WO2012043729A1

WO2012043729A1 - Secondary-battery porous-membrane slurry, secondary-battery porous membrane, secondary-battery electrode, secondary-battery separator, secondary battery, and method for manufacturing secondary-battery porous membrane

Info

Publication number: WO2012043729A1
Application number: PCT/JP2011/072403
Authority: WO
Inventors: 金田　拓也; 琢也石井
Original assignee: 日本ゼオン株式会社
Priority date: 2010-09-30
Filing date: 2011-09-29
Publication date: 2012-04-05
Also published as: JP5605591B2; KR20130114152A; CN103262297B; JPWO2012043729A1; KR101921659B1; CN103262297A

Abstract

[Problem] To provide a high-strength, highly uniform secondary-battery porous membrane that is capable of improving the cycle characteristics of a resulting secondary battery and is manufactured using a secondary-battery porous-membrane slurry that exhibits excellent coating performance and contains highly-dispersed nonconductive particles. Also, to provide a secondary-battery electrode and secondary-battery separator having good shutdown functionality. [Solution] This secondary-battery porous-membrane slurry is characterized by containing organic-polymer-containing nonconductive particles, a binder, and a solvent, and is further characterized in that said binder contains particles (A) of an acrylic polymer that has a sulfonic acid group and particles (B) of an acrylic polymer that has an epoxy group.

Description

Secondary battery porous membrane slurry, secondary battery porous membrane, secondary battery electrode, secondary battery separator, secondary battery, and method for producing secondary battery porous membrane

The present invention relates to a secondary battery porous membrane slurry, and more specifically, a secondary battery porous membrane formed on the surface of an electrode or separator of a lithium ion secondary battery, which has high reliability and can contribute to improvement of battery cycle characteristics. The present invention relates to a secondary battery porous membrane slurry for manufacturing. The present invention also relates to a secondary battery electrode, a secondary battery separator and a secondary battery provided with such a secondary battery porous membrane.

Among the batteries in practical use, lithium ion secondary batteries exhibit the highest energy density, and are often used especially for small electronics. In addition to small-sized applications, development for automobiles is also expected. Among them, there is a demand for extending the life of lithium ion secondary batteries and further improving safety.

In general, a lithium-ion secondary battery uses a polyolefin-based organic separator such as polyethylene or polypropylene in order to prevent a short circuit between the positive electrode and the negative electrode. Since the polyolefin-based organic separator has a physical property of melting at 200 ° C. or lower, when the battery becomes hot due to internal or external stimulation, the organic separator shrinks or melts, and the volume of the organic separator is increased. Change. As a result, an explosion or the like may occur due to a short circuit between the positive electrode and the negative electrode, discharge of electric energy, or the like.

In order to solve the problems caused by using such a polyolefin-based organic separator, a layer (porous film) containing non-conductive particles such as inorganic particles on the polyolefin-based organic separator or on the electrode (positive electrode or negative electrode) ) Is proposed. Furthermore, in order to prevent thermal runaway due to an abnormal reaction of the battery, a porous film including polymer particles that are melted by heat and polymer particles that increase the degree of swelling into an electrolyte solution by heat has been proposed. When the temperature of the secondary battery rises abnormally due to a short circuit or the like, fine pores in the porous film are blocked by melting or swelling of the polymer particles, thereby preventing ions from passing between the electrodes. It is considered to have a function (shutdown function) that cuts off current and suppresses further temperature rise.

For example, Patent Document 1 describes a porous film containing heat-resistant resin fine particles and organic fine particles having a shutdown function for improving safety. Further, it is described that an ethylene-vinyl acetate polymer is used as a binder for a porous film.

Patent Document 2 describes a method for improving powder-off of inorganic filler from a porous film by using water-dispersible acrylic polymer particles having a hydrophilic group such as sulfonic acid as a binder. Further, it is described that a water-dispersible acrylic polymer particle can have a tough and flexible porous film by further having a crosslinkable group.

JP 2006-139978 A International Patent Publication WO2009 / 123168

However, according to the study of the present inventor, since the porous film described in Patent Document 1 uses an ethylene-vinyl acetate polymer as a binder, the heat-resistant resin fine particles in the slurry for forming the porous film And the dispersibility of the organic fine particles is not sufficient, and the uniformity of the porous film is poor. As a result, the porous membrane may not have sufficient strength and a shutdown function. Moreover, the porous film described in Patent Document 2 is excellent in dispersibility of the inorganic filler in the porous film slurry. However, when a hydrophilic group and a crosslinkable group are contained in the acrylic polymer particles as a binder, It was found that there is a tendency to cause a crosslinking reaction in the slurry production process because there are functional groups having reactivity with each other. Therefore, the coating property of the slurry becomes unstable over time, and as a result, the uniformity and strength of the porous film may be insufficient.

Therefore, the present invention can be produced using a secondary battery porous membrane slurry excellent in coatability and dispersibility of non-conductive particles, and can improve the cycle characteristics of the obtained secondary battery. It aims at providing a secondary battery porous membrane with high intensity. Moreover, it aims at providing the secondary battery electrode and secondary battery separator with a favorable shutdown function.

Therefore, as a result of the study by the present inventors, the uniformity and strength of the porous film can be improved by introducing a sulfonic acid group and an epoxy group into different acrylic polymer particles and using them as a binder. It was found that it can be improved. That is, by using a specific binder, the crosslinking reaction in the slurry production process can be suppressed, and the viscosity of the slurry can be reduced. Therefore, the dispersibility of non-conductive particles in the porous membrane slurry and the coating property of the porous membrane slurry can be improved, and a porous membrane having high uniformity and strength can be obtained. Further, the present inventor has improved the dispersibility of non-conductive particles in the porous membrane slurry and the coating property of the porous membrane slurry, so that in addition to the productivity of the porous membrane, the secondary using the porous membrane It has been found that the cycle characteristics of the battery are also improved.

The gist of the present invention aimed at solving such problems is as follows.
(1) comprising non-conductive particles containing an organic polymer, a binder and a solvent;
The secondary battery porous membrane slurry in which the binder contains acrylic polymer particles A having sulfonic acid groups and acrylic polymer particles B having epoxy groups.

(2) The secondary battery according to (1), wherein the content of the nonconductive particles per 100% by mass of the total solid is 70 to 97% by mass and the content of the binder is 0.5 to 20% by mass. Porous membrane slurry.

(3) The acrylic polymer particles A and the acrylic polymer particles B are
The secondary battery porous membrane slurry according to (1) or (2), comprising a (meth) acrylonitrile monomer unit and a (meth) acrylate monomer unit.

(4) In the acrylic polymer particles A and the acrylic polymer particles B,
The content ratio of the (meth) acrylonitrile monomer unit in the polymer particles is 2.5 to 40% by mass,
The secondary battery porous membrane slurry according to (3), wherein the content ratio of the (meth) acrylic acid ester monomer unit in the polymer particles is 60 to 97.5% by mass.

(5) Any of (1) to (4), wherein a weight ratio of the acrylic polymer particles A to the acrylic polymer particles B (acrylic polymer particles A / acrylic polymer particles B) is 0.3 to 3. The secondary battery porous membrane slurry according to 1.

(6) The content ratio of sulfonic acid groups in the acrylic polymer particles A is 0.04 to 5.8 mass%, and the content ratio of epoxy groups in the acrylic polymer particles B is 0.03 to 3.0 mass%. The secondary battery porous membrane slurry according to any one of (1) to (5).

(7) In the binder, the weight ratio of the sulfonic acid group in the acrylic polymer particle A to the epoxy group in the acrylic polymer particle B (sulfonic acid group / epoxy group) is 0.2 to 3. (6) The secondary battery porous membrane slurry according to any one of (6).

(8) The temperature at which the weight loss ratio of the non-conductive particles reaches 10% by mass when heated at a heating rate of 10 ° C./min in a nitrogen atmosphere by a thermobalance is 250 ° C. or more,
The non-conductive particles have an average particle size of 0.1 to 2.0 μm;
The secondary battery porous membrane slurry according to any one of (1) to (7), wherein the non-conductive particles have an average circularity of 0.900 to 0.995.

(9) A secondary battery porous membrane formed by forming the secondary battery porous membrane slurry according to any one of (1) to (8) above into a film and drying it.

(10) current collector,
An electrode active material layer comprising an electrode active material and an electrode binder, which is attached to the current collector; and
A secondary battery electrode comprising the secondary battery porous film according to (9), which is laminated on the surface of the electrode active material layer.

(11) Organic separator,
A secondary battery separator comprising the secondary battery porous film according to (9), which is laminated on the organic separator.

(12) A secondary battery including a positive electrode, a negative electrode, an organic separator, and an electrolyte solution, wherein the secondary battery porous film according to (9) is laminated on any of the positive electrode, the negative electrode, and the organic separator. Next battery.

(13) A method for producing a secondary battery porous membrane comprising a step of applying the secondary battery porous membrane slurry according to any one of (1) to (8) above to a substrate and then drying.

According to the present invention, a secondary battery for producing a secondary battery porous film that is excellent in uniformity and strength and can contribute to cycle characteristics of a secondary battery by including non-conductive particles and a binder having a characteristic composition. A porous membrane slurry is provided. The porous film slurry is excellent in dispersibility and coatability. Furthermore, the secondary battery porous membrane produced using the porous membrane slurry is laminated on the surface of the electrode or organic separator, thereby preventing non-conductive particles and electrode active material from detaching (powder-off). Excellent shutdown function (reliability).

Hereinafter, (1) secondary battery porous membrane slurry, (2) secondary battery porous membrane, (3) secondary battery electrode, (4) secondary battery separator, and (5) secondary battery of the present invention will be described in order. To do.

(1) Secondary Battery Porous Membrane Slurry The secondary battery porous membrane slurry of the present invention (hereinafter sometimes referred to as “porous membrane slurry”) is a slurry for forming a secondary battery porous membrane described later. . The porous film slurry contains non-conductive particles and a binder having a characteristic composition, and the non-conductive particles, the binder and optional components are uniformly dispersed in a solvent described later as a solid content.

(Non-conductive particles)
The nonconductive particles used in the present invention include an organic polymer. In the present invention, by using non-conductive particles containing an organic polymer, metal contamination (hereinafter sometimes referred to as “metal foreign matter”) that adversely affects the performance of the secondary battery is reduced. In addition, the production cost of the secondary battery porous membrane slurry can be reduced.

The non-conductive particles preferably contain divinylbenzene monomer units. The content ratio of the divinylbenzene monomer unit in the total monomer weight in the non-conductive particles is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, and particularly preferably 30 to 60% by mass. . By setting the content ratio of the divinylbenzene monomer unit within the above range, the crosslink density of the nonconductive particles is increased, so that the heat resistance of the nonconductive particles is improved, and the reliability of the obtained secondary battery porous film is also improved. improves.

The non-conductive particles preferably further contain an ethyl vinyl benzene monomer unit. The content ratio of the ethyl vinylbenzene monomer unit in the total monomer weight in the non-conductive particles is preferably 3.2 to 48% by mass, more preferably 10 to 40% by mass. By making the content rate of an ethyl vinylbenzene monomer unit into the said range, while the binding property with the binder mentioned later becomes favorable, the softness | flexibility of the secondary battery porous film obtained becomes favorable. Further, when the secondary battery porous film is laminated on the electrode to produce a secondary battery electrode, it is possible to prevent the electrode active material from being detached (powder falling). As a result, the secondary battery using the secondary battery porous film exhibits excellent cycle characteristics.

The content ratio (divinylbenzene / ethylvinylbenzene) of the divinylbenzene monomer unit and the ethylvinylbenzene monomer unit contained in the nonconductive particles is preferably 1.0 to 5.25, more preferably 1. It is 25 to 5.00, particularly preferably 1.25 to 4.75. By setting the content ratio of the divinylbenzene monomer unit and the ethylvinylbenzene monomer unit contained in the nonconductive particles within the above range, the crosslink density of the nonconductive particles is increased, so that the heat resistance of the nonconductive particles is increased. Improves. As a result, the flexibility and strength of the obtained secondary battery porous membrane are improved. In addition, when a secondary battery electrode is produced, the electrode active material can be prevented from being detached (powder falling), and therefore a secondary battery using the secondary battery porous film exhibits excellent cycle characteristics.

The non-conductive particles preferably contain a polar group-containing monomer in addition to the two types of monomer units.

The polar group-containing monomer is a monomer that contains a polar group in the molecular structure and can be copolymerized with divinylbenzene and ethylvinylbenzene. A polar group refers to a functional group that can dissociate in water or a functional group having polarization. Specifically, a carboxyl group, a sulfonic acid group, a hydroxyl group, an amide group, a cationic group, a cyano group, an epoxy group, and the like. Is mentioned.

Examples of the carboxyl group-containing monomer include monocarboxylic acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof.
Monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid , Β-diaminoacrylic acid and the like.
Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid.
Examples of the dicarboxylic acid anhydride include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
Dicarboxylic acid derivatives include maleic esters such as methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

Examples of the sulfonic acid group-containing monomer include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropane sulfonic acid. And 3-allyloxy-2-hydroxypropanesulfonic acid.

Examples of the hydroxyl group-containing monomer include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate Ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate and di-2-hydroxypropyl itaconate Alkanol esters of acids; general formula CH ₂ ═CR ¹ —COO— (C _n H _2n O) _m —H (m is an integer from 2 to 9, n is an integer from 2 to 4, R ¹ is a hydrogen or methyl group 2-hydroxy ester of polyalkylene glycol and (meth) acrylic acid represented by Mono (meth) acrylic esters of dihydroxy esters of dicarboxylic acids such as til-2 ′-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether; Vinyl ethers such as 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2- Mono (meth) allyl ethers of alkylene glycols such as hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3 -Mono (meth) allyl ethers of halogen and hydroxy-substituted products of (poly) alkylene glycol, such as hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; polyphenols such as eugenol, isoeugenol (Meth) allylthio of alkylene glycol such as (meth) allyl-2-hydroxyethylthioether, (meth) allyl-2-hydroxypropylthioether, and the like Ether compounds; and the like.

Examples of the amide group-containing monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide and the like.

Examples of the cationic group-containing monomer include dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylate.

Examples of the cyano group-containing monomer include vinyl cyanide compounds such as acrylonitrile and methacrylonitrile.

Examples of the epoxy group-containing monomer include glycidyl acrylate and glycidyl methacrylate.

As salts of carboxyl group-containing monomers, sulfonic acid group-containing monomers, hydroxyl group-containing monomers, amide group-containing monomers, cationic group-containing monomers, and cyano group-containing monomers, the monomers listed above and appropriate combinations thereof can be used. Composed of various ions, alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, organic amine salts such as ammonium salt, monoethanolamine salt and triethanolamine salt Can be mentioned.

As the polar group-containing monomer, a carboxyl group-containing monomer and an amide group-containing monomer are preferable, and acrylic acid, methacrylic acid, itaconic acid, and acrylamide are particularly preferable.

The content ratio of the polar group-containing monomer in the total monomer weight in the non-conductive particles is preferably 0.05 to 4% by mass, more preferably 0.1 to 3% by mass, and particularly preferably 0.2 to 2%. % By mass. When the content ratio of the polar group-containing monomer in the total monomer weight in the non-conductive particles is in the above range, excellent dispersibility and low moisture content on the surface of the non-conductive particles have excellent cycle characteristics. Show.

The non-conductive particles may contain an arbitrary monomer unit in addition to the above three types of monomer units. Examples of the optional monomer include polyvalent (meth) acrylate compounds, aromatic monovinyl compounds, (meth) acrylic acid ester monomers, conjugated diene monomers, vinyl ester compounds, and α-olefin compounds. Two or more of these monomers may be contained in the nonconductive particles.

Examples of the polyvalent (meth) acrylate compound include polyethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexane glycol diacrylate, neopentyl glycol diacrylate, polypropylene glycol diacrylate, and 2,2′-bis. Diacrylate compounds such as (4-acryloxypropyroxyphenyl) propane and 2,2′-bis (4-acryloxydiethoxyphenyl) propane; trimethylolpropane triacrylate, trimethylolethane triacrylate, tetramethylolmethane triacrylate Triacrylate compounds such as; tetraacrylate compounds such as tetramethylol methane tetraacrylate; ethylene glycol dimethacrylate, diethylene glycol Dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexane glycol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol Dimethacrylate compounds such as dimethacrylate, polypropylene glycol dimethacrylate, and 2,2′-bis (4-methacryloxydiethoxyphenyl) propane; and trimethacrylate compounds such as trimethylolpropane trimethacrylate and trimethylolethane trimethacrylate . Among these, it is preferable to use ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate.

Examples of the aromatic monovinyl compound include styrene, α-methylstyrene, fluorostyrene, vinyl pyridine and the like.

Examples of the acrylate monomer include butyl acrylate, 2-ethylhexyl ethyl acrylate, N, N′-dimethylaminoethyl acrylate, and the like.

Examples of the methacrylic acid ester monomer include butyl methacrylate, 2-ethylhexyl methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, N, N′-dimethylaminoethyl methacrylate and the like.

Examples of the conjugated diene monomer include butadiene and isoprene.

Examples of vinyl ester compounds include vinyl acetate.

Examples of α-olefin compounds include 4-methyl-1-pentene.

Any one of the above monomers can be used alone or in combination of two or more. Among the above optional monomers, styrene, methyl methacrylate, or a combination thereof is particularly preferable from the viewpoint of reactivity with divinylbenzene and ethylvinylbenzene.

The content ratio of arbitrary monomer units in the total monomer weight in the non-conductive particles is preferably 3 to 80% by mass, more preferably 4 to 70% by mass, and particularly preferably 5 to 60% by mass. . In particular, when styrene and / or methyl methacrylate is included as an optional monomer, the preferable content ratio is 4.5 to 76.5% by mass based on the total amount of monomers constituting the non-conductive particles. is there. In the case where both styrene and methyl methacrylate are contained, it is preferable that the sum thereof is within this range. By setting the content ratio of styrene and / or methyl methacrylate to 76.5% by mass or less, the heat resistance of the non-conductive particles can be improved, the heat resistance of the porous film can be improved, and thus at a high temperature. Generation | occurrence | production of the short circuit of a battery can be reduced. On the other hand, by setting the content ratio of styrene and / or methyl methacrylate to 4.5% by mass or more, it is possible to prevent the dispersibility of the nonconductive particles from being lowered, to increase the strength of the porous film, and to achieve film uniformity. Can also be obtained.

(Method for producing non-conductive particles)
The production method of the non-conductive particles is not particularly limited, and the emulsion polymerization method or the soap-free polymerization method is performed by dissolving or dispersing the monomer constituting the non-conductive particles and other optional components as necessary in a dispersion medium. To polymerize in such a dispersion.

In emulsion polymerization, it is preferable to carry out the polymerization in a plurality of stages in order to obtain a desired particle diameter and average circularity. For example, a seed polymer particle is formed by first polymerizing a part of the monomer constituting the non-conductive particle, and then the other polymer is absorbed in the seed polymer particle and polymerized in that state. To produce non-conductive particles (seed polymerization method). Furthermore, when forming the seed polymer particles, the polymerization can be further divided into a plurality of stages.

More specifically, for example, the seed polymer particle A is formed by using a part of the monomer constituting the nonconductive particle, and the seed polymer particle A and another single amount constituting the nonconductive particle. A seed polymer particle B having a larger particle size using the body, and further, the seed polymer particle B, the remaining monomers constituting the non-conductive particles, and other optional components as necessary Can be used to form non-conductive particles having a larger particle size.
Thus, there is an advantage that a desired particle diameter and average circularity can be stably obtained by forming seed polymer particles by a two-step reaction and further forming non-conductive particles. In this case, using a part or all (preferably all) of the polar group-containing monomers of the monomers constituting the non-conductive particles when forming the seed polymer particles A and the seed polymer particles B, This is preferable for ensuring the stability of the particles. Furthermore, in this case, it is possible to use styrene, which is an arbitrary monomer, as the monomer for forming the seed polymer particles A. When forming the seed polymer particles B and the non-conductive particles, the seed polymer particles It is preferable in order to ensure the absorbability of the monomer.

Since the case where the polymerization is performed in a plurality of stages as described above is also included, the monomer constituting the nonconductive particles is not in a state where all the monomers are mixed in the polymerization. Also good. When the polymerization is carried out in a plurality of stages, the composition of the monomer derived from the polymerization unit constituting the nonconductive particles in the finally obtained nonconductive particles constitutes the nonconductive particles described above. It is preferable that the composition ratio of the monomers to be satisfied is satisfied.

Examples of the medium used for the polymerization of the monomers constituting the nonconductive particles include water, organic solvents, and mixtures thereof. As the organic solvent, those which are inert to radical polymerization and do not inhibit the polymerization of monomers can be used. Specific examples of the organic solvent include alcohols such as methanol, ethanol, propanol, cyclohexanol and octanol, esters such as dibutyl phthalate and dioctyl phthalate, ketones such as cyclohexanone, and mixtures thereof. Preferably, an aqueous medium such as water is used as a dispersion medium, and emulsion polymerization can be performed as polymerization.

The amount ratio of these when the seed polymer particles and the monomer are reacted is preferably 2 to 19 parts by weight, more preferably 3 to 16 parts by weight, based on 1 part by weight of the seed polymer particles. Even more preferably, it is 4 to 12 parts by mass. By making the usage-amount of a monomer 2 mass parts or more with respect to 1 mass part of seed polymer particles, the mechanical strength and heat resistance of the nonelectroconductive particle obtained can be improved. Moreover, since the monomer can be efficiently absorbed into the seed polymer particle by setting the amount of the monomer used to 19 parts by mass or less with respect to 1 part by mass of the seed polymer particle, a single amount that is not absorbed by the seed polymer particle. The body weight can be kept in a small range. In addition, since the particle size of the non-conductive particles can be controlled well, the generation of coarse particles having a wide particle size distribution and a large amount of fine particles can be prevented.

Specific operations for the polymerization include a method in which the monomer is added to the aqueous dispersion of seed polymer particles at a time, and a method in which the monomer is divided or continuously added while performing the polymerization. It is preferred that the monomer be absorbed by the seed polymer particles before polymerization begins and substantial crosslinking occurs in the seed polymer particles.
If the monomer is added after the middle of the polymerization, the monomer is not absorbed by the seed polymer particles, so that a large amount of fine particles are generated, the polymerization stability is deteriorated, and the polymerization reaction may not be maintained. Therefore, it is preferable to add all monomers to the seed polymer particles before the start of polymerization, or to finish adding all monomers before the polymerization conversion rate reaches about 30%. In particular, it is preferable to start the polymerization after the monomer is added to the aqueous dispersion of seed polymer particles and stirred before the polymerization starts, and the seed polymer particles absorb this.

An optional component can be added to the polymerization reaction system in addition to the monomer constituting the non-conductive particles and the dispersion medium. Specifically, components such as a polymerization initiator, a surfactant, and a suspension protective agent can be added. As the polymerization initiator, a general water-soluble radical polymerization initiator or oil-soluble radical polymerization initiator can be used, but a monomer that is not absorbed by the seed polymer particles rarely initiates polymerization in the aqueous phase. In view of this, it is preferable to use a water-soluble radical polymerization initiator. Examples of the water-soluble radical polymerization initiator include potassium persulfate, sodium persulfate, cumene hydroperoxide, hydrogen peroxide, or the water-soluble initiator or an oil-soluble initiator described later and a reducing agent such as sodium bisulfite. The redox initiator by the combination of these is mentioned. Oil-soluble radical polymerization initiators include benzoyl peroxide, α, α'-azobisisobutyronitrile, t-butylperoxy-2-ethylhexanoate, 3,5,5-trimethylhexanoyl A peroxide etc. can be mentioned. Of the oil-soluble radical polymerization initiators, t-butylperoxy-2-ethylhexanoate can be preferably used. In the polymerization reaction, it is preferable to add a small amount of a water-soluble polymerization inhibitor such as potassium dichromate, ferric chloride, or hydroquinone because generation of fine particles can be suppressed.
As the surfactant, a normal one can be used, and examples thereof include anionic emulsifiers such as sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dialkylsulfosuccinate, and a formalin condensate of naphthalenesulfonic acid. Furthermore, nonionic surfactants such as polyoxyethylene nonylphenyl ether, polyethylene glycol monostearate, sorbitan monostearate can be used in combination. Preferred examples of the suspension protective agent include polyvinyl alcohol, carboxymethyl cellulose, sodium polyacrylate, and a fine powder inorganic compound.

(Properties of non-conductive particles)
The shape of the non-conductive particles used in the present invention is not particularly limited, such as a spherical shape, a needle shape, a rod shape, a spindle shape, and a plate shape, but a spherical shape, a needle shape, and a spindle shape are preferable. Moreover, porous particles can also be used as the non-conductive particles. The content ratio of the non-conductive particles per 100% by mass of the total solid content of the porous membrane slurry is preferably 70 to 97% by mass, more preferably 80 to 95% by mass, and particularly preferably 85 to 95% by mass. By setting the content ratio of the nonconductive particles per 100% by mass of the total solid content of the porous membrane slurry within the above range, a porous membrane exhibiting high thermal stability can be obtained. In addition, desorption (powder removal) of non-conductive particles from the porous film can be suppressed, and a porous film having high strength can be obtained, and deterioration of battery characteristics such as cycle characteristics can be prevented.

It is preferable that the non-conductive particles have high heat resistance from the viewpoint of imparting heat resistance to the porous film and improving the reliability of a secondary battery electrode and a secondary battery separator described later. Specifically, the temperature at which the weight loss rate of the non-conductive particles reaches 10% by mass when heated at a heating rate of 10 ° C./min in a thermobalance analysis in a nitrogen atmosphere is preferably 250 ° C. or more, more preferably It is 300 ° C. or higher, particularly preferably 360 ° C. or higher. On the other hand, the upper limit of the temperature is not particularly limited, but can be, for example, 450 ° C. or less.

In the present invention, it is preferable to use non-conductive particles having a metal foreign matter content of 100 ppm or less. When non-conductive particles containing a large amount of metal foreign matter or metal ions are used, the metal foreign matter or metal ions are eluted in the porous membrane slurry, and this causes ionic crosslinking with the polymer in the porous membrane slurry. Aggregation results in a decrease in the porosity of the porous membrane. Therefore, there is a possibility that the rate characteristic (output characteristic) of the secondary battery using the porous film is deteriorated. As the metal, the inclusion of Ca, Co, Cu, Fe, Mg, Ni, Zn, Cr and the like is most undesirable. Therefore, the metal content in the non-conductive particles is preferably 100 ppm or less, more preferably 50 ppm or less, in terms of the total amount of these metal ions. The smaller the content, the less likely the battery characteristics will deteriorate. As used herein, “metal foreign matter” means a simple metal or a metal ion other than non-conductive particles. The content of the metal foreign matter in the non-conductive particles can be measured using ICP (Inductively Coupled Plasma).

The average particle diameter of the non-conductive particles used in the present invention is preferably 0.1 to 2 μm, more preferably 0.1 to 1 μm, and particularly preferably 0.1 to 0.8 μm. By making the average particle diameter of the non-conductive particles within the above range, it becomes easy to control the dispersion state of the porous film slurry, so that it becomes easy to produce a porous film having a uniform predetermined thickness. Moreover, since it can suppress that the particle filling rate in a porous film becomes high, it can suppress that the ionic conductivity in a porous film falls, and can implement | achieve the outstanding cycling characteristics. It is particularly preferable that the average particle diameter of the non-conductive particles is in the range of 0.1 to 0.8 μm because the dispersion, the ease of coating, and the controllability of the voids are excellent. The average particle diameter can be obtained from an average value obtained by observing an electron microscope and calculating (a + b) / 2 by taking the longest side of the particle image as a and the shortest side as b for 100 or more particles. .

The average circularity of the nonconductive particles used in the present invention is preferably 0.900 to 0.995, more preferably 0.91 to 0.98, and particularly preferably 0.92 to 0.97. By setting the average circularity of the non-conductive particles in the above range, the contact area between the non-conductive particles can be kept moderate, and the strength and heat resistance of the porous film can be improved. As a result, the reliability of the secondary battery using the porous film can be improved.

Further, the BET specific surface area of the non-conductive particles used in the present invention is specifically 0.9 to 200 m ² / from the viewpoint of suppressing aggregation of the non-conductive particles and optimizing the fluidity of the porous membrane slurry. g is preferable, and 1.5 to 150 m ² / g is more preferable.

The particle size distribution of the non-conductive particles is preferably 1.00 to 1.4, more preferably 1.00 to 1.3, and particularly preferably 1.00 to 1.2. By setting the particle size distribution of the non-conductive particles within the above range, a predetermined gap can be maintained between the non-conductive particles, so that the lithium migration is inhibited and the resistance is increased in the secondary battery of the present invention. This can be suppressed. In addition, the particle size distribution of the non-conductive particles is obtained by measuring the particle size with a laser diffraction scattering particle size distribution measuring device (LS230) manufactured by Beckman Co., Ltd., and then obtaining the volume average particle size V and the number average particle size. It can be determined by the ratio V / N with N.

(binder)
The binder used in the present invention includes acrylic polymer particles A having sulfonic acid groups and acrylic polymer particles B having epoxy groups. In the present invention, by using the binder containing the acrylic polymer particles A and the acrylic polymer particles B, gelation of the porous film slurry can be prevented, so that a uniform porous film can be formed. .

The acrylic polymer particle A having a sulfonic acid group includes a monomer unit having a sulfonic acid group. Specifically, the polymer as the acrylic polymer particle A includes a monomer unit having a sulfonic acid group.

Examples of monomers having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methyl. Examples thereof include propanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, sodium styrenesulfonate, and the like.

The content ratio of the monomer unit having a sulfonic acid group in the acrylic polymer particle A is preferably 0.3 to 10% by mass, more preferably 1.3 to 9% by mass. When the content ratio of the monomer unit having a sulfonic acid group in the acrylic polymer particle A is in the above range, the binder can be provided with a good binding property, and the non-conductive particles are detached from the porous film (powder off). ) Can be suppressed.

The content ratio of the sulfonic acid group in the acrylic polymer particles A is preferably 0.04 to 5.8% by mass, more preferably 0.1 to 4% by mass, and particularly preferably 0.5 to 3.5% by mass. is there. When the content ratio of the sulfonic acid group in the acrylic polymer particles A is within the above range, the increase in the viscosity of the porous film slurry can be prevented, and the coating property of the porous film slurry can be kept good. Moreover, while having sufficient binding force with respect to a nonelectroconductive particle, the reactivity with the epoxy group of the acrylic polymer particle B mentioned later becomes high. Furthermore, the dispersibility of the nonconductive particles in the porous membrane slurry is improved.

The acrylic polymer particle A preferably further contains a (meth) acrylonitrile monomer unit in addition to the monomer unit having a sulfonic acid group. The content ratio of the (meth) acrylonitrile monomer unit in the acrylic polymer particles A is preferably 2.5 to 40% by mass, more preferably 3 to 37% by mass, and particularly preferably 5 to 35% by mass. When the content ratio of the (meth) acrylonitrile monomer unit in the acrylic polymer particles A is within the above range, the strength of the binder is improved, so that a secondary battery having excellent cycle characteristics can be manufactured.

In the present invention, it is preferable that the acrylic polymer particle A having a sulfonic acid group further contains a (meth) acrylic acid ester monomer unit in addition to the monomer unit. The content ratio of the (meth) acrylic acid ester monomer unit in the acrylic polymer particles A is preferably 60 to 97.5% by mass, more preferably 62 to 96% by mass, and particularly preferably 65 to 95% by mass. . When the content ratio of the (meth) acrylic acid ester monomer unit in the acrylic polymer particle A is in the above range, the binder does not elute into the electrolytic solution of the secondary battery and exhibits an appropriate swelling property to the electrolytic solution. The lithium ion conductivity can be kept good. As a result, the cycle characteristics of the secondary battery can be improved.

Examples of (meth) acrylic acid ester monomers 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- Acrylic acid alkyl esters such as ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate , Pentyl methacrylate, hexyl methacrylate, heptyl methacrylate Rate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Among these, non-carbonylic oxygen atoms are shown because they exhibit lithium ion conductivity by moderate swelling into the electrolyte without eluting into the electrolyte, and in addition, they are less likely to cause bridging aggregation by the polymer in the dispersion of the active material. Preferred are ethyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth) acrylate having 2 to 13 carbon atoms in the alkyl group bonded to Preferred are n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate, in which the alkyl group to be bonded has 4 to 10 carbon atoms.

Further, the acrylic polymer particles A are in addition to the above monomer units (monomer units having a sulfonic acid group, (meth) acrylonitrile monomer units, and (meth) acrylic acid ester monomer units). It is preferable to contain other monomer units copolymerizable with. The content ratio of the other monomer units in the acrylic polymer particles A is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass. When the content ratio of the other monomer units in the acrylic polymer particles A is in the above range, the dispersibility of the particles does not decrease, and a porous film can be formed uniformly.

Other monomers include styrene-based monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, α-methylstyrene, and divinylbenzene. Acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diamino An ethylenically unsaturated carboxylic acid having a monocarboxylic acid such as acrylic acid; maleic acid, fumaric acid, itaconic acid, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and Dicarboxylic acid such as maleate ester Ethylenically unsaturated carboxylic acids and derivatives thereof; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl acetate and vinyl propionate Vinyl esters such as vinyl butyrate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; N-vinyl And heterocyclic ring-containing vinyl compounds such as pyrrolidone, vinylpyridine and vinylimidazole; amide monomers such as acrylamide and N-methylolacrylamide; The acrylic polymer particle A may contain only one type of other monomer unit, or may contain two or more types combined in any ratio.

The acrylic polymer particle B having an epoxy group comprises a monomer unit having an epoxy group. Specifically, the polymer as the acrylic polymer particle B includes a monomer unit having an epoxy group.

Monomers having an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy- Diene or polyene monoepoxides such as 2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; 3,4-epoxy-1-butene, 1,2 Alkenyl epoxides such as epoxy-5-hexene and 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate , Glycidyl-4-methyl-3-pentenoate, 3-glycidyl ester of cyclohexene carboxylic acid, glycidyl esters of unsaturated carboxylic acids such as 4-methyl-3-glycidyl ester of cyclohexene carboxylic acids; and the like. Among them, since the reactivity with the acid functional group is high, the binding property of the obtained porous film is high, the powder fall is low, and the cycle characteristics of the battery using the porous film are excellent. Therefore, vinyl glycidyl ether, allyl glycidyl Ether, glycidyl acrylate and glycidyl methacrylate are preferred, and glycidyl acrylate and glycidyl methacrylate are most preferred.

The content ratio of the monomer unit having an epoxy group in the acrylic polymer particle B is preferably 0.3 to 8% by mass, more preferably 0.3 to 5% by mass. When the content ratio of the monomer unit having an epoxy group in the acrylic polymer particle B is in the above range, the binder can be provided with a favorable binding property, and the non-conductive particles are detached from the porous film (powder off). Can be suppressed.

The content ratio of the epoxy group in the acrylic polymer particle B is preferably 0.03 to 3.0% by mass, more preferably 0.1 to 2.5% by mass, and particularly preferably 0.1 to 1.5% by mass. It is. When the content ratio of the epoxy group in the acrylic polymer particles B is within the above range, the viscosity of the porous film slurry can be prevented from increasing, and the coating property of the porous film slurry can be kept good. Moreover, since the reactivity with the sulfonic acid group of the acrylic polymer particle A mentioned above becomes high, the intensity | strength of a porous film improves.

Acrylic polymer particles B include (meth) acrylonitrile monomer units, (meth) acrylic acid ester monomer units and other monomer units copolymerizable therewith, in addition to monomer units having an epoxy group. It is preferable that it is further included. The content ratio of the (meth) acrylonitrile monomer unit in the acrylic particles B, the content ratio of the (meth) acrylic acid ester monomer unit, and the content ratio of other monomer units copolymerizable therewith are the above-mentioned acrylic. It is the same as the content ratio in the polymer particle A. Moreover, each monomer can illustrate the monomer similar to the monomer in the acrylic polymer particle A mentioned above.

The weight ratio of the acrylic polymer particles A to the acrylic polymer particles B (acrylic polymer particles A / acrylic polymer particles B) is preferably 0.3 to 3, more preferably 0.4 to 3, particularly preferably 0. .5-2. By setting the weight ratio of the acrylic polymer particles A to the acrylic polymer particles B within the above range, gelation (viscosity increase) of the porous membrane slurry can be prevented, and the coating property of the porous membrane slurry can be improved. The strength of the obtained porous membrane is improved.

The acrylic polymer particles A and the acrylic polymer particles B are used in the state of a dispersion or dissolved solution dispersed in a dispersion medium (water or organic solvent) (hereinafter referred to as “polymer particle dispersion A” and It may be described as “polymer particle dispersion B”). In the present invention, it is preferable to use water as a dispersion medium from the viewpoints of excellent environmental viewpoint and high drying speed. When an organic solvent is used as the dispersion medium, an organic solvent such as N-methylpyrrolidone (NMP) is used.

When acrylic polymer particles A and acrylic polymer particles B are dispersed in a dispersion medium, the average particle diameter of dispersed acrylic polymer particles A and acrylic polymer particles B (dispersed particles) The diameter is preferably 0.05 to 0.5 μm, more preferably 0.07 to 0.4 μm, and most preferably 0.1 to 0.25 μm. When the average particle diameter of the acrylic polymer particles A and the acrylic polymer particles B is in the above range, the strength and flexibility of the obtained porous film are improved.

When the acrylic polymer particles A and the acrylic polymer particles B are dispersed in the dispersion medium in a particulate form, the solid content concentration of the dispersion is usually 15 to 70% by mass, preferably 20 to 65% by mass, More preferably, it is 30 to 60% by mass. When the solid content concentration is within this range, workability in producing the porous membrane slurry is good.

The glass transition temperature (Tg) of the acrylic polymer particles A and B used in the present invention is preferably −50 to 25 ° C., more preferably −45 to 15 ° C., and particularly preferably −40 to 5 ° C. Since the porous film of the present invention has excellent strength and flexibility when the Tg of the acrylic polymer particle A and the acrylic polymer particle B is in the above range, the output characteristics of the secondary battery using the porous film are Can be improved. The glass transition temperatures of the acrylic polymer particles A and the acrylic polymer particles B can be prepared by combining various monomers.

The production method of the acrylic polymer particles A and the acrylic polymer particles B used in the present invention 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 may be used. it can. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Examples of the polymerization initiator used for the polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

Acrylic polymer particles A and acrylic polymer particles B used in the present invention have a particulate metal removal step of removing particulate metals contained in the polymer particle dispersion A and the polymer particle dispersion B in the production process. It is preferable that it was obtained through this. The content of the particulate metal component contained in the polymer particle dispersion A and the polymer particle dispersion B is 10 ppm or less, thereby preventing metal ion cross-linking between the polymers in the porous membrane slurry over time, and the viscosity. The rise can be prevented. Furthermore, there is little concern about self-discharge increase due to internal short circuit of the secondary battery or dissolution / precipitation during charging, and the cycle characteristics and safety of the battery are improved.

The method for removing the particulate metal component from the polymer particle dispersion A and the polymer particle dispersion B in the particulate metal removal step is not particularly limited. Examples of the removal method include a removal method by centrifugation, a removal method by magnetic force, and the like. Especially, since the removal object is a metal component, the method of removing by magnetic force is preferable. The method for removing by magnetic force is not particularly limited as long as the metal component can be removed. However, in consideration of productivity and removal efficiency, it is preferably in the production line of acrylic polymer particles A and acrylic polymer particles B. This is done by placing a magnetic filter.

The method for producing the binder used in the present invention is not particularly limited, and is produced by mixing the polymer particle dispersion A and the polymer particle dispersion B described above. The mixing device is not particularly limited as long as it can uniformly mix the polymer particle dispersion A and the polymer particle dispersion B. For example, a mixing device such as a stirring type, a shaking type, and a rotary type is used. A method is mentioned. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

The content ratio of the acrylic polymer particles A in the binder is preferably 30 to 75% by mass, more preferably 33 to 66% by mass, and the content ratio of the acrylic polymer particles B in the binder is preferably 25 to 70% by mass. More preferably, the content is 33 to 66% by mass. When the content ratio of the acrylic polymer particles A and the acrylic polymer particles B in the binder is in the above range, the binding force is good, and the binder is dispersed without thickening, so the smoothness of the porous film is also improved. Excellent.

The weight ratio of the sulfonic acid groups in the acrylic polymer particles A to the epoxy groups in the acrylic polymer particles B in the binder (sulfonic acid groups / epoxy groups) is preferably 0.2 to 3, more preferably 0.3 to 3. Particularly preferred is 0.3 to 2. When the weight ratio of the sulfonic acid group to the epoxy group in the binder (sulfonic acid group / epoxy group) is within the above range, gelation of the porous film slurry can be prevented, and the coating property of the porous film slurry can be improved. The strength of the obtained porous membrane is improved.

The average particle size of the binder is preferably 0.05 to 0.5 μm, more preferably 0.07 to 0.4 μm, and particularly preferably 0.10 to 0.25 μm. The average particle size can be determined by measuring the particle size distribution by laser diffraction. By making the average particle diameter of the binder within the above range, the binding property with the non-conductive particles becomes better, so the flexibility of the obtained secondary battery porous film is improved, and the secondary battery porous film is non-conductive. Detachment (powder falling) of the conductive particles can be prevented. As a result, the secondary battery using the secondary battery porous membrane exhibits excellent safety and cycle characteristics.

The content ratio of the binder per 100% by mass of the total solid content of the porous membrane slurry is preferably 0.5 to 20% by mass, more preferably 5 to 20% by mass, and particularly preferably 5 to 15% by mass. By making the content rate of the binder per 100% by mass of the total solid content of the porous membrane slurry within the above range, the binding force between the nonconductive particles can be kept good, and the flexibility of the porous membrane is improved. Moreover, the cycle characteristics of the obtained secondary battery can be improved.

(solvent)
As a solvent used for the porous membrane slurry, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; Esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; Acylonitriles such as acetonitrile and propionitrile; Tetrahydrofuran, Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methyl Amides such as lupyrrolidone and N, N-dimethylformamide are exemplified.

These solvents may be used alone or as a mixed solvent by mixing two or more of them. Among these, a solvent having excellent dispersibility of non-conductive particles and having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. Specifically, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, N-methylpyrrolidone, or a mixed solvent thereof is preferable.

(Optional ingredients)
In addition to the above components (nonconductive particles, binder and solvent), the porous membrane slurry may further contain optional components. Examples of such optional components include inorganic particles, dispersants, leveling agents, antioxidants, binders other than the above binders, thickeners, antifoaming agents, and electrolytic solution additives having functions such as suppression of electrolytic solution decomposition. And the like. These are not particularly limited as long as they do not affect the battery reaction.

As the inorganic particles, for example, various inorganic particles such as aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, aluminum nitride, calcium fluoride, barium fluoride talc, and montmorillonite can be used. In particular, non-spherical atypical particles are preferred. The content ratio of the inorganic particles per 100% by mass of the total solid content of the porous membrane slurry is 20% by mass or less, more preferably 10% by mass or less. When the content ratio of the inorganic particles is within this range, a porous film having high strength and good lithium ion permeability can be obtained.

Examples of the dispersant include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds. A dispersing agent is selected according to the nonelectroconductive particle to be used. The content ratio of the dispersing agent per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. When the content ratio of the dispersant is within this range, the coating property of the porous membrane slurry of the present invention is good, and a uniform porous membrane can be obtained.

Examples of leveling agents include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. The content ratio of the surfactant per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. By mixing the surfactant, repelling that occurs when the porous membrane slurry of the present invention is applied to a predetermined substrate can be prevented, and the smoothness of the porous membrane can be improved.

Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer type phenol compound is a polymer having a phenol structure in the molecule, and a polymer type phenol compound having a weight average molecular weight of 200 to 1000, preferably 600 to 700 is preferably used. The content ratio of the antioxidant per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. When the content ratio of the antioxidant is within this range, the cycle life of the battery is excellent.

Examples of binders other than the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylic acid derivatives, polyacrylonitrile derivatives, and soft polymers used in electrode binders described later. Can be used. The content rate of binder other than the said binder per 100 mass% of total solid content of a porous membrane slurry is 10 mass% or less. When the content ratio of the binder is within this range, the adhesion between the porous film of the present invention and the electrode active material layer and organic separator described later is good.

Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples thereof include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. The content ratio of the thickener per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. When the content of the thickener is within this range, the coating property of the porous membrane slurry of the present invention and the adhesion between the porous membrane of the present invention and the electrode active material layer and organic separator described later are good. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”.

As the antifoaming agent, metal soaps, polysiloxanes, polyethers, higher alcohols, perfluoroalkyls and the like are used. The content ratio of the antifoaming agent per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. By mixing an antifoaming agent, the defoaming step of the binder can be shortened.

As the electrolytic solution additive, vinylene carbonate used in an electrode slurry and an electrolytic solution described later can be used. The content ratio of the electrolytic solution additive per 100% by mass of the total solid content of the porous membrane slurry is preferably within a range that does not affect the battery characteristics, and specifically 10% by mass or less. By mixing the electrolyte additive, the cycle life of the battery is excellent.

Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nano fine particles, the thixotropy of the porous membrane slurry can be controlled, and the leveling properties of the porous membrane obtained thereby can be improved.

The total content of the above-mentioned arbitrary components per 100% by mass of the total solid content of the porous membrane slurry is preferably 40% by mass or less, more preferably 20% by mass or less. However, if the total of the non-conductive particles, binder, and optional components (excluding inorganic particles and binder) is less than 100% by mass, the content of the binder as an optional component is increased appropriately. And a composition can be obtained.

The solid content concentration of the porous membrane slurry is not particularly limited as long as the slurry can be applied and immersed and has a fluid viscosity, but is generally about 10 to 50% by mass.

Components other than the solid content are components that volatilize in the drying step, and include, in addition to the solvent, for example, a medium in which these are dissolved or dispersed during preparation and addition of non-conductive particles and a binder.

The production method of the secondary battery porous membrane slurry is not particularly limited, and is produced by mixing the non-conductive particles, the binder, the solvent, and optional components added as necessary. In the present invention, by using the above components (non-conductive particles, binder, solvent, and optional components added as necessary), the non-conductive particles are highly dispersed regardless of the mixing method and mixing order. A membrane slurry can be obtained. As the mixing apparatus, a mixing apparatus similar to the mixing apparatus used for the production of the binder described above can be used. Among them, it is particularly preferable to use a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix that can add a high dispersion share.

The viscosity of the porous membrane slurry is preferably 10 to 10,000 mPa · s, more preferably 50 to 500 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

(2) Secondary Battery Porous Membrane The secondary battery porous membrane of the present invention (hereinafter sometimes referred to as “porous membrane”) is formed by forming the above-described secondary battery porous membrane slurry into a film and drying it. .
The porous film is used by being laminated on an organic separator or an electrode, or used as an organic separator itself.

<Method for producing secondary battery porous membrane>
As a method for producing a porous film of the present invention, (I) a porous film slurry containing the above non-conductive particles, a binder, a solvent and an optional component is applied on a predetermined substrate (positive electrode, negative electrode or organic separator). (II) A method of drying the porous film slurry containing the above non-conductive particles, a binder, a solvent and an optional component after immersing the substrate in a substrate (positive electrode, negative electrode or organic separator); (III) A porous film slurry containing the above non-conductive particles, binder, solvent and optional components is applied and formed on a release film, and the resulting porous film is formed into a predetermined substrate (positive electrode, negative electrode or organic) And a method of transferring onto the separator). Among these, (I) The method of applying the porous film slurry to the substrate (positive electrode, negative electrode or organic separator) and then drying is most preferable because the film thickness of the porous film can be easily controlled.

The porous membrane of the present invention is manufactured by the above-described methods (I) to (III), and the detailed manufacturing method will be described below.
In the method (I), the porous membrane slurry of the present invention is produced by applying a porous membrane slurry onto a predetermined substrate (positive electrode, negative electrode or organic separator) and drying.

The method for applying the slurry onto the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the gravure method is preferable in that a uniform porous film can be obtained.

Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying temperature can vary depending on the type of solvent used. In order to completely remove the solvent, for example, when a low-volatility solvent such as N-methylpyrrolidone is used, it is preferably dried at a high temperature of 120 ° C. or higher with a blower-type dryer. Conversely, when a highly volatile solvent is used, it can be dried at a low temperature of 100 ° C. or lower. When forming a porous film on the organic separator mentioned later, since it is necessary to dry without causing shrinkage of the organic separator, drying at a low temperature of 100 ° C. or lower is preferable.

In the method (II), the porous membrane of the present invention is produced by immersing the porous membrane slurry in a substrate (positive electrode, negative electrode or organic separator) and drying. The method for immersing the slurry in the substrate is not particularly limited, and for example, the slurry can be immersed by dip coating with a dip coater or the like.
Examples of the drying method include the same methods as the drying method in the method (I) described above.

In the method (III), a porous film slurry is applied on a release film and formed into a film, thereby producing a porous film formed on the release film. Next, the obtained porous film is transferred onto a substrate (positive electrode, negative electrode or organic separator).
As a coating method, the same method as the coating method in the above-mentioned method (I) can be mentioned. The transfer method is not particularly limited.

The porous film obtained by the methods (I) to (III) is then subjected to pressure treatment using a die press or a roll press, if necessary, and a substrate (positive electrode, negative electrode or organic separator) and porous film. It is also possible to improve the adhesion. However, at this time, if the pressure treatment is excessively performed, the porosity of the porous film may be impaired, so the pressure and the pressure time are controlled appropriately.

The film thickness of the porous film is not particularly limited and is appropriately set according to the use or application field of the porous film. However, if the film is too thin, a uniform film cannot be formed. Since the capacity per volume (weight) decreases, 0.5 to 50 μm is preferable, and 0.5 to 10 μm is more preferable.

The porous film of the present invention is formed on the surface of a substrate (positive electrode, negative electrode or organic separator) and is particularly preferably used as a protective film or separator for an electrode active material layer described later. The porous film of the present invention may be formed on any surface of the positive electrode, negative electrode or organic separator of the secondary battery, or may be formed on all of the positive electrode, negative electrode and organic separator.

(3) Secondary battery electrode Examples of the secondary battery include a lithium ion secondary battery and a nickel metal hydride secondary battery. Among these, since the lithium ion secondary battery is preferable because safety improvement is most demanded and the effect of introducing the porous film is the highest, a case where it is used for a lithium ion secondary battery will be described below.
The secondary battery electrode of the present invention includes a current collector, an electrode active material layer comprising an electrode active material and a binder, which is attached to the current collector, and a laminate on the surface of the electrode active material layer. The above-described secondary battery porous membrane. That is, in the secondary battery electrode of the present invention, the electrode active material layer containing the electrode active material and the electrode binder is attached to the current collector, and the surface of the electrode active material layer has the above-mentioned secondary battery porosity. A film is laminated.

(Electrode active material)
The electrode active material used for the electrode for the lithium ion secondary battery is not particularly limited as long as it can reversibly insert and release lithium ions by applying a potential in the electrolyte, and can be an inorganic compound or an organic compound.

Electrode active materials (positive electrode active materials) for lithium ion secondary battery positive electrodes are broadly 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. As the transition metal, Fe, Co, Ni, Mn and the like are used. 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 It is done. These compounds may be partially element-substituted. As the positive electrode active material made of an organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene can be used. An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted.

The positive electrode active material for a lithium ion secondary battery may be a mixture of the above inorganic compound and organic compound. The particle diameter of the positive electrode active material is appropriately selected in consideration of the arbitrary constituent requirements of the battery. From the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, the 50% volume cumulative diameter is usually 0.1. It is ˜50 μm, preferably 1 to 20 μm. When the 50% volume cumulative diameter is within this range, a secondary battery having a large charge / discharge capacity can be obtained, and handling of the slurry for electrodes and the electrodes is easy. The 50% volume cumulative diameter can be determined by measuring the particle size distribution by laser diffraction.

Examples of electrode active materials (negative electrode active materials) for negative electrodes of lithium ion secondary batteries include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, pitch-based carbon fibers, and high conductivity such as polyacene. Molecular compounds and the like. In addition, as the negative electrode active material, metals such as silicon, tin, zinc, manganese, iron, nickel, alloys thereof, oxides or sulfates of the metals or alloys are used. In addition, lithium alloys such as lithium metal, Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitride, silicone, and the like can be used. As the electrode active material, a material obtained by attaching a conductivity imparting material to the surface by a mechanical modification method can be used. The particle size of the negative electrode active material is appropriately selected in consideration of the other structural requirements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics, a 50% volume cumulative diameter is usually The thickness is 1 to 50 μm, preferably 15 to 30 μm.

(Binder for electrode)
In the present invention, the electrode active material layer includes a binder (hereinafter sometimes referred to as “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 in the electrode is improved, the strength against the mechanical force applied during the process of winding the electrode is increased, and the electrode active material in the electrode is increased. Since the material layer is less likely to be detached, the risk of a short circuit due to the desorbed material is reduced.

Various resin components can be used as the electrode binder. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, and the like can be used. These may be used alone or in combination of two or more. Moreover, the binder used for the porous film of this invention can also be used as a binder for electrodes.

Furthermore, the soft polymer illustrated below can also be used as a binder for electrodes.
Acrylic acid such as polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer Or an acrylic soft polymer, which is a homopolymer of a methacrylic acid derivative or a copolymer with a monomer copolymerizable therewith;
Isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene / butadiene / Diene-based soft polymers such as styrene block copolymer, isoprene / styrene block copolymer, styrene / isoprene / styrene block copolymer;
Silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer, etc. Olefinic soft polymers of
Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
Epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
Examples thereof include other soft polymers such as natural rubber, polypeptide, protein, polyester-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer. These soft polymers may have a cross-linked structure or may have a functional group introduced by modification.

The amount of the electrode binder in the electrode active material layer is preferably from 0.1 to 5 parts by weight, more preferably from 0.2 to 4 parts by weight, particularly preferably from 0.1 to 100 parts by weight of the electrode active material. 5 to 3 parts by mass. When the amount of the electrode binder in the electrode active material layer is within the above range, it is possible to prevent the active material from being detached from the electrode without inhibiting the battery reaction.

The electrode binder is prepared as a solution or dispersion to produce an electrode. The viscosity at that time is usually in the range of 1 to 300,000 mPa · s, preferably 50 to 10,000 mPa · s. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

(Optional additive)
In the present invention, the electrode active material layer may contain an optional additive such as a conductivity-imparting material or a reinforcing material in addition to the electrode active material and the electrode binder. As the conductivity-imparting material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. Examples thereof include carbon powders such as graphite, and fibers and foils of various metals. As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using the conductivity imparting material, the electrical contact between the electrode active materials can be improved, and the discharge rate characteristics can be improved when used in a lithium ion secondary battery. The amount of the conductivity-imparting material and the reinforcing material used is usually 0 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the electrode active material. Further, an isothiazoline-based compound or a chelate compound may be included in the electrode active material layer.

The electrode active material layer can be formed by adhering a slurry containing an electrode active material, an electrode binder and a solvent (hereinafter also referred to as “electrode slurry”) to a current collector.

The solvent is not particularly limited as long as it dissolves or disperses the electrode binder, but preferably dissolves. When a solvent that dissolves the electrode binder is used, the electrode binder is adsorbed on the surface of the electrode active material or any additive, thereby stabilizing the dispersion of the electrode active material.

As the solvent used for the electrode slurry, either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate, γ-butyrolactone, ε -Esters such as caprolactone; Acylonitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether; Alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methyl Amides such as pyrrolidone and N, N-dimethylformamide are exemplified. These solvents may be used alone or in admixture of two or more and appropriately selected from the viewpoint of drying speed and environment.

The electrode slurry may further contain additives that exhibit various functions such as a thickener. As the thickener, a polymer soluble in the solvent used for the electrode slurry is used. Specifically, the thickener exemplified in the porous membrane slurry of the present invention can be used. The amount of the thickener used is preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the electrode active material. When the use amount of the thickener is within the above range, the coating property of the electrode slurry and the adhesion to the current collector are good.

Furthermore, in addition to the above components, the electrode slurry contains trifluoropropylene carbonate, vinylene carbonate, catechol carbonate, 1,6-dioxaspiro [4,4] nonane-2,7 in order to increase the stability and life of the battery. -Dione, 12-crown-4-ether and the like can be used. These may be used by being contained in an electrolyte solution described later.

The amount of the solvent in the electrode slurry is adjusted to a viscosity suitable for coating depending on the type of the electrode active material, the electrode binder, and the like. Specifically, the concentration of solids in the electrode slurry is preferably 30 to 90% by mass, and more preferably combined with any additive such as an electrode active material, an electrode binder, and a conductivity-imparting material. Is used by adjusting the amount to 40 to 80% by mass.

The electrode slurry is obtained by mixing an electrode active material, an electrode binder, an optional additive such as a conductivity imparting agent added as necessary, and a solvent using a mixer. Mixing may be performed by supplying the above components all at once to a mixer. When using electrode active materials, electrode binders, conductivity-imparting materials and thickeners as constituents of electrode slurries, conductivity is imparted by mixing the conductivity-imparting materials and thickeners in a solvent. It is preferable to disperse the material in the form of fine particles, and then add a binder for the electrode and an electrode active material and further mix, since the dispersibility of the slurry is improved. As the mixer, a ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer, etc. can be used. It is preferable because aggregation of the resin can be suppressed.

The particle size of the electrode slurry is preferably 35 μm or less, more preferably 25 μm or less. When the particle size of the slurry is in the above range, the conductivity imparting material is highly dispersible and a homogeneous electrode can be obtained.

(Current collector)
The current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material. From the viewpoint of having heat resistance, for example, iron, copper, aluminum, nickel, stainless steel, etc. Metal materials such as titanium, tantalum, gold, and platinum are preferable. Among these, aluminum is particularly preferable for the positive electrode of the lithium ion secondary battery, and copper is particularly preferable for the negative electrode of the lithium ion secondary battery. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength of the electrode active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the electrode active material layer.

The method for producing the electrode active material layer may be any method in which the electrode active material layer is bound in layers on at least one surface, preferably both surfaces of the current collector. For example, the electrode slurry is applied to a current collector and dried, and then heat-treated at 120 ° C. or higher for 1 hour or longer to form an electrode active material layer. The method for applying the electrode slurry to the current collector is not particularly limited. Examples thereof 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. Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams.

Next, it is preferable to lower the porosity of the electrode active material layer by pressure treatment using a mold press or a roll press. A preferable range of the porosity is 5 to 15%, more preferably 7 to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, there are problems that it is difficult to obtain a high volume capacity, or that the electrode active material layer is easily peeled off and is likely to be defective. Further, when a curable polymer is used, it is preferably cured.

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

The secondary battery electrode of the present invention is manufactured by laminating the secondary battery porous film of the present invention on the surface of the electrode active material layer of the current collector in which the electrode active material layer is bound in a layered manner.

The laminating method is not particularly limited, and examples thereof include the methods (I) to (III) described in the above method for producing a porous film.

(4) Secondary battery separator The secondary battery separator of the present invention comprises an organic separator and the above-described secondary battery porous film laminated on the organic separator. That is, the secondary battery separator of the present invention is formed by laminating the above-described secondary battery porous film on an organic separator.

(Organic separator)
As an organic separator for a lithium ion secondary battery, known ones such as a polyolefin resin such as polyethylene and polypropylene and a separator containing an aromatic polyamide resin are used.

As the organic separator used in the present invention, a porous membrane having a fine pore size, having no electron conductivity and ionic conductivity and high resistance to organic solvents is used. For example, polyolefin-based (polyethylene, polypropylene, polybutene, polychlorinated) Vinyl), and a microporous film made of a resin such as a mixture or a copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene Examples thereof include a microporous membrane made of a resin such as the above, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like. Among these, since the coating property of the porous membrane slurry of the present invention is excellent, the film thickness of the entire separator can be reduced and the active material ratio in the battery can be increased to increase the capacity per volume. A microporous membrane is preferred.

The thickness of the organic separator is usually 0.5 to 40 μm, preferably 1 to 30 μm, more preferably 1 to 20 μm. Within this range, the resistance due to the organic separator in the battery is reduced. Moreover, the workability | operativity at the time of coating the porous membrane slurry of this invention to an organic separator is good.

In the present invention, examples of the polyolefin-based resin used as the material for the organic separator include homopolymers such as polyethylene and polypropylene, copolymers, and mixtures thereof. Examples of the polyethylene include low density, medium density, and high density polyethylene, and high density polyethylene is preferable from the viewpoint of piercing strength and mechanical strength. These polyethylenes may be mixed in two or more types for the purpose of imparting flexibility. The polymerization catalyst used for these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. From the viewpoint of achieving both mechanical strength and high permeability, the viscosity average molecular weight of polyethylene is preferably 100,000 to 12 million, and more preferably 200,000 to 3 million. Examples of polypropylene include homopolymers, random copolymers, and block copolymers, and one kind or a mixture of two or more kinds can be used. The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts. The stereoregularity is not particularly limited, and isotactic, syndiotactic or atactic can be used. However, it is desirable to use isotactic polypropylene because it is inexpensive. Furthermore, an appropriate amount of a polyolefin other than polyethylene or polypropylene, and an additive such as an antioxidant or a nucleating agent may be added to the polyolefin as long as the effects of the present invention are not impaired.

As a method for producing a polyolefin-based organic separator, a publicly known one is used. For example, after forming a melt-extruded film of polypropylene and polyethylene, annealing is performed at a low temperature to grow a crystal domain, and in this state, stretching is performed. A dry method of forming a microporous film by extending the amorphous region; mixing a hydrocarbon solvent or other low molecular weight material with polypropylene or polyethylene, forming a film, and then forming a solvent or low molecular weight into the amorphous phase A wet method in which a microporous film is formed by removing the film that has started to form an island phase by using this solvent or low-molecular solvent with another volatile solvent is selected. Among these, a dry method is preferable in that a large void can be easily obtained for the purpose of reducing the resistance.

The organic separator used in the present invention may contain any filler or fiber compound for the purpose of controlling strength, hardness, and heat shrinkage. Further, when laminating the porous membrane of the present invention, a low molecular weight compound or A coating treatment with a polymer compound, an electromagnetic radiation treatment such as ultraviolet rays, or a plasma treatment such as corona discharge / plasma gas may be performed.
In particular, the coating treatment is preferably performed with a polymer compound containing a polar group such as a carboxylic acid group, a hydroxyl group, and a sulfonic acid group from the viewpoint that the impregnation property of the electrolytic solution is high and the adhesion with the porous film is easily obtained.

The secondary battery separator of the present invention is manufactured by laminating the secondary battery porous film of the present invention on the organic separator.

(5) Secondary Battery The secondary battery of the present invention includes a positive electrode, a negative electrode, an organic separator, and an electrolytic solution, and the above porous film is laminated on any of the positive electrode, the negative electrode, and the organic separator.

(Electrolyte)
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. A lithium salt is used as the supporting electrolyte. The lithium salt is not particularly _{_{_{limited, LiPF 6, LiAsF 6, LiBF}}} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferable. Two or more of these may be used in combination. Since the lithium ion conductivity increases as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

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

The concentration of the supporting electrolyte in the electrolytic solution is usually 1 to 30% by mass, preferably 5 to 20% by mass. The concentration is usually 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease. Since the degree of swelling of the polymer particles increases as the concentration of the electrolytic solution used decreases, the lithium ion conductivity can be adjusted by the concentration of the electrolytic solution.

As a specific method for producing a secondary battery, a positive electrode and a negative electrode are overlapped with an organic separator, and this is wound into a battery container according to the shape of the battery, put into a battery container, and an electrolytic solution is injected into the battery container. And sealing. The porous film of the present invention is laminated on any one of the positive electrode, the negative electrode, and the organic separator. The method of laminating the porous film of the present invention on the positive electrode, the negative electrode, and the organic separator is as described in the method (I) or (II). Moreover, it is also possible to laminate | stack only a porous film on a positive electrode, a negative electrode, or an organic separator independently as the above-mentioned method of (III). If necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

In the secondary battery of the present invention, the porous film of the present invention is preferably laminated on the surface of the electrode active material layer of the positive electrode or the negative electrode. By laminating the porous film of the present invention on the surface of the electrode active material layer, even if the organic separator is contracted by heat, a short circuit between the positive electrode and the negative electrode is not caused, and high safety is maintained. In addition, by laminating the porous membrane of the present invention on the surface of the electrode active material layer, the porous membrane can function as a separator without an organic separator, and a secondary battery can be produced at low cost. become. Further, even when an organic separator is used, higher rate characteristics can be expressed because the holes formed on the separator surface are not filled.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard. In Examples and Comparative Examples, various physical properties are evaluated as follows.

<Heat-resistant temperature of non-conductive particles (T10 value)>
In a nitrogen atmosphere, the mixture was heated from 30 ° C. at a heating rate of 10 ° C./min with a thermobalance, and the temperature [° C.] at which the non-conductive particle weight loss ratio reached 10% by mass was determined as the heat resistant temperature.

<Average particle size of non-conductive particles>
100 non-conductive particles are arbitrarily selected from a photograph taken with an electron microscope at a magnification of 25000 times, and when the longest side of the particle image is a and the shortest side is b, (a + b) / 2 The average particle diameter [μm] was calculated from the average of 100 particles.

<Average circularity of non-conductive particles>
100 non-conductive particles are arbitrarily selected from a photograph taken with an electron microscope at a magnification of 25000 times, the circumference of a circle having the same projected area as the particle image is L ₀ , and the circumference of the particle image is L In this case, L ₀ / L was defined as the circularity, and the average circularity was calculated from the average of 100 pieces.

<Particle size distribution of non-conductive particles>
The particle size distribution of the non-conductive particles is determined by measuring the particle size with a laser diffraction scattering particle size distribution measuring device (LS230) manufactured by Beckman Co., Ltd. N was determined by the following formula.
Particle size distribution = V / N

<Uniformity of porous film>
A secondary battery porous membrane (organic separator with a porous membrane) or a secondary battery electrode (electrode with a porous membrane) is cut into a width of 10 cm and a length of 1.5 m, and the cut secondary battery porous membrane or secondary battery electrode The thickness was measured at 60 points of 20 points every 3 cm in the width direction and every 5 cm in the length direction using a thickness meter (MH-15M) manufactured by Nikon Corporation. From the standard deviation and average value of the film thickness, Based on the formula, film thickness variation [%] was calculated and evaluated according to the following criteria.

Here, x represents an average value of the film thickness, and n represents the number of measurements.
(Evaluation criteria)
A: Less than 2% B: 2% to less than 3% C: 3% to less than 10% D: 10% or more

<Reliability test of secondary battery separator (organic separator with porous membrane)>
A secondary battery separator (organic separator with a porous film) was punched into a circle having a diameter of 19 mm, immersed in a 3 wt% methanol solution of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P), and air-dried. This circular secondary battery separator is impregnated with an electrolyte and sandwiched between a pair of circular SUS plates (diameter 15.5 mm), and the structure is (SUS plate) / (circular secondary battery separator) / (SUS plate). Superimposed. Here, the electrolytic solution is a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). The concentration of LiPF ₆ is 1 mol / liter. The solution dissolved in was used. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. While applying an alternating current with an amplitude of 10 mV and a frequency of 1 kHz, the temperature was raised to 200 ° C. at a temperature rising rate of 1.6 ° C./min, and the cell resistance during this time was measured to confirm the occurrence of a short circuit. In this test, the resistance value increases due to shutdown with a temperature rise and becomes at least 1000 Ω / cm ² or more. Thereafter, it was assumed that a short circuit occurred when the voltage dropped rapidly to 10 Ω / cm ² or less. In addition, this test was performed 20 times and evaluation was performed according to the following criteria.
(Evaluation criteria)
A: Number of short-circuit occurrences 0 B: Number of short-circuit occurrences 1 C: Number of short-circuit occurrences 2 to 3 D: Number of short-circuit occurrences 4 or more

<Reliability test of secondary battery electrode (electrode with porous film)>
An organic separator (single-layer polypropylene separator, porosity 55%, thickness 25 μm) is punched into a circle with a diameter of 19 mm, and immersed in a 3% by weight methanol solution of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P). And air dried. On the other hand, the secondary battery electrode (electrode with porous film) to be measured was punched into a circle having a diameter of 19 mm. These are impregnated with an electrolytic solution, and these are overlapped and sandwiched between a pair of circular SUS plates (diameter 15.5 mm), and (SUS plate) / (circular organic separator) / (circular secondary battery electrode) / ( SUS plate). The circular secondary battery electrode was arranged so that the surface on the porous membrane side was the organic separator side. Here, the electrolytic solution is a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). The concentration of LiPF ₆ is 1 mol / liter. The solution dissolved in was used. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. While applying an alternating current with an amplitude of 10 mV and a frequency of 1 kHz, the temperature was raised to 200 ° C. at a temperature rising rate of 1.6 ° C./min, and the cell resistance during this time was measured to confirm the occurrence of a short circuit. In this test, the resistance value increases due to shutdown with a rise in temperature and becomes at least 1000 Ω / cm ² or more. Thereafter, it was assumed that a short circuit occurred when the voltage dropped rapidly to 10 Ω / cm ² or less. In addition, this test was performed 20 times and evaluation was performed according to the following criteria.
(Evaluation criteria)
A: Number of short-circuit occurrences 0 B: Number of short-circuit occurrences 1 to 2 C: Number of short-circuit occurrences 3 or more

<Cycle characteristics of secondary battery>
The operation of charging the obtained secondary battery (coin-type battery) to 4.3 V at a constant current of 0.2 C at 20 ° C. and discharging to 3.0 V at a constant current of 0.2 C is defined as one cycle. The discharge was repeated. The ratio of the discharge capacity in the 100th cycle to the discharge capacity in the second cycle was calculated as a percentage to obtain charge / discharge cycle characteristics, and the determination was made according to the following criteria. It shows that the capacity | capacitance reduction by repeated charging / discharging is so small that this value is large.
(Evaluation criteria)
A: 97% or more B: 95% or more and less than 97% C: 90% or more and less than 95% D: 85% or more and less than 90% E: Less than 85%

<Powder removal property of secondary battery electrode (electrode with porous film)>
A secondary battery electrode (electrode with a porous film) was cut out at 5 cm square, put into a 500 ml glass bottle, and allowed to stand for 3 hours at 300 rpm with a machine. The mass of the dropped powder was a, the mass of the secondary battery electrode before the b was b, the mass of the electrode before laminating the porous film was c, and only the electrode without laminating the porous film was dropped The mass of the powder was d, and the ratio X [mass%] of the fallen powder was calculated by the following formula and evaluated according to the following criteria.
X = (ad) / (bca) × 100 [mass%]
(Evaluation criteria)
A: Less than 2% by mass B: 2% by mass or more and less than 5% by mass C: 5% by mass or more

<Powder removal performance of secondary battery separator (organic separator with porous membrane)>
A secondary battery separator (organic separator with a porous film) was cut out in a 5 cm square, placed in a 500 ml glass bottle, and allowed to stand for 3 hours at 300 rpm with a knitting machine. The mass of the secondary battery separator before the mating was a, the mass of the secondary battery separator after the mating was b, and the ratio X [% by mass] of the fallen powder was calculated by the following formula and evaluated according to the following criteria.
X = (ab) / a × 100 [mass%]
(Evaluation criteria)
A: Less than 1 mass% B: 1 mass% or more and less than 3 mass% C: 3 mass% or more and less than 5 mass% D: 5 mass% or more and less than 10 mass% E: 10 mass% or more

<Measurement of content ratio of sulfonic acid group and epoxy group in polymer particle>
The addition amount [g] of the monomer having a sulfonic acid group added during the polymerization of the acrylic polymer particle A is a, the molecular weight is b, the molecular weight corresponding to the sulfonic acid group portion is c (81.07), and the total amount of the monomer is Assuming d, the content ratio [% by mass] of the sulfonic acid group (relative to the total amount of monomers) in the acrylic polymer particles A is calculated as in the following formula.
Content ratio of sulfonic acid group in acrylic polymer particle A (A)
= (A / b) x c / d x 100 [mass%]

Similarly, the addition amount [g] of the monomer having an epoxy group added during the polymerization of the acrylic polymer particle B is e, the molecular weight is f, the molecular weight corresponding to the epoxy group portion is g (43.05), and the total amount of the monomer is Assuming that h, the content [% by mass] of the epoxy group (with respect to the total amount of the monomers) in the acrylic polymer particles B is calculated as in the following formula.
Content ratio of epoxy group in acrylic polymer particle B (B)
= (E / f) × g / h × 100 [mass%]

<Measurement of weight ratio of sulfonic acid group to epoxy group in binder (sulfonic acid group / epoxy group)>
The solid content [g] of the acrylic polymer particles A added at the time of slurry preparation was C, and the solid content [g] of the acrylic polymer particles B added at the time of slurry preparation was D. Furthermore, the content ratio (A) of the sulfonic acid group in the acrylic polymer particle A and the content of the sulfonic acid group in the acrylic polymer particle B obtained by measuring the content ratio of the sulfonic acid group and the epoxy group in the polymer particle. Using the ratio (B), the weight ratio of sulfonic acid group / epoxy group can be calculated as follows.
Sulfonic acid group / epoxy group = (A × C) / (B × D) [weight ratio]

Example 1
<(1) Production of seed polymer particle A>
In a reactor equipped with a stirrer, 100 parts of styrene, 1.0 part of sodium dodecylbenzenesulfonate, 100 parts of ion-exchanged water, and 0.5 part of potassium persulfate were placed and polymerized at 80 ° C. for 8 hours. Thereby, an aqueous dispersion of seed polymer particles A having an average particle diameter of 60 nm was obtained.

<(2) Production of seed polymer particle B>
In a reactor equipped with a stirrer, 2 parts of the aqueous dispersion of the seed polymer particles A obtained in the step (1) on a solids basis (that is, on the basis of the weight of the seed polymer particles A) and 0. 2% of sodium dodecylbenzenesulfonate. 2 parts, 0.5 part of potassium persulfate and 100 parts of ion exchange water were added and mixed to obtain a mixture, which was heated to 80 ° C. Meanwhile, in another container, 97 parts of styrene, 3 parts of methacrylic acid, 4 parts of t-dodecyl mercaptan, 0.5 part of sodium dodecylbenzenesulfonate, and 100 parts of ion-exchanged water were mixed to disperse the monomer mixture. The body was prepared. The monomer mixture dispersion was continuously added to the mixture for 4 hours to polymerize. The reaction was carried out while maintaining the temperature of the reaction system at 80 ° C. during continuous addition of the dispersion of the monomer mixture. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours.
Thereby, an aqueous dispersion of seed polymer particles B having an average particle diameter of 200 nm was obtained.

<(3) Production of non-conductive particles>
Next, in a reactor equipped with a stirrer, 10 parts of the aqueous dispersion of the seed polymer particles B obtained in the step (2) on the basis of the solid content (that is, based on the weight of the seed polymer particles B) and a monomer mixture (divinyl) Mixture of benzene and ethyl vinyl benzene, monomer mixing ratio: divinyl benzene / ethyl vinyl benzene = 60/40, manufactured by Nippon Steel Chemical Co., Ltd., product name: DVB-570), 1 part sodium dodecylbenzene sulfonate 5 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) as a polymerization initiator and 200 parts of ion-exchanged water are added and stirred at 35 ° C. for 12 hours. Thus, the monomer mixture and the polymerization initiator were completely absorbed in the seed polymer particles B. Thereafter, this was polymerized at 90 ° C. for 4 hours. Thereafter, steam was introduced to remove unreacted monomers.
This obtained the water dispersion of the nonelectroconductive particle with an average particle diameter of 0.4 micrometer.
Composition of monomers (styrene, methacrylic acid, divinylbenzene, and ethylvinylbenzene) used from formation of seed polymer particles to obtaining nonconductive particles, and heat resistance temperature (T10 value) of nonconductive particles, The average circularity and particle size distribution are as shown in Table 1.

<(4) Production of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 81.1 parts of n-butyl acrylate, 14.9 parts of acrylonitrile, 4.0 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 4.0%, the content ratio of the sulfonic acid group is 1.56%, the content ratio of the acrylonitrile monomer unit is 14.9%, The content ratio of the (meth) acrylic acid ester monomer unit was 81.1%.

<(5) Production of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 81.9 parts of n-butyl acrylate, 15.1 parts of acrylonitrile, 3.0 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 3.0%, the content ratio of the epoxy acid group is 0.91%, the content ratio of the acrylonitrile monomer unit is 15.1%, The content ratio of the (meth) acrylic acid ester monomer unit was 81.9%.

<(6) Production of porous membrane slurry>
As the thickener, carboxymethyl cellulose (Daicel Chemical Industries, Ltd. Daicel 1220) having a degree of etherification of 0.8 to 1.0 and a 1% aqueous solution viscosity of 10 to 20 mPa · s was used to prepare a 1% aqueous solution. Prepared.
An aqueous dispersion of non-conductive particles obtained in step (3), an aqueous dispersion of acrylic polymer particles A obtained in step (4), an aqueous dispersion of acrylic polymer particles B obtained in step (5), and A 1% aqueous solution of carboxymethylcellulose is mixed in water so that the solid content weight ratio is 83.1: 6.15: 6.15: 4.6, and water is added as a solvent, followed by dispersion using a bead mill. To obtain a porous membrane slurry. In addition, content of raw materials other than water (total solid content) in the porous membrane slurry was set to 50% by mass.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.7.

<(7) Production of positive electrode>
95 parts of lithium manganate having a spinel structure as a positive electrode active material and 3 parts of PVDF (polyvinylidene fluoride, manufactured by Kureha Chemical Co., Ltd., trade name: KF-1100) as an electrode binder in terms of solid content In addition, 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to obtain a slurry-like positive electrode composition (positive electrode slurry). This positive electrode slurry was applied to one side of an aluminum foil having a thickness of 18 μm, dried at 120 ° C. for 3 hours, and then roll-pressed to obtain a positive electrode having a positive electrode active material layer having a total thickness of 100 μm.

<(8) Production of negative electrode>
Solid amount of 98 parts of graphite having a particle diameter of 20 μm as a negative electrode active material and a specific surface area of 4.2 m ² / g and SBR (styrene-butadiene rubber, glass transition temperature: −10 ° C.) as an electrode binder 1 part is mixed, 1.0 part of carboxymethyl cellulose is further mixed with this mixture, water is further added as a solvent, and these are mixed with a planetary mixer to form a slurry-like negative electrode composition (negative electrode). Slurry) was prepared. This negative electrode slurry was applied to one side of a 18 μm thick copper foil, dried at 120 ° C. for 3 hours, and then roll pressed to obtain a negative electrode having a total thickness of 60 μm and having a negative electrode active material layer.

<(9) Production of secondary battery separator (organic separator with porous membrane)>
A single-layer polypropylene separator (porosity 55%, thickness 25 μm) produced by a dry method was prepared as an organic separator. On one surface of the organic separator, the porous membrane slurry obtained in the step (6) is applied using a wire bar so that the thickness after drying is 5 μm to obtain a slurry layer, and the slurry layer at 50 ° C. It was dried for 10 minutes to form a porous film. Subsequently, a porous film was similarly formed on the other surface of the organic separator, and an organic separator with a porous film having a porous film on both surfaces was obtained.

<(10) Production of Secondary Battery Having Secondary Battery Separator (Organic Separator with Porous Film)>
The positive electrode obtained in the step (7) was cut into a circle having a diameter of 13 mm to obtain a circular positive electrode. The negative electrode obtained in step (8) was cut into a circle having a diameter of 14 mm to obtain a circular negative electrode. Moreover, the organic separator with a porous film obtained in the step (9) was cut out into a circle having a diameter of 18 mm to obtain a circular organic separator with a porous film.
A circular positive electrode is placed on the inner bottom surface of a stainless steel coin-type outer container provided with polypropylene packing, a circular organic separator with a porous film is placed on it, and a circular negative electrode is placed thereon. They were placed and stored in a container. The circular positive electrode was placed so that the surface on the aluminum foil side faced the bottom surface side of the outer container and the surface on the positive electrode active material layer side faced upward. The circular negative electrode was placed so that the surface on the negative electrode active material layer side faced toward the organic separator with a circular porous film and the surface on the copper foil side faced upward. This container was vacuum-dried at 105 ° C. for 24 hours.
Inject the electrolyte into the container so that no air remains, fix the outer container with a 0.2 mm thick stainless steel cap through a polypropylene packing, seal the battery can, and 20 mm in diameter. A lithium ion secondary battery (coin cell CR2032) having a thickness of about 3.2 mm was manufactured. As an electrolytic solution, LiPF ₆ is mixed at a concentration of 1 mol / liter in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). The dissolved solution was used.

<(11) Evaluation>
The uniformity and reliability of the porous film of the obtained organic separator with a porous film, powder fall-off property, and cycle characteristics of the obtained secondary battery were evaluated. The results are shown in Table 1.

(Example 2)
After the negative electrode active material layer is completely covered with the porous film slurry obtained in the step (6) of Example 1 on the negative electrode active material layer side surface of the negative electrode obtained in the step (8) of Example 1, after drying Was applied so that the thickness of the porous film was 5 μm to obtain a slurry layer. The slurry layer was dried at 50 ° C. for 10 minutes to form a porous film, and a negative electrode with a porous film was obtained. The obtained negative electrode with a porous film had a layer structure of (porous film) / (negative electrode active material layer) / (copper foil). The uniformity and reliability of the porous film of the obtained negative electrode with a porous film, and powder fall-off property were evaluated. The results are shown in Table 1.

Instead of the organic separator with a porous membrane obtained in the step (9) of Example 1, an organic separator (single layer polypropylene separator, porosity 55%, thickness 25 μm, organic separator in the step (9) of Example 1 was used. The same as that used as a).

Further, a secondary battery was obtained and evaluated in the same manner as in Example 1 except that the above negative electrode with a porous film was used instead of the negative electrode obtained in Step (8) of Example 1. It was. The results are shown in Table 1. In placing the negative electrode with a circular porous film in the outer container, the negative electrode was placed so that the porous film side faced to the circular organic separator side and the copper foil side faced to the upper side.

(Example 3)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1. The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.7.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 89.0 parts of n-butyl acrylate, 7.0 parts of acrylonitrile, 4.0 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization. A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A1 was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. The acrylic polymer particle A has a sulfonic acid group-containing monomer unit content of 4.0%, a sulfonic acid group content of 1.56%, an acrylonitrile monomer unit content of 7%, ) The content of acrylic acid ester monomer units was 89%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 90.0 parts of n-butyl acrylate, 7.0 parts of acrylonitrile, 3.0 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization After adding 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, the mixture is sufficiently stirred, and then heated to 70 ° C. to carry out polymerization to give an unreacted monomer A polymer aqueous dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 3.0%, the content ratio of the epoxy acid group is 0.91%, the content ratio of the acrylonitrile monomer unit is 7%, ) The content of acrylic acid ester monomer units was 90.0%.

Example 4
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.7.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 66.1 parts of n-butyl acrylate, 29.9 parts of acrylonitrile, 4.0 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. The acrylic polymer particle A has a sulfonic acid group-containing monomer unit content of 4.0%, a sulfonic acid group content of 1.56%, an acrylonitrile monomer unit content of 29.9%, The content ratio of the (meth) acrylic acid ester monomer unit was 66.1%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 66.8 parts of n-butyl acrylate, 30.2 parts of acrylonitrile, 3.0 parts of glycidyl methacrylate, 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 3.0%, the content ratio of the epoxy acid group is 0.91%, the content ratio of the acrylonitrile monomer unit is 30.2%, The content ratio of the (meth) acrylic acid ester monomer unit was 66.8%.

(Example 5)
The same operation as in Example 1 was performed except that the porous film slurry was produced using the following nonconductive particles instead of the nonconductive particles obtained in the steps (1) to (3) of Example 1. The organic separator with a porous membrane and the secondary battery were obtained and evaluated. The results are shown in Table 1.

<Manufacture of non-conductive particles>
In a reactor equipped with a stirrer, 10 parts of an aqueous dispersion of seed polymer particles B obtained in steps (1) and (2) of Example 1 on a solids basis (ie, based on the weight of seed polymer particles B), divinyl A mixture of benzene and ethyl vinyl benzene (monomer mixture ratio: divinyl benzene / ethyl vinyl benzene = 60/40, manufactured by Nippon Steel Chemical Co., Ltd., product name: DVB-570), 33 parts, ethyl vinyl benzene 57 parts, 1 part of sodium dodecylbenzenesulfonate, 5 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: perbutyl O) as a polymerization initiator, and 200 parts of ion-exchanged water were added. By stirring at 35 ° C. for 12 hours, the seed polymer particles B were completely absorbed with the monomer mixture and the polymerization initiator. Thereafter, this was polymerized at 90 ° C. for 4 hours. Thereafter, steam was introduced to remove unreacted monomers.
This obtained the water dispersion of the nonelectroconductive particle with an average particle diameter of 0.4 micrometer.
Composition of monomers (styrene, methacrylic acid, divinylbenzene, and ethylvinylbenzene) used from formation of seed polymer particles to obtaining nonconductive particles, and heat resistance temperature (T10 value) of nonconductive particles, The average circularity and particle size distribution are as shown in Table 1.

(Example 6)
The same operation as in Example 1 was performed except that the porous film slurry was produced using the following nonconductive particles instead of the nonconductive particles obtained in the steps (1) to (3) of Example 1. The organic separator with a porous membrane and the secondary battery were obtained and evaluated. The results are shown in Table 1.

<Production of seed polymer particle A>
In a reactor equipped with a stirrer, 95 parts of styrene, 5 parts of divinylbenzene, 1.0 part of sodium dodecylbenzenesulfonate, 100 parts of ion-exchanged water, and 0.5 part of potassium persulfate are placed at 80 ° C. for 8 hours. Polymerized. Thereby, an aqueous dispersion of seed polymer particles A having an average particle diameter of 60 nm was obtained.

<Manufacture of non-conductive particles>
The average circularity is 0.91 except that the aqueous dispersion of the seed polymer particles A is used in a reactor equipped with a stirrer, in the same manner as in steps (2) and (3) of Example 1. An aqueous dispersion of non-conductive particles was obtained. Composition of monomers (styrene, methacrylic acid, divinylbenzene, and ethylvinylbenzene) used from formation of seed polymer particles to obtaining nonconductive particles, and heat resistance temperature (T10 value) of nonconductive particles, The average particle size and particle size distribution are as shown in Table 1.

(Example 7)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 3.4.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 80.2 parts of n-butyl acrylate, 14.8 parts of acrylonitrile, 5.0 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. The acrylic polymer particle A has a sulfonic acid group-containing monomer unit content of 5.0%, a sulfonic acid group content of 1.95%, and an acrylonitrile monomer unit content of 14.8%. The content ratio of the (meth) acrylic acid ester monomer unit was 80.2%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 82.9 parts of n-butyl acrylate, 15.2 parts of acrylonitrile, 1.9 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 1.9%, the content ratio of the epoxy acid group is 0.58%, the content ratio of the acrylonitrile monomer unit is 15.2%, The content ratio of the (meth) acrylic acid ester monomer unit was 82.9%.

(Example 8)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 0.6.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 82.6 parts of n-butyl acrylate, 15.2 parts of acrylonitrile, 2.2 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator Mercaptan 0.05 part, potassium persulfate 0.3 part as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier was added, and after stirring sufficiently, the mixture was heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 2.2%, the content ratio of the sulfonic acid group is 0.86%, the content ratio of the acrylonitrile monomer unit is 15.2%, The content ratio of the (meth) acrylic acid ester monomer unit was 82.6%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 80.5 parts of n-butyl acrylate, 14.8 parts of acrylonitrile, 4.7 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, and unreacted monomers are removed. An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 4.7%, the content ratio of the epoxy acid group is 1.42%, the content ratio of the acrylonitrile monomer unit is 14.8%, The content ratio of the (meth) acrylic acid ester monomer unit was 80.5%.

Example 9
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 2.8.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 76.2 parts of n-butyl acrylate, 14.0 parts of acrylonitrile, 9.8 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 9.8%, the content ratio of the sulfonic acid group is 3.82%, the content ratio of the acrylonitrile monomer unit is 14.0%, The content ratio of the (meth) acrylic acid ester monomer unit was 76.2%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 80.6 parts of n-butyl acrylate, 14.9 parts of acrylonitrile, 4.5 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 4.5%, the content ratio of the epoxy acid group is 1.36%, the content ratio of the acrylonitrile monomer unit is 14.9%, The content ratio of the (meth) acrylic acid ester monomer unit was 80.6%.

(Example 10)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.8.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 83.6 parts of n-butyl acrylate, 15.4 parts of acrylonitrile, 1.0 part of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization, A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 1.0%, the content ratio of the sulfonic acid group is 0.39%, the content ratio of the acrylonitrile monomer unit is 15.4%, The content ratio of the (meth) acrylic acid ester monomer unit was 83.6%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 83.9 parts of n-butyl acrylate, 15.4 parts of acrylonitrile, 0.7 part of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, and unreacted monomers are removed. An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 0.7%, the content ratio of the epoxy acid group is 0.21%, the content ratio of the acrylonitrile monomer unit is 15.4%, The content ratio of the (meth) acrylic acid ester monomer unit was 83.9%.

(Example 11)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles A were used. Moreover, the following acrylic polymer particle B was used instead of the acrylic polymer particle B obtained in the step (5) of Example 1. Except that the porous polymer slurry was produced using the acrylic polymer particles A and the acrylic polymer particles B, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation Went. The results are shown in Table 1.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.5.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion exchange water, 77.9 parts of n-butyl acrylate, 14.4 parts of acrylonitrile, 7.7 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization. A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 7.7%, the content ratio of the sulfonic acid group is 3.00%, the content ratio of the acrylonitrile monomer unit is 14.4%, The content ratio of the (meth) acrylic acid ester monomer unit was 77.9%.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 78.7 parts of n-butyl acrylate, 14.5 parts of acrylonitrile, 6.8 parts of glycidyl methacrylate, and 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, polymerization Put 0.3 parts of potassium persulfate as an initiator and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, and after sufficiently stirring, the mixture is heated to 70 ° C. to perform polymerization, and unreacted monomers are removed. An aqueous polymer dispersion containing was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle B, the content ratio of the monomer unit having an epoxy acid group is 6.8%, the content ratio of the epoxy acid group is 2.06%, the content ratio of the acrylonitrile monomer unit is 14.5%, The content ratio of the (meth) acrylic acid ester monomer unit was 78.7%.

(Example 12)
The same operation as in Example 1 was performed except that the porous film slurry was produced using the following nonconductive particles instead of the nonconductive particles obtained in the steps (1) to (3) of Example 1. The organic separator with a porous membrane and the secondary battery were obtained and evaluated. The results are shown in Table 1.

<Manufacture of seed polymer particles C>
In a reactor equipped with a stirrer, 2 parts of the aqueous dispersion of seed polymer particles B obtained in step (2) of Example 1 on a solids basis (ie, based on the weight of seed polymer particles B), sodium dodecylbenzenesulfonate 0.2 parts, 0.5 parts of potassium persulfate and 100 parts of ion-exchanged water were mixed to obtain a mixture, and the temperature was raised to 80 ° C. Meanwhile, in another container, 97 parts of styrene, 3 parts of methacrylic acid, 4 parts of t-dodecyl mercaptan, 0.5 part of sodium dodecylbenzenesulfonate, and 100 parts of ion-exchanged water were mixed to disperse the monomer mixture. The body was prepared. The monomer mixture dispersion was continuously added to the mixture for 4 hours to polymerize. The temperature of the reaction system during continuous addition of the dispersion of the monomer mixture was maintained at 80 ° C. to carry out the reaction. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours.
Thereby, an aqueous dispersion of seed polymer particles C having an average particle diameter of 400 nm was obtained.

<Manufacture of non-conductive particles>
Using the seed polymer particle C in place of the seed polymer particle B obtained in the step (2) of Example 1, the same operation as in the step (3) of Example 1 was performed to obtain a non-conductive material having an average particle diameter of 700 nm. An aqueous dispersion of conductive particles was obtained. Composition of monomers (styrene, methacrylic acid, divinylbenzene, and ethylvinylbenzene) used from formation of seed polymer to obtaining nonconductive particles, heat resistance temperature (T10 value) of nonconductive particles, average The circularity and particle size distribution are as shown in Table 1.

(Example 13)
The same operation as in Example 1 was performed except that the porous film slurry was produced using the following nonconductive particles instead of the nonconductive particles obtained in the steps (1) to (3) of Example 1. The organic separator with a porous membrane and the secondary battery were obtained and evaluated. The results are shown in Table 1.

<Manufacture of non-conductive particles>
Instead of the monomer mixture used in step (3) of Example 1, a mixture of divinylbenzene and ethylvinylbenzene (monomer mixture ratio: divinylbenzene / ethylvinylbenzene = 82/18, Nippon Steel Chemical Co., Ltd.) Product, product name: DVB-810) and non-conductive particles having an average particle diameter of 400 nm by performing the same operation as in step (3) of Example 1 except that 72 parts and 18 parts of methyl methacrylate were used. An aqueous dispersion was obtained. Composition of monomers (styrene, methacrylic acid, divinylbenzene, ethylvinylbenzene, and methyl methacrylate) used from formation of seed polymer particles to obtaining nonconductive particles, and heat resistance temperature of nonconductive particles (T10) Value), average circularity and particle size distribution are as shown in Table 1.

(Example 14)
<Preparation of NMP dispersion of non-conductive particles>
After adding 200 parts of N-methyl-2-pyrrolidone (NMP) to 100 parts of an aqueous dispersion of non-conductive particles obtained in step (3) of Example 1 (solid content concentration: 20%) and mixing them well. The water and NMP in the system were distilled off in a 90 ° C. reduced pressure environment to obtain an NMP dispersion of nonconductive particles (solid content concentration 20%).

<Preparation of NMP dispersion of acrylic polymer particles A>
After adding 760 parts of NMP to 100 parts of the aqueous dispersion of acrylic polymer particles A obtained in the step (4) of Example 1 (solid content is 40%) and mixing them well, And NMP were distilled off to obtain an NMP dispersion (solid content: 10%) of acrylic polymer particles A.

<Preparation of NMP dispersion of acrylic polymer particles B>
After adding 760 parts of NMP to 100 parts (solid content is 40%) of the aqueous dispersion of acrylic polymer particles B obtained in the step (5) of Example 1 and mixing them well, And NMP were distilled off to obtain an NMP dispersion (solid content: 10%) of acrylic polymer particles B.

<Manufacture of porous membrane slurry>
The solid content ratio of the NMP dispersion of non-conductive particles, the NMP dispersion of acrylic polymer particles A, and the NMP dispersion of acrylic polymer particles B obtained in the above steps is 87.0: 6.5: 6. To obtain a porous membrane slurry having a solid content concentration of 18%.
The weight ratio of acrylic polymer particles A to acrylic polymer particles B in the porous membrane slurry (acrylic polymer particles A / acrylic polymer particles B) is 1, and the weight ratio of sulfonic acid groups to epoxy groups in the binder (sulfone Acid group / epoxy group) was 1.7.

<Manufacture of negative electrode with porous film>
On the negative electrode active material layer side surface of the negative electrode obtained in the step (8) of Example 1, the negative electrode active material layer is completely covered with the porous film slurry obtained in the above step, and the porous film thickness after drying is The slurry layer was obtained by applying to 5 μm. The slurry layer was dried at 100 ° C. for 10 minutes to form a porous film, and a negative electrode with a porous film was obtained. The obtained negative electrode with a porous film had a layer structure of (porous film) / (negative electrode active material layer) / (copper foil). The uniformity and reliability of the porous film of the obtained negative electrode with a porous film, and powder fall-off property were evaluated. The results are shown in Table 1.

<Production of secondary battery having negative electrode with porous film>
Instead of the organic separator with a porous membrane obtained in the step (9) of Example 1, an organic separator (single layer polypropylene separator, porosity 55%, thickness 25 μm, organic separator in the step (9) of Example 1 was used. The same as that used as a).

(Comparative Example 1)
Example 1 except that the porous polymer slurry was produced using the following acrylic polymer particles C instead of the acrylic polymer particles A and B obtained in the steps (4) and (5) of Example 1. The same operation was performed to obtain an organic separator with a porous film and a secondary battery and evaluated. The results are shown in Table 1.

<Preparation of acrylic polymer particle C>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 81.5 parts of n-butyl acrylate, 15.0 parts of acrylonitrile, 2.0 parts of 2-acrylamido-2-methylpropanesulfonic acid, 1.5 parts of glycidyl methacrylate and Add 0.05 parts of t-dodecyl mercaptan as a molecular weight regulator, 0.3 parts of potassium persulfate as a polymerization initiator, and 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier. Polymerization was performed by heating to obtain an aqueous polymer dispersion containing unreacted monomers. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles C was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. The acrylic polymer particle C had a sulfonic acid group and an epoxy group, and the acrylic polymer particle C had a sulfonic acid group content of 0.78% and an epoxy group content of 0.45%.

(Comparative Example 2)
Instead of the acrylic polymer particles B obtained in the step (5) of Example 1, instead of using the acrylic polymer particles A obtained in the step (4) of Example 1, the following acrylic polymer particles B were used. Except that the porous membrane slurry was produced, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation was performed. The results are shown in Table 1.

(Comparative Example 3)
Instead of the acrylic polymer particles A obtained in the step (4) of Example 1, instead of using the acrylic polymer particles B obtained in the step (5) of Example 1, the following acrylic polymer particles A were used. Except that the porous membrane slurry was produced, the same operation as in Example 1 was performed to obtain an organic separator with a porous membrane and a secondary battery, and evaluation was performed. The results are shown in Table 1.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 78.7 parts of n-butyl acrylate, 14.5 parts of acrylonitrile, 6.8 parts of 2-acrylamido-2-methylpropanesulfonic acid and t-dodecyl as a molecular weight regulator 0.05 parts of mercaptan, 0.3 parts of potassium persulfate as a polymerization initiator, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, sufficiently stirred, and then heated to 70 ° C. for polymerization. A polymer aqueous dispersion containing an unreacted monomer was obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained. The polymerization conversion rate determined from the solid content concentration was approximately 99%. In the acrylic polymer particle A, the content ratio of the monomer unit having a sulfonic acid group is 6.8%, the content ratio of the sulfonic acid group is 2.65%, the content ratio of the acrylonitrile monomer unit is 14.5%, The content ratio of the (meth) acrylic acid ester monomer unit was 78.7%.

(Comparative Example 4)
The same operation as in Example 1 was performed except that a porous membrane slurry was produced using the following acrylic polymer particles A instead of the acrylic polymer particles A obtained in the step (4) of Example 1. An organic separator with a porous film and a secondary battery were obtained and evaluated. The results are shown in Table 1. In addition, the acrylic polymer particle B used the thing similar to the acrylic polymer particle B obtained at the process (5) of Example 1. FIG.

<Preparation of acrylic polymer particle A>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 84.5 parts of n-butyl acrylate, 15.5 parts of acrylonitrile, 0.05 part of t-dodecyl mercaptan as a molecular weight regulator, and potassium persulfate as a polymerization initiator were added in an amount of 0. 3 parts, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier is added, and after sufficiently stirring, polymerization is carried out by heating to 70 ° C., and a polymer aqueous dispersion containing unreacted monomers is prepared. Obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles A was obtained.
The polymerization conversion rate determined from the solid content concentration was approximately 99%. The content ratio of the monomer unit having a sulfonic acid group in the acrylic polymer particle A is 0%, the content ratio of the sulfonic acid group is 0%, the content ratio of the acrylonitrile monomer unit is 15.5%, (meth) acrylic The content rate of the acid ester monomer unit was 84.5%.

(Comparative Example 5)
The same operation as in Example 1 was performed except that a porous membrane slurry was produced using the following acrylic polymer particles B instead of the acrylic polymer particles B obtained in the step (5) of Example 1. An organic separator with a porous film and a secondary battery were obtained and evaluated. The results are shown in Table 1. In addition, the acrylic polymer particle A used the thing similar to the acrylic polymer particle A obtained at the process (4) of Example 1. FIG.

<Preparation of acrylic polymer particle B>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 84.5 parts of n-butyl acrylate, 15.5 parts of acrylonitrile, 0.05 part of t-dodecyl mercaptan as a molecular weight modifier, and potassium persulfate as a polymerization initiator were added in an amount of 0. 3 parts, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier is added, and after sufficiently stirring, polymerization is carried out by heating to 70 ° C., and a polymer aqueous dispersion containing unreacted monomers is prepared. Obtained. Next, the aqueous polymer dispersion was cooled to 25 ° C., and aqueous ammonia was added to adjust the pH to 7. Steam was introduced to remove unreacted monomers, and the average particle size was reduced to 0. An aqueous dispersion of 18 μm acrylic polymer particles B was obtained.
The polymerization conversion rate determined from the solid content concentration was approximately 99%.
The content ratio of the monomer unit having an epoxy acid group in the acrylic polymer particle B is 0%, the content ratio of the epoxy acid group is 0%, the content ratio of the acrylonitrile monomer unit is 15.5%, (meth) acrylic The content rate of the acid ester monomer unit was 84.5%.

(Comparative Example 6)
Other than having produced the porous membrane slurry using the acrylic polymer C obtained in Comparative Example 1 instead of the acrylic polymer particles A and B obtained in the steps (4) and (5) of Example 2, The same operation as in Example 2 was performed to obtain a negative electrode with a porous film and a secondary battery, and evaluation was performed. The results are shown in Table 1.

From the results in Table 1, the following can be said.
Secondary battery porous membrane slurry comprising non-conductive particles containing an organic polymer, and a binder, wherein the binder comprises acrylic polymer particles A having sulfonic acid groups and acrylic polymer particles B having epoxy groups The secondary battery separator, the secondary battery electrode and the secondary battery having the secondary battery porous film formed using Examples 1 to 14 are excellent in the balance of the uniformity, reliability and cycle characteristics of the porous film.
On the other hand, when using a binder having a sulfonic acid group and an epoxy group in one polymer particle (Comparative Examples 1 and 6), using a binder having no sulfonic acid group (Comparative Examples 2 and 4), and In the case of using a binder having no epoxy group (Comparative Examples 3 and 5), the balance of the uniformity, reliability, and cycle characteristics of the porous film is inferior.

Claims

Comprising non-conductive particles containing organic polymer, binder and solvent,
The secondary battery porous membrane slurry in which the binder contains acrylic polymer particles A having sulfonic acid groups and acrylic polymer particles B having epoxy groups.
The secondary battery porous membrane slurry according to claim 1, wherein the content ratio of the nonconductive particles per 100 mass% of the total solid content is 70 to 97 mass%, and the content ratio of the binder is 0.5 to 20 mass%. .
The acrylic polymer particles A and the acrylic polymer particles B are
The secondary battery porous membrane slurry according to claim 1 or 2, comprising a (meth) acrylonitrile monomer unit and a (meth) acrylic acid ester monomer unit.
In the acrylic polymer particles A and the acrylic polymer particles B,
The content ratio of the (meth) acrylonitrile monomer unit in the polymer particles is 2.5 to 40% by mass,
The secondary battery porous membrane slurry according to claim 3, wherein the content ratio of the (meth) acrylate monomer units in the polymer particles is 60 to 97.5 mass%.
The secondary according to any one of claims 1 to 4, wherein a weight ratio of the acrylic polymer particles A to the acrylic polymer particles B (acrylic polymer particles A / acrylic polymer particles B) is 0.3 to 3. Battery porous membrane slurry.
The sulfonic acid group content in the acrylic polymer particles A is 0.04 to 5.8% by mass, and the epoxy group content in the acrylic polymer particles B is 0.03 to 3.0% by mass. Item 6. The secondary battery porous membrane slurry according to any one of Items 1 to 5.
The weight ratio of the sulfonic acid groups in the acrylic polymer particles A to the epoxy groups in the acrylic polymer particles B (sulfonic acid groups / epoxy groups) in the binder is 0.2 to 3. A secondary battery porous membrane slurry according to claim 1.
The temperature at which the weight loss ratio of the non-conductive particles reaches 10% by mass when heated at a rate of temperature increase of 10 ° C./min in a nitrogen atmosphere by a thermobalance is 250 ° C. or more,
The non-conductive particles have an average particle size of 0.1 to 2.0 μm;
The secondary battery porous membrane slurry according to any one of claims 1 to 7, wherein the non-conductive particles have an average circularity of 0.900 to 0.995.
A secondary battery porous membrane obtained by forming the secondary battery porous membrane slurry according to any one of claims 1 to 8 into a film shape and drying it.
Current collector,
An electrode active material layer comprising an electrode active material and an electrode binder, which is attached to the current collector; and
A secondary battery electrode comprising the secondary battery porous film according to claim 9, which is laminated on a surface of the electrode active material layer.
Organic separator,
A secondary battery separator comprising the secondary battery porous film according to claim 9, which is laminated on the organic separator.
A secondary battery including a positive electrode, a negative electrode, an organic separator, and an electrolyte solution, wherein the secondary battery porous film according to claim 9 is laminated on any of the positive electrode, the negative electrode, and the organic separator.
A method for producing a secondary battery porous membrane, comprising a step of applying the secondary battery porous membrane slurry according to any one of claims 1 to 8 to a substrate and then drying.