JP2016048670A - Binder for nonaqueous secondary battery porous film, composition for nonaqueous secondary battery porous film, porous film for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for a nonaqueous secondary battery porous film, which enables the formation of a porous film superior in endurance and enables the increase in stability of a composition for a porous film under a high shear condition.SOLUTION: A binder for a nonaqueous secondary battery porous film comprises: a particulate polymer; and a sulfonate compound. The particulate polymer is a random copolymer including 35 mass% or more of (meth)acrylic acid alkyl ester monomer units, and 20-65 mass% of aromatic monovinyl monomer units. A value determined by dividing a blend amount of the sulfonate compound by a blend amount of the particulate polymer is 0.005 or larger.SELECTED DRAWING: None

Description

  The present invention relates to a binder for a nonaqueous secondary battery porous membrane, a composition for a nonaqueous secondary battery porous membrane, a porous membrane for a nonaqueous secondary battery, and a nonaqueous secondary battery.

  Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as “secondary batteries”) have the characteristics of being small and light, having high energy density, and capable of repeated charge and discharge. Is used in a wide range of applications. The secondary battery generally includes an electrode (positive electrode, negative electrode) and a battery member such as a separator that separates the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.

Here, in recent years, in secondary batteries, battery members including a porous film as a protective layer are used for the purpose of improving heat resistance and strength.
Specific examples of the porous film include those formed by binding non-conductive particles such as organic particles and inorganic particles with a binder. Such a porous film is usually referred to as a slurry composition in which a porous film material such as non-conductive particles or a binder is dissolved or dispersed in a dispersion medium such as water (hereinafter referred to as “a composition for a porous film”). And the porous membrane composition is applied and dried on an electrode base material or a separator base material provided with an electrode mixture layer on a current collector.

In recent years, porous membranes have been actively improved for the purpose of further improving the performance of non-aqueous secondary batteries (see, for example, Patent Documents 1 and 2).
Specifically, in Patent Document 1, for example, secondary particles containing 50 to 99% by mass of non-conductive particles and 0.1 to 10% by mass of a graft polymer having a degree of swelling with respect to the electrolyte of 100% to 300%. It has been proposed to improve rate characteristics and high-temperature characteristics of nonaqueous secondary batteries by using a battery porous membrane.
Patent Document 2 includes 0.5 to 40% by mass of a monomer unit containing a water-soluble polymer such as a sodium salt or an ammonium salt of a cellulose semisynthetic polymer, inorganic particles, and a hydrophilic group. It has been proposed to use a porous film containing a particulate polymer to ensure adhesion between the porous film and an electrode and to improve the cycle characteristics of the secondary battery.

International Publication No. 2010/134501 International Publication No. 2009/123168

Here, in recent years, further improvement in performance has been demanded for non-aqueous secondary batteries. Specifically, non-aqueous secondary batteries exhibit excellent durability even under severe usage conditions, such as when mounted on an electric vehicle that is continuously subjected to large vibrations during use. It is demanded. For this reason, the porous membrane is also required to further improve the durability in the electrolytic solution when mounted on a non-aqueous secondary battery.
However, in the above conventional technique, the durability of the porous membrane is not sufficient, and the durability of the non-aqueous secondary battery cannot be set to a sufficiently high level.

  Moreover, when forming the porous film on the substrate, the composition for the porous film used for forming the porous film is subjected to a high shearing force due to the rotation of the gravure roll, for example, when applied with a gravure coating apparatus. However, the composition for a porous film used for the formation of the above-mentioned conventional porous film has low dispersion stability when subjected to a high shearing force, and therefore the composition for a porous film is porous for a long time. When the film is formed or the rotational speed of the gravure roll is increased in order to perform high-speed molding, there is a problem that the contained components aggregate and it is difficult to obtain a porous film having a uniform thickness.

Thus, the present invention provides a binder for a nonaqueous secondary battery porous membrane that can form a porous membrane with excellent durability and can also enhance the stability of the composition for porous membrane under high shear. The purpose is to do.
Another object of the present invention is to provide a composition for a porous membrane of a nonaqueous secondary battery that is excellent in stability under high shear and can form a porous membrane that is excellent in durability.
And an object of this invention is to provide the nonaqueous secondary battery provided with the porous film for nonaqueous secondary batteries excellent in durability, and the said porous film for nonaqueous secondary batteries.

  The present inventor has intensively studied for the purpose of solving the above problems. Then, the inventor of the present invention provides a particulate polymer comprising a random copolymer containing a (meth) acrylic acid alkyl ester monomer unit and an aromatic monovinyl monomer unit at a ratio within a specific range, and a sulfone. The composition under high shear of the porous membrane composition is obtained by using a binder for a porous membrane that contains an acid salt compound and the blending ratio of the sulfonate compound to the particulate polymer is a specific value or more. And it discovered that it was possible to ensure the durability of a porous membrane, and completed this invention.

  That is, the present invention aims to advantageously solve the above-mentioned problems, and the binder for a nonaqueous secondary battery porous membrane of the present invention comprises a particulate polymer and a sulfonate compound, and the particles The polymer is a random copolymer containing 35% by mass or more of (meth) acrylic acid alkyl ester monomer units and 20% by mass to 65% by mass of aromatic monovinyl monomer units, A value obtained by dividing the compounding amount of the acid salt compound by the compounding amount of the particulate polymer is 0.005 or more. Thus, a particulate polymer comprising a random copolymer containing a (meth) acrylic acid alkyl ester monomer unit and an aromatic monovinyl monomer unit within the above ranges, and the particulate polymer, On the other hand, when a binder containing a sulfonate compound is used in an amount ratio or more as described above, the stability of the composition for a porous membrane using the binder under high shear can be improved, and the binder The durability of the porous film formed using can be made excellent.

  Here, in the binder for a nonaqueous secondary battery porous membrane of the present invention, it is preferable that the particulate polymer further contains 0.1 mass% to 5 mass% of an acid group-containing monomer unit. If the particulate polymer contains an acidic group-containing monomer unit within the above range, the stability of the composition for porous membranes under high shear and the increase in moisture brought into the secondary battery are suppressed. The durability of the porous membrane can be further enhanced. In addition, it is possible to improve electrical characteristics such as life characteristics of the secondary battery including the porous film.

  Furthermore, in the binder for a nonaqueous secondary battery porous membrane of the present invention, the acidic group-containing monomer unit is preferably a monomer unit derived from an ethylenically unsaturated dicarboxylic acid. If the particulate polymer contains a monomer unit derived from an ethylenically unsaturated dicarboxylic acid as an acidic group-containing monomer unit, the content of the acidic group-containing monomer unit is reduced and brought into a secondary battery. Even when the increase in water content is further suppressed, the stability under high shear, the durability of the porous membrane, and the electrical characteristics of the secondary battery can be sufficiently enhanced.

  And as for the binder for non-aqueous secondary battery porous films of this invention, it is preferable that the volume average particle diameter D50 of the said particulate polymer is 100 nm or more and 500 nm or less. When the volume average particle diameter D50 of the particulate polymer is within the above range, the stability under high shear and the durability of the porous film can be further improved.

  In addition, in the binder for a nonaqueous secondary battery porous membrane of the present invention, the degree of swelling of the particulate polymer with respect to the nonaqueous electrolyte solution is preferably more than 1 time and 2 times or less. If the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte is within the above range, the durability of the porous membrane is further improved, and the electrical characteristics such as the life characteristics of the secondary battery including the porous membrane are improved. Can do.

  Moreover, this invention aims at solving the said subject advantageously, The composition for non-aqueous secondary battery porous films of this invention is for any of the above-mentioned non-aqueous secondary battery porous films. It contains a binder, non-conductive particles and water. A porous film having excellent durability can be obtained by using any of the above-described compositions containing a binder for a porous film of a nonaqueous secondary battery for forming a porous film. Moreover, the composition containing any of the binders for a non-aqueous secondary battery porous membrane described above is excellent in stability under high shear and hardly aggregates during the formation of the porous membrane.

  Moreover, this invention aims at solving the said subject advantageously, The porous film for non-aqueous secondary batteries of this invention is formed from the above-mentioned composition for non-aqueous secondary battery porous films. It is characterized by that. The porous film is excellent in durability.

  Moreover, this invention aims at solving the said subject advantageously, The non-aqueous secondary battery of this invention is equipped with the porous film for non-aqueous secondary batteries mentioned above. The non-aqueous secondary battery has excellent durability and high performance.

ADVANTAGE OF THE INVENTION According to this invention, the binder for non-aqueous secondary battery porous films which can form the porous film which is excellent in durability, and can also improve the stability under the high shear of the composition for porous films is provided. can do.
Moreover, according to this invention, the composition for non-aqueous secondary battery porous membranes which can form the porous membrane which is excellent in stability under high shear and excellent in durability can be provided.
And according to this invention, the nonaqueous secondary battery provided with the porous film for nonaqueous secondary batteries excellent in durability and the said porous film for nonaqueous secondary batteries can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder for nonaqueous secondary battery porous membranes of the present invention is used as a material for preparing a composition for nonaqueous secondary battery porous membranes. And the composition for non-aqueous secondary battery porous films of this invention is prepared using the binder for non-aqueous secondary battery porous films of this invention. Moreover, the porous film for nonaqueous secondary batteries of this invention is formed using the composition for nonaqueous secondary battery porous films of this invention. In addition, the non-aqueous secondary battery of the present invention is provided with the porous membrane for a non-aqueous secondary battery of the present invention on the surface of at least one battery member.

(Binder for nonaqueous secondary battery porous membrane)
The binder for a porous film of the present invention is a composition containing a particulate polymer having binding ability and a sulfonate compound, and optionally containing other components and a dispersion medium such as water. And the said particulate polymer is at least the following (1), (2):
(1) 35% by mass or more of (meth) acrylic acid alkyl ester monomer unit, 20% by mass to 65% by mass of aromatic monovinyl monomer unit,
(2) a random copolymer;
It has the characteristics of. In addition, the value obtained by dividing the blending amount of the sulfonate compound by the blending amount of the particulate polymer (the blending ratio of the sulfonate compound to the particulate polymer) is 0.005 or more. It is one of the characteristics of the binder for porous films.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”. In the present invention, “(meth) acryl” means acrylic and / or methacrylic.
And the composition for porous films containing the binder for porous films of this invention is excellent in stability under high shear. Moreover, the porous film formed using the binder for porous films of this invention is excellent in durability.

<Particulate polymer>
The particulate polymer ensures the strength of the obtained porous film and holds the components contained in the porous film so as not to be detached from the porous film.
Here, normally, the particulate polymer is not a water-soluble polymer but is present in the form of particles in an aqueous medium.

[(Meth) acrylic acid alkyl ester monomer unit]
Examples of (meth) acrylic acid alkyl ester monomers that can form (meth) acrylic acid alkyl ester monomer units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl. Alkyl acrylates such as acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate Esters: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate , Methacrylic acid alkyl esters such as stearyl methacrylate and glycidyl methacrylate; Among these, 2-ethylhexyl acrylate, ethyl acrylate, and butyl acrylate are preferable from the viewpoint of improving the durability of the porous film and the life characteristics of the secondary battery, and reducing the water content of the porous film, and 2-ethylhexyl. Acrylate is more preferred. From the viewpoint of improving the electrical characteristics (especially the life characteristics) of the secondary battery by reducing the amount of moisture brought into the secondary battery due to the particulate polymer and suppressing the decomposition of the electrolyte in the electrolyte. The (meth) acrylic acid alkyl ester monomer preferably does not have a hydrophilic group such as an acidic group (for example, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, etc.).
These can be used alone or in combination of two or more.

  The content ratio of the (meth) acrylic acid alkyl ester monomer unit in the particulate polymer needs to be 35% by mass or more, preferably 45% by mass or more, more preferably 50% by mass or more, and Preferably it is 55 mass% or more, Preferably it is 80 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 60 mass% or less. When the content ratio of the (meth) acrylic acid alkyl ester monomer unit is less than 35% by mass, the adhesion of the particulate polymer is impaired, and the durability of the porous film cannot be ensured. On the other hand, the lifetime characteristic of a secondary battery can be improved because the content rate of a (meth) acrylic-acid alkylester monomer unit shall be 80 mass% or less.

[Aromatic monovinyl monomer unit]
Examples of the aromatic monovinyl monomer that can form an aromatic monovinyl monomer unit include styrene, styrene sulfonic acid and salts thereof (for example, sodium styrene sulfonate), α-methylstyrene, vinyl toluene, 4- (tert -Butoxy) styrene and the like. Among these, styrene and sodium styrenesulfonate are preferable, and styrene is more preferable. In addition, the amount of moisture brought into the secondary battery due to the particulate polymer is surely reduced to suppress the decomposition of the electrolyte in the electrolytic solution, thereby improving the electrical characteristics (especially the life characteristics) of the secondary battery. From the viewpoint, the aromatic monovinyl monomer preferably does not have a hydrophilic group such as an acidic group (for example, a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, etc.). These can be used alone or in combination of two or more.

  The content of the aromatic monovinyl monomer unit in the particulate polymer needs to be 20% by mass or more and 65% by mass or less, preferably 25% by mass or more, more preferably 30% by mass or more, and further Preferably it is 35 mass% or more, Preferably it is 64.9 mass% or less, More preferably, it is 55 mass% or less, More preferably, it is 50 mass% or less. When the content ratio of the aromatic monovinyl monomer unit is less than 20% by mass, the durability of the porous film cannot be ensured, and the electrical characteristics such as the life characteristics of the secondary battery are deteriorated. On the other hand, if the content ratio of the aromatic monovinyl monomer unit exceeds 65% by mass, the adhesion of the particulate polymer is impaired, and the durability of the porous film cannot be ensured.

[Other monomer units]
The particulate polymer may contain a monomer unit other than the above-described (meth) acrylic acid alkyl ester monomer unit and aromatic monovinyl monomer unit. Such other monomer units are not particularly limited, and examples thereof include acidic group-containing monomer units and crosslinkable monomer units.
As described above, the acidic group-containing monomer unit and the crosslinkable monomer unit are monomer units other than the (meth) acrylic acid alkyl ester monomer unit and the aromatic monovinyl monomer unit. Accordingly, the acidic group-containing monomer that can form an acidic group-containing monomer unit and the crosslinkable monomer that can form a crosslinkable monomer unit include the above-mentioned (meth) acrylic acid alkyl ester monomers. And aromatic monovinyl monomers (such as styrene sulfonic acid and its salts) are not included.

[[Acid group-containing monomer unit]]
Examples of the acidic group-containing monomer that can form an acidic group-containing monomer unit include a carboxylic acid group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer.

Examples of the carboxylic acid group-containing monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof.
Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E monomethoxyacrylic. Examples include acid and β-diaminoacrylic acid.
Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, mesaconic acid and the like. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. In addition, examples of ethylenically unsaturated dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, diphenyl maleate, nonyl maleate, decyl maleate , Dodecyl maleate, octadecyl maleate, fluoroalkyl maleate and the like.

Examples of the sulfonic acid group-containing monomer include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, 3 -Allyloxy-2-hydroxypropane sulfonic acid etc. are mentioned.
In the present invention, “(meth) allyl” means allyl and / or methallyl.

Examples of phosphoric acid group-containing monomers include 2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, ethyl- (meth) acryloyloxyethyl phosphate, and the like.
In the present invention, “(meth) acryloyl” means acryloyl and / or methacryloyl.

Among these, the acidic group-containing monomer is preferably an acidic group-containing monomer having two or more acidic groups in one molecule. When the particulate polymer has an acidic group-containing monomer unit, the presence of the acidic group can further increase the stability of the composition for a porous membrane under high shear and the durability of the porous membrane. The rate characteristics of the secondary battery can be improved by increasing the degree of swelling of the polymer in the non-aqueous electrolyte. However, on the other hand, when the amount of the acidic group-containing monomer used in preparing the particulate polymer is increased, the amount of moisture brought into the secondary battery due to the particulate polymer is increased. Battery life characteristics are degraded. Therefore, from the viewpoint of increasing the stability under high shear of the porous membrane composition, the durability of the porous membrane and the rate characteristics of the secondary battery while suppressing an increase in the amount of moisture brought into the secondary battery. It is preferable to use an acidic group-containing monomer having two or more acidic groups in one molecule.
From the viewpoint of improving the stability under high shear of the composition for porous membrane, the durability of the porous membrane and the rate characteristics of the secondary battery, the acidic group-containing monomer may be a carboxylic acid group-containing monomer. A sulfonic acid group-containing monomer and a phosphoric acid group-containing monomer are preferable, and a carboxylic acid group-containing monomer is more preferable.
Therefore, from these viewpoints, a carboxylic acid group-containing monomer having two or more carboxylic acid groups as acidic groups in one molecule is preferable, and more specifically, the above-described ethylenically unsaturated dicarboxylic acid is preferable. Among these, itaconic acid, maleic acid, and fumaric acid are more preferable, and itaconic acid is more preferable.
That is, the particulate polymer preferably contains a monomer unit derived from an ethylenically unsaturated dicarboxylic acid, a monomer unit derived from itaconic acid, a monomer unit derived from maleic acid, and a single amount derived from fumaric acid. It is more preferable to include at least one selected from the group consisting of body units, and it is even more preferable to include a monomer unit derived from itaconic acid.

The content ratio of the acidic group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.3% by mass or more, preferably Is 5% by mass or less, more preferably 2% by mass or less, still more preferably 1.8% by mass or less, and particularly preferably 1.5% by mass or less. When the content ratio of the acidic group-containing monomer unit is 0.1% by mass or more, the stability under high shear and the rate characteristics of the secondary battery are improved. On the other hand, when the content ratio of the acidic group-containing monomer unit is 5% by mass or less, the elution of the particulate polymer into the non-aqueous electrolyte is suppressed, the durability of the porous film is improved, and the particulate weight Since the amount of moisture brought into the secondary battery due to coalescence is reduced, the electrical characteristics (especially the life characteristics) of the secondary battery are improved.
In addition, the composition for porous membranes using the binder for porous membranes containing the particulate polymer mentioned above is dispersible by the aromatic monovinyl monomer unit contained in the particulate polymer in a relatively high proportion. And improved stability under high shear. Therefore, in this particulate polymer, even when the content ratio of the acidic group-containing monomer unit is reduced to improve the durability of the porous membrane and reduce the amount of moisture brought into the secondary battery, The film composition can sufficiently exhibit stability under high shear.

[[Crosslinkable monomer unit]]
As the crosslinkable monomer capable of forming a crosslinkable monomer unit, a monomer capable of forming a crosslinked structure upon polymerization can be used. Specifically, a monofunctional monomer having a thermally crosslinkable crosslinkable group and one ethylenically unsaturated bond per molecule, and a polyfunctionality having two or more ethylenically unsaturated bonds per molecule Monomer. Examples of thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. By containing the crosslinkable monomer unit, the degree of swelling of the particulate polymer described later with respect to the non-aqueous electrolyte can be made moderate while increasing the durability of the porous membrane.

The crosslinkable monomer may be hydrophobic or hydrophilic.
In the present invention, that the crosslinkable monomer is “hydrophobic” means that the crosslinkable monomer does not contain a hydrophilic group, and the crosslinkable monomer is “hydrophilic”. The term “crosslinkable monomer” includes a hydrophilic group. Here, the “hydrophilic group” in the crosslinkable monomer means a carboxylic acid group, a hydroxyl group, a sulfonic acid group, a phosphoric acid group, an epoxy group, a thiol group, an aldehyde group, an amide group, an oxetanyl group, or an oxazoline group.

Hydrophobic crosslinkable monomers include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, trimethylol Polyfunctional (meth) acrylates such as propane-tri (meth) acrylate; polyfunctional allyl / vinyl ethers such as dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane And divinylbenzene and the like.
Examples of the hydrophilic crosslinkable monomer include vinyl glycidyl ether, allyl glycidyl ether, methylol acrylamide, acrylamide, and allyl methacrylamide.
These can be used alone or in combination of two or more.
Among these, from the viewpoint of reducing the amount of moisture brought into the secondary battery and improving the electrical characteristics (especially life characteristics) of the secondary battery, a hydrophobic cross-linkable monomer is preferable, and allyl methacrylate is preferable. More preferred is ethylene dimethacrylate. And from a viewpoint of improving the stability under the high shear of the composition for porous films containing a porous film binder, ethylene dimethacrylate is especially preferable.
In the present invention, “(meth) acrylate” means acrylate and / or methacrylate.

  The content ratio of the crosslinkable monomer unit in the particulate polymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5% by mass or more, preferably It is 5 mass% or less, More preferably, it is 2 mass% or less, More preferably, it is 1.8 mass% or less, Most preferably, it is 1.5 mass% or less. When the content ratio of the crosslinkable monomer unit is 0.1% by mass or more, the elution of the particulate polymer into the electrolytic solution is suppressed, and the durability of the porous film is increased. Further, the shape of the particulate polymer is hardly deformed even under high shear, and the stability of the porous membrane composition under high shear can be enhanced. On the other hand, when the content ratio of the crosslinkable monomer unit is 5% by mass or less, the adhesiveness of the particulate polymer can be sufficiently secured, and the durability of the porous film can be enhanced.

[Preparation of particulate polymer]
And a particulate polymer is prepared by superposing | polymerizing the monomer composition containing the monomer mentioned above. By starting the polymerization in the monomer state rather than the oligomer state obtained by polymerizing the monomers in the monomer composition to some extent, the formation of block copolymers and graft copolymers can be suppressed, and random copolymerization can be achieved. The particulate polymer of the present invention which is a polymer can be obtained.
Here, the content ratio of each monomer in the monomer composition is usually the same as the content ratio of the monomer units in the desired particulate polymer.
The polymerization mode of the particulate polymer is not particularly limited as long as the obtained particulate polymer becomes a random copolymer, and examples thereof include a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method. Any method may be used. As the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, and living radical polymerization can be used. And generally used emulsifiers, dispersants, polymerization initiators, polymerization aids and the like used for the polymerization can be used, and the amount used is also generally used.

[Properties of particulate polymer]
The particulate polymer of the present invention needs to be a random copolymer. In addition, even when a particulate polymer is provided with a core structure and a shell structure, when the shell structure is a random copolymer, it is included in the particulate polymer of the present invention.

[[Random copolymer structure and glass transition temperature]]
When the particulate polymer is a random copolymer, the polymer can be homogenized, the durability of the polymer with respect to the electrolytic solution can be increased, and the dispersibility in the composition for a porous membrane can be increased. it can. Furthermore, since the viscosity of the composition for porous membrane can be suppressed, it becomes easy to remove moisture from the porous membrane during drying.
In the present invention, whether or not the particulate polymer is a random copolymer is determined by measuring the glass transition temperature.
Specifically, when the particulate polymer that is a copolymer has one glass transition temperature, the particulate polymer corresponds to a random copolymer. On the other hand, when the particulate polymer has two or more glass transition temperatures, the particulate polymer does not have a random copolymer structure and corresponds to a block copolymer or a graft copolymer.
In the present invention, the “glass transition temperature” of the particulate polymer can be measured using the measuring method described in the examples of the present specification.

  And the glass transition temperature of the particulate polymer which is a random copolymer becomes like this. Preferably it is 10 degrees C or less, More preferably, it is 5 degrees C or less, Most preferably, it is 0 degrees C or less. Moreover, although the minimum of the glass transition temperature of a particulate polymer is not specifically limited, Usually, it is -100 degreeC or more.

[[Swelling degree with respect to non-aqueous electrolyte]]
In the present invention, the “swelling degree with respect to the non-aqueous electrolyte” of the particulate polymer is the immersion when a film (binder film) formed from the particulate polymer is immersed in a specific non-aqueous electrolyte under predetermined conditions. It can be determined as a value (times) obtained by dividing the subsequent weight by the weight before immersion. Specifically, a binder film is formed using the method described in the examples of the present specification, and is described in the examples. Measure using the measurement method of
Here, the degree of swelling of the particulate polymer with respect to the nonaqueous electrolytic solution is usually more than 1 time, preferably 2 times or less, more preferably 1.9 times or less, and further preferably 1.8 times or less. When the degree of swelling of the particulate polymer with respect to the nonaqueous electrolytic solution is 2 times or less, elution of the particulate polymer into the electrolytic solution is suppressed, and the durability of the porous film and the life characteristics of the secondary battery are improved.
The degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte can be adjusted by changing the type and amount of the monomer used. For example, the amount of the aromatic monovinyl monomer or the crosslinkable monomer The degree of swelling with respect to the non-aqueous electrolyte solution can be decreased by increasing the polymerization molecular weight by increasing the polymerization temperature or increasing the polymerization reaction time.

[[Contact angle with water]]
In the present invention, the “contact angle with water” of the particulate polymer means the water droplet contact angle of a film (binder film) formed from the particulate polymer, and specifically, measured by the following method. can do.
The aqueous dispersion of particulate polymer is applied to an electrolytic copper foil (NC-WS (registered trademark) manufactured by Furukawa Electric) using a table coater, dried at 50 ° C. for 20 minutes, at 120 ° C. for 20 minutes, and dried with hot air Dry in a vessel to produce three 1 cm × 1 cm binder films (thickness 500 μm). A drop of distilled water was dropped on the film, and the contact angle of the formed water drop was measured with a contact angle meter (model CA-DT-A, mfd. Kyowa) under an RH condition of an ambient temperature of 23 degrees and 50%. Measured by Interface Science Co., Ltd. For each of the three binder films, the contact angle is measured at two points, and the average of the measured values for a total of six times is taken as the contact angle. In addition, the diameter of the water droplet of distilled water is 2 mm, and the value measured 1 minute after dropping the water droplet of distilled water is adopted as the numerical value of the contact angle appearing on the measuring meter.
The contact angle of the particulate polymer with water is preferably more than 80 °, more preferably 85 ° or more, particularly preferably 90 ° or more, preferably 120 ° or less, more preferably 115 ° or less, particularly Preferably it is 110 degrees or less.

[[Particle size]]
The volume average particle diameter D50 of the particulate polymer is preferably 100 nm or more, more preferably 110 nm or more, still more preferably 120 nm or more, preferably 500 nm or less, more preferably 400 nm or less, still more preferably 300 nm or less. . When the volume average particle diameter D50 of the particulate polymer is 100 nm or more, the aggregation of the particulate polymer is suppressed, and the stability of the porous membrane composition under high shear is improved. On the other hand, when the volume average particle diameter D50 of the particulate polymer is 500 nm or less, the adhesion of the porous film is secured and the durability of the porous film can be improved.
The “volume average particle diameter D50” of the particulate polymer represents a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle size distribution (volume basis) measured by the laser diffraction method.

<Sulfonate compound>
The sulfonate compound is not particularly limited as long as it is a salt of a compound having a sulfonic acid group (—SO ₃ H). It is presumed that such a sulfonate compound is added to the porous membrane binder so that the compound suppresses aggregation of the particulate polymer or the like. Stability under shear can be ensured. In addition, the sulfonate compound does not adversely affect the electrical characteristics of the secondary battery, and is suitable for blending into the binder for the porous membrane from this point.
Although it does not specifically limit as a form of a salt, Alkaline-earth metal salts, such as alkali metal salts, such as a sodium salt, and a calcium salt, are mentioned. The sulfonate compound is preferably a non-polymer, and its molecular weight is preferably in the range of 100 to 1,000.
And as a sulfonate compound, a sulfonate-type surfactant is preferable. Examples of the sulfonate surfactant include sulfosuccinates, alkylbenzene sulfonates, and alpha olefin sulfonates exemplified by dialkylsulfosuccinates such as sodium dioctylsulfosuccinate. Among these, from the viewpoint of further improving the stability of the composition for porous membranes under high shear and reducing the amount of moisture brought into the secondary battery, sulfosuccinates are preferred, and dialkylsulfosuccinates are preferred. More preferred is sodium dioctyl sulfosuccinate.
In addition, a sulfonate compound may be used individually by 1 type, and may be used in combination of 2 or more types.

  Here, in the binder for a nonaqueous secondary battery porous membrane of the present invention, the value obtained by dividing the blending amount of the sulfonate compound by the blending amount of the particulate polymer (the blending ratio of the sulfonate compound to the particulate polymer) ) Must be 0.005 or more, preferably 0.008 or more, more preferably 0.01 or more, preferably 0.05 or less, more preferably 0.04 or less, and still more preferably 0. 0.03 or less. When the blending amount ratio of the sulfonate compound to the particulate polymer is less than 0.005, the stability of the porous membrane composition under high shear cannot be ensured. In addition, the durability of the porous film is lowered, and the rate characteristics and life characteristics of the secondary battery are lowered. On the other hand, when the blending ratio of the sulfonate compound to the particulate polymer is 0.05 or less, the amount of moisture brought into the secondary battery is reduced, and the rate characteristics and life characteristics of the secondary battery are improved. Can do.

<Preparation of binder for nonaqueous secondary battery porous membrane>
The method for preparing the binder for the porous membrane is not particularly limited. For example, when the particulate polymer is prepared in an aqueous medium and the particulate polymer is obtained as an aqueous dispersion, the particulate polymer water is used. The sulfonate compound may be added to the dispersion as it is to serve as a porous membrane binder, or the sulfonate compound may be added to the aqueous dispersion of the particulate polymer, and any other components may be added to the binder for the porous membrane. It is good. Here, as other components, other components described in the section “Composition for non-aqueous secondary battery porous membrane” described later can be given.

(Composition for non-aqueous secondary battery porous membrane)
The composition for a nonaqueous secondary battery porous membrane of the present invention is an aqueous slurry composition in which the above-mentioned particulate polymer, sulfonate compound, and nonconductive particles are dispersed in water as a dispersion medium. The particulate polymer and the sulfonate compound were contained in the binder for the nonaqueous secondary battery porous membrane of the present invention, and the preferred abundance ratio thereof was suitable for the porous membrane binder. It is the same as the abundance ratio.
And the porous film formed using the composition for porous films of this invention is excellent in durability.

<Non-conductive particles>
Non-conductive particles are non-conductive and do not dissolve in water used as a dispersion medium in the composition for porous membranes and non-aqueous electrolytes of secondary batteries, and their shape is maintained in them. Particles. And since nonelectroconductive particle is electrochemically stable, it exists stably in a porous film under the use environment of a secondary battery. Since the porous membrane composition contains non-conductive particles, the network structure of the obtained porous membrane is moderately clogged, lithium dendrites and the like are prevented from penetrating the porous membrane, and the short circuit of the electrode is suppressed. This is because it can be made even more certain. As non-conductive particles, for example, various inorganic particles and organic particles can be used.

Examples of inorganic particles include oxide particles such as aluminum oxide (alumina), silicon oxide, magnesium oxide, titanium oxide, BaTiO ₂ , ZrO, and alumina-sili force composite oxide, and nitride particles such as aluminum nitride and boron nitride. And covalently bonded crystal particles such as silicon and diamond, sparingly soluble ion crystal particles such as barium sulfate, calcium fluoride and barium fluoride, and clay fine particles such as talc and montmorillonite.
Examples of organic particles include polyethylene, polystyrene, polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked products, and various types of cross-linked polymers such as polyimide, polyamide, polyamideimide, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate. Examples thereof include molecular particles and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. Here, the organic particles differ from the above-mentioned particulate polymer in that the particulate polymer has binding ability, whereas the organic particles have no binding ability. The particulate polymer is not included.

Among these, from the viewpoint of improving the durability of the porous film and the electrical characteristics of the secondary battery including the porous film, the non-conductive particles are preferably inorganic particles, and more preferably aluminum oxide.
In addition, the particle size of nonelectroconductive particle is not specifically limited, It can be made to be the same as that of the nonelectroconductive particle conventionally used.

<Combination ratio of non-conductive particles and binder for porous film>
The compounding ratio of the non-conductive particles and the porous membrane binder in the porous membrane composition is not particularly limited. For example, in the composition for a porous membrane, the amount of the particulate polymer is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, particularly preferably 3 parts by mass, per 100 parts by mass of the non-conductive particles. The porous membrane binder is contained in an amount of 25 parts by mass or less, more preferably 20 parts by mass or less, further preferably 18 parts by mass or less, and particularly preferably 15 parts by mass or less. If the blending amount of the particulate polymer is 0.1 parts by mass or more per 100 parts by mass of the non-conductive particles, the adhesion between the porous film and the electrode substrate or separator substrate is ensured and the durability of the porous film is improved. If it is 25 parts by mass or less, the amount of moisture brought into the secondary battery due to the particulate polymer can be reduced, and the electrical characteristics of the secondary battery can be improved. Moreover, the stability under high shear of the composition for porous membranes can also be improved.

<Other ingredients>
The composition for porous films may contain other arbitrary components in addition to the components described above. The optional component is not particularly limited as long as it does not have an excessively unfavorable influence on the battery reaction in the secondary battery using the porous film. Further, the kind of the arbitrary component may be one kind or two or more kinds.
Examples of the optional component include a wetting agent, a leveling agent, an electrolytic solution decomposition inhibitor, and a water-soluble polymer.

[Water-soluble polymer]
Among the other components described above, the porous membrane composition preferably contains a water-soluble polymer. When the porous membrane composition, which is an aqueous slurry composition, contains a water-soluble polymer, the viscosity of the porous membrane composition can be increased and adjusted to be easy to apply. In addition, since the water-soluble polymer has a binding property and an electrolytic solution resistance, in the secondary battery, the components in the porous film are bound to each other by the particulate polymer, and the porous film and the base material Can play a role in assisting adhesion. Therefore, the durability of the porous membrane can be further improved by using the water-soluble polymer.
Here, a substance in the present invention is “water-soluble” means that an insoluble content is less than 1.0% by mass when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. Say. A substance whose solubility changes depending on the pH of water is considered to be “water-soluble” if it falls under the above-mentioned “water-soluble” at least at any pH.
Examples of the water-soluble polymer include natural polymers, semi-synthetic polymers, and synthetic polymers. The water-soluble polymer does not include the sulfonate compound described above.

[Natural polymer]
Examples of natural polymers include plant- or animal-derived polysaccharides and proteins, fermentation-treated products of these microorganisms, and heat-treated products thereof.
These natural polymers can be classified into plant-based natural polymers, animal-based natural polymers, and microorganism-produced natural polymers.
Examples of plant-based natural polymers include gum arabic, gum tragacanth, galactan, guar gum, carob gum, caraya gum, carrageenan, pectin, cannan, quince seed (malmello), arche colloid (gasso extract), starch (rice, corn, potato, wheat) Etc.) and glycyrrhizin. Examples of animal natural polymers include collagen, casein, albumin, and gelatin. Examples of the microorganism-produced natural polymer include xanthan gum, dextran, succinoglucan, and bullulan.

[Semi-synthetic polymer]
Examples of the semisynthetic polymer include cellulose semisynthetic polymers. The cellulose semisynthetic polymer can be classified into nonionic cellulose semisynthetic polymer, anionic cellulose semisynthetic polymer and cationic cellulose semisynthetic polymer.

  Nonionic cellulose-based semisynthetic polymers include, for example, alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystalline cellulose; hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxy Examples thereof include hydroxyalkylcelluloses such as propylmethylcellulose stearoxy ether, carboxymethylhydroxyethylcellulose, alkylhydroxyethylcellulose, and nonoxynylhydroxyethylcellulose.

  Examples of the anionic cellulose semisynthetic polymer include substituted products obtained by substituting the above nonionic cellulose semisynthetic polymer with various derivative groups and salts thereof (sodium salt, ammonium salt, etc.). Specific examples include sodium cellulose sulfate, methyl cellulose, methyl ethyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC) and salts thereof.

  Examples of the cationic cellulose semisynthetic polymer include low nitrogen hydroxyethylcellulose dimethyl diallylammonium chloride (polyquaternium-4), O- [2-hydroxy-3- (trimethylammonio) propyl] hydroxyethylcellulose (polyquaternium-10). ), O- [2-hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethylcellulose chloride (polyquaternium-24).

[Synthetic polymer]
Synthetic polymers include polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, acrylic acid or copolymers of acrylate and vinyl alcohol, maleic anhydride, maleic acid or fumaric acid. Completely or partially saponified copolymer of acid and vinyl acetate, modified polyvinyl alcohol, modified polyacrylic acid, polyethylene glycol, polycarboxylic acid, ethylene-vinyl alcohol copolymer, vinyl acetate polymer, carboxylic acid group introduced Acrylamide polymer prepared.

Among these water-soluble polymers, from the viewpoint of imparting heat resistance to the porous membrane and suppressing heat shrinkage of an organic separator such as polypropylene, carboxymethyl cellulose, its salt, and an acrylamide polymer into which a carboxylic acid group has been introduced are used. preferable. Furthermore, an acrylamide polymer into which a carboxylic acid group is introduced is particularly preferred from the viewpoint of reducing the amount of moisture brought into the secondary battery and improving the electrical characteristics.
The blending amount of the water-soluble polymer in the porous membrane composition is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, preferably 100 parts by mass of the non-conductive particles. It is 10 mass parts or less, More preferably, it is 5 mass parts or less. When the blending amount of the water-soluble polymer is within the above range, an appropriate viscosity is imparted to the porous membrane composition, and the durability of the obtained porous membrane can be improved.

<Preparation of composition for nonaqueous secondary battery porous membrane>
The method for preparing the composition for the porous film is not particularly limited. Usually, the porous film binder, the non-conductive particles, water, and any components used as necessary are mixed. can get. The mixing method is not particularly limited, but in order to disperse each component efficiently, mixing is performed using a disperser as a mixing device.
The disperser is preferably an apparatus capable of uniformly dispersing and mixing the above components. Examples include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Among them, a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix is particularly preferable because a high dispersion share can be added.

  And normally, what is necessary is just to arbitrarily set the solid content density | concentration of the composition for porous films in the range which the slurry composition has the viscosity of the range which does not impair workability | operativity when manufacturing a porous film. Specifically, the solid content concentration of the composition for a porous membrane can usually be 10 to 50% by mass.

(Porous membrane for non-aqueous secondary batteries)
For example, the above-described composition for a secondary battery porous membrane is applied to the surface of an appropriate base material to form a coating film, and the formed coating film is dried to provide a non-aqueous secondary battery on the base material. A porous film can be formed. This porous film is excellent in durability, and the nonaqueous secondary battery including the porous film is excellent in durability.

Here, the base material which apply | coats the composition for porous films is a member used as the object which forms the coating film of the composition for porous films. There is no limitation on the substrate, for example, a coating film of the composition for porous film is formed on the surface of the release substrate, the coating film is dried to form a porous film, and the release substrate is peeled off from the porous film. It may be. Thus, the porous film peeled off from the mold release substrate can be used for a secondary battery as a self-supporting film.
However, it is preferable to use a separator substrate or an electrode substrate as the substrate from the viewpoint of improving the production efficiency by omitting the step of peeling the porous film. The porous film provided on the separator substrate and the electrode substrate can be suitably used as a protective layer for improving the heat resistance and strength of the separator and the electrode.

<Separator substrate>
Although it does not specifically limit as a separator base material, Known separator base materials, such as an organic separator base material, are mentioned. Here, the organic separator substrate is a porous member made of an organic material, and examples of the organic separator substrate include a microporous film or a nonwoven fabric containing a polyolefin resin such as polyethylene and polypropylene, an aromatic polyamide resin, and the like. Among them, a polyethylene microporous film and a nonwoven fabric are preferable because of their excellent strength. In addition, the thickness of an organic separator base material can be made into arbitrary thickness, Usually, 0.5 micrometer or more, Preferably it is 5 micrometers or more, Usually, 40 micrometers or less, Preferably it is 30 micrometers or less, More preferably, it is 20 micrometers or less.

<Electrode base material>
Although it does not specifically limit as an electrode base material (a positive electrode base material and a negative electrode base material), The electrode base material with which the electrode compound-material layer was formed on the electrical power collector is mentioned.
Here, the current collector, the electrode active material in the electrode mixture layer (positive electrode active material, negative electrode active material) and the binder for electrode mixture layer (binder for positive electrode mixture layer, binder for negative electrode mixture layer) As the method for forming the electrode mixture layer on the current collector and the current collector, known methods can be used, and examples thereof include those described in JP2013-145663A.

<Method for forming porous film for non-aqueous secondary battery>
Examples of a method for forming a porous film on a substrate such as the above-described separator substrate or electrode substrate include the following methods.
1) A method of applying a composition for a porous membrane to the surface of a separator substrate or an electrode substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side, the same applies hereinafter), and then drying;
2) A method of drying the separator substrate or electrode substrate after immersing the separator substrate or electrode substrate in the porous membrane composition;
3) A method for producing a porous film by applying a composition for a porous film on a release substrate and drying it, and transferring the resulting porous film to the surface of a separator substrate or an electrode substrate;
Among these, the method 1) is particularly preferable because the film thickness of the porous film can be easily controlled. Specifically, the method 1) includes a step of applying the porous membrane composition onto the substrate (application step), and drying the porous membrane composition applied onto the substrate to form a porous membrane. A process (porous film formation process) is provided.

In the coating step, the method for coating the porous membrane composition on the substrate is not particularly limited. A method is mentioned. Of these, the gravure method is preferable in that a uniform porous film can be obtained.
In the porous film forming step, the method for drying the composition for the porous film on the substrate is not particularly limited, and a known method can be used, for example, drying with hot air, hot air, low-humidity air, vacuum drying, A drying method by irradiation with infrared rays or electron beams can be mentioned. The drying conditions are not particularly limited, but the drying temperature is preferably 50 to 150 ° C., and the drying time is preferably 5 to 30 minutes.

  In addition, the separator and the electrode may be provided with components other than these separator base material or electrode base material, and the porous film of this invention mentioned above, unless the effect of this invention is impaired remarkably. For example, you may provide another layer between the separator base material or electrode base material, and the porous film of this invention as needed. In this case, the porous film of the present invention is indirectly provided on the surface of the separator substrate or the electrode substrate. Further, another layer may be provided on the surface of the porous membrane of the present invention.

  The thickness of the porous film formed on the substrate is preferably 0.01 μm or more, more preferably 0.1 μm or more, particularly preferably 1 μm or more, preferably 20 μm or less, more preferably 10 μm or less, particularly Preferably it is 5 micrometers or less. When the thickness of the porous film is 0.01 μm or more, the strength of the porous film can be sufficiently ensured, and when it is 20 μm or less, the diffusibility of the electrolytic solution is secured and the secondary film using the porous film is used. The rate characteristics of the battery can be improved.

(Non-aqueous secondary battery)
The non-aqueous secondary battery of the present invention includes the above-described porous membrane for a non-aqueous secondary battery of the present invention. More specifically, the non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the above-described porous film for a non-aqueous secondary battery is a battery member of a positive electrode, a negative electrode, and a separator. Included in at least one.
Since the nonaqueous secondary battery of the present invention includes the porous film obtained from the composition for porous film of the present invention, it has excellent durability and high performance.

<Positive electrode, negative electrode and separator>
At least one of the positive electrode, the negative electrode, and the separator used in the secondary battery of the present invention includes a porous film. Specifically, as a positive electrode and a negative electrode having a porous film, an electrode in which a porous film is provided on an electrode substrate formed by forming an electrode mixture layer on a current collector can be used. Moreover, as a separator which has a porous film, the separator which provides a porous film on a separator base material, and the separator which consists of a porous film can be used. In addition, as an electrode base material and a separator base material, the thing similar to the thing quoted by the term of the "porous film for non-aqueous secondary batteries" can be used.
Moreover, as a positive electrode which does not have a porous film, a negative electrode, and a separator, it does not specifically limit, The electrode which consists of an electrode base material mentioned above, and the separator which consists of a separator base material mentioned above can be used.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used in 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, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable because they are easily dissolved in a solvent and exhibit a high degree of dissociation. In addition, electrolyte may be used individually by 1 type and may be used in combination of 2 or more types. Usually, the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, so that the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in a lithium ion secondary battery, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC). Carbonates such as propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane, Sulfur-containing compounds such as dimethyl sulfoxide; are preferably used. Moreover, you may use the liquid mixture of these solvents. Among these, carbonates are preferable because they have a high dielectric constant and a wide stable potential region. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted depending on the type of solvent.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Moreover, you may add a known additive to electrolyte solution.

<Method for producing non-aqueous secondary battery>
A non-aqueous secondary battery, for example, stacks a positive electrode and a negative electrode through a separator, and rolls or folds this as necessary into a battery container, and injects an electrolyte into the battery container to seal it. Can be manufactured. Of the positive electrode, the negative electrode, and the separator, at least one member is a member with a porous film. Here, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like may be placed in the battery container as necessary to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard.
In Examples and Comparative Examples, the glass transition temperature of the particulate polymer, the volume average particle diameter D50, the degree of swelling with respect to the non-aqueous electrolyte, the durability and moisture content of the porous film, and the high shear of the composition for porous film The rate characteristics and life characteristics of the non-aqueous secondary battery were measured and evaluated by the following methods.

<Glass transition temperature>
The aqueous dispersion containing the particulate polymer was dried for 3 days in an environment of 50% humidity and 23 to 25 ° C. to obtain a film having a thickness of 1 ± 0.3 mm. The film was dried in a 120 ° C. hot air oven for 1 hour. Then, using the dried film as a sample, using a differential scanning calorimeter (DSC 6220SII, manufactured by Nanotechnology Co., Ltd.) at a measurement temperature of −100 ° C. to 180 ° C. and a heating rate of 5 ° C./min according to JIS K7121. The glass transition temperature (° C.) was measured.
<Volume average particle diameter D50>
The aqueous dispersion containing the produced particulate polymer is diluted with ion-exchanged water to prepare a measurement sample having a solid content concentration of 2% by mass, and a laser diffraction / light scattering type particle size distribution measuring device (LS230, manufactured by Beckman Coulter, Inc.) ) Was used to measure the volume average particle diameter D50 of the particulate polymer.
<Swelling degree of particulate polymer with respect to non-aqueous electrolyte>
An aqueous dispersion containing a particulate polymer is applied to an electrolytic copper foil (NC-WS (registered trademark) manufactured by Furukawa Electric) using a table coater, and heated at 50 ° C. for 20 minutes, 120 ° C. for 20 minutes, hot air It dried with the drier and produced the binder film (thickness 500 micrometers) of 1 cm x 1 cm, and measured the weight M0. Thereafter, the obtained film was immersed in a nonaqueous electrolytic solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 (volume ratio), electrolyte: LiPF _{6 having a} concentration of 1 M) at 60 ° C. for 72 hours. . The non-aqueous electrolyte solution on the surface of the film after immersion was wiped off, and the weight M1 was measured. And the swelling degree with respect to non-aqueous electrolyte solution was computed according to the following formula.
Swelling degree with respect to non-aqueous electrolyte = M1 / M0
<Durability of porous membrane>
The separator with a porous membrane was cut out to 5 cm × 5 cm, the weight was measured, and the weight M0 of the porous membrane was calculated by subtracting the weight of the separator substrate. Subsequently, the separator with a porous film cut out was placed in a nonaqueous electrolyte solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 (volume ratio), electrolyte: LiPF _{6 with a} concentration of 1 M) at 60 ° C. It was immersed and subjected to 30 kHz ultrasonic vibration for 10 minutes. Thereafter, the separator with the porous film was taken out and dried in an atmosphere of 60 ° C. for 10 hours, and the weight M1 of the porous film after drying was calculated in the same manner as the weight M0. Then, the vibration dropout rate ΔM (%) was calculated using an equation of ΔM = {(M0−M1) / M0} × 100, and evaluated as follows. It shows that it is excellent in durability, so that this value is small.
A: Vibration drop rate ΔM is less than 20% B: Vibration drop rate ΔM is 20% or more and less than 40% C: Vibration drop rate ΔM is 40% or more and less than 60% D: Vibration drop rate ΔM is 60% or more Water content>
A separator with a porous film was cut into a size of 10 cm × 10 cm to obtain a test piece. This test piece is left for 24 hours at a temperature of 25 ° C. and a humidity of 50%, and then a test piece is obtained by a Karl Fischer method (JIS K-0068 (2001) water vaporization method, vaporization temperature 150 ° C.) using a coulometric titration moisture meter. The water content W (ppm) of was measured. The smaller this value, the smaller the water content in the porous film, and the smaller the amount of water brought into the secondary battery.
A: Moisture content W is 500 ppm or less B: Moisture content W is more than 500 ppm to 600 ppm or less C: Moisture content W is more than 600 ppm to 700 ppm or less D: Moisture content W is more than 700 ppm <under high shear of the porous membrane composition Stability at>
The composition for porous membrane was applied on a separator substrate (made of polyethylene) using a gravure roll (number of lines: 95) under the conditions of a conveyance speed of 50 m / min and a gravure rotation ratio of 100%. The material was cut out and the coating amount M0 (mg / cm ² ) per unit area was calculated. Moreover, the coating amount M1 (mg / cm ² ) was similarly calculated after 1 hour from the start of coating. Then, a coating amount change rate ΔM (%) was calculated using an equation of ΔM = (| M0−M1 |) / M0 × 100 (%) and evaluated as follows. It shows that stability under the high shear of the composition for porous films is so high that this value is small.
A: Application rate change rate ΔM is less than 5% B: Application rate change rate ΔM is 5% or more and less than 10% C: Application rate change rate ΔM is 10% or more and less than 20% D: Application rate change rate ΔM is 20% or more <Rate characteristics>
The fabricated secondary battery was allowed to stand for 24 hours in an environment of 25 ° C., and then charged with 4.2 V, 0.1 C, and 5 hours in an environment of 25 ° C., and the voltage V0 ( V) was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., and a voltage V1 (V) 15 seconds after the start of discharge was measured. The voltage change ΔV (mV) was calculated using the equation: ΔV = {V0−V1} × 1000, and evaluated as follows. It shows that it is excellent in a rate characteristic (low temperature characteristic), so that this value is small.
A: Voltage change ΔV is 500 mV or less B: Voltage change ΔV is more than 500 mV and 700 mV or less C: Voltage change ΔV is more than 700 mV and 900 mV or less D: Voltage change ΔV is more than 900 mV <Life characteristics>
The prepared secondary battery was allowed to stand for 24 hours in a 25 ° C. environment, and then charged and discharged with a 4.35 V, 0.1 C charge and a 2.75 V, 0.1 C discharge in a 25 ° C. environment. Was performed. Thereafter, the battery was charged at 4.35 V and 0.1 C, and allowed to stand at 60 ° C. for 168 hours (7 days). Thereafter, the cell voltage V2 (V) was measured at 25 ° C. The voltage drop ΔV (mV) was calculated using the equation: ΔV = {4.35−V2} × 1000 and evaluated as follows. It shows that it is excellent in the lifetime characteristic (self-discharge characteristic), so that this value is small.
A: Voltage drop ΔV is 200 mV or less B: Voltage drop ΔV is more than 200 mV and 400 mV or less C: Voltage drop ΔV is more than 400 mV and 600 mV or less D: Voltage drop ΔV is more than 600 mV

(Example 1)
<Preparation of binder for nonaqueous secondary battery porous membrane>
In a reactor A equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of polyoxyethylene lauryl ether (manufactured by Kao Chemical Co., “Emulgen (registered trademark) 120”) as an emulsifier, and 0. 5 parts were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, 50 parts of ion-exchanged water in another container B, 0.5 part of polyoxyethylene lauryl ether (“Emulgen (registered trademark) 120” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and a single amount of alkyl (meth) acrylate 2-ethylhexyl acrylate (2-EHA) 58.2 parts, aromatic monovinyl monomer 40 parts styrene (ST), acidic group-containing monomer itaconic acid (IA) 0.8 parts, As a monomer, 1.0 part of ethylene dimethacrylate (EDMA) was mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor A over 4 hours for polymerization. During the addition, the reaction was carried out at 70 ° C. After completion of the addition, the reaction was terminated by further stirring at 80 ° C. for 3 hours to produce an aqueous dispersion containing a particulate polymer.
When the glass transition temperature of the obtained particulate polymer was measured, the observed glass transition temperature was only one point (−8 ° C.), and it was confirmed that the particulate polymer was a random copolymer. In addition, the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte and the volume average particle diameter D50 were measured. The results are shown in Table 1.
2 parts (particulate polymer) of dioctyl sulfosuccinate sodium (DOSS, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a sulfonate compound was added to the aqueous dispersion containing the obtained particulate polymer. The binder amount for the nonaqueous secondary battery porous membrane was prepared by adding 0.02).

<Preparation of composition for nonaqueous secondary battery porous membrane>
6.12 parts of the above-mentioned porous membrane binder containing a particulate polymer and a sulfonate compound is equivalent to a solid content with respect to 100 parts of alumina filler (Nippon Light Metal Co., Ltd., “LS256”) as non-conductive particles. (6 parts of particulate polymer, 0.12 part of sulfonate compound), acrylamide polymer having a carboxylic acid group introduced as a thickening agent (Arakawa Chemical Co., Ltd., “Polystron (registered trademark) 117”) 5 parts and 0.2 part of a polyethylene glycol type surfactant (manufactured by San Nopco, “San Nopco (registered trademark) SN wet 366”) were mixed to prepare a composition for a porous membrane.
Using the obtained porous membrane composition, the stability under high shear was evaluated. The results are shown in Table 1.

<Manufacture of porous membrane and separator with porous membrane>
An organic separator substrate made of a polyethylene porous substrate (manufactured by Celgard, thickness 16 μm) was prepared. The porous membrane composition obtained as described above was applied to one side of the prepared organic separator substrate, and dried at 60 ° C. for 10 minutes. Thereby, a separator with a porous film having a thickness of 18 μm was obtained.
Durability and water content were evaluated using the obtained separator with a porous membrane. The results are shown in Table 1.

<Manufacture of negative electrode>
In a 5 MPa pressure vessel with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of IA, 63.5 parts of ST, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and potassium persulfate as a polymerization initiator After adding 0.5 part and stirring sufficiently, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the binder for negative electrode mixture layer (SBR). After adding a 5% aqueous sodium hydroxide solution to the mixture containing the binder for the negative electrode mixture layer and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then up to 30 ° C. or lower. The mixture was cooled to obtain an aqueous dispersion containing the desired binder for the negative electrode mixture layer.
100 parts of artificial graphite (average particle diameter: 15.6 μm) as a negative electrode active material, 1 part of a 2% aqueous solution of carboxymethylcellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a water-soluble polymer, And ion-exchanged water were mixed to prepare a solid concentration of 68%, and then further mixed at 25 ° C. for 60 minutes. Further, the solid concentration was adjusted to 62% with ion-exchanged water, and further mixed at 25 ° C. for 15 minutes. The above mixed solution is mixed with 1.5 parts of the above binder for the negative electrode mixture layer in a solid equivalent amount and ion-exchanged water, adjusted so that the final solid content concentration is 52%, and further for 10 minutes. Mixed. This was defoamed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode having good fluidity.
The obtained negative electrode slurry composition was applied on a copper foil having a thickness of 20 μm, which was a current collector, with a comma coater so that the film thickness after drying was about 150 μm, and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material before pressing. The negative electrode raw material before pressing was rolled with a roll press to obtain a negative electrode after pressing with a negative electrode mixture layer thickness of 80 μm (single-sided negative electrode).
Moreover, the same application | coating is implemented on the back surface of the negative electrode original fabric before the said press, a negative electrode compound material layer is formed on both surfaces, it rolls with a roll press, and the negative electrode after the press whose thickness of a negative electrode compound material layer is 80 micrometers each (Double-sided negative electrode) was obtained.

<Production of positive electrode>
100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as a positive electrode active material, ₂ parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., “HS-100”) as a conductive material, and as a binder for a positive electrode mixture layer Polyvinylidene fluoride (manufactured by Kureha, “# 7208”) in an amount corresponding to the solid content and 2 parts of N-methylpyrrolidone were mixed to make the total solid content concentration 70%. These were mixed to prepare a positive electrode slurry composition.
The obtained positive electrode slurry composition was applied onto a 20 μm-thick aluminum foil as a current collector by a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by transporting the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a positive electrode raw material before pressing. The positive electrode raw material before pressing was rolled with a roll press to obtain a positive electrode after pressing with a positive electrode mixture layer thickness of 80 μm (single-sided positive electrode).
In addition, the same application is performed on the back surface of the positive electrode original fabric before pressing, a positive electrode mixture layer is formed on both surfaces, and rolling is performed by a roll press. (Double-sided positive electrode) was obtained.

<Manufacture of secondary batteries>
The single-sided positive electrode obtained above was cut out to 5 cm × 15 cm, and a separator with a porous film cut out to 6 cm × 16 cm was disposed thereon (on the side of the composite layer) so that the porous film was opposed to the single-sided positive electrode, and Further, a double-sided negative electrode cut out to 5.5 cm × 15.5 cm was disposed thereon to obtain a laminate A. On the double-sided negative electrode side of this laminate A, a separator with a porous film cut out to 6 cm × 16 cm was disposed so that the separator substrate faced the double-sided negative electrode, and a double-sided positive electrode cut out to 5 cm × 15 cm thereon Then, a separator with a porous film cut out to 6 cm × 16 cm was placed thereon so that the porous film faced the double-sided positive electrode, and finally, one side cut into 5.5 cm × 5.5 cm thereon The negative electrode was laminated so that the negative electrode composite material layer faced the separator base material of the separator with a porous film, to obtain a laminate B. This laminate B is wrapped in an aluminum wrapping case as a battery case, and a non-aqueous electrolyte (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 (volume ratio), electrolyte: concentration 1M) LiPF ₆ ) was injected so that no air remained. Furthermore, after heat sealing at 150 ° C. and closing the aluminum packaging outer packaging, the obtained battery outer packaging was flat-pressed at 100 ° C. for 2 minutes at 100 kgf to produce a 1000 mAh stacked lithium ion secondary battery. did.
Using the obtained secondary battery, life characteristics and rate characteristics were evaluated. The results are shown in Table 1.

(Examples 2 to 5)
The same as Example 1 except that the amount of DOSS used as the sulfonate compound was changed to 1.2 parts, 2.8 parts, 0.7 parts, and 4.8 parts, respectively, when preparing the binder for the porous membrane. Then, a particulate polymer, a porous membrane binder, a porous membrane composition, a separator with a porous membrane, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 1.

(Example 6)
Example 1 except that DOSS as the sulfonate compound was changed to alkylbenzene sulfonic acid sodium salt (LAS, manufactured by Kao Chemicals Co., Ltd., “Neopelex (registered trademark) G-15”) at the time of preparing the porous membrane binder. In the same manner, a particulate polymer, a porous membrane binder, a porous membrane composition, a separator with a porous membrane, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 1.

(Examples 7 and 8)
In the same manner as in Example 1 except that the amount of IA and 2-EHA used was changed as shown in Table 1 when preparing the particulate polymer contained in the porous membrane binder, the particulate polymer and the porous membrane were used. A binder, a composition for a porous film, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 1.

Example 9
In the same manner as in Example 1, except that maleic acid (MA) was used instead of IA as the acidic group-containing monomer when preparing the particulate polymer contained in the porous membrane binder, the particulate polymer was used. A porous membrane binder, a porous membrane composition, a separator with a porous membrane, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 1.

(Examples 10, 11, and 15)
In the same manner as in Example 1 except that the amount of ST and 2-EHA used was changed as shown in Table 1 when preparing the particulate polymer contained in the porous membrane binder, the particulate polymer and the porous membrane were used. A binder, a composition for a porous film, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 1.

(Examples 12 and 13)
When preparing the particulate polymer contained in the binder for the porous membrane, the addition amount of polyoxyethylene lauryl ether as an emulsifier to the reactor A / container B is 0.25 / 0.4 part and 0 / 0.65, respectively. In the same manner as in Example 1, except that the particulate polymer, the porous membrane binder, the porous membrane composition, the separator with the porous membrane, the negative electrode, the positive electrode, and the secondary battery were produced in the same manner as in Example 1. Was evaluated. The results are shown in Table 2.

(Example 14)
In the same manner as in Example 1 except that the amount of 2-EHA and EDMA used was changed as shown in Table 2 when preparing the particulate polymer contained in the porous membrane binder, the particulate polymer and the porous membrane were used. A binder, a composition for a porous film, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 2.

(Comparative Example 1)
When preparing the binder for the porous membrane, in place of DOSS as the sulfonate compound, water-soluble polymer sodium polyacrylate (SPA, manufactured by Toagosei Co., Ltd., “Aron (registered trademark) T50”) was used. Produced a particulate polymer, a binder for a porous film, a composition for a porous film, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery in the same manner as in Example 1, and evaluated the same items. The results are shown in Table 2.

(Comparative Example 2)
In the same manner as in Example 1 except that the amount of ST and 2-EHA used was changed as shown in Table 2 during the preparation of the particulate polymer contained in the porous membrane binder, the particulate polymer and the porous membrane were used. A binder, a composition for a porous film, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were produced, and the same items were evaluated. The results are shown in Table 2.

(Comparative Example 3)
Except for using a particulate polymer that is a graft copolymer prepared as follows, the binder for porous film, the composition for porous film, the separator with porous film, the negative electrode, and the positive electrode were the same as in Example 1. , And secondary batteries were manufactured and evaluated for similar items. The results are shown in Table 2.
<Preparation of particulate polymer (graft copolymer)>
In a reactor equipped with a stirrer, 230 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (“Emar (registered trademark) 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, 49.2 of n-butyl acrylate (BA) Part, 50 parts of styrene macromonomer (STMM, one-end methacryloylated polystyrene oligomer, manufactured by Toagosei Co., Ltd., “AS-6”), 0.8 part of itaconic acid (IA), t-butylperoxy as a polymerization initiator After adding 1 part of 2-ethylhexanate and stirring sufficiently, it heated and polymerized at 90 degreeC and the aqueous dispersion of the particulate polymer was obtained. When the glass transition temperature of the obtained particulate polymer was measured, two glass transition temperatures (−40 ° C. and 97 ° C.) were confirmed, and it was confirmed that the particulate polymer was a graft copolymer.

Random copolymers containing (meth) acrylic acid alkyl ester monomer units and aromatic monovinyl monomer units in a specific range from Examples 1 to 15 and Comparative Examples 1 to 3 in the above table. If a porous membrane binder comprising a particulate polymer and a sulfonate compound, the value obtained by dividing the blending amount of the sulfonate compound by the blending amount of the particulate polymer is a specific value or more, It can be seen that a composition for a porous membrane excellent in stability under high shear, a porous membrane excellent in durability and a low water content, and a secondary battery excellent in rate characteristics and life characteristics can be obtained.
Here, from Examples 1 to 5 in the above table, by adjusting the blending ratio of the sulfonate compound to the particulate polymer, the stability of the composition for porous membranes under high shear and the secondary battery It can be seen that the rate characteristics and life characteristics of the porous film can be further improved, and the water content of the porous film can be further reduced.
In addition, from Examples 1 and 6 in the above table, by changing the type of the sulfonate compound, the high shear property of the porous membrane composition can be further improved, and the moisture content of the porous membrane can be further increased. It can be seen that it can be reduced.
And from Examples 1, 7 to 11, 14, and 15 in the above table, by changing the composition of the particulate polymer, the stability of the porous membrane composition under high shear and the durability of the porous membrane In addition, it can be seen that the rate characteristics and life characteristics of the secondary battery can be further improved, and the moisture content of the porous film can be further reduced. In particular, Examples 1 and 14 show that the durability of the porous membrane and the life characteristics of the secondary battery can be further improved by adjusting the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte.
Furthermore, from Examples 1, 12, and 13 in the above table, the stability of the porous membrane composition under high shear can be further improved by adjusting the volume average particle diameter D50 of the particulate polymer. I understand.

ADVANTAGE OF THE INVENTION According to this invention, the binder for non-aqueous secondary battery porous films which can form the porous film which is excellent in durability, and can also improve the stability under the high shear of the composition for porous films is provided. can do.
Moreover, according to this invention, the composition for non-aqueous secondary battery porous membranes which can form the porous membrane which is excellent in stability under high shear and excellent in durability can be provided.
And according to this invention, the nonaqueous secondary battery provided with the porous film for nonaqueous secondary batteries excellent in durability and the said porous film for nonaqueous secondary batteries can be provided.

Claims (8)

Including a particulate polymer and a sulfonate compound;
The particulate polymer is a random copolymer containing 35% by mass or more of (meth) acrylic acid alkyl ester monomer units and 20% by mass to 65% by mass of aromatic monovinyl monomer units,
The binder for nonaqueous secondary battery porous membranes whose value which remove | divided the compounding quantity of the said sulfonate compound by the compounding quantity of the said particulate polymer is 0.005 or more.   The binder for a nonaqueous secondary battery porous film according to claim 1, wherein the particulate polymer further contains 0.1 mass% to 5 mass% of an acidic group-containing monomer unit.   The binder for a nonaqueous secondary battery porous membrane according to claim 2, wherein the acidic group-containing monomer unit is a monomer unit derived from an ethylenically unsaturated dicarboxylic acid.   The binder for non-aqueous secondary battery porous membranes in any one of Claims 1-3 whose volume average particle diameter D50 of the said particulate polymer is 100 nm or more and 500 nm or less.   The binder for a non-aqueous secondary battery porous membrane according to any one of claims 1 to 4, wherein the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte is more than 1 time and 2 times or less.   A composition for a non-aqueous secondary battery porous membrane, comprising the binder for a non-aqueous secondary battery porous membrane according to any one of claims 1 to 5, non-conductive particles, and water.   A porous membrane for a non-aqueous secondary battery, formed from the composition for a non-aqueous secondary battery porous membrane according to claim 6.   A non-aqueous secondary battery comprising the porous membrane for a non-aqueous secondary battery according to claim 7.