JP2015185530A - Binder for secondary battery porous films, slurry composition for secondary battery porous films, porous film for secondary batteries, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a binder and a slurry composition which are arranged for forming a porous film for secondary batteries, which enable the enhancement of secondary battery performances, such as a rate characteristic and a high-temperature cycle characteristic, the achievement of a porous film with a high peel strength, and the reduction in volume change involved in charge and discharge of a secondary battery, and which produce a less amount of production of harmful substance such as formaldehyde; such a porous film for secondary batteries; and a secondary battery.SOLUTION: A binder for secondary battery porous films comprises (meth)acrylic polymer. In the binder for secondary battery porous films, the (meth)acrylic polymer includes 50 wt% or more of an alkyl(meth)acrylate monomer unit, a (meth)acrylic amide monomer unit having an N-methylol group, and a (meth)acrylic amide monomer unit of primary amine. A slurry composition for secondary battery porous films comprises the binder. A porous film for secondary batteries is formed by use of the slurry composition. A secondary battery comprises the porous film.

Description

  The present invention relates to a binder for a secondary battery porous film, a slurry composition for a secondary battery porous film including the binder, a porous film for a secondary battery, and a secondary battery.

  Secondary batteries have been widely used in recent years as power sources for portable devices. In particular, lithium ion secondary batteries have characteristics such as being small and light, having high energy density, and being capable of repeated charge and discharge, and are expected to expand demand. Lithium ion secondary batteries are used in devices such as mobile phones and notebook personal computers, taking advantage of their high energy density. Secondary batteries are required to further improve performance in order to improve the performance of the devices used. For example, it is possible to improve performance such as the ability to charge / discharge a large capacity even at a high charge / discharge rate (rate characteristic) and the ability to maintain the capacity even after repeated charge / discharge in a high temperature environment (high temperature cycle characteristic). It has been demanded. Moreover, in a secondary battery, even if charging / discharging is repeated, the cell volume change etc. are not caused, but the performance which can be used stably is calculated | required.

  In secondary batteries, a separator is provided between a positive electrode and a negative electrode in order to improve performance. As a separator, a porous film obtained by applying a slurry layer containing non-conductive particles and a binder to a substrate to form a layer and drying the layer is known. As the slurry for forming a porous film, a so-called aqueous slurry prepared using water as a solvent for reducing the environmental load is becoming widespread. Moreover, it is known that various polymers are used as a binder as a component of a slurry for forming a porous film (Patent Documents 1 and 2).

International Publication No. WO2013 / 125645 International Publication No. WO2009 / 123168

  As such an aqueous slurry, a slurry containing a particulate binder that is insoluble in water and can maintain a particulate shape in water is known. When the slurry contains such a particulate binder, it is possible to obtain effects such as increasing the adhesion strength (peel strength) of the obtained porous film with the substrate. Various types of such particulate polymers are known, and one of them is a (meth) acrylic polymer mainly containing units obtained by polymerizing alkyl (meth) acrylate. It has been. When such a (meth) acrylic polymer is used as a particulate binder, it is required to increase the degree of crosslinking in order to obtain physical properties suitable for the binder.

  In general, in order to form a crosslinked structure in a (meth) acrylic polymer, a crosslinkable unit is provided in the polymer chain. Various types of such crosslinkable units are known, and a preferred example among them is a combination of N-methylol (meth) acrylamide (NMA) and allyl glycidyl ether (AGE).

However, when NMA and AGE are used in the production of a (meth) acrylic polymer as a particulate binder, the reaction of NMA and AGE becomes insufficient in the polymerization reaction and the crosslinking reaction, and unreacted groups in the resulting slurry. May remain. If the remaining amount of unreacted groups is large, the adhesiveness of the binder is adversely affected, and the peel strength of the porous film may be reduced. In addition, due to insufficient crosslinking reaction, a large amount of the binder component may be eluted in the electrolyte when the secondary battery is used. When these undesirable phenomena occur, the performance of the secondary battery can be adversely affected. Moreover, harmful formaldehyde may be generated due to the reaction between NMA molecules. Not only is there anxiety for the health of workers during the manufacture of battery members, but the presence of a large amount of formaldehyde in the battery results in an increase in battery performance. There was a risk of causing a drop.
Therefore, the object of the present invention is to improve the performance of the secondary battery such as rate characteristics and high-temperature cycle characteristics, to obtain a high peel strength of the porous film, and to change the volume accompanying charging / discharging of the secondary battery. It is an object of the present invention to provide a binder and a slurry composition for forming a porous film for a secondary battery that can reduce the amount of harmful substances such as formaldehyde and the like.
Further objects of the present invention are to improve the performance of the secondary battery such as rate characteristics and high temperature cycle characteristics, high peel strength, can reduce the volume change accompanying charging and discharging of the secondary battery, and Another object of the present invention is to provide a porous membrane for a secondary battery that generates less harmful substances such as formaldehyde, and a secondary battery excellent in such performance.

  The inventor has studied to achieve the above object. As a result, the present inventor, as the (meth) acrylic polymer constituting the particulate binder, the (meth) acrylamide monomer unit having an N-methylol group in the molecular chain, and ( ) It was found that the above-mentioned problems can be solved by adopting a combination of acrylamide monomer units, and the present invention was completed. That is, according to the present invention, the following [1] to [6] are provided.

[1] A binder for a secondary battery porous membrane containing a (meth) acrylic polymer,
The (meth) acrylic polymer contains 50% by weight or more of an alkyl (meth) acrylate monomer unit, and has a (meth) acrylamide monomer unit having an N-methylol group, and a (meth) acrylate of a primary amine. ) A binder for a secondary battery porous membrane containing an acrylamide monomer unit.
[2] The ratio of the (meth) acrylamide monomer unit of the primary amine in the total monomer units of the (meth) acrylic polymer is 0.5 wt% or more and 5 wt% or less,
In the (meth) acrylic polymer, the ratio of the (meth) acrylamide monomer unit of the primary amine to 100 parts by weight of the (meth) acrylamide monomer unit having the N-methylol group is 50 parts by weight or more. The binder for a secondary battery porous membrane according to [1], which is 200 parts by weight or less.
[3] The (meth) acrylic polymer further contains a (meth) acrylonitrile monomer unit,
The ratio of the (meth) acrylonitrile monomer unit in the total monomer units of the (meth) acrylic polymer is 0.5% by weight or more and 5% by weight or less, in [1] or [2] The binder for a secondary battery porous film according to the description.
[4] A slurry composition for a secondary battery porous film, comprising non-conductive particles and the binder for a secondary battery porous film according to any one of [1] to [3].
[5] A porous film for a secondary battery formed by using the slurry composition for a secondary battery porous film according to [4].
[6] A secondary battery comprising the porous film for a secondary battery according to [5].

The binder for a secondary battery porous membrane of the present invention and the slurry composition for a secondary battery porous membrane of the present invention can improve the performance of the secondary battery such as rate characteristics and high temperature cycle characteristics, and have a high peel strength. Strength can be obtained, volume change accompanying charge / discharge of the secondary battery can be reduced, and generation of harmful substances such as formaldehyde can be reduced.
The porous membrane for a secondary battery of the present invention can improve the performance of the secondary battery such as rate characteristics and high-temperature cycle characteristics, has high peel strength, and reduces the volume change associated with charge / discharge of the secondary battery. And generation of harmful substances such as formaldehyde can be reduced. In addition, the secondary battery of the present invention is excellent in the performance of such a secondary battery, has a small volume change due to charge / discharge, and generates less harmful substances such as formaldehyde in the disposal after its manufacture and use. can do.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the present application, the term “(meth) acryl” means either or both of acrylic and methacrylic. For example, (meth) acrylic acid means acrylic acid, methacrylic acid or a combination thereof. Similarly, for example, the phrase “(meth) acrylate” means acrylate, methacrylate, or a combination thereof, and the phrase “(meth) acrylonitrile” means acrylonitrile, methacrylonitrile, or a combination thereof.

[1. Porous membrane binder)
The binder for a secondary battery porous membrane of the present invention (hereinafter sometimes simply referred to as “a binder for a porous membrane”) contains a specific (meth) acrylic polymer. This specific (meth) acrylic polymer may be referred to as (meth) acrylic polymer (A) below.

  The (meth) acrylic polymer (A) contains 50% by weight or more of an alkyl (meth) acrylate monomer unit and has an N-methylol group and a primary amine. Contains (meth) acrylamide monomer units. That is, the (meth) acrylic polymer (A) has an alkyl (meth) acrylate monomer unit and an N-methylol group as units constituting the polymer molecule in the polymer molecule (meth). Contains an acrylamide monomer unit and a primary amine (meth) acrylamide monomer unit.

[1.1. Alkyl (meth) acrylate monomer unit]
The (meth) acrylic polymer (A) contains 50% by weight or more of alkyl (meth) acrylate monomer units. The alkyl (meth) acrylate unit refers to a structural unit having a structure formed by polymerizing alkyl (meth) acrylate.
Examples of the alkyl (meth) acrylate include alkyl (meth) acrylates having an alkyl group having 1 to 20 carbon atoms. Among them, the alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl (meth) acrylate having an alkyl group having 1 to 6 carbon atoms. More preferably. One or more of these alkyl (meth) acrylates can be used in combination as an alkyl (meth) acrylate for polymerization of the (meth) acrylic polymer (A).

Examples of alkyl (meth) acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate Alkyl acrylates such as nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate , Hexyl methacrylate, heptyl methacrylate DOO, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate include alkyl methacrylates such as stearyl methacrylate. Moreover, these may use only 1 type and may be used combining two or more types by arbitrary ratios. As the alkyl (meth) acrylate, n-butyl acrylate is particularly preferable.
The proportion of the alkyl (meth) acrylate monomer unit in the (meth) acrylic polymer (A) is 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and still more preferably. 90% by weight or more. By making the ratio of the alkyl (meth) acrylate monomer unit in the (meth) acrylic polymer (A) equal to or higher than the lower limit, the flexibility of the binder for the porous film is increased and the peel strength of the porous film is improved. Can do.

[1.2. (Meth) acrylamide monomer unit having N-methylol group]
The (meth) acrylic polymer (A) contains a (meth) acrylamide monomer unit having an N-methylol group. The “(meth) acrylamide monomer unit having an N-methylol group” refers to a structural unit having a structure formed by polymerizing a (meth) acrylamide monomer having an N-methylol group.

Examples of (meth) acrylamide monomers having an N-methylol group include N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylol acrylamide, and N, N-dimethylol methacrylamide, and these Combinations are mentioned, and N-methylolacrylamide is particularly preferable.
The proportion of the (meth) acrylamide monomer unit having an N-methylol group in the (meth) acrylic polymer (A) is preferably 0.5% by weight or more, more preferably 0.7% by weight or more. More preferably 0.9% by weight or more, particularly still more preferably 1.0% by weight or more, while preferably 5.0% by weight or less, more preferably 4.5% by weight or less, even more preferably 4. It is 0% by weight or less, particularly preferably 3.5% by weight or less.

  When the ratio of the (meth) acrylamide monomer unit having an N-methylol group in the (meth) acrylic polymer (A) is equal to or more than the lower limit, the crosslinking proceeds rapidly, and the binder is converted into the electrolytic solution. Solubility can be kept in the desired low range, thereby improving high temperature cycling characteristics. When the proportion of the (meth) acrylamide monomer unit having an N-methylol group in the (meth) acrylic polymer (A) is not more than the above upper limit, the polymerization stability can be increased, and coarse particles are generated. Can be suppressed and the peel strength can be improved. In addition, the amount of formaldehyde produced can be reduced.

[1.3. (Meth) acrylamide monomer unit of primary amine]
The (meth) acrylic polymer (A) contains a primary amine (meth) acrylamide monomer unit. The “primary amine (meth) acrylamide monomer unit” refers to a structural unit having a structure formed by polymerizing a primary amine (meth) acrylamide monomer. The (meth) acrylic polymer (A) contains a (meth) acrylamide monomer unit of a primary amine in combination with a (meth) acrylamide monomer unit having an N-methylol group. Good crosslinks suitable for forming can be formed with high reactivity.

  Examples of primary amine (meth) acrylamide monomers include acrylamide, methacrylamide and combinations thereof, with acrylamide being particularly preferred.

  The proportion of primary amine (meth) acrylamide monomer units in the (meth) acrylic polymer (A) is preferably 0.5% by weight or more, more preferably 0.7% by weight or more, and even more. Preferably it is 0.9% by weight or more, even more preferably 1.0% by weight or more, while preferably 5.0% by weight or less, more preferably 4.5% by weight or less, even more preferably 4.0%. % By weight or less, even more preferably 3.5% by weight or less. By making the ratio of the (meth) acrylamide monomer unit of the primary amine in the (meth) acrylic polymer (A) above the lower limit, the halogen trap function is improved and the gas in the secondary battery is increased. Generation | occurrence | production can be suppressed, and the volume change accompanying charging / discharging of a secondary battery can be reduced. In addition, the amount of formaldehyde produced can be reduced. By setting the ratio of the (meth) acrylamide monomer unit of the primary amine in the (meth) acrylic polymer (A) to the upper limit or less, the polymerization stability can be improved and the generation of coarse particles can be improved. It can suppress and can improve peel strength.

  The ratio of the (meth) acrylamide monomer unit of the primary amine to 100 parts by weight of the (meth) acrylamide monomer unit having an N-methylol group in the (meth) acrylic polymer (A) is preferably 50. Parts by weight or more, more preferably 55 parts by weight or more, even more preferably 60 parts by weight or more, even more preferably 70 parts by weight or more, while preferably 200 parts by weight or less, more preferably 150 parts by weight or less, 140 parts by weight or less, even more preferably 130 parts by weight or less. By making the ratio of the (meth) acrylamide monomer unit of the primary amine to the (meth) acrylamide monomer unit having an N-methylol group equal to or higher than the lower limit, the halogen trap function is improved, and the inside of the secondary battery The generation of gas can be suppressed, and the volume change associated with charging / discharging of the secondary battery can be reduced. In addition, the amount of formaldehyde produced can be reduced. By making the ratio of the (meth) acrylamide monomer unit of the primary amine to the (meth) acrylamide monomer unit having an N-methylol group not more than the above upper limit, the ratio of uncrosslinked amide is reduced, and the binder Can be maintained in a desired low range, thereby improving the high-temperature cycle characteristics.

[1.4. (Meth) acrylonitrile monomer unit]
The (meth) acrylic polymer (A) can contain a (meth) acrylonitrile monomer unit. The (meth) acrylonitrile monomer unit refers to a structural unit having a structure formed by polymerizing a (meth) acrylonitrile monomer. Examples of (meth) acrylonitrile monomers include acrylonitrile, methacrylonitrile and combinations thereof, with acrylonitrile being particularly preferred.

  The proportion of the (meth) acrylonitrile monomer unit in the (meth) acrylic polymer (A) is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, and even more preferably 1.5%. % By weight, preferably 5.0% by weight or less, more preferably 4.0% by weight or less, and even more preferably 3.0% by weight or less. By setting the ratio of the (meth) acrylonitrile monomer unit in the (meth) acrylic polymer (A) to be equal to or higher than the lower limit, the polymerization stability can be improved, the generation of coarse particles is suppressed, and the peel Strength can be improved. By maintaining the ratio of the (meth) acrylonitrile monomer unit in the (meth) acrylic polymer (A) to the upper limit or less, the degree of swelling in the electrolyte solution of the porous membrane is maintained in a desired low range, Good binding force can be expressed and high-temperature cycle characteristics can be improved.

[1.5. (Acid group-containing monomer unit)
The (meth) acrylic polymer (A) can contain an acidic group-containing monomer unit. The acidic group-containing monomer unit is a structure formed by polymerizing acidic group-containing monomers such as carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. It is a structural unit. Especially, it is preferable that a (meth) acrylic polymer (A) contains a carboxylic acid group containing monomer unit.

  The carboxylic acid group-containing monomer may be a compound having a —COOH group (carboxylic acid group) and a group capable of undergoing a polymerization reaction. For example, a monomer capable of generating a carboxylic acid group by hydrolysis can also be used as the carboxylic acid group-containing monomer. Specific examples of such carboxylic acid group-containing monomers include acid anhydrides that can generate carboxylic acid groups by hydrolysis.

  The carboxylic acid group-containing monomer unit is preferably an ethylenically unsaturated carboxylic acid monomer unit. An ethylenically unsaturated carboxylic acid monomer unit is a structural unit having a structure formed by polymerizing an ethylenically unsaturated carboxylic acid monomer. By including such a unit, a (meth) acrylic polymer (A) satisfying desired physical properties can be easily obtained.

  Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof. Examples of ethylenically unsaturated monocarboxylic acids and derivatives thereof include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α- Examples include chloro-β-E-methoxyacrylic acid and β-diaminoacrylic acid. Examples of ethylenically unsaturated dicarboxylic acids and derivatives thereof include maleic acid, fumaric acid, itaconic acid; substituents such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid And maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate. Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like. Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, particularly methacrylic acid, are preferable because the dispersibility of the (meth) acrylic polymer (A) in water can be further improved. Further, one type of ethylenically unsaturated carboxylic acid monomer may be used alone, or two or more types may be used in combination at any ratio.

  The proportion of the acidic group-containing monomer unit in the (meth) acrylic polymer (A) is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, and even more preferably 1.5% by weight. On the other hand, it is preferably 5.0% by weight or less, more preferably 4.0% by weight or less, and even more preferably 3.0% by weight or less. By making the ratio of the acidic group-containing monomer units in the (meth) acrylic polymer (A) equal to or higher than the above lower limit, the dispersibility of the obtained slurry composition for porous membranes is improved and the rate characteristics are improved. Can be made. By setting the ratio of the carboxylic acid group-containing monomer unit in the (meth) acrylic polymer (A) to be equal to or less than the above upper limit, the polymerization stability can be improved, the generation of coarse particles is suppressed, and the peel strength is increased. Can be improved.

[1.6. Other units]
Furthermore, the (meth) acrylic polymer (A) can contain an arbitrary structural unit in addition to the structural units described above. Examples of arbitrary structural units that can be included in the particulate polymer include structural units having a structure formed by polymerizing the following monomers. That is, aliphatic conjugated diene monomers such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene; styrene , Aromatic vinyl monomers such as chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl benzene; Α, β-unsaturated nitrile compound monomers other than (meth) acrylonitrile, such as chloroacrylonitrile and α-ethylacrylonitrile; olefin monomers such as ethylene and propylene; and halogen atom-containing single amounts such as vinyl chloride and vinylidene chloride Body: Vinyl acetate such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc. Steal monomers; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; and N -Structural units having a structure formed by polymerizing one or more of a heterocyclic compound containing a heterocyclic compound such as vinylpyrrolidone, vinylpyridine, and vinylimidazole. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

[1.7. Properties of (meth) acrylic polymer]
The weight average molecular weight of the (meth) acrylic polymer (A) is preferably 10,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 500,000 or less. . By keeping the weight average molecular weight of the (meth) acrylic polymer (A) within the above range, the strength of the porous film and the dispersibility of the non-conductive particles are easily improved. Here, the weight average molecular weight of the (meth) acrylic polymer (A) can be obtained as a value in terms of polystyrene using tetrahydrofuran as a developing solvent by gel permeation chromatography (GPC).

  The glass transition temperature of the (meth) acrylic polymer (A) is preferably −75 ° C. or higher, more preferably −55 ° C. or higher, particularly preferably −45 ° C. or higher, preferably 40 ° C. or lower, more preferably 30. C. or lower, even more preferably 20 ° C. or lower, particularly preferably 15 ° C. or lower. By keeping the glass transition temperature of the (meth) acrylic polymer (A) within the above range, the flexibility and rollability of the separator and electrode provided with the porous film, and the connection between the porous film and the separator substrate or electrode plate are obtained. Characteristics such as wearability are highly balanced and suitable. The glass transition temperature of the (meth) acrylic polymer (A) can be adjusted, for example, by combining various monomers.

  In the porous membrane binder of the present invention, the (meth) acrylic polymer (A) is usually present in a particulate form. The (meth) acrylic polymer (A) is usually water-insoluble, and at least does not dissolve in the slurry composition, and may exist in a dispersed state in a particle shape. In the porous membrane, the (meth) acrylic polymer (A) can be present while maintaining part or all of the particle shape. Such a particulate polymer can be obtained by appropriately adjusting the proportion of the monomer units as constituent elements.

  The volume average particle diameter D50 of the particles of the (meth) acrylic polymer (A) is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.1 μm or more, while preferably 1. It is 0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less. By keeping the volume average particle diameter of the (meth) acrylic polymer (A) particles in the above range, the strength and flexibility of the porous film can be improved.

[1.8. (Method for producing (meth) acrylic polymer]
The (meth) acrylic polymer (A) can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. The content ratio of each monomer in the monomer composition in the polymerization reaction is usually adjusted to the same ratio as the content ratio of the repeating unit in the desired (meth) acrylic polymer (A).

  As the aqueous solvent, one in which the (meth) acrylic polymer (A) can be dispersed in a particle state can be selected. An aqueous solvent having a boiling point at normal pressure of preferably 80 to 350 ° C, more preferably 100 to 300 ° C can be selected.

  Examples of aqueous solvents include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol tertiary Glycol ethers such as butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; 1,3-dioxolane, 1 , 4-dioxolane, ethers such as tetrahydrofuran; and the like. Among these, water is particularly preferable from the viewpoint that it is not flammable and a dispersion of particles of the (meth) acrylic polymer (A) can be easily obtained. In addition, water may be used as the main solvent, and an aqueous solvent other than the above water may be mixed and used within a range in which the dispersion state of the (meth) acrylic polymer (A) particles can be ensured.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. The reaction mode of the polymerization may be any of ionic polymerization, radical polymerization, living radical polymerization, and the like. It is easy to obtain a high molecular weight body, and since the polymer is obtained as it is dispersed in water, redispersion treatment is unnecessary, and it can be used for production of the slurry composition for a porous membrane of the present invention as it is. From the viewpoint of production efficiency, the emulsion polymerization method is particularly preferable. Emulsion polymerization can be performed according to a conventional method.

  Commonly used additives may be used as the emulsifier, dispersant, polymerization initiator, polymerization aid and the like used in the polymerization. The amount of these additives used may also be a commonly used amount. The polymerization conditions can be appropriately adjusted according to the polymerization method and the type of polymerization initiator.

[1.9. Optional ingredients)
The binder for a porous film of the present invention may consist only of the (meth) acrylic polymer (A), or may be a mixture of the (meth) acrylic polymer (A) and other components. . The porous membrane binder of the present invention may contain only one type of (meth) acrylic polymer (A) or two or more types of (meth) acrylic polymer (A) in any ratio. May be.

  The porous membrane binder of the present invention may have a low formaldehyde content. Specifically, the percentage of the amount of formaldehyde with respect to the amount of (meth) acrylic polymer (A) is preferably 30 ppm or less, more preferably 25 ppm or less, and even more preferably 20 ppm or less. Thus, the low formaldehyde content can reduce the environmental load in its use. Thus, the binder for porous membranes with low formaldehyde content contains the (meth) acrylamide monomer unit which has N-methylol group as a crosslinkable unit, and the (meth) acrylamide monomer unit of a primary amine. And, if necessary, the content can be obtained within the preferred range described above.

[2. Slurry composition for porous film]
The slurry composition for a secondary battery porous membrane of the present invention (hereinafter sometimes referred to as “slurry composition for porous membrane” or simply “slurry composition”) includes non-conductive particles and the porous composition of the present invention. Contains a membrane binder.

  The amount of the binder for a porous film in the slurry composition of the present invention can be appropriately adjusted so that the ratio of the (meth) acrylic polymer (A) to the nonconductive particles is within a preferable range. The ratio of the (meth) acrylic polymer (A) to 100 parts by weight of the nonconductive particles is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, and even more preferably 1 part by weight or more. On the other hand, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 8 parts by weight or less. By making the amount of the (meth) acrylic polymer (A) equal to or higher than the lower limit, non-conductive particles and the adhesion between the non-conductive particles and the base material are improved, powder falling off the porous film, etc. The occurrence of problems can be reduced. Moreover, it can suppress that a particulate polymer blocks the hole of a base material and a Gurley value increases by making it into an upper limit or less.

[2.1. Non-conductive particles
The slurry composition of the present invention includes non-conductive particles. Non-conductive particles are components filled in the porous film, and the gaps between the non-conductive particles can form pores of the porous film. Since the non-conductive particles have non-conductivity, the porous film can be made insulative, and therefore a short circuit in the secondary battery can be prevented. In general, non-conductive particles have high rigidity, which can increase the mechanical strength of the porous membrane. For this reason, even if stress that causes shrinkage occurs in the base material such as the separator base material due to heat, the porous film can resist the stress, so it is possible to prevent the occurrence of a short circuit due to the shrinkage of the base material. It is.
As the non-conductive particles, inorganic particles or organic particles may be used.

  Inorganic particles are usually excellent in dispersion stability in water, hardly settled in a slurry composition, and can maintain a uniform slurry state for a long time. In addition, when inorganic particles are used, the heat resistance of the porous film can usually be increased.

As the material for the non-conductive particles, an electrochemically stable material is preferable. From this point of view, preferable examples of inorganic materials for non-conductive particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ )), bakelite, Oxide particles such as iron oxide, silicon oxide, magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO, alumina-silica composite oxide; aluminum nitride, silicon nitride, boron nitride Nitride particles such as silicon; covalently bonded crystal particles such as silicon and diamond; sparingly soluble ionic crystal particles such as barium sulfate, calcium fluoride and barium fluoride; and clay fine particles such as silica, talc and montmorillonite.

  Among these, alumina, boehmite, and barium sulfate are preferable, and alumina is particularly preferable from the viewpoint of low water absorption and excellent heat resistance (for example, resistance to high temperature of 180 ° C. or higher).

  As the organic particles, polymer particles are usually used. The organic particles can control the affinity for water by adjusting the type and amount of the functional group on the surface of the organic particles, and thus can control the amount of water contained in the porous film. Organic particles are excellent in that they usually have little metal ion elution.

  Examples of the polymer that forms the non-conductive particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, phenol resin, and acrylic resin. The polymer compound forming the particles may be a homopolymer or a copolymer. In the case of a copolymer, any of a block copolymer, a random copolymer, a graft copolymer, and an alternating copolymer is used. it can. Furthermore, it may be at least partially modified or a crosslinked product. And a mixture of these may be sufficient. In the case of a cross-linked product, the cross-linking agent includes a cross-linked product having an aromatic ring such as divinylbenzene, a polyfunctional acrylate cross-linked product such as ethylene glycol dimethacrylate, and a cross-linked product having an epoxy group such as glycidyl acrylate and glycidyl methacrylate. Can be mentioned.

  When organic particles are used as the non-conductive particles, the organic particles are usually polymer particles having no glass transition temperature or polymer particles having a high glass transition temperature. When the polymer has a glass transition temperature, the glass transition temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, particularly preferably 250 ° C. or higher, and usually 500 ° C. or lower.

  The method for producing the organic particles as the non-conductive particles is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as the material of the slurry composition. Moreover, when manufacturing organic particles, it is preferable to include a dispersant in the reaction system. The organic particles are generally composed of a polymer that substantially constitutes the organic particles, but may be accompanied by any component such as an additive added during the polymerization.

  The non-conductive particles may be subjected to, for example, element substitution, surface treatment, solid solution, or the like as necessary. Further, the non-conductive particles may include one kind of the above materials alone in one particle, or may contain two or more kinds in combination at an arbitrary ratio. . Further, the non-conductive particles may be used in combination of two or more kinds of particles formed of different materials.

  Examples of the shape of the nonconductive particles include a spherical shape, an elliptical spherical shape, a polygonal shape, a tetrapod (registered trademark) shape, a plate shape, and a scale shape.

  The volume average particle diameter of the non-conductive particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, preferably 5 μm or less, more preferably 1 μm or less. By making the volume average particle diameter of the non-conductive particles equal to or more than the lower limit of the above range, the dispersibility of the non-conductive particles in the porous film can be improved, and thus a porous film having excellent uniformity can be obtained. . Moreover, the porous film excellent in durability can be obtained by making it into an upper limit or less. Here, the volume average particle diameter of the particles represents a particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle diameter distribution measured by the laser diffraction method.

The BET specific surface area of the non-conductive particles is, for example, preferably 0.9 m ² / g or more, more preferably 1.5 m ² / g or more. Further, from the viewpoint of suppressing aggregation of non-conductive particles and optimizing the fluidity of the slurry composition, the BET specific surface area is preferably not too large, for example, 150 m ² / g or less.

[2.2. Water-soluble polymer)
The slurry composition of the present invention may contain a water-soluble polymer. The water-soluble polymer has an effect of binding non-conductive particles by interposing between non-conductive particles in the porous film, and intervening between the non-conductive particles and the separator substrate or electrode plate. By doing so, the effect | action which bind | bond | couples a porous film, a separator base material, or an electrode plate can be show | played. Moreover, the viscosity of a slurry composition can be raised by adding a water-soluble polymer to a slurry composition, and the viscosity of a slurry composition can be made suitable for application | coating.

As the water-soluble polymer, various thickening polysaccharides can be used. As the thickening polysaccharide, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof is preferably used, and carboxymethyl cellulose or a salt thereof is particularly preferable.
Since thickening polysaccharides, such as carboxymethylcellulose salt, can raise the viscosity of a slurry composition, the applicability | paintability of a slurry composition can be made favorable. In addition, the carboxymethyl cellulose salt can usually increase the dispersion stability of the nonconductive particles in the slurry composition, and can increase the binding property between the porous film and the separator substrate or the electrode plate. Examples of the carboxymethyl cellulose salt include a sodium salt and an ammonium salt. A thickening polysaccharide may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the water-soluble polymer in the slurry composition of the present invention is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, as the amount of the water-soluble polymer with respect to 100 parts by weight of the non-conductive particles. Even more preferably, it is 0.5 parts by weight or more, while it is preferably 3.5 parts by weight or less, preferably 3.0 parts by weight or less, more preferably 2.5 parts by weight or less. Heat shrinkage resistance can be improved by setting the amount of the water-soluble polymer to the above lower limit or more. By setting the amount of the water-soluble polymer below the upper limit, the moisture content of the porous membrane can be reduced.

[2.3. Water and other ingredients
The slurry composition of the present invention usually contains water. Water functions as a medium or solvent or dispersion medium in the slurry composition. Usually, in the slurry composition, the non-conductive particles and the (meth) acrylic polymer (A) are dispersed in water. On the other hand, the water-soluble polymer is usually dissolved in water.

  Further, as a medium, a medium other than water may be used in combination with water. Examples of media that can be used in combination with water include cycloaliphatic hydrocarbon compounds such as cyclopentane and cyclohexane; aromatic hydrocarbon compounds such as toluene and xylene; ketone compounds such as ethyl methyl ketone and cyclohexanone; ethyl acetate and acetic acid Ester compounds such as butyl, γ-butyrolactone, ε-caprolactone; nitrile compounds such as acetonitrile and propionitrile; ether compounds such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, and the like And alcohol compounds; amide compounds such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide; One of these may be used alone, or two or more of these may be used in combination at any ratio. The amount of medium other than water is preferably 5 parts by weight or less with respect to 100 parts by weight of water.

  The amount of the solvent in the slurry composition is preferably set so that the solid content concentration of the slurry composition falls within a desired range. The solid content concentration of the specific slurry composition is preferably 10% by weight or more, more preferably 15% by weight or more, still more preferably 20% by weight or more, preferably 80% by weight or less, more preferably 75% by weight. % Or less, still more preferably 70% by weight or less, particularly preferably 65% by weight or less. In the present application, the solid content of the composition means a substance remaining after the composition is dried. By setting the solid content concentration to the above lower limit or more, a slurry composition having a suitable concentration can be easily produced, and therefore, water can be easily removed during the production of the porous film using the composition. The amount of water in the porous film can be reduced. By setting the solid content concentration to the upper limit or less, a slurry composition suitable for coating can be easily obtained.

  The slurry composition of the present invention may further contain acidic and / or basic components for adjusting the pH. Examples of such acidic and basic components include hydrogen chloride; ammonia (ammonium hydroxide); alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide; and calcium hydroxide and magnesium hydroxide. And alkaline earth metal hydroxides.

  Further, the slurry composition of the present invention includes, for example, isothiazoline compounds, pyrithione compounds, dispersants, leveling agents, antioxidants, thickeners other than those described above, particulate polymers, antifoaming agents, A wetting agent and an electrolyte solution additive having a function of inhibiting decomposition of the electrolyte solution may be included.

  The slurry composition of this invention can contain arbitrary components other than the component mentioned above. As such optional components, those which do not exert an excessively unfavorable influence on the battery reaction can be used. As an arbitrary component, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

  Since the slurry composition of this invention contains the binder composition for porous films of this invention as a binder, it can be made into a thing with low formaldehyde content. Specifically, the percentage of the amount of formaldehyde with respect to the amount of (meth) acrylic polymer (A) is preferably 30 ppm or less, more preferably 25 ppm or less, and even more preferably 20 ppm or less. Thus, the low formaldehyde content can reduce the environmental load in its use.

[2.4. Properties of slurry composition]
The slurry composition of the present invention is a slurry composition and can be prepared to have a viscosity suitable for application. The viscosity of the slurry composition of the present invention is preferably 50 mPa · s or more, more preferably 60 mPa · s or more, even more preferably 70 mPa · s or more, while preferably 200 mPa · s or less, more preferably 180 mPa · s. Hereinafter, it is still more preferably 150 mPa · s or less. By setting the viscosity of the slurry composition to be equal to or higher than the lower limit, occurrence of defective coating can be reduced and high high-temperature cycle characteristics can be achieved. By setting the viscosity of the slurry composition to be equal to or lower than the above upper limit, it is possible to achieve coating with little coating unevenness and to achieve high high-temperature cycle characteristics. The viscosity of the slurry composition is a value measured using a B-type viscometer at a temperature of 25 ° C. and a rotation speed of 60 rpm. The viscosity of the slurry composition can be adjusted by adjusting the type and amount of the water-soluble polymer and the content of other components.

[2.5. Method for producing slurry composition]
The slurry composition of the present invention can be produced by any production method. For example, the production can be performed by mixing the components of the slurry composition of the present invention in an arbitrary order.
In the mixing operation, if necessary, the above components, particularly non-conductive particles can be dispersed in the slurry composition using a disperser. As the disperser, it is preferable to use a medialess disperser because the particle size of the non-conductive particles is hardly reduced undesirably.
Furthermore, the pH can be adjusted as necessary before or after such mixing. The pH can be adjusted by appropriately adding an acid or a base.

[3. (Porous membrane)
The porous membrane for a secondary battery of the present invention (hereinafter sometimes simply referred to as a porous membrane) is formed using the slurry composition of the present invention. Specifically, the porous film of the present invention can be obtained by forming a layer of the secondary battery slurry composition of the present invention and drying it.

  In the porous membrane of the present invention, the (meth) acrylic polymer (A) reacts with a (meth) acrylamide monomer unit having an N-methylol group and a (meth) acrylamide monomer unit of a primary amine. The formed crosslinks are in the membrane. By having this bridge | crosslinking, a peel strength becomes favorable and it can improve the performance of a battery by it. Further, by having such cross-linking, it is possible to reduce the elution of the component of the (meth) acrylic polymer (A) into the electrolytic solution during the use of the secondary battery, thereby improving the battery performance. Can be improved.

  The layer of the slurry composition can be obtained by applying the slurry composition on a substrate. A base material is a member used as the object which forms the film | membrane of a slurry composition. There is no restriction | limiting in a base material, For example, the film | membrane of a slurry composition is formed in the surface of a peeling film, A solvent is removed from the film | membrane, a porous film may be formed, and a porous film may be peeled from a peeling film. However, normally, from the viewpoint of improving the production efficiency by omitting the step of peeling the porous film, the constituent elements of the battery are used as the base material. Examples of such battery components include separator substrates and electrode plates.

  Examples of the coating method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the dip method and the gravure method are preferable in that a uniform porous film can be obtained. Since the slurry composition of the present invention contains a specific composition and physical properties, its application is easy, a high-quality layer can be easily obtained, and the amount of moisture remaining in the porous film is reduced. Can be made.

  Specific examples of the method for drying the slurry composition layer include drying with warm air, hot air, low-humidity air, and the like; vacuum drying; drying by irradiation with infrared rays, far infrared rays, and electron beams. .

  The temperature during drying is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, particularly preferably 50 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower. By setting the drying temperature to be equal to or higher than the lower limit of the above range, the solvent and the low molecular weight compound from the slurry composition can be efficiently removed. Moreover, the deformation | transformation by the heat | fever of a base material can be suppressed by setting it as below an upper limit.

  The drying time is preferably 5 seconds or more, more preferably 10 seconds or more, particularly preferably 15 seconds or more, preferably 3 minutes or less, more preferably 2 minutes or less. By setting the drying time to be at least the lower limit of the above range, the solvent can be sufficiently removed from the slurry composition, so that the output characteristics of the battery can be improved. Moreover, manufacturing efficiency can be improved by setting it as an upper limit or less.

In the method for producing a porous membrane of the present invention, any operation other than those described above may be performed.
For example, the porous film may be subjected to pressure treatment by a pressing method such as a mold press and a roll press. By performing the pressure treatment, the binding property between the substrate and the porous film can be improved. However, from the viewpoint of keeping the porosity of the porous film within a preferable range, it is preferable to appropriately control the pressure and the pressurization time so as not to become excessively large.
In order to remove residual moisture, it is preferable to dry in, for example, vacuum drying or a dry room.

  The thickness of the porous membrane of the present invention is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.3 μm or more, preferably 20 μm or less, more preferably 15 μm or less, particularly preferably 10 μm or less. It is. By setting the thickness of the porous film to be equal to or more than the lower limit of the above range, the heat resistance of the porous film can be increased. Moreover, the fall of the ionic conductivity by a porous film can be suppressed by setting it as an upper limit or less.

[4. (Separator for secondary battery)
When a separator base material is used as the base material, a separator for a secondary battery including the separator base material and the porous membrane of the present invention is obtained. The porous membrane of the present invention may be provided on only one side of the separator substrate, or may be provided on both sides.
In the secondary battery, when the separator provided with the porous membrane of the present invention is used as a separator, the peel strength of the porous membrane is high, and effects such as gas trapping can be expressed. The performance of the secondary battery can be improved, and the volume change accompanying the charge / discharge of the secondary battery can be reduced. In addition, due to the low formaldehyde content of the binder for the secondary battery porous membrane, the secondary battery manufacturing process using the secondary battery separator, and the disposal process of the secondary battery after use, etc. The amount of formaldehyde released into the environment can be reduced.

  As the separator substrate, for example, a porous substrate having fine pores can be used. By using such a separator base material, it is possible to prevent a short circuit without interfering with charge / discharge of the battery in the secondary battery. Specific examples of the separator substrate include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene resins and polypropylene resins, aromatic polyamide resins, and cellulose.

  The thickness of the separator substrate is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 40 μm or less, more preferably 30 μm or less. Within this range, the resistance due to the separator substrate in the secondary battery is reduced, and the workability during battery production is excellent.

[5. Secondary battery electrode)
When an electrode plate is used as the substrate, an electrode for a secondary battery comprising the electrode plate and the porous film of the present invention is obtained. In the present application, the “electrode plate” refers to a member other than the porous film among the electrodes including the porous film. The electrode plate usually includes a current collector and an electrode active material layer. The electrode for a secondary battery including the electrode plate and the porous film of the present invention usually includes a current collector, an electrode active material layer, and the porous film of the present invention in this order. For example, when the electrode active material layer is provided only on one side of the current collector in the electrode plate, a layer configuration of current collector / electrode active material layer / porous film can be taken. Further, for example, in the electrode plate, when electrode active material layers are provided on both sides of the current collector, a layer configuration of porous film / electrode active material layer / current collector / electrode active material layer / porous film can be taken.

  In the secondary battery, when an electrode including the porous membrane of the present invention is used as an electrode, the peel strength of the porous membrane is high and effects such as gas capture can be expressed. The performance of the secondary battery can be improved, and the volume change accompanying the charge / discharge of the secondary battery can be reduced. Moreover, due to the low formaldehyde content of the binder for the secondary battery porous membrane, the process of manufacturing the secondary battery using the electrode for the secondary battery and the process of disposal after use of the secondary battery The amount of formaldehyde released into the environment can be reduced.

[5.1. Current collector]
As the current collector of the electrode plate, an electrically conductive and electrochemically durable material can be used. Usually, a metal material is used as the material of the current collector. Examples thereof include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, the current collector used for the positive electrode is preferably aluminum, and the current collector used for the negative electrode is preferably copper. Moreover, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.

[5.2. Electrode active material layer
The electrode active material layer is a layer provided on the current collector and includes an electrode active material. There are various types of electrode active materials depending on the types of secondary batteries. Here, electrode active materials for lithium ion secondary batteries will be described in particular. However, the electrode active material is not limited to those listed below.

  As the electrode active material of the lithium ion secondary battery, a material capable of reversibly inserting or releasing lithium ions by applying a potential in an electrolytic solution can be used. As the electrode active material, an inorganic compound or an organic compound may be used.

The positive electrode active material is roughly classified into those made of inorganic compounds and those made of organic compounds. Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, and Mn. Specific examples of the inorganic compound used for the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO _{4, and} other lithium-containing composite metal oxides; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _13, etc. Can be mentioned. On the other hand, examples of the positive electrode active material made of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.

Furthermore, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
These positive electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Moreover, you may use the mixture of the above-mentioned inorganic compound and organic compound as a positive electrode active material.

  The particle diameter of the positive electrode active material can be selected in consideration of other constituent elements of the secondary battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the volume average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 50 μm or less, more preferably 20 μm or less. It is. When the volume average particle diameter of the positive electrode active material is within this range, a battery having a large charge / discharge capacity can be obtained, and handling of the electrode slurry composition and the electrode is easy.

  The ratio of the positive electrode active material in the electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, and preferably 99.9% by weight or less, more preferably 99% by weight or less. By setting the amount of the positive electrode active material in the above range, the capacity of the secondary battery can be increased, and the flexibility of the positive electrode and the binding property between the current collector and the positive electrode active material layer can be improved.

  Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, artificial graphite, mesocarbon microbeads, pitch-based carbon fibers, and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used. Furthermore, an electrode active material having a conductive material attached to the surface by a mechanical modification method may be used. These negative electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the secondary battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, the volume average particle diameter of the negative electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more. Is 100 μm or less, more preferably 50 μm or less, and still more preferably 20 μm or less.

The specific surface area of the negative electrode active material, the output from the viewpoint of improving the density, preferably ^2m 2 / g or more, more preferably ^3m 2 / g or more, more preferably ^{5 m} 2 / g or more, and preferably ^{20 m} 2 / g or less, more preferably 15 m ² / g or less, and further preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

  The ratio of the negative electrode active material in the electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, and preferably 99% by weight or less, more preferably 97% by weight or less. By setting the amount of the negative electrode active material in the above range, it is possible to realize a negative electrode that exhibits excellent flexibility and binding properties while exhibiting high capacity.

  The electrode active material layer preferably contains an electrode binder in addition to the electrode active material. By including the binder for the electrode, the binding property of the electrode active material layer is improved, and the strength against the mechanical force applied in the process of winding the electrode is increased. In addition, since the electrode active material layer is less likely to be peeled off from the current collector and the porous film, the risk of short-circuiting due to the detached desorbed material is reduced.

  As the electrode binder, for example, a polymer can be used. Examples of the polymer that can be used as an electrode binder include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, poly An acrylonitrile derivative or the like may be used.

Furthermore, the soft polymer particles exemplified below may be used as the particulate polymer. As a soft polymer, for example,
(I) Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer, etc. An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative or a copolymer thereof with a monomer copolymerizable therewith;
(Ii) isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
(Iii) Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene・ Diene-based soft polymers such as butadiene, styrene, block copolymers, isoprene, styrene, block copolymers, styrene, isoprene, styrene, block copolymers;
(Iv) silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
(V) Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer Olefinic soft polymers such as polymers;
(Vi) Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
(Vii) epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
(Viii) Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
(Ix) Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer, and the like. These soft polymers may have a cross-linked structure or may have a functional group introduced by modification.
The polymer may be in the form of particles or non-particulates.
Furthermore, the binder for electrodes may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the binder for the electrode in the electrode active material layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the electrode active material. It is preferably 5 parts by weight or less, more preferably 3 parts by weight or less. When the amount of the electrode binder is within the above range, it is possible to prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction.

  The electrode active material layer may contain any component other than the electrode active material and the electrode binder as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductive material and a reinforcing material. Moreover, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube; carbon powder such as graphite; fibers and foils of various metals; . By using a conductive material, electrical contact between electrode active materials can be improved, and battery characteristics such as cycle characteristics can be improved.

The specific surface area of the conductive material is preferably 50 m ² / g or more, more preferably 60 m ² / g or more, particularly preferably 70 m ² / g or more, preferably 1500 m ² / g or less, more preferably 1200 m ² / g. Hereinafter, it is particularly preferably 1000 m ² / g or less. By setting the specific surface area of the conductive material to be equal to or higher than the lower limit of the above range, the low-temperature output characteristics of the secondary battery can be improved. Moreover, the binding property of an electrode active material layer and an electrical power collector can be improved by setting it as an upper limit or less.

  As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using the reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be obtained.

  The amount of the conductive material and the reinforcing agent used is usually 0 part by weight or more, preferably 1 part by weight or more, preferably 20 parts by weight or less, more preferably 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is as follows.

  The thickness of the electrode active material layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 300 μm or less, more preferably 250 μm or less for both the positive electrode and the negative electrode.

  The method for producing the electrode active material layer is not particularly limited. The electrode active material layer can be produced by, for example, applying an electrode active material and a solvent, and, if necessary, an electrode slurry composition containing an electrode binder and optional components onto a current collector and drying it. As the solvent, either water or an organic solvent can be used.

[6. Secondary battery)
The secondary battery of the present invention includes the porous film of the present invention. A secondary battery usually includes a positive electrode, a negative electrode, and an electrolyte, and satisfies the following requirement (A), the requirement (B), or both the requirements (A) and (B).
(A) At least one of the positive electrode and the negative electrode of the secondary battery of the present invention is an electrode including the electrode plate and the porous film of the present invention.
(B) The secondary battery of the present invention includes a separator, and the separator includes a separator base material and the porous film of the present invention.

  By providing the porous membrane of the present invention, the secondary battery of the present invention can enjoy its high peel strength, gas trapping effect, etc., and improve performance such as rate characteristics and high temperature cycle characteristics. It is possible to reduce the volume change accompanying charging and discharging. Further, due to the low formaldehyde content of the binder for the secondary battery porous membrane, it is released to the environment in the process of manufacturing the secondary battery of the present invention and in the process of disposal after use of the secondary battery. The amount of formaldehyde can be reduced.

[6.1. separator〕
In principle, the secondary battery of the present invention includes a separator including the porous film of the present invention as a separator. However, in the case where the secondary battery of the present invention includes a battery including the porous film of the present invention as at least one of a positive electrode and a negative electrode, a separator other than the separator including the porous film of the present invention may be provided as a separator. Moreover, since the porous film in the electrode provided with the porous film of the present invention has a function as a separator, the separator may be omitted when the electrode includes the porous film of the present invention.

[6.2. electrode〕
In principle, the secondary battery of the present invention includes an electrode including the porous film of the present invention as one or both of a positive electrode and a negative electrode. However, when the secondary battery of the present invention includes a separator including the porous film of the present invention as a separator, an electrode that does not include the porous film of the present invention may be provided as both a positive electrode and a negative electrode.

[6.3. Electrolyte)
As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. 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. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the supporting electrolyte is preferably 1% by weight or more, more preferably 5% by weight or more, preferably 30% by weight or less, more preferably 20% by weight or less, as the concentration in the electrolytic solution. By keeping the amount of the supporting electrolyte within this range, the ion conductivity can be increased and the charging characteristics and discharging characteristics of the secondary battery can be improved.

  As a solvent used for the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of such a solvent include alkyl carbonate compounds such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC). Ester compounds such as γ-butyrolactone and methyl formate; ether compounds such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. A solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, electrolyte solution may contain an additive as needed. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

[6.4. Secondary battery manufacturing method)
The manufacturing method of the secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode may be overlapped via a separator, and this may be wound or folded in accordance with the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed. Furthermore, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily set within the scope of the claims and equivalents of the present invention. Can be changed and implemented. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified.

  In Examples and Comparative Examples, evaluation of separator peel strength, evaluation of secondary battery rate characteristics, evaluation of secondary battery high temperature cycle characteristics, evaluation of cell volume change, measurement of THF insoluble components, and formaldehyde content The quantity measurement was performed as follows.

[Peel strength]
The separators obtained in the examples and comparative examples were cut into rectangles having a width of 10 mm and a length of 100 mm to obtain test pieces. Cellophane tape (specified in JIS Z1522) was attached to the porous film surface of the test piece. The cellophane tape is fixed to the horizontal surface of the test table in a flat state, and one end of the separator is pulled at a pulling speed of 10 mm / min in the direction of 180 ° C. toward the end facing the one end of the separator. Stress was measured. The measurement was performed three times, the average value was obtained, and this was taken as the peel strength, and evaluated according to the following criteria. The higher the peel strength, the greater the binding force between the porous membrane and the separator substrate, that is, the higher the adhesion strength.

A: Peel strength is 150 N / m or more B: Peel strength is 100 N / m or more and less than 150 N / m C: Peel strength is 50 N / m or more and less than 100 N / m D: Peel strength is less than 50 N / m

[Evaluation of rate characteristics of secondary battery]
The lithium ion secondary batteries obtained in Examples and Comparative Examples were allowed to stand for 24 hours in an environment at 25 ° C., and then charge / discharge operation was performed at a charge / discharge rate of 4.2 V and 0.1 C. . Thereafter, the battery is charged to 4.2 V at a charge rate of 0.1 C at 25 ° C., discharged to 3.0 V at a discharge rate of 1.0 C, and discharged to 3.0 V at a discharge rate of 3.0 C. Each charge / discharge cycle was performed. The ratio of the battery capacity at 3.0C to the battery capacity at 1.0C was calculated as a percentage to obtain the charge / discharge rate characteristics, and was judged according to the following criteria. The higher this value, the smaller the internal resistance, indicating that high speed charge / discharge is possible.
(Evaluation criteria)
A: Charging / discharging rate characteristic is 80% or more.
B: Charging / discharging rate characteristic is 70% or more and less than 80% C: Charging / discharging rate characteristic is 60% or more and less than 70% D: Charging / discharging rate characteristic is less than 60%

[Evaluation of high-temperature cycle characteristics of secondary batteries]
The lithium ion secondary batteries obtained in Examples and Comparative Examples were allowed to stand for 24 hours in an environment at 25 ° C., and then charged at 4.35 V and 0.1 C in an environment at 25 ° C., 2.75 V. The charge / discharge operation was performed at a discharge of 0.1 C, and the initial capacity C0 was measured. Further, under a 60 ° C. environment, a charge / discharge cycle with one cycle of 4.35 V and 0.1 C charge and 2.75 V and 0.1 C discharge was repeated, and the capacity C1 after 1000 cycles was measured. From the values of C0 and C1, the capacity retention rate was determined by the formula ΔC = (C1 / C0) × 100 (%) and evaluated according to the following criteria. Higher values indicate better high temperature cycle characteristics.

A: Capacity maintenance ratio is 70% or more B: Capacity maintenance ratio is 60% or more and less than 70% C: Capacity maintenance ratio is 50% or more and less than 60% D: Capacity maintenance ratio is less than 50%

[Evaluation of cell volume change]
The batteries obtained in Examples and Comparative Examples were allowed to stand for 24 hours in an environment of 25 ° C. Thereafter, in an environment of 25 ° C., a charge / discharge operation was performed in which the battery was charged at 0.1 C to 4.35 V and discharged at 0.1 C to 2.75 V. Thereafter, the battery was immersed in liquid paraffin and its volume V0 was measured.
Furthermore, in a 60 ° C. environment, an operation of charging and discharging, which was charged to 0.15 C at 4.35 V and discharged at 0.1 C to 2.75 V, was repeated 1000 cycles. Thereafter, the battery was immersed in liquid paraffin, and its volume V1 was measured.
The volume change ΔV of the battery cell before and after repeating 1000 cycles of charge / discharge was calculated by the formula ΔV = (V1−V0) / V0 × 100 (%) and evaluated according to the following criteria. It shows that it is excellent in the capability to suppress generation | occurrence | production of gas, so that the value of this volume variation | change_quantity (DELTA) V is small.

A: ΔV value is less than 20% B: ΔV value is 20% or more and less than 30% C: ΔV value is 30% or more and less than 40% D: ΔV value is 40% or more

[Measurement of THF-insoluble components]
The aqueous dispersion containing the particulate (meth) acrylic polymer obtained in the step of producing the (meth) acrylic polymer in the examples and comparative examples was dried at room temperature for 2 days to obtain a polymer film. Was made. The polymer film was cut into a large number of small square pieces having a side length of about 1 mm. About 1.5 g of a small piece was weighed and weighed, and after measuring the weight W0, it was immersed in tetrahydrofuran for 3 days. After immersion, the small piece was taken out from tetrahydrofuran, dried in a vacuum dryer at 100 ° C. for 3 hours, the weight of the small piece was measured again, and the weight W1 was measured. The amount of THF insoluble component was calculated by the formula: amount of THF insoluble component (%) = W1 / W0 × 100.
It shows that there are few components of the (meth) acrylic polymer which can be eluted to electrolyte solution, so that THF insoluble component amount is large.

[Measurement of formaldehyde content]
The aqueous dispersion containing the particulate (meth) acrylic polymer obtained in the step of producing the (meth) acrylic polymer in Examples and Comparative Examples was solidified with 3% hydrochloric acid and filtered, and the solution was filtered. Obtained. This solution was placed in a 20 ml volumetric flask and diluted to 20 ml with water to obtain a diluted solution. This diluted solution was put into a separatory funnel, and 10 ml of 2,4-dinitrophenylhydrazine (DNPH) / 10% hydrochloric acid solution was added and allowed to stand for 24 hours. To this solution was added 5 ml of chloroform, the DNPH derivative was transferred to the chloroform phase, the chloroform phase was analyzed by HPLC, the formaldehyde content was measured, and the amount of (meth) acrylic polymer in the aqueous dispersion was used as a reference. The parts per million (ppm) was determined. As a standard solution, a commercially available formaldehyde 2,4-dinitrophenylhydrazone standard solution 40 μg (formaldehyde) / ml (acetonitrile solution) was appropriately diluted.

HPLC conditions Column: UnisilQ C18 5 μm (manufactured by GL Sciences Inc.)
Length: 250mm x 4.6φ
Temperature: 40 ° C
Mobile phase: CH ₃ CN / H ₂ O = 55/45 (20 min)
Measurement wavelength: 360 nm

<Example 1>
(1-1. Production of (meth) acrylic polymer)
In a 5 MPa pressure vessel equipped with a stirrer, 100.0 parts of the monomer composition, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and 0.3 part of potassium persulfate as a polymerization initiator are sufficient. Then, the mixture was heated to 50 ° C. to initiate polymerization. The monomer composition was composed of 92.8 parts of n-butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, 1.6 parts of N-methylolacrylamide and 1.6 parts of acrylamide. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate polymer. After adding a 5% aqueous sodium hydroxide solution to the mixture containing the particulate polymer and adjusting to pH 6, the unreacted monomer is removed by heating under reduced pressure, and the mixture is cooled to 30 ° C. or lower to obtain particles. An aqueous dispersion containing a (meth) acrylic polymer was obtained.
Using the obtained aqueous dispersion containing the (meth) acrylic polymer as a sample, the THF-insoluble component amount and formaldehyde content of the (meth) acrylic polymer were measured. The volume average particle diameter of the particulate (meth) acrylic polymer was 380 nm, and the glass transition temperature was −40 ° C.

(1-2. Production of slurry composition for porous membrane)
As non-conductive particles, alumina particles (average particle size 0.5 μm, BET specific surface area 5.0 m ² / g) 100 parts, carboxymethylcellulose sodium salt (“1220” manufactured by Daicel Corporation) 2 parts, and the step (1-1) 6 parts (corresponding to solid content) of the (meth) acrylic polymer obtained in (1) was mixed, and further mixed with water to adjust the solid content concentration to 40% by weight. A composition was prepared.

(1-3. Production of separator with porous membrane)
On a single-layer polypropylene separator substrate (“Celguard 2500” manufactured by Celgard), the slurry composition for porous film obtained in the above step (1-2) was coated with a gravure coater and the coating amount after drying was 6 mg. / Cm < ² > was applied and dried. This drying was performed by conveying the separator base material in an oven at 100 ° C. at a speed of 20 m / min for 1 minute. Thereby, the separator provided with the separator base material and the porous film formed on one surface thereof was obtained.
About the obtained separator, the peel strength was measured.

(1-4. Production of positive electrode)
100 parts of LiCoO ₂ (volume average particle diameter D50: 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 PVDF (binder for the positive electrode active material layer) Polyvinylidene fluoride, manufactured by Kureha Co., Ltd., # 7208) was mixed with 2 parts corresponding to the solid content and NMP (N-methylpyrrolidone) to make the total solid content concentration 70%. These were mixed by a planetary mixer to obtain 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, the positive electrode raw material was rolled by a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 95 μm.

(1-5. Production of negative electrode)
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, ion exchange After adding 150 parts of water and 0.5 part of potassium peroxodisulfate as a polymerization initiator and stirring sufficiently, the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing the negative electrode active material layer binder (SBR). A 5% aqueous sodium hydroxide solution was added to the mixture containing the negative electrode active material layer binder, and the pH was adjusted to 8. Then, unreacted monomers were removed by heating under reduced pressure. Then, it cooled to 30 degrees C or less, and obtained the water dispersion liquid containing the binder for desired negative electrode active material layers.

  A mixture of 100 parts of artificial graphite (volume average particle diameter D50: 15.6 μm) and 1 part of a 2% aqueous solution of sodium salt of carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC350HC) as a thickener. The solid content was adjusted to 68% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Furthermore, after adjusting to 62% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC. The above-mentioned binder for negative electrode active material layer (SBR) was added in an amount corresponding to a solid content of 1.5 parts and ion-exchanged water, adjusted to a final solid content concentration of 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to prepare a slurry composition for 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. Then, the negative electrode original fabric was rolled by a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 100 μm.

(1-6. Production of lithium ion secondary battery)
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained in the step (1-4) was cut into a square of 4.6 cm × 4.6 cm to obtain a rectangular positive electrode. The separator obtained in the step (1-3) was cut into a 5.5 cm × 5.5 cm square to obtain a rectangular separator. Furthermore, the negative electrode obtained in the step (1-5) was cut into a 5 cm × 5 cm square to obtain a rectangular negative electrode. A rectangular positive electrode was placed in the packaging material exterior so that the current collector-side surface was in contact with the aluminum packaging exterior. On the surface of the rectangular positive electrode on the positive electrode active material layer side, a rectangular separator was disposed so that the surface on the porous membrane side was in contact with the rectangular positive electrode. Further, a rectangular negative electrode was placed on the separator so that the surface on the negative electrode active material layer side faces the separator. An electrolytic solution (solvent: EC / EMC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF ₆ having a concentration of 1 M) was injected so that no air remained. Further, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the exterior of the aluminum packaging material, and a lithium ion secondary battery was manufactured.
About this lithium ion secondary battery, the rate characteristic, the high temperature cycling characteristic, and the cell volume variation | change_quantity were evaluated.

<Example 2>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 94.0 parts of butyl acrylate, 1.8 parts of acrylonitrile, 1.8 parts of methacrylic acid, and N-methylolacrylamide. The composition was changed to 2 parts and 1.2 parts of acrylamide.

<Example 3>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 88.6 parts of butyl acrylate, 2.5 parts of acrylonitrile, 2.5 parts of methacrylic acid, and N-methylolacrylamide. The composition was changed to 2 parts and 3.2 parts of acrylamide.

<Example 4>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 90.3 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. The amount was changed to 2 parts and 2.5 parts of acrylamide.

<Example 5>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 90.3 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, N-methylol acrylamide. The amount was changed to 5 parts and 3.2 parts of acrylamide.

<Example 6>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by adding 93.6 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. The amount was changed to 8 parts and acrylamide 1.6 parts.

<Example 7>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 93.5 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. The amount was changed to 6 parts and 0.9 parts of acrylamide.

<Example 8>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In manufacture of the (meth) acrylic polymer of (1-1), monomer composition is made into 88.7 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, N-methylol acrylamide. The amount was changed to 5 parts and 4.8 parts of acrylamide.

<Example 9>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 94.2 parts of butyl acrylate, 0.6 part of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. 6 parts and acrylamide 1.6 parts.

<Example 10>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 92.0 parts of butyl acrylate, 2.8 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. 6 parts and acrylamide 1.6 parts.

<Example 11>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 94.2 parts of butyl acrylate, 2.0 parts of acrylonitrile, 0.6 parts of methacrylic acid, and N-methylolacrylamide. 6 parts and acrylamide 1.6 parts.

<Example 12>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 92.0 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.8 parts of methacrylic acid, and N-methylolacrylamide. 6 parts and acrylamide 1.6 parts.

<Comparative Example 1>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition was prepared by using 92.8 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide. The composition was changed to 6 parts and 1.6 parts of allyl glycidyl ether.

<Comparative Example 2>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition is composed of 92.8 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, β-hydroxyethyl acrylate 1 .6 parts and acrylamide 1.6 parts.

<Comparative Example 3>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
-In the manufacture of the (meth) acrylic polymer of (1-1), the monomer composition is composed of 92.8 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and 3.2 parts of acrylamide. It changed to what consists of.

<Comparative Example 4>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following matters were changed, and measurements and evaluations on the lithium ion secondary battery and its components were performed.
In the production of the (meth) acrylic polymer of (1-1), the monomer composition is composed of 92.8 parts of butyl acrylate, 2.0 parts of acrylonitrile, 2.0 parts of methacrylic acid, and N-methylolacrylamide 3 Changed to 2 parts.

  Evaluation results in Examples and Comparative Examples are shown in Tables 1 to 3.

The meanings of the abbreviations in the table are as follows.
BA ratio: The ratio of butyl acrylate in the monomer composition used for the preparation of the (meth) acrylic polymer (A). Unit weight%.
NMA ratio: Ratio of N-methylolacrylamide (β-HEA (hydroxyethyl acrylate) only in Comparative Example 2) in the monomer composition used for the preparation of the (meth) acrylic polymer (A). Unit weight%.
AAm ratio: The ratio of acrylamide (all glycidyl ether only in Comparative Example 1) in the monomer composition used for the preparation of the (meth) acrylic polymer (A). Unit weight%.
AAm / NMA: 100 parts by weight of N-methylolacrylamide (β-HEA (hydroxyethyl acrylate) only in Comparative Example 2) in the monomer composition used for the preparation of the (meth) acrylic polymer (A) Parts by weight of acrylamide (only Comparative Example 1 is allyl glycidyl ether).
AN ratio: ratio of acrylonitrile in the monomer composition used for the preparation of the (meth) acrylic polymer (A). Unit weight%.
MAA ratio: ratio of methacrylic acid in the monomer composition used for the preparation of the (meth) acrylic polymer (A). Unit weight%.
HA amount: Formaldehyde content in the aqueous dispersion containing the obtained (meth) acrylic polymer (A). The parts per million based on the amount of (meth) acrylic polymer in the aqueous dispersion.
THF-insoluble component amount: ratio of (meth) acrylic polymer (A) not dissolved in THF. Unit weight%.

  As shown from the results of Tables 1 to 3, in Examples using a slurry composition containing a predetermined (meth) acrylic polymer (A) as a binder, a low amount of formaldehyde can be achieved and electrolysis can be achieved. The components that could be eluted in the liquid could be reduced. Furthermore, high peel strength of the porous film, good rate characteristics and high-temperature cycle characteristics of the secondary battery, and low cell volume change could be realized in a well-balanced manner.

Claims (6)

A binder for a secondary battery porous membrane containing a (meth) acrylic polymer,
The (meth) acrylic polymer contains 50% by weight or more of an alkyl (meth) acrylate monomer unit, and has a (meth) acrylamide monomer unit having an N-methylol group, and a (meth) acrylate of a primary amine. ) A binder for a secondary battery porous membrane containing an acrylamide monomer unit. The proportion of (meth) acrylamide monomer units of the primary amine in the total monomer units of the (meth) acrylic polymer is 0.5 wt% or more and 5 wt% or less,
In the (meth) acrylic polymer, the ratio of the (meth) acrylamide monomer unit of the primary amine to 100 parts by weight of the (meth) acrylamide monomer unit having the N-methylol group is 50 parts by weight or more. The binder for secondary battery porous membranes of Claim 1 which is 200 weight part or less. The (meth) acrylic polymer further contains a (meth) acrylonitrile monomer unit,
The ratio of the (meth) acrylonitrile monomer unit in the total monomer units of the (meth) acrylic polymer is 0.5 wt% or more and 5 wt% or less. The binder for a secondary battery porous film according to the description.   The slurry composition for secondary battery porous films containing a nonelectroconductive particle and the binder for secondary battery porous films of any one of Claims 1-3.   The porous film for secondary batteries formed using the slurry composition for secondary battery porous films of Claim 4.   A secondary battery comprising the porous membrane for a secondary battery according to claim 5.