains repeating units derived from the monomer".

[0018] In addition, the "content ratio" of a certain monomer unit in the polymer can be determined using 1 H-NMR, 13 C-NMR and other nuclear magnetic resonance (NMR) methods.

[0019] Here, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the volume average particle diameter of the particulate polymer is 0.30 μm or less. If the volume average particle diameter of the particulate polymer is 0.30 μm or less, the heat shrinkage resistance of the obtained heat-resistant layer can be improved.

[0020] In addition, the meaning of the "volume average particle diameter" of the particulate polymer is "the particle diameter (D50) at which the cumulative volume calculated from the small particle diameter side in the particle size distribution (volume basis) measured by the laser diffraction method is 50%".

[0021] In addition, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the above-mentioned monomer unit containing an acidic group contains a monomer unit containing a carboxyl group. If the monomer unit containing an acidic group in the particulate polymer contains a monomer unit containing a carboxyl group, the peel strength of the obtained heat-resistant layer can be further improved.

[0022] Furthermore, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the above-mentioned particulate polymer further contains a crosslinkable monomer unit. If the particulate polymer contains a crosslinkable monomer unit in addition to the above-mentioned various monomer units, the rate performance of the obtained secondary battery can be improved.

[0023] Moreover, in the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention, it is preferable that the above-mentioned particulate polymer is a (meth)acrylate copolymer. If the particulate polymer is a (meth)acrylate copolymer, the peel strength of the obtained heat-resistant layer can be further improved.

[0024] In addition, in this specification, the meaning of "(meth)acrylate copolymer" is a copolymer in which the content ratio of the (meth)acrylate monomer unit in the copolymer is greater than 50% by mass when all the repeating units (all monomer units) contained in the copolymer are 100% by mass. In addition, in this specification, (meth)acrylic acid means acrylic acid or methacrylic acid.

[0025] In addition, an object of the present invention is to advantageously solve the above problems. The slurry composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention is characterized by containing non-conductive particles and any one of the binder compositions for a heat-resistant layer of a non-aqueous secondary battery described above. If a slurry composition containing non-conductive particles and any one of the above binder compositions is used, a heat-resistant layer with a sufficiently high peel strength can be formed.

[0026] Here, in the slurry composition for a heat-resistant layer of a non-aqueous secondary battery of the present invention, it is preferable that the volume average particle diameter of the above non-conductive particles is 0.7 μm or less. If the volume average particle diameter of the non-conductive particles is 0.7 μm or less, the heat shrinkage resistance of the resulting heat-resistant layer can be improved.

[0027] In addition, the meaning of the volume average particle diameter of the non-conductive particles is "the particle diameter (D50) at which the cumulative volume calculated from the small particle diameter side in the particle size distribution (volume basis) measured by the laser diffraction method is 50%".

[0028] Moreover, an object of the present invention is to advantageously solve the above problems. The heat-resistant layer for a non-aqueous secondary battery of the present invention is characterized in that it is formed from the above slurry composition for a heat-resistant layer of a non-aqueous secondary battery. The peel strength of the heat-resistant layer formed from the above slurry composition is sufficiently high.

[0029] In addition, an object of the present invention is to advantageously solve the above problems. The non-aqueous secondary battery of the present invention is characterized by having the above heat-resistant layer for a non-aqueous secondary battery. A secondary battery having a battery member with the above heat-resistant layer has excellent battery performance.

[0030] Advantages of the Invention

[0031] According to the present invention, it is possible to provide a binder composition for a heat-resistant layer of a non-aqueous secondary battery, which can prepare a slurry composition for a heat-resistant layer of a non-aqueous secondary battery that can form a heat-resistant layer for a non-aqueous secondary battery with a sufficiently high peel strength.

[0032] In addition, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a non-aqueous secondary battery, which can form a heat-resistant layer for a non-aqueous secondary battery with a sufficiently high peel strength.

[0033] Furthermore, according to the present invention, it is possible to provide a heat-resistant layer for a non-aqueous secondary battery with a sufficiently high peel strength, and a non-aqueous secondary battery having the heat-resistant layer. Detailed Embodiments

[0034] Hereinafter, the embodiments of the present invention will be described in detail.

[0035] Here, the binder composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention can be used to prepare the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention. Moreover, the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention can be used to form the heat-resistant layer of non-aqueous secondary batteries such as lithium-ion secondary batteries. Furthermore, the heat-resistant layer for the non-aqueous secondary battery of the present invention is characterized in that it is formed from the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention. In addition, the non-aqueous secondary battery of the present invention is characterized by having a heat-resistant layer for the non-aqueous secondary battery made from the slurry composition for the heat-resistant layer of the non-aqueous secondary battery of the present invention.

[0036] (Binder composition for heat-resistant layer of non-aqueous secondary battery)

[0037] The binder composition of the present invention contains granular polymers, and may also optionally contain a dispersion medium and other components.

[0038] Here, the binder composition of the present invention is characterized in that the granular polymer contains acidic group monomer units and cyano group monomer units, and further, the content ratio of the acidic group monomer units in the granular polymer is 1% by mass or more and 5% by mass or less, and the content ratio of the cyano group monomer units is 4.5% by mass or more and 25% by mass or less.

[0039] Moreover, since the binder composition of the present invention contains granular polymers that satisfy the above-described specified properties, the resulting heat-resistant layer can be bonded to the substrate with sufficient strength, and as a result, the peel strength of the heat-resistant layer can be sufficiently improved. The reason for obtaining the above effect by using the binder composition containing the granular polymer as described above is not clear, but it is speculated that the reason is that by including the acidic group monomer units and cyano group monomer units in the granular polymer within the above-described specified ranges, the acidic group monomer units tend to exist preferentially near the surface of the granular polymer, thereby improving the stability of the granular polymer and making it less likely to aggregate in the slurry composition, and enabling the adhesive force to the adherend to be exhibited well.

[0040] <Granular polymer>

[0041] The granular polymer contained in the binder composition of the present invention is a component that can function as an adhesive material in the heat-resistant layer formed using the slurry composition, and is a component that imparts adhesiveness to the heat-resistant layer formed from the slurry composition containing the binder composition and can keep the non-conductive particles contained in the heat-resistant layer from detaching from the heat-resistant layer.

[0042] Moreover, the granular polymer is a water-insoluble particle formed from a specified polymer. In addition, in the present invention, "water-insoluble" for the particle means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble component is 90% by mass or more.

[0043] Here, the particulate polymer contains monomer units having an acidic group and monomer units having a cyano group, and may optionally contain other monomer units. Hereinafter, various monomer units will be described in detail.

[0044] <<Monomer units having an acidic group>>

[0045] Monomer units having an acidic group are monomer units obtained by polymerizing monomers having an acidic group. Examples of the acidic group include, for example, -COOH group (carboxylic acid group), -SO 3 H group (sulfonic acid group); -PO 3 H 2 groups and acidic functional groups such as phosphoric acid groups such as -PO(OH)(OR) group (R represents a hydrocarbon group). Therefore, examples of monomers having an acidic group that can form monomer units having an acidic group include monomers having these acidic groups. In addition, examples of monomers having an acidic group also include monomers that can generate the above acidic groups by hydrolysis. When specific examples of such monomers having an acidic group are given, examples include acid anhydrides that can generate a carboxylic acid group by hydrolysis. Each of the various monomers having an acidic group listed below may be used alone, or two or more thereof may be used in any ratio in combination.

[0046] Examples of monomers having a carboxylic acid group include, for example, monocarboxylic acids, dicarboxylic acids, acid anhydrides of dicarboxylic acids, and their derivatives. Examples of monocarboxylic acids include, for example, acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of dicarboxylic acids include monomers containing a carboxylic acid group such as maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of acid anhydrides of dicarboxylic acids include, for example, maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride.

[0047] Examples of monomers having a sulfonic acid group include, for example: vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, 2-sulfoethyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, 2-(N-acryloyl)amino-2-methyl-1,3-propanedisulfonic acid and other monomers having a sulfonic acid group.

[0048] Examples of monomers having -PO 3 H 2 groups and phosphoric acid groups such as -PO(OH)(OR) group (R represents a hydrocarbon group) include, for example: 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate and other monomers having a phosphoric acid group. In addition, in the present specification, (meth)acryloyl means acryloyl or methacryloyl.

[0049] In addition, salts of the above various monomers can also be used as monomers containing acidic groups. Among the above monomers containing acidic groups, monomers containing carboxyl groups are preferably used, and the above monocarboxylic acids are more preferably used, and at least one of acrylic acid and methacrylic acid is particularly preferably used. If the particulate polymer contains a monomer unit containing a carboxyl group formed from a monomer containing a carboxyl group as a monomer unit containing an acidic group, the peel strength of the resulting heat-resistant layer can be further improved.

[0050] When the amount of all repeating units (all monomer units) contained in the particulate polymer is 100% by mass, the content ratio of the monomer unit containing an acidic group in the particulate polymer is preferably 1% by mass or more, more preferably 1.5% by mass or more, preferably 5% by mass or less, and more preferably 4% by mass or less. If the content ratio of the monomer unit containing an acidic group in the particulate polymer is at least the above lower limit value, the peel strength of the resulting heat-resistant layer can be sufficiently improved. In addition, if the content ratio of the monomer unit containing an acidic group in the particulate polymer is at most the above upper limit value, the heat shrinkage resistance of the resulting heat-resistant layer can be sufficiently improved.

[0051]

[0052] The monomer unit containing a cyano group is a monomer unit obtained by polymerizing a monomer containing a cyano group. Examples of the monomer containing a cyano group that can form the monomer unit containing a cyano group include α,β-unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile. These can be used alone or in combination of two or more in any ratio.

[0053] When the amount of all repeating units contained in the particulate polymer is 100% by mass, the content ratio of the monomer unit containing a cyano group in the particulate polymer is preferably 4.5% by mass or more, more preferably 6% by mass or more, preferably 25% by mass or less, and more preferably 22% by mass or less. If the content ratio of the monomer unit containing a cyano group in the particulate polymer is at least the above lower limit value, the rate characteristics of the resulting secondary battery can be improved. In addition, if the content ratio of the monomer unit containing a cyano group in the particulate polymer is at most the above upper limit value, the peel strength of the resulting heat-resistant layer can be sufficiently improved.

[0054]

[0055] The other monomer units are not particularly limited, and examples thereof include crosslinkable monomer units, (meth)acrylate monomer units, olefinically unsaturated carboxamide monomer units, aromatic vinyl monomer units, fluorine atom-containing monomer units, and aliphatic conjugated diene monomer units.

[0056] [Crosslinkable monomer units]

[0057] ​​A crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. In addition, a crosslinkable monomer is a monomer capable of forming a crosslinked structure during or after polymerization under conditions such as heating or irradiation with energy rays. More specifically, as the crosslinkable monomer unit, there can be mentioned a crosslinkable monomer having a thermally crosslinkable crosslinking group and one ethylenic double bond per molecule (hereinafter sometimes referred to as "crosslinkable monomer 1"), a crosslinkable monomer having two or more ethylenic double bonds per molecule (hereinafter sometimes referred to as "crosslinkable monomer 2"), and the like. These can be used alone or in combination of two or more in any ratio. In addition, the crosslinkable monomer unit does not include monomer units belonging to the various monomer units described above and hereinafter.

[0058] Examples of the thermally crosslinkable crosslinking group that can be included as crosslinkable monomer 1 include an epoxy group, a hydroxymethyl group, an oxetanyl group, an oxazolinyl group, and combinations thereof. And, as specific examples of crosslinkable monomer 1, there can be mentioned glycidyl acrylate and glycidyl methacrylate (thermally crosslinkable crosslinking group: epoxy group), (meth)acrylamides having a hydroxymethyl group such as N-hydroxymethyl(meth)acrylamide (thermally crosslinkable crosslinking group: hydroxymethyl group). Among them, N-hydroxymethyl(meth)acrylamide is preferably used, and N-hydroxymethylacrylamide is more preferably used.

[0059] Furthermore, examples of crosslinkable monomer 2 include: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and the like. In addition, in this specification, (meth)acrylate means acrylate or methacrylate. Among them, allyl (meth)acrylate is preferably used, and allyl methacrylate is more preferably used.

[0060] When the particulate polymer contains a crosslinkable monomer unit, when the amount of all repeating units contained in the particulate polymer is taken as 100% by mass, the content ratio of the crosslinkable monomer unit in the particulate polymer is preferably 0.001% by mass or more and 10% by mass or less. If the content ratio of the crosslinkable monomer unit in the particulate polymer is at or above the above lower limit value, the rate characteristics of the resulting secondary battery can be improved.

[0061] [(Meth)acrylate monomer unit]

[0062] (Meth)acrylate monomer units are monomer units obtained by polymerizing (meth)acrylate monomers. Examples of (meth)acrylate alkyl ester monomers that can form (meth)acrylate monomer units include: acrylate esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (n-butyl acrylate), isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate (2-ethylhexyl acrylate), 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate; methacrylate esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, benzyl methacrylate, etc. These can be used alone or in combination of two or more in any ratio. Among them, as the (meth)acrylate monomer, n-butyl acrylate (n-butyl acrylate) and 2-ethylhexyl acrylate (2-ethylhexyl acrylate) are preferred.

[0063] When the granular polymer contains (meth)acrylate monomer units, when the amount of all repeating units (all monomer units) contained in the granular polymer is taken as 100% by mass, the content ratio of (meth)acrylate monomer units in the granular polymer is preferably greater than 50% by mass, more preferably 60% by mass or more, preferably 93% by mass or less, and more preferably 90% by mass or less. If the content ratio of (meth)acrylate monomer units in the granular polymer is within the above range, the peel strength of the resulting heat-resistant layer can be further improved.

[0064] [Ethylenically unsaturated carboxamide monomer units]

[0065] Ethylenically unsaturated carboxamide monomer units are monomer units obtained by polymerizing ethylenically unsaturated carboxamide monomers. Examples of ethylenically unsaturated carboxamide monomers include acrylamide, methacrylamide, N-methoxymethyl methacrylamide, N-methoxymethyl methylacrylamide, etc. Among them, acrylamide and methacrylamide are preferred, and acrylamide is more preferred. These can be used alone or in combination of two or more in any ratio.

[0066] In the case where the granular polymer contains an ethylenically unsaturated carboxylic acid amide monomer unit, when the amount of all repeating units (all monomer units) contained in the granular polymer is 100% by mass, the content ratio of the ethylenically unsaturated carboxylic acid amide monomer unit in the granular polymer is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 10% by mass or less, and more preferably 8% by mass or less. If the content ratio of the ethylenically unsaturated carboxylic acid amide monomer unit in the granular polymer is within the above range, the peel strength of the resulting heat-resistant layer can be improved.

[0067] [Aromatic vinyl monomer unit]

[0068] The aromatic vinyl monomer unit is a monomer unit obtained by polymerizing an aromatic vinyl monomer. There is no particular limitation on the aromatic vinyl monomer, and examples thereof include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, etc. In addition, these aromatic vinyl monomers can be used alone or in combination of two or more in any ratio. Among them, as the aromatic vinyl monomer, styrene is preferred.

[0069] [Fluorine atom-containing monomer unit]

[0070] The fluorine atom-containing monomer unit is a monomer unit obtained by polymerizing a fluorine atom-containing monomer. Examples of the fluorine atom-containing monomer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, perfluoroalkyl vinyl ether, etc. These can be used alone or in combination of two or more in any ratio.

[0071] [Aliphatic conjugated diene monomer unit]

[0072] The aliphatic conjugated diene monomer unit is a monomer unit obtained by polymerizing an aliphatic conjugated diene monomer. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc. These can be used alone or in combination of two or more in any ratio.

[0073] [<Properties>]

[0074] [Volume average particle diameter]

[0075] In addition, the volume average particle diameter of the particulate polymer is preferably 0.08 μm or more, more preferably 0.10 μm or more, preferably 0.30 μm or less, more preferably 0.25 μm or less, further preferably 0.20 μm or less, and particularly preferably 0.18 μm or less. If the volume average particle diameter of the particulate polymer is at least the above lower limit value, it is possible to suppress an excessively low air permeability of the resulting heat-resistant layer. Further, if the volume average particle diameter of the particulate polymer is at most the above upper limit value, it is possible to improve the heat shrinkage resistance of the resulting heat-resistant layer.

[0076] Moreover, the volume average particle diameter of the particulate polymer can be adjusted by changing, for example, the type or amount of the monomer, polymerization initiator, and / or polymerization accelerator used in the preparation of the particulate polymer.

[0077] [Degree of swelling in the electrolyte]

[0078] The degree of swelling of the particulate polymer in the electrolyte is preferably 2 times or more, more preferably 4.5 times or more, further preferably 5 times or more, preferably 11 times or less, more preferably 10 times or less, and further preferably 9 times or less. If the degree of swelling of the particulate polymer is at least the above lower limit value, it is possible to improve the rate characteristics of the resulting secondary battery. If the degree of swelling of the particulate polymer is at most the above upper limit value, it is possible to improve the adhesiveness of the particulate polymer. In addition, in the present specification, the "degree of swelling" of the particulate polymer means: the degree of swelling in an electrolyte (a solution obtained by dissolving LiPF at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a mass ratio of 3:7), which can be measured by the method described in the examples. 6 and obtained solution), which can be measured by the method described in the examples.

[0079] <<Method for preparing particulate polymer>>

[0080] Here, the polymerization method of the particulate polymer is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. In addition, as the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Moreover, as the polymerization solvent, emulsifier, dispersant, polymerization initiator, chain transfer agent, etc. that can be used in the polymerization, those commonly used can be used, and their usage amounts can also be the usual usage amounts.

[0081] In addition, in the binder composition of the present invention, the content of the particulate polymer is not particularly limited.

[0082] <Dispersion medium>

[0083] Examples of the dispersion medium that may optionally be contained in the binder composition of the present invention include water, organic solvents (such as esters, ketones, and alcohols), and mixtures thereof. In addition, the binder composition of the present invention may contain one organic solvent or two or more organic solvents. Among them, water is preferably used as the dispersion medium.

[0084] <Other components>

[0085] The binder composition of the present invention may contain a water-soluble polymer, a reinforcing material, a leveling agent, a wetting agent, a dispersant, a viscosity modifier, an electrolyte additive, a preservative, a mildew-proof agent, an antifoaming agent, a polymerization inhibitor, and a binder material other than the particulate polymer as described above. These substances are not particularly limited as long as they do not affect the battery reaction, and known substances can be used. In addition, these other components may be used alone or in combination of two or more in any ratio.

[0086] The water-soluble polymer that may optionally be contained in the binder composition for the heat-resistant layer of the non-aqueous secondary battery is a component that can function as a viscosity modifier in the binder composition and the slurry composition containing the binder composition.

[0087] In addition, the polymer being "water-soluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble component is less than 1.0 mass%.

[0088] There is no particular limitation on the water-soluble polymer, and various thickening polysaccharides can be used. As the thickening polysaccharides, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, or their salts are preferably used, and carboxymethyl cellulose or its salts are particularly preferably used.

[0089] Examples of the carboxymethyl cellulose salt include sodium salt, ammonium salt, etc. The thickening polysaccharides may be used alone or in combination of two or more in any ratio.

[0090] In addition, there is no particular limitation on the wetting agent that may optionally be contained in the binder composition for the heat-resistant layer of the non-aqueous secondary battery, and ethylene oxide-propylene oxide-based surfactants (EO·PO-based surfactants), fluorine-based surfactants, silicone-based surfactants, etc. can be used. Among them, EO·PO-based surfactants and fluorine-based surfactants are preferably used, and EO·PO-based surfactants are more preferably used.

[0091] In addition, there is no particular limitation on the dispersant, and polycarboxylic acids such as polyacrylic acid, polycarboxylate salts such as sodium polyacrylate, polycarboxylic acid ammonium salts such as ammonium polyacrylate, polycarboxylic acid sulfonic acid copolymers, sodium polycarboxylic acid sulfonic acid copolymers, ammonium polycarboxylic acid sulfonic acid copolymers, etc. can be used. Among them, sodium polyacrylate is preferably used.

[0092] Specific examples of other components in addition to the above-mentioned wetting agents and dispersants are not particularly limited, and examples thereof include the components described in International Publication No. 2012 / 115096.

[0093] <Preparation of Binder Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery>

[0094] Moreover, the binder composition of the present invention can be prepared by mixing the above-mentioned particulate polymer with any other components used as needed by a known method. Specifically, the binder composition can be prepared by mixing the above components using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, grinder, ultrasonic disperser, homogenizer, planetary mixer, Filmix, etc.

[0095] In addition, for example, when the particulate polymer is polymerized in an aqueous solution and prepared, the aqueous dispersion state of the particulate polymer can be directly used as the binder composition.

[0096] (Slurry Composition for Heat-Resistant Layer of Non-Aqueous Secondary Battery)

[0097] The slurry composition of the present invention is a composition for forming a heat-resistant layer, contains non-conductive inorganic particles and the above-mentioned binder composition, and also optionally contains other components. That is, the slurry composition of the present invention generally contains non-conductive particles, particulate polymers and a dispersion medium, and optionally also contains other components. Moreover, since the slurry composition of the present invention contains the above-mentioned binder composition, a heat-resistant layer with a sufficiently high peel strength can be formed.

[0098] <Non-Conductive Particles>

[0099] Here, the non-conductive particles contained in the slurry composition for the heat-resistant layer are not particularly limited, and examples thereof include particles composed of inorganic materials (i.e., non-conductive inorganic particles) and particles composed of organic materials (i.e., non-conductive organic particles) that stably exist and are electrochemically stable in the use environment of the secondary battery. Among them, non-conductive inorganic particles are preferred. If preferred examples of non-conductive inorganic particles are given, they include: alumina (aluminum oxide, Al 2 O 3 ), hydrate of alumina (boehmite, AlOOH), gibbsite (Al(OH) 3 ), silica, magnesia (magnesium oxide), magnesium hydroxide, calcium oxide, titanium oxide (titanium dioxide), barium titanate (BaTiO 3) Inorganic oxide particles such as ZrO and alumina-silica composite oxides; nitride particles such as aluminum nitride and boron nitride; covalent bond crystals such as silicon and diamond; sparingly soluble ionic crystals such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite. Among these, from the viewpoint of improving the adhesion between the heat-resistant layer and the substrate, as non-conductive particles, particles composed of alumina (alumina particles), particles composed of boehmite (boehmite particles), particles composed of titanium dioxide (titanium dioxide particles), and particles composed of barium sulfate (barium sulfate particles) are preferred. Alumina particles, boehmite particles, and barium sulfate particles are more preferred, and alumina particles and barium sulfate particles are further preferred.

[0100] In addition, these particles can be subjected to element substitution, surface treatment, solid solution formation, etc. as needed. In addition, these particles can be used alone or in combination of two or more in any ratio.

[0101] In addition, the non-conductive organic particles are organic compounds different from the particulate polymer as the binder material. That is, the non-conductive organic particles do not have adhesiveness. If preferred examples of non-conductive organic particles are given, there are: various crosslinked polymer particles such as crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked product of styrene-divinylbenzene copolymer, polystyrene, polyimide, polyamide, polyamideimide, melamine resin, phenolic resin, phenylguanamine-formaldehyde condensate; and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramide, polyacetal, and thermoplastic polyimide. In addition, as the non-conductive organic particles, their modified products and derivatives can also be used. These particles can be used alone or in combination of two or more in any ratio.

[0102] In addition, the glass transition temperature of the organic particles as non-conductive particles is preferably greater than 20°C and usually 350°C or lower. The glass transition temperature of the organic particles can be measured based on JIS K7121.

[0103] The volume average particle diameter of the non-conductive particles is preferably 0.7 μm or less, more preferably 0.5 μm or less, and further preferably 0.4 μm or less. If the volume average particle diameter of the non-conductive particles is below the above upper limit value, the heat shrinkage resistance of the obtained heat-resistant layer can be improved. In addition, the volume average particle diameter of the non-conductive particles can usually be 0.05 μm or more. The volume average particle diameter of the non-conductive particles can be measured by the laser diffraction method based on JIS Z8825 for the non-conductive particles pretreated according to JIS Z 8824.

[0104] <Binder composition>

[0105] As the binder composition, the binder composition of the present invention described above is used.

[0106] In addition, from the viewpoint of suppressing an excessively low air permeability of the resulting heat-resistant layer, the content of the above-specified particulate polymer in the slurry composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 6 parts by mass or less in terms of solid content based on 100 parts by mass of the non-conductive particles. Further, from the viewpoint of further improving the peel strength of the resulting heat-resistant layer, the content of the specified particulate polymer in the slurry composition is preferably 1 part by mass or more, more preferably 1.2 parts by mass or more, and still more preferably 1.5 parts by mass or more in terms of solid content based on 100 parts by mass of the non-conductive particles. In addition, when the slurry composition contains a water-soluble polymer as an optional component described later, it is preferable that the content of the particulate polymer is more than the content of the water-soluble polymer.

[0107] <Other components>

[0108] There is no particular limitation on other components that can be incorporated into the slurry composition, and examples thereof include the same components as those that can be incorporated into the binder composition of the present invention. Further, the other components may be used alone or in combination of two or more at any ratio.

[0109] Moreover, from the viewpoint of improving the heat shrinkage of the resulting heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 0.5 part by mass or more, more preferably 1 part by mass or more in terms of solid content based on 100 parts by mass of the non-conductive particles (especially non-conductive inorganic particles). Further, from the viewpoint of suppressing an excessively low air permeability of the resulting heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 5 parts by mass or less, more preferably 4 parts by mass or less in terms of solid content based on 100 parts by mass of the non-conductive particles (especially non-conductive inorganic particles).

[0110] In addition, the content of the above-described wetting agent as an optional component in the slurry composition is preferably 0.01 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less based on 100 parts by mass of the non-conductive particles (especially non-conductive inorganic particles). If the content of the wetting agent is at least the above lower limit value, the peel strength of the resulting heat-resistant layer can be further improved. In addition, if the content of the wetting agent is at most the above upper limit value, the cycle characteristics of the secondary battery can be improved.

[0111] In addition, the content of the above dispersant as an optional component in the slurry composition is preferably 0.1 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and still more preferably 1 part by mass or less, relative to 100 parts by mass of the non-conductive particles (especially non-conductive inorganic particles). If the content of the dispersant is at least the above lower limit value, the heat resistance shrinkage of the heat-resistant layer can be improved. In addition, if the content of the dispersant is at most the above upper limit value, the rate characteristics of the secondary battery can be improved.

[0112] <Preparation of a Slurry Composition for a Heat-Resistant Layer of a Non-Aqueous Secondary Battery>

[0113] The above slurry composition can be prepared by mixing the above components using the above-known mixing method described in the <Preparation of a Binder Composition for a Heat-Resistant Layer of a Non-Aqueous Secondary Battery> item.

[0114] (Heat-resistant layer for non-aqueous secondary battery)

[0115] The heat-resistant layer of the present invention is formed from the above slurry composition of the present invention, and can be formed, for example, by applying the above slurry composition to the surface of a suitable substrate to form a coating film and then drying the formed coating film. That is, the heat-resistant layer of the present invention is formed from the dried product of the above slurry composition and generally contains at least non-conductive particles and particulate polymers. In addition, each component contained in the heat-resistant layer is the same as each component contained in the above slurry composition, and thus the preferred ratio of the presence of these components is the same as the preferred ratio of the presence of the components in the slurry composition.

[0116] Moreover, since the heat-resistant layer of the present invention is formed from the slurry composition of the present invention containing the binder composition of the present invention, the peel strength is sufficiently high.

[0117] <Substrate>

[0118] Here, there is no limitation on the substrate to which the slurry composition is applied. For example, a coating film of the slurry composition can be formed on the surface of a release substrate, and the coating film can be dried to form a heat-resistant layer, and the release substrate can be peeled off from the heat-resistant layer. The heat-resistant layer peeled off from the release substrate in this way can also be used as a self-supporting film for forming a battery member of a secondary battery.

[0119] However, from the viewpoint of improving the manufacturing efficiency of the battery member by omitting the step of peeling the heat-resistant layer, as the substrate, a spacer substrate or an electrode substrate is preferably used. Specifically, it is preferable to apply the slurry composition to the spacer substrate or the electrode substrate, and more preferably to the spacer substrate.

[0120] <<Spacer substrate>>

[0121] As the spacer base material, there is no particular limitation, and known spacer base materials such as organic spacer base materials can be cited. The organic spacer base material is a porous member made of an organic material. When examples of the organic spacer base material are cited, microporous membranes or non-woven fabrics containing polyolefin resins such as polyethylene and polypropylene, and aromatic polyamide resins, etc. can be cited. From the viewpoint of excellent strength, a polyethylene microporous membrane or non-woven fabric is preferred.

[0122] <<Electrode base material>>

[0123] As the electrode base material (positive electrode base material and negative electrode base material), there is no particular limitation, and an electrode base material in which an electrode composite material layer containing an electrode active material and a binder material is formed on a current collector can be cited.

[0124] For the current collector, the electrode active materials (positive electrode active material, negative electrode active material) in the electrode composite material layer, the binder materials for the electrode composite material layer (binder material for the positive electrode composite material layer, binder material for the negative electrode composite material layer), and the method of forming the electrode composite material layer on the current collector, known ones can be used, and those described in, for example, Japanese Patent Laid-Open No. 2013-145763 can be cited.

[0125] <Method for forming heat-resistant layer>

[0126] As a method for forming a heat-resistant layer on the above-mentioned base materials such as the spacer base material and the electrode base material, the following methods can be cited.

[0127] 1) A method of applying the slurry composition of the present invention to the surface of the base material (in the case of an electrode base material, the surface on the side of the electrode composite material layer, the same hereinafter), and then drying;

[0128] 2) A method of impregnating the base material in the slurry composition of the present invention and then drying it; and

[0129] 3) A method of applying the slurry composition of the present invention to a release base material, drying to produce a heat-resistant layer, and transferring the obtained heat-resistant layer to the surface of the base material.

[0130] Among these, from the viewpoint of easily controlling the layer thickness of the heat-resistant layer, the method 1) above is particularly preferred. The method 1) above specifically includes: a step of applying the slurry composition to the base material (coating step), and a step of drying the slurry composition applied to the base material to form a heat-resistant layer (drying step).

[0131] <<Coating step>>

[0132] Then, in the coating step, as a method of applying the slurry composition to the base material, there is no particular limitation, and methods such as a doctor blade method, a reverse roll method, a direct roll method, a gravure printing method, an extrusion method, a brush coating method, etc. can be cited.

[0133] <<Drying process>>

[0134] In addition, in the drying process, as the method for drying the slurry composition on the substrate, there is no particular limitation, and known methods can be used. Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiating infrared rays or electron beams.

[0135] <Thickness of the heat-resistant layer>

[0136] The thickness of the heat-resistant layer is preferably 4 μm or less, more preferably 3 μm or less, still more preferably 2.5 μm or less, and particularly preferably 2 μm or less. In addition, the thickness of the heat-resistant layer is not particularly limited and may be, for example, 0.2 μm or more. If the thickness of the heat-resistant layer is below the above upper limit value, the rate characteristics of the resulting secondary battery can be improved. Further, if the thickness of the heat-resistant layer is above the above lower limit value, the heat shrinkage resistance of the heat-resistant layer is excellent.

[0137] (Non-aqueous secondary battery)

[0138] The secondary battery of the present invention has the heat-resistant layer of the present invention described above. More specifically, the secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the heat-resistant layer is included in at least one of the positive electrode, the negative electrode, and the separator as battery components.

[0139] <Positive electrode, negative electrode, and separator>

[0140] At least one of the positive electrode, the negative electrode, and the separator used in the secondary battery of the present invention is a battery component having the heat-resistant layer of the present invention described above. In addition, there is no particular limitation on the positive electrode, the negative electrode, and the separator that do not have the heat-resistant layer of the present invention, and known positive electrodes, negative electrodes, and separators can be used.

[0141] <Electrolytic solution>

[0142] As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is generally used. As the supporting electrolyte, a lithium salt can be used in, for example, a lithium ion secondary battery. Examples of the lithium salt include LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlCl 4 , LiClO 4 , CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF3 CO) 2 NLi, (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 )NLi, etc. Among them, since it is highly soluble in solvents and shows a high degree of dissociation, LiPF 6 , LiClO 4 , CF 3 SO 3 Li is preferably used. In addition, the electrolyte can be used alone or in combination of two or more in any ratio. Generally, there is a tendency that the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be adjusted by the type of the supporting electrolyte.

[0143] As the organic solvent used in the electrolyte solution, there is no particular limitation as long as it can dissolve the supporting electrolyte. For example, in a lithium ion secondary battery, alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC) are preferably used; and esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide, etc. In addition, a mixed solution of these solvents can also be used. Among them, since the carbonate esters have a high dielectric constant and a wide stable potential region, they are preferred.

[0144] In addition, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted. In addition, known additives such as vinylene carbonate (VC) can also be added to the electrolyte solution.

[0145] <Method for manufacturing non-aqueous secondary battery>

[0146] The non-aqueous secondary battery of the present invention can be manufactured, for example, by overlapping a positive electrode and a negative electrode with a spacer in between, winding, folding, etc. according to the shape of the battery as needed and placing them in a battery container, injecting the electrolyte solution into the battery container and sealing it. In addition, at least one of the positive electrode, the negative electrode, and the spacer is a member with a heat-resistant layer. In order to prevent the increase in pressure inside the secondary battery and the occurrence of overcharge and over-discharge, etc., overcurrent protection elements such as fuses and PTC elements, porous metal meshes, guide plates, etc. can also be provided as needed. The shape of the secondary battery can be, for example, one of the shapes such as coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0147] [Examples]

[0148] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, in the following description, unless otherwise specified, "%" and "parts" representing amounts are based on mass.

[0149] In addition, unless otherwise specified, in a polymer produced by polymerizing a plurality of monomers, the proportion of the monomer unit formed by polymerizing a certain monomer in the above polymer is usually the same as the proportion (feed ratio) of the certain monomer in all the monomers used for polymerizing the polymer. And, in the examples and comparative examples, the measurement and evaluation of various properties were carried out according to the following methods.

[0150] <Volume average particle diameter of granular polymer>

[0151] The volume average particle diameter of the granular polymer prepared in the examples and comparative examples was measured by the laser diffraction method. Specifically, an aqueous dispersion (solid component concentration adjusted to 0.1% by mass) containing the object to be measured (granular polymer) was used as a sample. Then, in the particle size distribution (volume basis) measured using a laser diffraction particle size analyzer (manufactured by Beckman Coulter, Inc., product name "LS-13 320"), the particle diameter D50 at which the cumulative volume calculated from the small particle size side is 50% was taken as the volume average particle diameter.

[0152] <Swelling degree in electrolyte>

[0153] The granular polymer prepared in the examples and comparative examples was formed into a film with a thickness of about 0.1 mm, and cut into a square with a size of about 2 inches as a test piece. The mass of the test piece (mass before impregnation) was measured. Then, the test piece was impregnated in the electrolyte at a temperature of 60 °C for 72 hours. After the impregnated test piece was lifted and the electrolyte was wiped off, the mass was immediately measured (mass after impregnation), and the value of (mass after impregnation) / (mass before impregnation) was taken as the swelling degree.

[0154] In addition, as the electrolyte, a solution in which LiPF was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a ratio of 3:7 (mass ratio) was used. 6 The smaller the obtained swelling degree value, the higher the electrolyte resistance of the granular polymer.

[0155] <Water solubility of granular polymer>

[0156] For the granular polymer prepared in the examples and comparative examples, 0.5 g of the polymer was dissolved in 100 g of water at a temperature of 25 °C. In all the examples and comparative examples, it was confirmed that the insoluble component was 90% by mass or more.

[0157] <Adhesion of heat-resistant layer for non-aqueous secondary battery>

[0158] The spacers with heat-resistant layers produced in the examples and comparative examples were each cut into a width of 10 mm and a length of 50 mm to serve as test pieces.

[0159] Next, a SUS (stainless steel) plate with a double-sided tape (manufactured by NITTO DENKO CORPORATION, No. 5608) pasted thereon was prepared, and the surface of the above test piece on the heat-resistant layer side was pasted onto this double-sided tape. Then, one end of the spacer substrate was pulled at a speed of 50 mm / minute at an angle of 180° with respect to the peeling surface, and the peeling strength at the time of peeling was measured and evaluated according to the following criteria. The higher the peeling strength, the higher the adhesion between the spacer substrate and the heat-resistant layer.

[0160] A: The peeling strength is 40 N / m or more;

[0161] B: The peeling strength is 30 N / m or more and less than 40 N / m;

[0162] C: The peeling strength is 20 N / m or more and less than 30 N / m;

[0163] D: The peeling strength is less than 20 N / m.

[0164] <Increase in air permeability>

[0165] Using a digital Ono-type air permeability / smoothness tester (manufactured by Asahi Seiko Co., Ltd., EYO-5-1M-R), the Gurley value (seconds / 100 cc) was measured for the spacer substrate used when manufacturing the spacer with a heat-resistant layer and the manufactured spacer with a heat-resistant layer. Specifically, based on the Gurley value G0 of the "spacer substrate" and the Gurley value G1 of the "spacer with a heat-resistant layer" manufactured, the increase amount ΔG of the Gurley value (=G1 - G0) was obtained and evaluated according to the following criteria. The smaller the increase amount ΔG of this Gurley value, the more excellent the ionic conductivity of the spacer.

[0166] A: The increase amount of the Gurley value is less than 70 seconds / 100 cc;

[0167] B: The increase amount of the Gurley value is 70 seconds / 100 cc or more and less than 100 seconds / 100 cc;

[0168] C: The increase amount of the Gurley value is 100 seconds / 100 cc or more.

[0169] <Heat shrinkage of heat-resistant layer for non-aqueous secondary battery>

[0170] The spacers with heat-resistant layers prepared in the examples and comparative examples were cut into squares with a width of 12 cm and a length of 12 cm. A square with a side length of 10 cm was drawn inside the square to make a test piece. Then, the test piece was placed in a constant temperature bath at 150 °C for 1 hour, and the area change of the square drawn inside (={(the area of the square before placement - the area of the square after placement) / the area of the square before placement}×100%) was determined as the heat shrinkage rate, and the evaluation was carried out according to the following criteria. The smaller the heat shrinkage rate, the more excellent the heat shrinkage resistance of the heat-resistant layer.

[0171] A: The heat shrinkage rate is less than 10%;

[0172] B: The heat shrinkage rate is 10% or more and less than 20%;

[0173] C: The heat shrinkage rate is 20% or more.

[0174] <Rate performance of non-aqueous secondary battery>

[0175] For the lithium-ion secondary batteries prepared in the examples and comparative examples, they were charged to 4.3 V by a constant current method of 0.1C, and then discharged to 3.0 V at 0.1C to obtain the 0.1C discharge capacity. Then, they were charged to 4.3 V at 0.1C and then discharged to 3.0 V at 4C to obtain the 2C discharge capacity. These measurements were carried out on 10 lithium-ion secondary battery cells, and the average value of each measured value was taken as the 0.1C discharge capacity a and the 2C discharge capacity b. The capacity retention rate expressed as the ratio (b / a (%)) of the 2C discharge capacity b to the 0.1C discharge capacity a was calculated, and the rate performance was evaluated according to the following criteria. The higher the value of the capacity retention rate, the more excellent the rate performance.

[0176] A: The capacity retention rate is 90% or more;

[0177] B: The capacity retention rate is 60% or more and less than 90%;

[0178] C: The capacity retention rate is less than 60%.

[0179] (Example 1)

[0180] <Preparation of aqueous dispersion containing particulate polymer A>

[0181] In a reactor equipped with a stirrer, 90 parts of ion-exchanged water, 0.05 part of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Corporation, "NEOPELEX G-15") as an emulsifier, and 0.23 part of ammonium persulfate were respectively supplied. The gas phase part was replaced with nitrogen, and the temperature was raised to 70 °C.

[0182] On the other hand, 50 parts of ion-exchanged water, 0.1 part of sodium dodecylbenzenesulfonate as an emulsifier, 2.5 parts of methacrylic acid (MAA) as an acidic functional group-containing monomer, 10 parts of acrylonitrile (AN) as a cyano group-containing monomer, and 85.3 parts of n-butyl acrylate (BA) as a (meth)acrylate monomer as other monomers, 0.2 part of allyl methacrylate (AMA) as a crosslinkable monomer, and 2.0 parts of acrylamide (AAm) as an ethylenically unsaturated carboxamide monomer are mixed in another container to obtain a monomer composition. The monomer composition is continuously added to the above reactor over 4 hours for polymerization. During the addition, the reaction is carried out at 80°C. After the addition is terminated, stirring is continued at 80°C for 3 hours to terminate the reaction, and an aqueous dispersion (heat-resistant layer binder composition) containing granular polymer A is produced. For the obtained granular polymer A, the volume average particle diameter and the degree of swelling in the electrolyte are measured or calculated according to the above method. The results are shown in Table 1. In addition, the obtained granular polymer A is a (meth)acrylate copolymer (ACL), in which the content ratio of butyl acrylate units as acrylate monomer units is 85.3% by mass.

[0183] <Preparation of Heat-Resistant Layer Slurry Composition>

[0184] Aluminum oxide particles (manufactured by Sumitomo Chemical Co., Ltd., AKP-30, volume average particle diameter D50 (catalog value): 0.3 μm) are used as non-conductive particles, sodium polyacrylate (manufactured by Toa Gosei Co., Ltd., Aron T-50) is used as a dispersant, and carboxymethyl cellulose with an etherification degree of 0.8 to 1.0 (manufactured by Daicel FineChem Ltd., D1220) is used as a water-soluble polymer. In addition, the viscosity of a 1% aqueous solution of the water-soluble polymer is 10 to 20 mPa·s.

[0185] 100 parts of non-conductive particles, 0.5 part of the dispersant, and ion-exchanged water are mixed and treated with a bead mill (manufactured by Ashizawa Finetech Ltd., LMZ015) for 1 hour to obtain a dispersion. Further, 3 parts of the heat-resistant layer binder composition prepared as described above in terms of the solid content equivalent of granular polymer A, 1.5 parts of a 4% aqueous solution of carboxymethyl cellulose in terms of the solid content equivalent, and 0.3 part of an ethylene oxide-propylene oxide-based surfactant (manufactured by San Nopco Limited, Noptex ED-052) as a wetting agent are mixed to prepare a heat-resistant layer slurry composition with a solid content concentration of 40% by weight.

[0186] <Fabrication of Spacer with Heat-Resistant Layer Having Heat-Resistant Layer on One Side>

[0187] A polyethylene spacer substrate (manufactured by Asahi Kasei Corporation, ND509, thickness: 9 μm) was prepared. The above-prepared heat-resistant layer slurry composition was applied to the surface of the prepared spacer substrate, and dried at a temperature of 50°C for 3 minutes to obtain a spacer with a heat-resistant layer on one side (thickness of the heat-resistant layer: 2 μm). Using the obtained spacer with a heat-resistant layer, the air permeability increase value, the adhesion of the heat-resistant layer, and the heat shrinkage resistance were evaluated according to the above method. The results are shown in Table 1.

[0188] <Production of negative electrode>

[0189] In a 5mPa pressure-resistant container with a stirrer, add 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid and 63.5 parts of styrene, 0.4 parts of sodium dodecylbenzene sulfonate as an emulsifier, 150 parts of ion exchange water and 0.5 parts of potassium persulfate as a polymerization initiator, stir thoroughly, and heat to 50°C to start polymerization. Cool at the moment when the polymerization conversion rate reaches 96%, terminate the polymerization reaction, and obtain a mixture containing a granular binder (styrene-butadiene copolymer). Add 5% sodium hydroxide aqueous solution to the above mixture to adjust the pH to 8, and then remove unreacted monomers by heating and reducing pressure distillation. Then, cool the mixture to below 30°C to obtain an aqueous dispersion containing a binder for the negative electrode.

[0190] In a planetary mixer, 48.75 parts of artificial graphite (theoretical capacity: 360 mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity: 360 mAh / g) and 1 part of carboxymethyl cellulose as a thickener in terms of solid content were added. Furthermore, the mixture was diluted with ion exchange water to a solid content concentration of 60%, and then kneaded at a speed of 45 rpm for 60 minutes. Then, 1.5 parts of the above-obtained negative electrode binder in terms of solid content were added and kneaded at a speed of 40 rpm for 40 minutes. Then, ion exchange water was added so that the viscosity became 3000 ± 500 mPa·s (measured by a B-type viscometer at 25°C and 60 rpm), thereby preparing a slurry composition for a negative electrode composite material layer.

[0191] The negative electrode composite material layer slurry composition was coated with a notch wheel coater at a coating amount of 11±0.5 mg / cm 2It is coated on the surface of a copper foil with a thickness of 15 μm serving as a current collector in such a manner. Then, the copper foil coated with the slurry composition for the negative composite material layer is transported in an oven at a temperature of 80°C at a speed of 400 mm / minute for 2 minutes, and then transported in an oven at a temperature of 110°C for 2 minutes, thereby drying the slurry composition on the copper foil to obtain a negative electrode raw material having a negative composite material layer formed on the current collector.

[0192] Then, the side of the negative composite material layer of the produced negative electrode raw material is roll-pressed under the condition of a line pressure of 11 t (tons) in an environment at a temperature of 25 ± 3°C to obtain a negative electrode with a density of the negative composite material layer of 1.60 g / cm 3 Then, the negative electrode is placed in an environment at a temperature of 25 ± 3°C and a relative humidity of 50 ± 5% for 1 week.

[0193] <Fabrication of the positive electrode>

[0194] In a planetary mixer, 96 parts of an active material of a lithium composite oxide system of Co-Ni-Mn (NMC111, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ) serving as a positive electrode active material, 2 parts of acetylene black (manufactured by Denka Co., Ltd., HS-100) serving as a conductive material, and 2 parts of polyvinylidene fluoride (manufactured by KUREHA CORPORATION, KF-1100) serving as a binder material are added, and then N-methyl-2-pyrrolidone (NMP) serving as a dispersion medium is added and mixed to make the total solid component concentration 67% to prepare a slurry composition for the positive composite material layer.

[0195] Next, the obtained slurry composition for the positive composite material layer is coated on an aluminum foil with a thickness of 20 μm serving as a current collector in such a manner that the coating amount is 20 ± 0.5 mg / cm 2 Then, it is transported in an oven at a temperature of 90°C at a speed of 200 mm / minute for 2 minutes, and then transported in an oven at a temperature of 120°C for 2 minutes, thereby drying the slurry composition on the aluminum foil to obtain a positive electrode raw material having a positive composite material layer formed on the current collector.

[0196] Furthermore, it is transported in an oven at a temperature of 90°C at a speed of 200 mm / minute for 2 minutes, and then transported in an oven at a temperature of 120°C for 2 minutes, thereby drying the slurry composition on the aluminum foil to obtain a positive electrode raw material having a positive composite material layer formed on the current collector.

[0197] Then, the side of the positive composite material layer of the produced positive electrode raw material is roll-pressed under the condition of a line pressure of 14 t (tons) in an environment at a temperature of 25 ± 3°C to obtain a positive electrode with a density of the positive composite material layer of 3.40 g / cm 3 Then, the positive electrode is placed in an environment at a temperature of 25 ± 3°C and a relative humidity of 50 ± 5% for 1 week.

[0198] <Fabrication of Secondary Battery>

[0199] Using the above-mentioned negative electrode, positive electrode, and separator, a wound battery cell (discharge capacity equivalent to 520 mAh) was fabricated and placed inside an aluminum packaging material. Then, a 1.0 M LiPF solution as the electrolyte (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio), containing an additive: 2 vol% (solvent ratio) of vinylene carbonate) was filled inside the aluminum packaging material. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 °C was performed to seal the aluminum packaging material, and a lithium-ion secondary battery was manufactured. The rate characteristics were evaluated using this lithium-ion secondary battery. The results are shown in Table 1. 6 Solution (solvent: a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (mass ratio), containing an additive: 2 vol% (solvent ratio) of vinylene carbonate). Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 °C was performed to seal the aluminum packaging material, and a lithium-ion secondary battery was manufactured. The rate characteristics were evaluated using this lithium-ion secondary battery. The results are shown in Table 1.

[0200] (Examples 2 - 6, 8 - 9, 12 - 13)

[0201] When synthesizing the granular polymer, the composition of the monomer composition used in the polymerization was changed as needed so that the types, content ratios, particle diameters, and swelling degrees in the electrolyte of various monomer units in the obtained granular polymer were as shown in Table 1, respectively. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0202] In addition, in Table 1, for each granular polymer prepared in these examples, which has a composition different from that of Example 1, they are respectively denoted as granular polymers B - F, J - K, L - N.

[0203] (Example 7)

[0204] When synthesizing the granular polymer I, the polymerization conditions of the monomer composition were changed (specifically, the amount of emulsifier added to the reactor was changed to 0.02 parts), so that the particle diameter of the obtained granular polymer I was as shown in Table 1. Except for this point, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0205] (Example 10)

[0206] In the <Preparation of Heat-Resistant Layer Slurry Composition> process, as the non-conductive particles, alumina particles with a larger particle diameter (manufactured by Sumitomo Chemical Co., Ltd., AKP - 3000, volume average particle diameter D50 (catalog value): 0.7 μm) were used. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0207] (Example 11)

[0208] In the process of <preparation of heat-resistant layer slurry composition>, the non-conductive particles used were changed from alumina particles to barium sulfate particles (manufactured by Takehara Kagaku Kogyo Co., Ltd., TS-2, volume average particle diameter D50 (catalog value): 0.3 μm). Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0209] (Comparative Examples 1-4)

[0210] When synthesizing granular polymers, the composition of the monomer composition used in the polymerization was changed as needed so that the types, content ratios, particle diameters, and swelling degrees in the electrolyte of various monomer units in the resulting granular polymers were as shown in Table 1, respectively. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0211] In addition, in Table 1, for each granular polymer prepared in these comparative examples, whose composition etc. are different from those in Example 1, they are respectively denoted as granular polymers O to R.

[0212] In addition, in Table 1 shown below

[0213] "MAA" represents a methacrylic acid unit;

[0214] "AN" represents an acrylonitrile unit;

[0215] "AMA" represents an allyl methacrylate unit;

[0216] "BA" represents a n-butyl acrylate unit;

[0217] "Aam" represents an acrylamide unit;

[0218] "ACL" represents a (meth)acrylate copolymer;

[0219] "CMC" represents carboxymethyl cellulose;

[0220] "MAN" represents a methacrylonitrile unit;

[0221] "AA" represents an acrylic acid unit;

[0222] "NMA" represents an N-hydroxymethylacrylamide unit;

[0223] "2EHA" represents a 2-ethylhexyl acrylate unit;

[0224] "MMA" represents a methyl methacrylate unit;

[0225] "Al 2 O 3” represents alumina particles;

[0226] “BaSO 4 ” represents barium sulfate particles.

[0227] [Table 1]

[0228]

[0229] As can be seen from Table 1, in Examples 1 to 13, a binder composition containing a particulate polymer containing an acidic group monomer unit in a content ratio of 1% by mass or more and 5% by mass or less and a cyano group monomer unit in a content ratio of 4.5% by mass or more and 25% by mass or less was used, and a heat-resistant layer having a sufficiently high peel strength and high adhesion to a substrate was obtained. In addition, it can be seen that the heat-resistant layers of Examples 1 to 13 can enable a secondary battery to exhibit excellent rate characteristics.

[0230] On the other hand, it can be seen that in Comparative Examples 1 to 4, a binder composition containing a particulate polymer in which the content ratio of the cyano group monomer unit or the acidic group monomer unit does not satisfy the above-specified range was used, and a heat-resistant layer having a sufficiently high peel strength could not be formed, and the adhesion of the heat-resistant layer to the substrate was also insufficient.

[0231] Industrial applicability

[0232] According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery heat-resistant layer, which can prepare a non-aqueous secondary battery heat-resistant layer slurry composition capable of forming a non-aqueous secondary battery heat-resistant layer having a sufficiently high peel strength.

[0233] In addition, according to the present invention, it is possible to provide a non-aqueous secondary battery heat-resistant layer slurry composition, which can form a non-aqueous secondary battery heat-resistant layer having a sufficiently high peel strength.

[0234] Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery heat-resistant layer having a sufficiently high peel strength, and a non-aqueous secondary battery having the heat-resistant layer.

Claims

1. A binder composition for a heat-resistant layer of a non-aqueous secondary battery, which comprises a particulate polymer, The particulate polymer comprises an acidic group-containing monomer unit, a cyano group-containing monomer unit, and an ethylenically unsaturated carboxamide monomer unit, The content ratio of the acidic group-containing monomer unit in the particulate polymer is 1% by mass or more and 5% by mass or less, the content ratio of the cyano group-containing monomer unit is 4.5% by mass or more and 25% by mass or less, and the content ratio of the ethylenically unsaturated carboxamide monomer unit is 1% by mass or more and 10% by mass or less, The swelling degree of the particulate polymer in the electrolyte is 5.5 times or more and 10 times or less, The ethylenically unsaturated carboxamide monomer unit is selected from an acrylamide unit, a methacrylamide unit, an N-methoxymethylacrylamide unit, and an N-methoxymethylmethacrylamide unit.

2. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1, wherein, The volume average particle diameter of the particulate polymer is 0.30 μm or less.

3. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1 or 2, wherein, The acidic group-containing monomer unit comprises a carboxyl group-containing monomer unit.

4. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1 or 2, wherein, The particulate polymer further comprises a crosslinkable monomer unit.

5. The binder composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 1 or 2, wherein, The particulate polymer is a (meth)acrylate copolymer.

6. A slurry composition for a heat-resistant layer of a non-aqueous secondary battery, which comprises non-conductive particles and the binder composition for a heat-resistant layer of a non-aqueous secondary battery according to any one of claims 1 to 5.

7. The slurry composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 6, wherein, The volume average particle diameter of the non-conductive particles is 0.7 μm or less.

8. A heat-resistant layer for a non-aqueous secondary battery, which is formed by using the slurry composition for a heat-resistant layer of a non-aqueous secondary battery according to claim 6 or 7.

9. A non-aqueous secondary battery, which has the heat-resistant layer for a non-aqueous secondary battery according to claim 8.

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