JP6337554B2 - Nonaqueous secondary battery porous membrane binder, nonaqueous secondary battery porous membrane composition, nonaqueous secondary battery porous membrane and nonaqueous secondary battery - Google Patents

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 abbreviated as “secondary batteries”) have the characteristics of being small and lightweight, having high energy density, and capable of repeated charge and discharge. It is used for a wide range of purposes. The secondary battery generally includes a battery member such as a positive electrode, a negative electrode, and a separator that separates the positive electrode and the negative electrode and prevents a short circuit between the positive electrode and the negative electrode. In the secondary battery, a porous film may be provided as a protective layer on the electrodes (positive electrode and negative electrode) or separator for the purpose of improving their heat resistance and strength.

  Here, 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 this porous film composition is applied and dried on a substrate such as an electrode or a separator.

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.
In Patent Document 2, a porous film comprising a water-soluble polymer, inorganic particles, and a particulate polymer containing 0.5 to 40% by mass of a monomer unit containing a hydrophilic group is used. Thus, it has been proposed to secure the adhesion of the porous film to the electrode and 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. Therefore, further improvement in durability is also demanded for the porous film used in the 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.

  In general, when moisture is brought into the secondary battery, the electrolyte in the electrolytic solution is decomposed to generate gas, and the electrical characteristics (particularly, life characteristics) of the secondary battery are deteriorated. Therefore, it is required to reduce the amount of water contained in the porous film even in the porous film. However, in the above conventional technique, particularly the technique described in Patent Document 2, the amount of moisture in the porous film increases due to the composition of the particulate polymer used, and the amount of moisture brought into the secondary battery is small. There is also a problem that the electrical characteristics (especially the life characteristics) of the secondary battery are reduced due to the increase.

Then, an object of this invention is to provide the binder for non-aqueous secondary battery porous membranes which is excellent in durability and can form a porous membrane with little water content. The durability of the porous film refers to the durability of the porous film in the electrolytic solution when the porous film is mounted on the battery.
Another object of the present invention is to provide a composition for a porous membrane of a non-aqueous secondary battery that is excellent in durability and can form a porous membrane with a low water content.
And this invention aims at providing a nonaqueous secondary battery provided with the porous membrane for nonaqueous secondary batteries which is excellent in durability and has a low water content, and the porous membrane for nonaqueous secondary batteries. And

  The present inventor has intensively studied for the purpose of solving the above problems. And this inventor contains a (meth) acrylic-acid alkylester monomer unit and an aromatic monovinyl monomer unit in a specific ratio, and the swelling degree with respect to non-aqueous electrolyte solution is controlled in a specific range. It was found that by using a particulate polymer made of a random copolymer as a binder for a porous membrane, it is possible to reduce the water content of the porous membrane while ensuring the durability of the porous membrane. Completed the invention.

  That is, this invention aims at solving the said subject advantageously, The binder for nonaqueous secondary battery porous films of this invention is for nonaqueous secondary battery porous films containing a particulate polymer. It is a binder, and the particulate polymer contains 65% by mass or more of (meth) acrylic acid alkyl ester monomer units and 0.1 to 30% by mass of aromatic monovinyl monomer units. It is a random copolymer, and 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. As described above, random containing a (meth) acrylic acid alkyl ester monomer unit and an aromatic monovinyl monomer unit in a specific ratio, and the degree of swelling with respect to the non-aqueous electrolyte is controlled within a specific range. If a binder containing a particulate polymer made of a copolymer is used, the durability of the porous film formed using the binder can be made excellent, and the porous film originates from the particulate polymer. It can suppress that the amount of moisture in the inside increases.

  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 acidic group-containing monomer unit. If the particulate polymer contains an acidic group-containing monomer unit within the above range, the durability of the porous film can be further enhanced while suppressing an increase in moisture in 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 includes a monomer unit derived from an ethylenically unsaturated dicarboxylic acid as the acidic group-containing monomer unit, the content ratio of the acidic group-containing monomer unit is reduced to reduce the moisture content in the porous film. Even when the increase is further suppressed, the durability of the porous membrane and the electrical characteristics of the secondary battery can be sufficiently enhanced. In addition, the stability when a porous film composition is applied to a substrate to form a porous film, particularly the stability under shear of the porous film composition that receives a shearing force when applied to the substrate is also improved. be able to.

  Moreover, the composition for nonaqueous secondary battery porous membranes of the present invention is characterized by containing any of the above-mentioned binder for nonaqueous secondary battery porous membranes, nonconductive particles, and water. By using any of the above-described compositions containing the binder for a nonaqueous secondary battery porous membrane for forming a porous membrane, a porous membrane having excellent durability and low water content can be obtained.

  The porous membrane for a non-aqueous secondary battery of the present invention is formed from the above-described composition for a porous membrane of a non-aqueous secondary battery. The porous film has excellent durability and low water content.

  The nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the nonaqueous secondary battery described above is formed on the surface of at least one battery member selected from the group consisting of the positive electrode, the negative electrode, and the separator. A porous membrane for a secondary battery is provided. The non-aqueous secondary battery is excellent in durability, has a low water content, and has high performance.

ADVANTAGE OF THE INVENTION According to this invention, the binder for non-aqueous secondary battery porous membranes which is excellent in durability and can form a porous membrane with little water content can be provided.
Moreover, according to this invention, the composition for non-aqueous secondary battery porous membranes which is excellent in durability and can form a porous membrane with little water content can be provided.
According to the present invention, there is provided a porous membrane for a non-aqueous secondary battery having excellent durability and a low water content, and a non-aqueous secondary battery comprising the porous membrane for a non-aqueous secondary battery. Can do.

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 non-aqueous 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 optionally containing other components and a dispersion medium such as water. And the said particulate polymer is at least the following (1)-(3):
(1) 65% by mass or more of (meth) acrylic acid alkyl ester monomer unit, 0.1% by mass or more and less than 30% by mass of aromatic monovinyl monomer unit,
(2) a random copolymer,
(3) The degree of swelling with respect to the non-aqueous electrolyte is more than 1 time and 2 times or less,
It has the characteristics of.
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 porous film formed using the binder for porous films of this invention is excellent in durability, and has little water content.
Hereinafter, the particulate polymer contained in the binder for a nonaqueous secondary battery porous membrane of the present invention will be described in detail.

<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, and is contained in the porous film while maintaining the particle shape.

[(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, from the viewpoint of improving the durability of the porous membrane, reducing the moisture content of the porous membrane, and improving the battery life characteristics, the (meth) acrylic acid alkyl ester monomer is (Meth) acrylic acid alkyl esters (2-ethylhexyl acrylate, butyl acrylate, octyl acrylate, etc.) having 4 or more carbon atoms in the alkyl group bonded to the non-carbonyl oxygen atom are preferred, and those having 5 or more carbon atoms (meta ) Acrylic acid alkyl ester (2-ethylhexyl acrylate, octyl acrylate, etc.) 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 65% by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more. Yes, preferably 97% by mass or less, more preferably 90% by mass or less. When the content ratio of the (meth) acrylic acid alkyl ester monomer unit is in the above-described range, the adhesion of the particulate polymer is increased, and the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte is appropriately large. Moreover, since elution of the particulate polymer into the electrolytic solution can be suppressed, the durability of the porous membrane can be ensured.

[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, and the like. Among these, styrene and sodium styrenesulfonate are 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 has no 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.). Especially preferred is styrene. These can be used alone or in combination of two or more.

  The content ratio of the aromatic monovinyl monomer unit in the particulate polymer needs to be 0.1% by mass or more and less than 30% by mass, preferably 3% by mass or more, more preferably 10% by mass or more. And preferably less than 28% by mass, more preferably less than 25% by mass. When the content ratio of the aromatic monovinyl monomer unit is in the above range, elution of the particulate polymer into the electrolytic solution can be suppressed and the resistance of the porous film can be increased. Moreover, the amount of moisture brought into the secondary battery due to the particulate polymer can be reduced.

[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 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 enhances the stability under shear and the durability of the porous membrane when applying the porous membrane composition to the substrate. In addition, the output characteristics of the secondary battery can be improved by increasing the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte. In addition, for example, when the composition for a porous film is applied to a substrate by a gravure coating apparatus, the composition for the porous film is sheared by the rotation of the gravure roll, but the stability under the shear of the composition for the porous film is increased. And even if it apply | coats for a long time, the composition for porous films does not aggregate, and the porous film of uniform thickness can be formed on a base material. 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 of the porous membrane composition under shear, the durability of the porous membrane and the output 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.
In addition, from the viewpoint of enhancing the stability of the porous membrane composition under shear, the durability of the porous membrane, and the output characteristics of the secondary battery, the acidic group-containing monomer includes a carboxylic acid group-containing monomer, A sulfonic acid group-containing monomer and a phosphoric acid group-containing monomer are preferred. Among the carboxylic acid group-containing monomers, ethylenically unsaturated dicarboxylic acids having two or more acidic groups in one molecule are more preferable, and itaconic acid and maleic acid are particularly preferable.
That is, the particulate polymer preferably contains a monomer unit derived from an ethylenically unsaturated dicarboxylic acid, and more preferably contains a monomer unit derived from itaconic acid and / or a monomer unit derived from maleic acid. preferable.

The content ratio of the acidic group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more, more preferably 0.15% by mass or more, particularly preferably 0.2% by mass or more, preferably Is 5% by mass or less, more preferably less than 2% by mass, and particularly preferably 1% by mass or less. When the content ratio of the acidic group-containing monomer unit is 0.1% by mass or more, the stability of the porous membrane composition under shear, the durability of the porous membrane, and the output 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 improves dispersibility by the aromatic monovinyl monomer unit contained in the polymer, and is good even under shear Stable stability. 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 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 heat-crosslinkable crosslinkable group and one ethylenic double bond per molecule, and a polyfunctionality having two or more ethylenic double 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 with respect to the non-aqueous electrolyte can be made moderate while enhancing 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 crosslinking monomers (hydrophobic crosslinking agents) include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di ( Polyfunctional (meth) acrylates such as (meth) acrylate and trimethylolpropane-tri (meth) acrylate; dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, etc. And polyfunctional allyl / vinyl ethers; and divinylbenzene.
Examples of the hydrophilic crosslinkable monomer (hydrophilic crosslinker) include vinyl glycidyl ether, allyl glycidyl ether, methylol acrylamide, and acrylamide.
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 crosslinkable monomer is preferable, More preferred are methacrylate and divinylbenzene. And from a viewpoint of improving the stability under the shear of the composition for porous films containing a porous film binder, ethylene dimethacrylate is especially preferable.

  The content ratio of the crosslinkable monomer unit in the particulate polymer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, preferably It is 5 mass% or less, More preferably, it is 4 mass% or less, Most preferably, it is 3 mass% or less. When the content ratio of the crosslinkable monomer unit is 0.01% 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 shear, and the stability of the porous membrane composition under 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 is a random copolymer, and in addition, the degree of swelling with respect to the non-aqueous electrolyte solution needs to be more than 1 time and 2 times or less. 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. Hereinafter, the properties of the particulate polymer including these properties will be described in detail.

[[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 the porous membrane can be increased. Can do. Moreover, since the viscosity of the composition for porous membranes 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 0 degrees C or less, More preferably, it is -5 degrees C or less, Most preferably, it is -10 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 non-aqueous electrolyte solution needs to be more than 1 time and 2 times or less, preferably 1.9 times or less, more preferably 1.8 times or less, and still more preferably. Is 1.6 times or less. If the degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte is more than twice, the particulate polymer is eluted into the electrolyte and the durability of the porous membrane is impaired.
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 a particulate polymer means the water droplet contact angle of a film (binder film) formed by molding the particulate polymer. A binder film is molded using the method described in the examples, and measured using the measurement method described in the same example.
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 0.05 μm or more, more preferably 0.2 μm or more, preferably 0.6 μm or less, more preferably 0.5 μm or less. When the volume average particle diameter D50 of the particulate polymer is in the above range, the durability of the obtained 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.

<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 dispersion may be used as the porous membrane binder as it is, or any other component may be added to the aqueous dispersion of the particulate polymer to form the porous membrane binder. 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 derived from a binder for a porous membrane and nonconductive particles are dispersed in water as a dispersion medium. .
And the porous film formed using the composition for porous films of this invention is excellent in durability, and there is little water content.

<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 aluminum oxide (alumina), silicon oxide, magnesium oxide, titanium oxide, BaTiO ₂ , ZrO, oxide particles such as 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.
Organic particles include, for example, polyethylene, polystyrene, polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked products, and various cross-linking heights 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 are different from the above-mentioned particulate polymer in that the particulate polymer has binding ability, whereas the organic particles do not have binding ability.

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 membrane and the battery member can be ensured and the durability of the porous membrane can be 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. In addition, the stability of the porous membrane composition under shear can be improved.

<Other ingredients>
The slurry 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 effect 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 battery member It can play a role of 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.

[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 has a low water content. And a non-aqueous secondary battery provided with the said porous film is excellent in durability, and is highly efficient.

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 battery member as the base material from the viewpoint of improving the production efficiency by omitting the step of peeling the porous film. Specific examples of such battery members include separators and electrodes. The porous film provided on the separator and the electrode can be suitably used as a protective layer for improving the heat resistance and strength.

<Separator>
Although it does not specifically limit as a separator, Well-known separators, such as an organic separator, are mentioned. Here, the organic separator is a porous member made of an organic material. Examples of the organic separator include a microporous film or a nonwoven fabric containing a polyolefin resin such as polyethylene and polypropylene, an aromatic polyamide resin, and the like. A polyethylene microporous film and a nonwoven fabric are preferable. In addition, the thickness of an organic separator can be made into arbitrary thickness, and is 0.5 micrometer or more normally, Preferably it is 5 micrometers or more, and is 40 micrometers or less normally, Preferably it is 30 micrometers or less, More preferably, it is 20 micrometers or less.

<Electrode>
Although it does not specifically limit as an electrode (a positive electrode and a negative electrode), The electrode with which the electrode compound-material layer was formed on the electrical power collector is mentioned.
Current collector, electrode active material in electrode mixture layer (positive electrode active material, negative electrode active material) and 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, 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 the method for forming the porous film on the battery member such as the separator and the electrode described above include the following methods.
1) A method of applying a composition for a porous membrane to the surface of a battery member (in the case of an electrode, the surface on the electrode mixture layer side, the same shall apply hereinafter), and then drying;
2) A method of drying a battery member after immersing it in the composition for a porous membrane;
3) A method for producing a porous film by applying the composition for porous film onto a release substrate and drying it, and transferring the obtained porous film to the surface of the battery member;
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 battery member (application step), and drying the porous membrane composition applied onto the battery member to form a porous membrane. A process (porous film formation process) is provided.

In the coating process, the method for coating the porous membrane composition on the battery member is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. 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 battery member 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 positive electrode, the negative electrode, and the porous film may include components other than these battery members and the above-described porous film of the present invention as long as the effects of the present invention are not significantly impaired. For example, you may provide another layer between a battery member 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 battery member. 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 output characteristics of the battery can be improved.

(Non-aqueous secondary battery)
The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the above non-aqueous secondary battery is formed on the surface of at least one battery member selected from the group consisting of the positive electrode, the negative electrode, and the separator. A porous membrane for a battery is provided.
Since the non-aqueous secondary battery of the present invention includes a porous film obtained from the composition for porous film of the present invention, it has excellent durability, low water content, and high performance.

<Positive electrode, negative electrode, separator, and porous membrane>
As the positive electrode, the negative electrode, the separator, and the porous film, the same materials as those mentioned in the section “Porous film for non-aqueous secondary battery” can be used, and a method of providing the porous film on the surface of the positive electrode, the negative electrode, and the separator Also, the methods mentioned in these sections can be adopted.

<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 it as necessary to put it in a battery container, and injects an electrolyte into the battery container and seals it. Can be manufactured. In addition, let at least 1 member be a member with a porous film among a positive electrode, a negative electrode, and a separator. 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 the examples and comparative examples, the glass transition temperature and the volume average particle diameter D50 of the particulate polymer were measured using the following methods. The degree of swelling of the particulate polymer with respect to the non-aqueous electrolyte and the contact angle with water, the durability and moisture content of the porous membrane, the stability of the porous membrane composition under shear, and the non-aqueous secondary battery The life characteristics and output characteristics were 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 volume average particle diameter D50 of the particulate polymer was measured using a laser diffraction / light scattering particle size distribution analyzer (LS230, manufactured by Beckman Coulter, Inc.).
<Swelling degree of particulate polymer with respect to non-aqueous electrolyte>
A binder for non-aqueous secondary battery porous membrane (aqueous dispersion of particulate polymer) was applied to an electrolytic copper foil (NC-WS (registered trademark) manufactured by Furukawa Electric) using a table coater at 50 ° C. It was dried with a hot air dryer for 20 minutes at 120 ° C. to prepare a 1 cm × 1 cm binder film (thickness: 500 μm), and the weight M0 was measured. 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
<Contact angle of particulate polymer with water (waterdrop contact angle of binder film)>
Three 1 cm × 1 cm binder films (thickness: 500 μm) were produced in the same manner as the above “swelling degree of particulate polymer with respect to non-aqueous electrolyte”. 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 was measured at two points, and the average value of the measured values for a total of six times was shown as the contact angle. In addition, the diameter of the water droplet of distilled water is 2 mm, and the numerical value of the contact angle which appeared on the measuring meter is a value measured 1 minute after dropping the water droplet of distilled water.
<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. Subsequently, the porous membrane-separated separator was placed in a nonaqueous electrolyte solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 (volume ratio), electrolyte: LiPF _{6 having 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 at 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 membrane was cut into 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 the shear of the porous membrane composition Stability>
The composition for porous membrane was applied on a separator (made of polyethylene) using a gravure roll (number of lines: 95) under the conditions of a conveyance speed of 10 m / min and a gravure rotation ratio of 100%, and the separator after application was cut out. The coating amount M0 (mg / cm ² ) per unit area was calculated. Moreover, 1 hour after application | coating, application | coating amount M1 (mg / cm < ² >) was computed similarly. 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 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 <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, left as it was for 168 hours (7 days) at 60 ° C., and then the cell voltage V 1 (V) was measured at 25 ° C. The voltage drop ΔV (mV) was calculated using the equation: ΔV = {4.35−V1} × 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 <Output 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 a −10 ° C. environment, and the voltage V2 (V) 15 seconds after the start of discharge was measured. The voltage change ΔV (mV) was calculated using the equation: ΔV = {V0−V2} × 1000, and evaluated as follows. The smaller this value, the better the output characteristics (low temperature characteristics).
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

Example 1
<Preparation of binder for nonaqueous secondary battery porous membrane>
In a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.15 part of sodium lauryl sulfate (“Emar (registered trademark) 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate are added. The gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, and 78.2 parts of 2-ethylhexyl acrylate (2-EHA) as a (meth) acrylic acid alkyl ester monomer , 20 parts of styrene (ST) as an aromatic monovinyl monomer, 0.8 part of itaconic acid (IA) as an acidic group-containing monomer, and 1.0 part of ethylene dimethacrylate (EDMA) as a crosslinkable monomer As a result, a monomer composition was obtained. This monomer composition was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to produce an aqueous dispersion containing a particulate polymer (porous membrane binder).
The volume average particle diameter D50 of the obtained particulate polymer was 0.36 μm. The observed glass transition temperature was only one point (−44 ° 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 contact angle with water were measured. The results are shown in Table 1.

<Preparation of composition for nonaqueous secondary battery porous membrane>
8 parts of binder for a porous film containing a particulate polymer in solids equivalent to 100 parts of alumina filler (Nippon Light Metal Co., Ltd., “LS256”) as non-conductive particles, and a carboxylic acid group as a thickener Introduced acrylamide polymer (Arakawa Chemical Co., “Polystron (registered trademark) 117”) 1.5 parts, polyethylene glycol type surfactant (San Nopco, “San Nopco (registered trademark) SN wet 366”) 0 2 parts were mixed to prepare a porous membrane composition.
Using the obtained porous membrane composition, the stability under shear was evaluated.

<Manufacture of porous membrane and separator with porous membrane>
An organic separator 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 and dried at 60 ° C. for 10 minutes. As a result, a separator having a porous film having a thickness of 18 μm was obtained.
Durability and moisture content were evaluated using the obtained separator with a porous membrane.

<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 the positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and as the binder for the 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. A separator with a porous film cut out to 6 cm × 16 cm is disposed on the double-sided negative electrode side of the laminate A so that the organic separator faces the double-sided negative electrode, and a double-sided positive electrode cut out to 5 cm × 15 cm is formed thereon. Then, a separator with a porous film cut out to 6 cm × 16 cm was placed thereon so that the porous film was opposed to the double-sided positive electrode, and finally a single-sided negative electrode cut out to 5.5 cm × 5.5 cm thereon Was laminated so that the negative electrode mixture layer faced the organic separator 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 output characteristics were evaluated. The results are shown in Table 1.

(Examples 2 to 4)
Except for changing the amount of 2-EHA and ST used as shown in Table 1 when preparing the binder for porous membrane, the binder for porous membrane, the composition for porous membrane, and the separator with porous membrane were the same as in Example 1. A negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Example 5)
Porous membrane binder, porous membrane composition, separator with porous membrane, negative electrode, in the same manner as in Example 1, except that sodium styrenesulfonate (NaSS) was used instead of ST when preparing the porous membrane binder A positive electrode and a secondary battery were manufactured, and similar items were evaluated. The results are shown in Table 1.

(Example 6)
Except that octyl acrylate (OA) was used instead of 2-EHA when preparing the porous membrane binder, the porous membrane binder, the porous membrane composition, the separator with the porous membrane, and the negative electrode were the same as in Example 1. A positive electrode and a secondary battery were manufactured, and similar items were evaluated. The results are shown in Table 1.

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

(Examples 9 and 10)
Except for using methacrylic acid (MAA) and vinyl sulfonic acid (VSA) in place of IA at the time of preparing the porous membrane binder, in the same manner as in Example 1, the porous membrane binder, the porous membrane composition, A separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Example 11)
Except for changing the amount of 2-EHA and EDMA used as shown in Table 1 when preparing the binder for porous membrane, the binder for porous membrane, the composition for porous membrane, and the separator with porous membrane were the same as in Example 1. A negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Example 12)
Porous membrane binder, porous membrane composition, separator with porous membrane, negative electrode, positive electrode in the same manner as in Example 1 except that divinylbenzene (DVB) was used instead of EDMA when preparing the porous membrane binder , And secondary batteries were manufactured and evaluated for similar items. The results are shown in Table 1.

(Example 13)
Except that n-butyl acrylate (BA) was used instead of 2-EHA when preparing the porous membrane binder, the porous membrane binder, the porous membrane composition, and the separator with porous membrane were the same as in Example 1. A negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Example 14)
In the same manner as in Example 1, except that 16 parts of the aqueous dispersion of the particulate polymer (porous film binder) was used corresponding to the solid content during the preparation of the porous film composition, A separator with a film, a negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Comparative Example 1)
When preparing the porous membrane binder, the amount of 2-EHA used was changed as shown in Table 1, ST was not used, 3 parts of MAA was used instead of IA 0.8 part, and 1 part of EDMA was replaced with acrylamide ( AAm) 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 in the same manner as in Example 1 except that 1.5 parts were used. Items were evaluated. The results are shown in Table 1.

(Comparative Example 2)
Porous membrane binder and porous membrane composition in the same manner as in Comparative Example 1 except that 55.5 parts of BA were used instead of 95.5 parts of 2-EHA and ST40 parts were used when preparing the binder for porous membranes. Products, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were manufactured, and the same items were evaluated. The results are shown in Table 1.

(Comparative Example 3)
A porous membrane was prepared in the same manner as in Comparative Example 2, except that 90 parts of 2-EHA was used instead of 55.5 parts of BA and the amount of ST and MAA used was changed as shown in Table 1 when preparing the binder for porous membrane. Binders, porous membrane compositions, separators with porous membranes, negative electrodes, positive electrodes, and secondary batteries were produced, and the same items were evaluated. The results are shown in Table 1.

(Comparative Example 4)
A porous film composition, a separator with a porous film, a negative electrode, a positive electrode, and a secondary battery were produced in the same manner as in Example 1 except that a porous film binder prepared as follows was used. Items were evaluated. The results are shown in Table 1.
<Preparation of binder for porous membrane>
In a reactor equipped with a stirrer, 230 parts of ion-exchanged water, 65 parts of BA, 35 parts of styrene macromonomer (STMM, one-end methacryloylated polystyrene oligomer, “AS-6” manufactured by Toagosei Co., Ltd.), lauryl as an emulsifier Sodium sulfate (manufactured by Kao Chemicals Co., Ltd., “Emar (registered trademark) 2F”) 0.15 part, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added and stirred sufficiently, then at 90 ° C. Polymerization was conducted by heating to obtain an aqueous dispersion of the polymer. The polymerization conversion rate determined from the solid content concentration was 98%.
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.

From Table 1, random containing a (meth) acrylic acid alkyl ester monomer unit and an aromatic monovinyl monomer unit in a specific ratio, and a degree of swelling with respect to the non-aqueous electrolyte being controlled within a specific range In Examples 1 to 14 using a particulate polymer made of a copolymer, the composition for a porous membrane containing the particulate polymer is excellent in stability under shear, the porous membrane is excellent in durability, and moisture. It can be seen that a secondary battery having a low content and excellent in life characteristics and output characteristics can be obtained.
On the other hand, a comparative example in which at least one of the content ratio of the (meth) acrylic acid alkyl ester monomer unit, the content ratio of the aromatic monovinyl monomer unit, and the degree of swelling with respect to the non-aqueous electrolyte is outside the specific range of the present application It can be seen that 1-3 are inferior in terms of overall performance.
Further, Comparative Example 4 using a particulate polymer which is a graft copolymer having a large degree of swelling with respect to the non-aqueous electrolyte solution is inferior in stability of the composition for the porous film, and the porous film is inferior in durability and has a moisture content. It can be seen that there are many. And it turns out that it is inferior to the lifetime characteristic and output characteristic of a secondary battery.

From Table 1, the following can be further read.
From Examples 1-4, 7, 8, and 11, the (meth) acrylic acid alkyl ester monomer unit, the aromatic monovinyl monomer unit, the acidic group-containing monomer unit, and the crosslinkable monomer of the particulate polymer. It can be seen that by adjusting the content ratio of the body unit, the durability of the porous membrane can be improved and the water content of the porous membrane can be reduced. And it turns out that the lifetime characteristic of a secondary battery can be improved.
From Examples 1, 5, 6, 9, 10, 12, and 13, the (meth) acrylic acid alkyl ester monomer unit, the aromatic monovinyl monomer unit, the acidic group-containing monomer unit of the particulate polymer, and It can be seen that by changing the type of the crosslinkable monomer unit, the stability of the composition for the porous membrane and the durability of the porous membrane can be improved, and the water content of the porous membrane can be reduced. And it turns out that the lifetime characteristic and output characteristic of a secondary battery can be improved.
From Examples 1 and 14, it is possible to improve the stability of the composition for the porous membrane by adjusting the blending amount of the particulate polymer with respect to the non-conductive particles, and to reduce the water content of the porous membrane. Recognize. And it turns out that the output characteristic of a secondary battery can be improved.

ADVANTAGE OF THE INVENTION According to this invention, the binder for non-aqueous secondary battery porous membranes which is excellent in durability and can form a porous membrane with little water content can be provided.
Moreover, according to this invention, the composition for non-aqueous secondary battery porous membranes which is excellent in durability and can form a porous membrane with little water content can be provided.
According to the present invention, there is provided a porous membrane for a non-aqueous secondary battery having excellent durability and a low water content, and a non-aqueous secondary battery comprising the porous membrane for a non-aqueous secondary battery. Can do.

Claims (6)

A binder for a non-aqueous secondary battery porous membrane containing a particulate polymer,
The particulate polymer is a random copolymer containing 65% by mass or more of (meth) acrylic acid alkyl ester monomer units and 0.1% by mass or more and less than 30% by mass of aromatic monovinyl monomer units. Yes,
Ri der degree of swelling 1 fold 2 times or less with respect to the measurement for a non-aqueous electrolyte solution of the particulate polymer,
The non-aqueous electrolyte for measurement is a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume ratio: ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5), and 1 mol of LiPF ₆ . Is a solution dissolved at a concentration of / liter,
The degree of swelling was determined by drying the aqueous dispersion of the particulate polymer at 50 ° C. for 20 minutes and 120 ° C. for 20 minutes to obtain a 1 cm × 1 cm binder film (thickness: 500 μm). Is measured, and the binder film is immersed in the non-aqueous electrolyte for measurement at 60 ° C. for 72 hours, and the weight M1 of the binder film after the immersion is measured. Using the weights M0 and M1, the formula: degree of swelling = Binder for non-aqueous secondary battery porous membrane , calculated by M1 / M0 .   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 composition for non-aqueous secondary battery porous films containing the binder for non-aqueous secondary battery porous films in any one of Claims 1-3, a nonelectroconductive particle, and water.   A porous film for a non-aqueous secondary battery, formed from the composition for a non-aqueous secondary battery porous film according to claim 4. A positive electrode, a negative electrode, a separator, and an electrolyte solution,
A nonaqueous secondary battery comprising the porous film for a nonaqueous secondary battery according to claim 5 on the surface of at least one battery member selected from the group consisting of the positive electrode, the negative electrode, and the separator.