JP5516919B2 - Secondary battery porous membrane, slurry for secondary battery porous membrane, and secondary battery - Google Patents

Description

  The present invention relates to a porous membrane, and more particularly to a secondary battery porous membrane that is formed on the surface of an electrode or separator of a lithium ion secondary battery or an electric double layer capacitor and can contribute to improvement of flexibility and battery cycle characteristics. The present invention also relates to a slurry for a secondary battery porous film for forming such a porous film, and a secondary battery provided with such a porous film.

  Among batteries in practical use, lithium ion secondary batteries exhibit the highest energy density, and are often used particularly 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.

  A lithium ion secondary battery generally includes a positive electrode and a negative electrode including an electrode mixture layer (hereinafter sometimes referred to as an “electrode active material layer”) carried on a current collector, a separator, and a non-aqueous electrolyte. . The electrode mixture layer includes an electrode active material having an average particle size of about 5 to 50 μm and a binder. The electrode is manufactured by applying a mixture slurry containing a powdered electrode active material on a current collector to form an electrode mixture layer. Moreover, as a separator for separating a positive electrode and a negative electrode, a very thin separator having a thickness of about 10 to 50 μm is used. A lithium ion secondary battery is manufactured through a lamination process of an electrode and a separator, a cutting process of cutting into a predetermined electrode shape, and the like. However, while passing through this series of manufacturing steps, the active material may fall off from the electrode mixture layer, and a part of the dropped active material may be included in the battery as foreign matter.

  Such a foreign substance has a particle size of about 5 to 50 μm and is about the same as the thickness of the separator, so that it causes a problem of penetrating the separator in the assembled battery and causing a short circuit. Further, heat is generated when the battery is operated. As a result, the separator made of stretched polyethylene resin or the like is also heated. In general, a separator made of a stretched polyethylene resin or the like tends to shrink even at a temperature of 150 ° C. or lower, and easily leads to a short circuit of the battery. Further, when a sharply shaped protrusion such as a nail penetrates the battery (for example, during a nail penetration test), a short circuit occurs instantaneously, reaction heat is generated, and the short circuit part expands.

  In order to solve such problems, it has been proposed to provide a porous protective film on the electrode surface. By providing a porous protective film, the active material is prevented from falling off during the battery production process, and a short circuit during battery operation is prevented. Furthermore, since the protective film is porous, the electrolytic solution penetrates into the protective film and does not inhibit the battery reaction.

On the other hand, as the negative electrode active material, carbon materials such as graphite, which can occlude and release lithium ions, lithium metals or alloys thereof, and metal oxides such as TiO ₂ and SnO ₂ are also used. In the negative electrode active material, conductive impurities such as a very small amount of iron may be included, and as these charge and discharge, a dendritic metal deposit is formed on the negative electrode surface, so the capacity and life of the battery are reduced. There is a problem to decrease safety. As the positive electrode active material, an active material containing a transition metal such as iron, manganese, cobalt, chromium and copper is used. When secondary batteries using these active materials are repeatedly charged and discharged, transition metal ions are eluted into the electrolytic solution, resulting in a decrease in battery capacity and cycle characteristics, which is a big problem.

  Another major problem is that transition metal ions eluted from the positive electrode are reduced and deposited on the negative electrode surface to form dendritic metal precipitates, which damage the separator, thereby reducing the safety of the battery. It is said that.

  Patent Document 1 describes a porous film formed using a slurry in which an inorganic filler is dispersed in a resin binder composed of a water-soluble polymer such as carboxymethyl cellulose and an acrylonitrile-acrylate copolymer. Patent Document 2 describes a porous film formed using an aqueous slurry composed of a binder containing ethyl acrylate, itaconic acid, and acrylonitrile, and an inorganic filler. Further, a secondary battery manufactured by laminating the porous film on an active material layer of an electrode is described. Furthermore, Patent Document 2 describes that a positive electrode active material containing cobalt is used, and excellent filler dispersibility and improvement in cycle characteristics at room temperature have been confirmed.

International Patent Publication WO2005 / 011043 International Patent Publication WO2009 / 123168

  However, according to the inventor's study, the aqueous slurry described in Patent Documents 1 and 2 can be stored for a long period of time during storage in a storage tank after manufacture, during filling and shipping in a transport container such as a container or a plastic container. Then, a change in viscosity of the slurry may occur, and further, aggregates may be generated. As a result, a porous film having a uniform film thickness may not be manufactured.

  Furthermore, when the secondary battery described in Patent Document 2 is repeatedly charged and discharged at a high temperature, there is a problem that transition metal ions (cobalt ions) are eluted in the electrolytic solution, resulting in a decrease in battery capacity. As a result, it was found that there is a problem that the life (cycle characteristics) and safety of the battery are lowered due to dendritic precipitation of the eluted transition metal ions on the negative electrode surface.

  Therefore, the present invention uses a porous membrane that is manufactured using a slurry for porous membranes that is excellent in long-term storage stability and can improve the cycle characteristics and safety at high temperatures of the obtained secondary battery, and uses the porous membrane. The purpose is to provide a secondary battery.

  Therefore, as a result of the study by the present inventors, it was found that long-term slurry for porous membranes can be obtained by containing a binder having a specific composition, non-conductive particles, a specific amount of isothiazoline-based compound, and a specific amount of chelate compound. It has been found that the storage stability is improved, the flexibility of the resulting porous membrane is improved, and the cycle characteristics and safety at high temperatures of a secondary battery using the porous membrane can be improved.

The gist of the present invention aimed at solving such problems is as follows.
(1) a binder comprising a polymer unit of a (meth) acrylic acid ester monomer, a polymer unit of a vinyl monomer having an acidic group, and a polymer unit of an α, β-unsaturated nitrile monomer, non-conductive particles, Including an isothiazoline-based compound and a chelate compound,
The content of the isothiazoline-based compound is 0.001 to 1.0 parts by mass with respect to 100 parts by mass of the binder,
The secondary battery porous membrane whose content of the said chelate compound is 0.001-1.0 mass part with respect to 100 mass parts of said binders.

(2) The isothiazoline compound comprises a benzoisothiazoline compound and 2-methyl-4-isothiazolin-3-one,
The secondary battery porous film according to (1), wherein a mass ratio of the benzoisothiazoline-based compound to the 2-methyl-4-isothiazolin-3-one is in a range of 2/8 to 8/2.

(3) The content ratio of the polymerization unit of the (meth) acrylic acid ester monomer is 50 to 98 mass%, and the content ratio of the polymerization unit of the vinyl monomer having an acidic group is 1.0 to 3.0 mass%. The secondary battery porous membrane according to (1) or (2), wherein the polymer unit content ratio of the α, β-unsaturated nitrile monomer is 1.0 to 50% by mass.

(4) The binder further comprises a polymerized unit having crosslinkability,
The secondary battery porous membrane according to any one of (1) to (3), wherein a content ratio of the cross-linkable polymer unit is 0.01 to 2.0 mass%.

(5) a polymerization unit of (meth) acrylic acid ester monomer, a polymerization unit of vinyl monomer having an acidic group, and a binder comprising a polymerization unit of α, β-unsaturated nitrile monomer, non-conductive particles, Including an isothiazoline-based compound, a chelate compound, and a solvent,
The content of the isothiazoline-based compound is 0.001 to 1.0 parts by mass with respect to 100 parts by mass of the binder,
The slurry for secondary battery porous films whose content of the said chelate compound is 0.001-1.0 mass part with respect to 100 mass parts of said binders.

(6) A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte solution,
A secondary battery in which the porous film according to any one of (1) to (4) is laminated on any of the positive electrode, the negative electrode, and the separator.

  According to the present invention, the secondary battery porous membrane includes a polymerization unit of (meth) acrylate monomer, a polymerization unit of vinyl monomer having an acidic group, and a polymerization unit of α, β-unsaturated nitrile monomer. The flexibility of the porous film is improved by including a binder, non-conductive particles, a specific amount of an isothiazoline-based compound, and a specific amount of a chelate compound. Further, the cycle characteristics and safety at a high temperature of the secondary battery using the porous film are improved. Furthermore, the slurry for a secondary battery porous membrane for forming the porous membrane is excellent in long-term storage stability.

  Hereinafter, (1) secondary battery porous membrane, (2) slurry for secondary battery porous membrane, and (3) secondary battery of the present invention will be described in order.

(1) Secondary Battery Porous Membrane The secondary battery porous membrane of the present invention (hereinafter sometimes referred to as “porous membrane”) is a porous membrane installed between the positive electrode and the negative electrode of the secondary battery. And contains a binder having a specific composition, non-conductive particles, a specific amount of an isothiazoline-based compound, and a specific amount of a chelate compound. The porous film is used by being laminated on a separator or an electrode. Note that the porous membrane itself can function as a separator.

(binder)
The binder comprises a polymerization unit of (meth) acrylic acid ester monomer, a polymerization unit of vinyl monomer having an acidic group, and a polymerization unit of α, β-unsaturated nitrile monomer. Specifically, each polymer unit is contained in a polymer as a binder.

  In the present invention, the polymerization unit of (meth) acrylate monomer is, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate. , Alkyl acrylates such as octyl acrylate, 2-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, hex Methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Among these, non-carbonyl oxygen is shown because it exhibits lithium ion conductivity by moderate swelling into the electrolyte without eluting into the electrolyte, and in addition, it is difficult to cause bridging aggregation by the polymer in the dispersion of the active material. Preferred are heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, and lauryl acrylate, which are alkyl acrylates having 7 to 13 carbon atoms in the alkyl group bonded to the atom, and bonded to a non-carbonyl oxygen atom. More preferred are octyl acrylate, 2-ethylhexyl acrylate, and nonyl acrylate having 8 to 10 carbon atoms in the alkyl group.

In the present invention, the vinyl monomer having an acidic group may be any vinyl monomer having an acidic group. Among them, preferred examples of the acidic group include -COOH group (carboxylic acid group), -OH group ( hydroxyl), - SO ₃ H group (sulfonic acid group), - _PO 3 _{H 2} group, the -PO (OH) (oR) group (R represents a hydrocarbon group), and a lower polyoxyalkylene groups. Moreover, the vinyl monomer which has an acid anhydride group which produces | generates a carboxylic acid group by hydrolysis can be used similarly.

  Examples of the monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids, and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, and the like. Can be mentioned. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like. Dicarboxylic acid derivatives include methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid and the like methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, And maleate esters such as octadecyl maleate and fluoroalkyl maleate. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; 2-hydroxyethyl acrylate, 2-hydroxy acrylate Ethylenic unsaturation such as propyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate alkanol esters of carboxylic acids; formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m -H (m is 2 to 9 integer, n represents 2 to 4 integer, ^{R 1} is hydrogen or methyl Ester of polyalkylene glycol and (meth) acrylic acid represented by 2-hydride; Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as xylethyl-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 Ters; 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 Mono (meth) allyl ethers of halogen and hydroxy-substituted products of (poly) alkylene glycols such as -3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; eugenol, isoeugenol Mono (meth) allyl ethers of monohydric phenols and halogen-substituted products thereof; (meth) ants of alkylene glycols such as (meth) allyl-2-hydroxyethylthioether and (meth) allyl-2-hydroxypropylthioether Thioethers; and the like.

  Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropane sulfone. Acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like.

Examples of the monomer having a —PO ₃ H ₂ group and / or —PO (OH) (OR) group (R represents a hydrocarbon group) include 2- (meth) acryloyloxyethyl phosphate, methyl-2 phosphate -(Meth) acryloyloxyethyl, ethyl phosphate- (meth) acryloyloxyethyl and the like.

  Examples of the monomer having a lower polyoxyalkylene group include poly (alkylene oxide) such as poly (ethylene oxide).

  Among these, a monomer having a carboxylic acid group is preferable because the obtained porous film has excellent adhesion to an electrode active material layer or a separator, which will be described later, and efficiently captures transition metal ions eluted from the positive electrode active material. Among them, among them, a monocarboxylic acid having 5 or less carbon atoms having one carboxylic acid group such as acrylic acid or methacrylic acid, or a dicarboxylic acid having 5 or less carbon atoms having two carboxylic acid groups such as maleic acid or itaconic acid. Is preferred. Furthermore, acrylic acid and methacrylic acid are preferable from the viewpoint that the prepared slurry has high storage stability.

  In the present invention, the polymerization unit of the α, β-unsaturated nitrile monomer is preferably acrylonitrile or methacrylonitrile from the viewpoint of improving the mechanical strength and binding power of the binder.

  In the present invention, the content ratio of the polymerization units of the (meth) acrylate monomer in the binder (hereinafter sometimes referred to as “component A”) is preferably 50 to 98% by mass, more preferably 60 to 97.5. It is 70 mass%, Most preferably, it is 70-95 mass%. Further, the content ratio of the polymerization unit of the vinyl monomer having an acidic group (hereinafter sometimes referred to as “component B”) is preferably 1.0 to 3.0% by mass, more preferably 1.5 to 2.%. 5% by mass. In addition, the content ratio of the polymerization units of the α, β-unsaturated nitrile monomer (hereinafter sometimes referred to as “component C”) is preferably 1.0 to 50% by mass, more preferably 2.5 to 40%. It is 5.0 mass%, Most preferably, it is 5.0-30 mass%. When the content ratio of Component A, Component B, and Component C is in the above range, the binder can be improved in mechanical strength, flexibility, production stability, and storage stability, and sufficient binder binding strength can be obtained. Therefore, the cycle characteristics of the secondary battery using the porous film of the present invention are improved.

In the present invention, it is preferable that the binder to be used further contains a polymerized unit having crosslinkability in addition to the above components A, B and C. The polymerized unit having crosslinkability in the present invention may be a polymerized unit of a monomer having a crosslinkable group.
Examples of the method for introducing a polymerized unit of a monomer having a crosslinkable group into the binder include a method for introducing a photocrosslinkable crosslinkable group into the binder and a method for introducing a heat crosslinkable crosslinkable group. Among these, the method of introducing a heat-crosslinkable crosslinkable group into the binder can crosslink the binder by applying heat treatment to the substrate (electrode or separator) after applying the slurry for the porous membrane, and further electrolyzing the binder. It is preferable because dissolution in the liquid can be suppressed, a tough and flexible substrate with a porous film can be obtained, and battery life characteristics are improved. In the case of introducing a heat-crosslinkable crosslinkable group into the binder, a method using a monofunctional monomer having one olefinic double bond having a heat-crosslinkable crosslinkable group, and at least two olefinic double bonds There is a method using a polyfunctional monomer having a bond.

  The thermally crosslinkable group contained in the monofunctional monomer having one olefinic double bond is at least one selected from the group consisting of an epoxy group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. The epoxy group is more preferable in terms of easy crosslinking and adjustment of the crosslinking density.

Examples of the monomer containing an epoxy group include a monomer containing a carbon-carbon double bond and an epoxy group.
Examples of the monomer containing a carbon-carbon double bond and an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; butadiene monoepoxide, chloroprene mono Monoepoxides of dienes or polyenes such as epoxides, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene; 3,4-epoxy Alkenyl epoxides such as -1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl Glycidyl esters of unsaturated carboxylic acids such as disorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid; It is done.

  Examples of the monomer containing an N-methylolamide group include (meth) acrylamides having a methylol group such as N-methylol (meth) acrylamide.

  Examples of the monomer containing an oxetanyl group include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl)- 2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, 2-((meth) acryloyloxymethyl) -4-trifluoromethyloxetane, and the like can be given.

  Monomers containing an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, Examples include 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline and the like.

  Polyfunctional monomers having at least two olefinic double bonds include allyl acrylate or allyl methacrylate, trimethylolpropane-triacrylate, trimethylolpropane-methacrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol diethylene. Preference is given to vinyl ether, hydroquinone diallyl ether, tetraallyloxyethane or other allyl or vinyl ethers of polyfunctional alcohols, tetraethylene glycol diacrylate, triallylamine, trimethylolpropane-diallyl ether, methylenebisacrylamide and / or divinylbenzene. In particular, allyl acrylate, allyl methacrylate, trimethylolpropane-triacrylate and / or trimethylolpropane-methacrylate and the like can be mentioned.

  Among these, a polyfunctional monomer having at least two olefinic double bonds is preferable because the crosslinking density is easily improved, and allyl acrylate or allyl is preferable because the crosslinking density is improved and the copolymerization is high. An acrylate or methacrylate having an allyl group such as methacrylate is preferred.

  The content ratio of the polymerization unit of the monomer having a crosslinkable group in the binder is the same as the blending amount of the monomer containing the crosslinkable group at the time of polymerization. Preferably it is 0.01-2.0 mass%, More preferably, it is 0.05-1.5 mass%, Most preferably, it is the range of 0.1-1.0 mass%. The polymerized unit of the monomer having a crosslinkable group is preferably a polymerized unit of a monomer having a heat crosslinkable crosslinkable group. The content ratio of the polymerized unit having a crosslinkable group in the binder can be controlled by the monomer charge ratio when the binder is produced. In particular, the content ratio of the heat-crosslinkable crosslinkable group in the binder is within the above range, so that the storage stability of the binder is improved and the cycle characteristics of the secondary battery using the porous film of the present invention are improved. To do.

  When the binder is produced, the thermally crosslinkable group is copolymerized with a monomer containing a thermally crosslinkable crosslinking group and / or another monomer copolymerizable therewith in addition to the above-mentioned monomers. By doing so, it can be introduced into the binder.

  The binder used for this invention may contain the monomer copolymerizable with these other than the monomer component mentioned above. Monomers copolymerizable with these include halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; And vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; and acrylamide. By copolymerizing these monomers by an appropriate technique, the binder having the above-described structure can be obtained.

  The binder used in the present invention is used in the state of a dispersion or dissolved solution dispersed in a dispersion medium (water or organic solvent) (hereinafter, these may be collectively referred to as “binder dispersion”). is there.). In the present invention, it is preferable to use water as a dispersion medium from the viewpoint of excellent environmental protection and a high drying speed. When an organic solvent is used as the dispersion medium, an organic solvent such as N-methylpyrrolidone (NMP) is used.

  When the binder is dispersed in the dispersion medium in the form of particles, the average particle diameter (dispersed particle diameter) of the binder dispersed in the form of particles is preferably 50 to 500 nm, more preferably 70 to 400 nm, and most preferably. 100-250 nm. When the average particle size of the binder is within this range, the strength and flexibility of the obtained electrode are improved.

  When the binder is dispersed in the dispersion medium in the form of particles, the solid content concentration of the dispersion is usually 15 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. When the solid content concentration is in this range, workability in producing a slurry for a porous film, which will be described later, is good.

  The glass transition temperature (Tg) of the binder used in the present invention is preferably −50 to 25 ° C., more preferably −45 to 15 ° C., and particularly preferably −40 to 5 ° C. When the Tg of the binder is in the above range, since the porous film of the present invention has excellent strength and flexibility, the output characteristics of a secondary battery using the porous film can be improved. The glass transition temperature of the binder can be adjusted by combining various monomers.

  The method for producing the polymer which is the binder 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 can be used. 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 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.

  The binder used in the present invention is preferably obtained through a particulate metal removal step of removing particulate metal contained in the binder dispersion in the binder production step. When the content of the particulate metal component contained in the binder is 10 ppm or less, it is possible to prevent metal ion cross-linking over time between the polymers in the porous film slurry described later, and to prevent an increase in viscosity. 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 binder dispersion in the particulate metal removal step is not particularly limited. For example, the removal method by filtration using a filtration filter, the removal method by a vibrating sieve, and the removal method by centrifugation. And a method of removing by magnetic force. 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 it is a method capable of removing a metal component, but in consideration of productivity and removal efficiency, it is preferably performed by arranging a magnetic filter in the production line of the binder.

  In the production process of the binder used in the present invention, the dispersant used in the above polymerization method may be one used in ordinary synthesis, and specific examples include sodium dodecylbenzenesulfonate, sodium dodecylphenylethersulfonate, and the like. Benzene sulfonates; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate; fatty acid salts such as sodium laurate; polyoxyethylene lauryl ether sulfate sodium Salts, ethoxy sulfate salts such as polyoxyethylene nonyl phenyl ether sulfate sodium salt; alkane sulfonate salts; alkyl ether phosphate sodium salts; Nonionic emulsifiers such as xylethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, polyoxyethylene-polyoxypropylene block copolymer; gelatin, maleic anhydride-styrene copolymer, polyvinyl pyrrolidone, sodium polyacrylate, Examples thereof include water-soluble polymers such as polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more, and these may be used alone or in combination of two or more. Among these, benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecylsulfate are preferable, and oxidation resistance is more preferable. From this point, it is a benzenesulfonate such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate. The addition amount of a dispersing agent can be set arbitrarily, and is about 0.01-10 mass parts normally with respect to 100 mass parts of monomer total amounts.

  The pH when the binder used in the present invention is dispersed in the dispersion medium is preferably 5 to 13, more preferably 5 to 12, and most preferably 10 to 12. When the pH of the binder is in the above range, the storage stability of the binder is improved, and further, the mechanical stability is improved.

  PH adjusting agents for adjusting the pH of the binder include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide, alkaline earth metal oxides such as calcium hydroxide, magnesium hydroxide and barium hydroxide, Hydroxides such as hydroxides of metals belonging to Group IIIA in a long periodic table such as aluminum hydroxide; carbonates such as alkali metal carbonates such as sodium carbonate and potassium carbonate, alkaline earth metal carbonates such as magnesium carbonate Examples of organic amines include alkylamines such as ethylamine, diethylamine and propylamine; alcohol amines such as monomethanolamine, monoethanolamine and monopropanolamine; ammonia such as ammonia water; Can be mentioned. Among these, alkali metal hydroxides are preferable from the viewpoints of binding properties and operability, and sodium hydroxide, potassium hydroxide, and lithium hydroxide are particularly preferable.

  The content ratio of the binder in the porous film is preferably 0.5 to 20% by mass, more preferably 0.5 to 10% by mass, and particularly preferably 1 to 5% by mass. When the content ratio of the binder in the porous film is in the above range, non-conductive particles described later can be prevented from falling off (pouring off) from the porous film of the present invention, and the flexibility of the porous film can be improved. Therefore, the cycle characteristics of a secondary battery using the porous film can be improved.

(Non-conductive particles)
It is desired that the non-conductive particles used in the present invention exist stably in a use environment of a secondary battery (such as a lithium ion secondary battery or a nickel hydride secondary battery) and are electrochemically stable. As non-conductive particles, for example, various inorganic particles and organic particles can be used. Organic particles are preferable from the viewpoint of producing particles with less metal contamination (hereinafter sometimes referred to as “metal foreign matter”) that adversely affect battery performance at low cost.

Examples of inorganic particles include oxide particles such as aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, BaTiO ₂ , ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; silicone and diamond Covalent crystal particles; poorly soluble ion crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite are used. These particles may be subjected to element substitution, surface treatment, solid solution, or the like, if necessary, or may be a single or a combination of two or more. Among these, oxide particles are preferable from the viewpoints of stability in an electrolytic solution and potential stability.

Organic particles include various types such as crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, polyamide, polyamideimide, melamine resin, phenolic resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include crosslinked polymer particles, heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide.
The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).

In addition, by electrically treating the surface of conductive metal such as carbon black, graphite, SnO ₂ , ITO, metal powder and fine powders of conductive compounds and oxides with a non-electrically conductive material, electrical insulation is achieved. It is also possible to use it as non-conductive particles with imparting properties. These non-electrically conductive substance-treated particles may be used in combination of two or more.

  In the present invention, it is preferable to use non-conductive particles having a foreign metal content of 100 ppm or less. When non-conductive particles containing a large amount of metal foreign matter or metal ions are used, in the slurry for porous film described later, the metal foreign matter or metal ion is eluted, which causes ionic crosslinking with the polymer in the slurry for porous film, The slurry for the porous film is aggregated, and as a result, the porosity of the porous film is lowered. Therefore, there is a possibility that the rate characteristic (output characteristic) of the secondary battery using the porous film is deteriorated. As the metal, it is most preferable to contain Fe, Ni, Cr and the like which are particularly easily ionized. Accordingly, the metal content in the non-conductive particles is preferably 100 ppm or less, more preferably 50 ppm or less. The smaller the content, the less likely the battery characteristics will deteriorate. The term “metal foreign matter” as used herein means a simple metal other than non-conductive particles. The content of metal foreign matter in the non-conductive particles can be measured using ICP (Inductively Coupled Plasma).

  The volume average particle diameter (D50, hereinafter sometimes referred to as “50% volume cumulative diameter”) of the non-conductive particles used in the present invention is preferably 5 nm to 10 μm, more preferably 10 nm to 5 μm, particularly preferably. 100 nm to 2 μm. By setting the volume average particle diameter of the non-conductive particles in the above range, it becomes easy to control the dispersion state of the slurry for the porous film, which will be described later, and hence it becomes easy to manufacture 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. Furthermore, the porous membrane of the present invention can be formed thin. It is particularly preferable that the volume average particle diameter of the non-conductive particles be in the range of 200 nm to 2 μm because the dispersion, the ease of coating, and the controllability of the voids are excellent.

Further, the BET specific surface area of the non-conductive particles used in the present invention is specifically 0.9 to 0.9 in terms of suppressing aggregation of the non-conductive particles and optimizing the fluidity of the slurry for a porous film described later. is preferably 200m ² / g, more preferably 1.5~150m ² / g.

When the non-conductive particles are organic particles, it is preferable that the organic particles have high heat resistance from the viewpoint of imparting heat resistance to the porous film and improving the stability of the secondary battery. Specifically, the temperature at which 10% by weight is reduced when heated at a heating rate of 10 ° C./min in thermobalance analysis is preferably 250 ° C. or higher, more preferably 300 ° C. or higher, and particularly preferably 350 ° 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.

  The particle size distribution (CV value) of the non-conductive particles is preferably 0.5 to 40%, more preferably 0.5 to 30%, and particularly preferably 0.5 to 20%. 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. The particle size distribution (CV value) of the non-conductive particles is obtained by observing the non-conductive particles with an electron microscope, measuring the particle size of 200 or more particles, and obtaining the average particle size and the standard deviation of the particle size. , (Standard deviation of particle diameter) / (average particle diameter). It means that the larger the CV value, the larger the variation in particle diameter.

  The shape of the non-conductive particles used in the present invention is spherical, needle-shaped, rod-shaped, spindle-shaped, plate-shaped or the like, and is not particularly limited, but is preferably spherical, needle-shaped or spindle-shaped. Moreover, porous particles can also be used as the non-conductive particles. The content of non-conductive particles in the porous film is preferably 70 to 99% by mass, more preferably 75 to 99% by mass, and particularly preferably 80 to 99% by mass. By setting the content of non-conductive particles in the porous film in the above range, a porous film exhibiting high thermal stability can be obtained. Moreover, since desorption (powder falling) of non-conductive particles from the porous film can be suppressed, a porous film having high strength can be obtained.

(Isothiazoline compounds)
The porous membrane of the present invention contains a specific amount of isothiazoline-based compound. Since the porous film of the present invention contains a specific amount of an isothiazoline-based compound and can suppress the growth of fungi, the generation of off-flavors in the slurry for the porous film for forming the porous film and the It can prevent thickening and has excellent long-term storage stability.

An isothiazoline-based compound is a compound well known as a preservative, and is generally represented by the following structural formula (1).

(In the formula, Y represents hydrogen or an optionally substituted hydrocarbon group, and X ¹ and X ² each represent a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms. X ¹ X ² may form an aromatic ring together, and X ¹ and X ² may be the same or different from each other.)

First, the isothiazoline compound represented by the structural formula (1) will be described.
In the structural formula (1), Y represents a hydrogen atom or an optionally substituted hydrocarbon group. Examples of the substituent of the optionally substituted hydrocarbon group represented by Y include a hydroxyl group, a halogen atom (for example, a chlorine atom, a fluorine atom, a bromine atom, an iodine atom, etc.), a cyano group, an amino group, a carboxyl group, C1-C4 alkoxy group (for example, methoxy group, ethoxy group, etc.), C6-C10 aryloxy group (for example, phenoxy group, etc.), C1-C4 alkylthio group (for example, methylthio group, ethylthio group, etc.) ) And an arylthio group having 6 to 10 carbon atoms (for example, a phenylthio group). Among the substituents, a halogen atom and an alkoxy group having 1 to 4 carbon atoms are preferable. These substituents may be substituted with hydrogen of the hydrocarbon group in the range of 1 to 5, preferably 1 to 3, and the substituents may be the same or different.

  Examples of the hydrocarbon group of the optionally substituted hydrocarbon group represented by Y include an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, and carbon. A C3-C10 cycloalkyl group, a C6-C14 aryl group, etc. are mentioned. Among the hydrocarbon groups, an alkyl group having 1 to 10 carbon atoms and a cycloalkyl group having 3 to 10 carbon atoms are preferable, and an alkyl group having 1 to 10 carbon atoms is more preferable.

  Examples of the alkyl group having 1 to 10 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, Examples include an octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, a nonyl group, and a decyl group. Among these alkyl groups, an alkyl group having 1 to 3 carbon atoms such as a methyl group and an ethyl group, and an alkyl group having 7 to 10 carbon atoms such as an octyl group and a tert-octyl group are more preferable. An alkyl group of ˜3 is more preferred.

  Examples of the alkenyl group having 2 to 6 carbon atoms include a vinyl group, an allyl group, an isopropenyl group, a 1-propenyl group, a 2-propenyl group, and a 2-methyl-1-propenyl group. Among the alkenyl groups, a vinyl group and an allyl group are preferable.

  Examples of the alkynyl group having 2 to 6 carbon atoms include ethynyl group, 1-propynyl group, 2-propynyl group, butynyl group, pentynyl group and the like. Among the alkynyl groups, an ethynyl group and a propynyl group are preferable.

  Examples of the cycloalkyl group having 3 to 10 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group. Among the cycloalkyl groups, a cyclopentyl group and a cyclohexyl group are preferable.

  Examples of the aryl group having 6 to 14 carbon atoms include a phenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Of the aryl groups, a phenyl group is preferred.

  As described above, various examples of the optionally substituted hydrocarbon group represented by Y can be mentioned. Among these hydrocarbon groups, a methyl group and an octyl group are more preferable, and a methyl group is more preferable. .

In the structural formula (1), X ¹ and X ^{2 each} represent the same or different hydrogen atom, halogen atom, or alkyl group having 1 to 6 carbon atoms.
As said halogen atom, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are mentioned, for example, Among these, a chlorine atom is preferable.

Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, and a pentyl group. Among the alkyl groups, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, and a propyl group is preferable. Among the substituents described above, X ¹ is more preferably a hydrogen atom or a chlorine atom, and further preferably a chlorine atom. X ² is more preferably a hydrogen atom or a chlorine atom, and even more preferably a hydrogen atom.

Specific examples of the isothiazoline-based compound represented by the structural formula (1) include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2- n-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin-3-one, 4,5-dichloro- Examples include 2-cyclohexyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, and 5-chloro-2-t-octyl-4-isothiazolin-3-one.
Among these compounds, 5-chloro-2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as “CIT”), 2-methyl-4-isothiazolin-3-one (hereinafter referred to as “CIT”). "MIT"), 2-n-octyl-4-isothiazolin-3-one (hereinafter sometimes referred to as "OIT"), 4,5-dichloro-2-n-octyl- 4-isothiazolin-3-one is preferred, and 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one are more preferred.

The following structural formula (2) shows a case where a benzene ring is formed (benzoisothiazoline-based compound) among X ¹ and X ² that form an aromatic ring in the above structural formula (1).

(In the formula, Y is the same as in the structural formula (1), and X ^{3 to} X ⁶ are a hydrogen atom, a halogen atom, a hydroxyl group, a cyano group, an amino group, a carboxyl group, or an alkyl group having 1 to 4 carbon atoms. Or an alkoxy group having 1 to 4 carbon atoms.)

In the structural formula (2), X ^{3 to} X ⁶ are a hydrogen atom, a hydroxyl group, a halogen atom (for example, a chlorine atom, a fluorine atom, a bromine atom, and an iodine atom), a cyano group, an amino group, a carboxyl group, and a carbon number. 1-4 alkyl groups (for example, methyl group, ethyl group, propyl group, etc.), C 1-4 alkoxy groups (for example, methoxy group, ethoxy group, etc.) and the like can be mentioned. Among these, halogen atoms and An alkyl group having 1 to 4 carbon atoms is preferred. These X ^{3 to} X ⁶ may be the same or different.

  Examples of the benzoisothiazoline-based compound represented by the structural formula (2) include 1,2-benzisothiazolin-3-one (hereinafter sometimes referred to as “BIT”), N-methyl-1,2-benzisothiazoline. -3-one etc. are mentioned.

  These isothiazoline compounds can be used alone or in combination of two or more. Among these, in terms of long-term storage stability of the slurry for the porous membrane of the present invention and battery characteristics (cycle characteristics) using the porous membrane of the present invention, it is preferable that a benzoisothiazoline-based compound is included, and 1,2-benz It is particularly preferred that isothiazoline-3-one is included. Further, as the isothiazoline-based compound used in the present invention, it is possible to use a combination of a benzisothiazoline-based compound and 2-methyl-4-isothiazolin-3-one (MIT) for the long-term storage stability of the porous film slurry and the porous film. Is more preferable from the viewpoint of improving the cycle characteristics of a secondary battery using a combination of 1,2-benzisothiazolin-3-one (BIT) and 2-methyl-4-isothiazolin-3-one (MIT). It is particularly preferable to use them. The mass ratio (benzisothiazoline compound / MIT) when the benzoisothiazoline compound and MIT are used in combination is preferably 2/8 to 8/2, more preferably 3/7 to 7/3.

  The content of the isothiazoline-based compound is 0.001 to 1.0 part by mass, preferably 0.005 to 0.5 part by mass, and more preferably 0.01 to 100 parts by mass (in terms of solid content) of the above-mentioned binder. -0.1 mass part. If the content of the isothiazoline-based compound is less than 0.001 part by mass, the growth of fungi in the slurry for the porous membrane cannot be suppressed, so the long-term storage stability of the slurry for the porous membrane is reduced. In addition, with the propagation of fungi in the slurry for the porous membrane, the slurry for the porous membrane is denatured and the viscosity of the slurry for the porous membrane is increased. As a result, the handling of the slurry for the porous membrane becomes difficult and the peel strength decreases. When the content of the isothiazoline-based compound exceeds 1.0 part by mass, not only a further antiseptic effect can be expected, but also the cycle characteristics of the secondary battery using the porous film of the present invention are deteriorated.

  In addition, in this invention, in the range which does not prevent the effect of this invention, it does not prevent using preservatives other than said isothiazoline type compound at all.

(Chelate compound)
The porous film of the present invention contains a specific amount of a chelate compound. Since the porous membrane of the present invention contains a specific amount of a chelate compound, it captures the transition metal ions eluted in the electrolyte during charging / discharging of the secondary battery using the porous membrane, and secondary ions caused by the transition metal ions It is possible to prevent a decrease in cycle characteristics and safety of the battery.

  The chelate compound is not particularly limited, but is preferably selected from the group consisting of an aminocarboxylic acid chelate compound, a phosphonic acid chelate compound, gluconic acid, citric acid, malic acid and tartaric acid. Among these, chelate compounds that can selectively capture transition metal ions without capturing lithium ions are preferably used, and aminocarboxylic acid-based chelate compounds and phosphonic acid-based chelate compounds as described below are particularly preferable. Used.

  Examples of aminocarboxylic acid-based chelate compounds include ethylenediaminetetraacetic acid (hereinafter sometimes referred to as “EDTA”), nitrilotriacetic acid (hereinafter sometimes referred to as “NTA”), trans-1,2-diamino. Cyclohexanetetraacetic acid (hereinafter sometimes referred to as “DCTA”), diethylene-triaminepentaacetic acid (hereinafter sometimes referred to as “DTPA”), bis- (aminoethyl) glycol ether-N, N, N ', N'-tetraacetic acid (hereinafter sometimes referred to as “EGTA”), N- (2-hydroxyethyl) ethylenediamine-N, N ′, N′-triacetic acid (hereinafter referred to as “HEDTA”) Selected from the group consisting of dihydroxyethylglycine (hereinafter sometimes referred to as “DHEG”). It is preferred that the.

  As the phosphonic acid-based chelate compound, 1-hydroxyethane-1,1-diphosphonic acid (hereinafter sometimes referred to as “HEDP”) is preferable.

  Content of a chelate compound is 0.001-1.0 mass part with respect to 100 mass parts (solid content conversion) of the above-mentioned binder, Preferably it is 0.005-0.5 mass part, More preferably, 0.01- 0.3 parts by mass. When the content of the chelate compound is less than 0.001 part by mass, the ability to capture transition metal ions is poor, so the cycle characteristics of the secondary battery are degraded. Moreover, when it exceeds 1.0 mass part, not only the transition metal capture effect beyond it can be expected, but the cycling characteristics of the secondary battery using the porous film of this invention may fall.

  The porous membrane of the present invention is preferably 0.001 to 1.0 parts by mass, more preferably 0.005 to 0.5 parts by mass, particularly 100 parts by mass (in terms of solid content) of the binder described above. Preferably 0.01 to 0.1 parts by mass of a pyrithione compound is contained.

  By the way, in the substance used as an industrial antibacterial composition, the antibacterial effect and safety are contradictory, and the substance excellent in antibacterial activity tends to have a problem in safety, for example, having mutagenicity. Among the isothiazoline-based compounds, CIT is known to have a safety problem that it has a high antibacterial effect but is mutagenic or easily causes allergies. Further, when the pH in the system is 9 or more, the antibacterial activity is greatly reduced. MIT is highly safe, but has a slightly inferior antibacterial effect compared to CIT, and it is alkaline and less stable than CIT. BIT has relatively high stability, but its immediate effect is slightly low, and when the pH in the system is 9 or more, the antibacterial activity gradually decreases.

  Since pyrithione compounds are stable even when alkaline, they can be used in combination with isothiazoline-based compounds to extend the antiseptic performance effect even under alkaline conditions and to obtain a high antibacterial effect due to a synergistic effect.

  Examples of pyrithione compounds include alkali metal salts such as sodium, potassium and lithium; monovalent salts such as ammonium salts, and polyvalent salts such as calcium, magnesium, zinc, copper, aluminum and iron, but are water-soluble. Monovalent salts are preferable, and alkali metal salts such as sodium, potassium and lithium are particularly preferable from the viewpoint of versatility to secondary batteries and cycle characteristics. Specific examples of preferred pyrithione compounds include sodium pyrithione, potassium pyrithione, and lithium pyrithione. Among these, sodium pyrithione is preferable because of its high solubility.

  The porous film of the present invention is obtained by applying and drying a slurry (slurry for a porous film) containing the binder, non-conductive particles, isothiazoline-based compound, chelate compound, and solvent described above on a predetermined substrate. Is obtained.

  In addition to the above components, the slurry for a porous film may further contain an arbitrary component. Such optional components include components such as a dispersant, a leveling agent, an antioxidant, a binder other than the above binder, a thickener, an antifoaming agent, and an electrolytic solution additive having a function of inhibiting decomposition of the electrolytic solution. Can be mentioned. These are not particularly limited as long as they do not affect the battery reaction.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. A dispersing agent is selected according to the nonelectroconductive particle to be used. The content ratio of the dispersant in the porous film is preferably within a range that does not affect the battery characteristics, and specifically 10 mass% or less.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, repelling that occurs when the slurry for porous membrane of the present invention is applied to a predetermined substrate can be prevented, and the smoothness of the electrode 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.

  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.

  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 include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. When the use amount of the thickener is within this range, the coating property of the slurry for a porous membrane of the present invention and the adhesion between the porous membrane of the present invention and an electrode active material layer and a 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. By mixing the antifoaming agent, the defoaming step of the binder can be shortened.

  As the electrolytic solution additive, vinylene carbonate used in a mixture slurry and an electrolytic solution described later can be used. 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 nanoparticles, the thixotropy of the slurry for forming a porous film can be controlled, and the leveling property of the porous film obtained thereby can be improved.

  The content ratio of the optional component in the porous film is preferably in a range that does not affect the battery characteristics. Specifically, each component is 10% by mass or less, and the total content of the optional components is 40% by mass. Hereinafter, it is more preferably 20% by mass or less. However, if the total of the non-conductive particles, the predetermined binder, and any component (excluding the binder) is less than 100% by mass, the content of the binder as an optional component is increased appropriately. A composition can be obtained.

(Method for producing porous membrane)
As a method for producing the porous membrane of the present invention, (I) a slurry for a porous membrane containing the above binder, non-conductive particles, isothiazoline-based compound, chelate compound and solvent is used as a predetermined substrate (positive electrode, negative electrode or separator). (II) After immersing the slurry for porous film containing the binder, non-conductive particles, isothiazoline-based compound, chelate compound and solvent in a substrate (positive electrode, negative electrode or separator), (III) A slurry for porous film containing the above binder, non-conductive particles, isothiazoline-based compound, chelate compound and solvent is applied and formed on a release film, and the resulting porous film is coated. And a method of transferring onto a predetermined substrate (positive electrode, negative electrode or separator). Among these, the method of applying the slurry for porous film (I) to the substrate (positive electrode, negative electrode or separator) and then drying is most preferable because the film thickness of the porous film can be easily controlled.

The porous film 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 of the present invention is produced by applying a slurry for a porous membrane on a predetermined substrate (positive electrode, negative electrode or 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 by 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 the porous film is formed on the separator to be described later, it is necessary to dry the separator without causing shrinkage of the separator. Therefore, 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 slurry for porous membrane in a substrate (positive electrode, negative electrode or separator) and drying it. 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 slurry for a porous film is applied on a release film and formed into a film to produce a porous film formed on the release film. Subsequently, the porous film of this invention is manufactured by transcribe | transferring the obtained porous film on a base material (a positive electrode, a negative electrode, or a separator).
As the 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 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 separator) and is particularly preferably used as an electrode active material layer or a protective film for a separator described later. Note that the porous film itself can function as a separator. The porous film of the present invention may be formed on any surface of the positive electrode, the negative electrode, or the separator of the secondary battery, or may be formed on all of the positive electrode, the negative electrode, and the separator.

(2) Slurry for secondary battery porous membrane The slurry for secondary battery porous membrane of the present invention (in this specification, sometimes referred to as "slurry for porous membrane") forms the above-mentioned secondary battery porous membrane. The above binder, non-conductive particles, isothiazoline-based compound, chelate compound, and optional components are uniformly dispersed in a solvent described later as a solid content. The solvent is not particularly limited as long as it can uniformly disperse solid contents (binder, non-conductive particles, isothiazoline-based compound, chelate compound, and optional components). In the slurry, some components may be dissolved.

  As the solvent used for the slurry for the porous membrane, 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, ethylmethylketone, diisopropylketone, 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, ethylene glycol monomethyl ether; N-methyl Amides such as lupyrrolidone and N, N-dimethylformamide are exemplified.

  These solvents may be used alone, or two or more of these may be mixed and used as a mixed solvent. 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.

  As described above, the solid content concentration of the slurry for the porous membrane is not particularly limited as long as the slurry can be used for coating and dipping, and has a fluid viscosity. About 50 mass%.

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

  Since the slurry for porous film of the present invention is for forming the porous film of the present invention, the content ratio of the binder and non-conductive particles in the total solid content of the slurry for porous film is naturally The porous membrane of the invention is as described above. That is, the content of the binder is preferably 0.5 to 20% by mass, and the content of the non-conductive particles is preferably 70 to 99% by mass.

(Method for producing slurry for porous film)
The method for producing the slurry for the porous membrane is not particularly limited, and can be obtained by mixing the above binder, non-conductive particles, isothiazoline-based compound, chelate compound, solvent and optional components added as necessary.

  In the present invention, a porous film slurry in which non-conductive particles are highly dispersed can be obtained by using the above components, regardless of the mixing method and mixing order. The mixing device is not particularly limited as long as it can uniformly mix the above components, and a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and the like can be used. In particular, 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. In the production of the binder dispersion described above, the chelate compound is added, the monomer constituting the binder is polymerized in the presence of the chelate compound, and then the unreacted monomer is removed by heating under reduced pressure, and after cooling, A slurry for a porous membrane can also be produced by adding and mixing conductive particles, an isothiazoline-based compound, and optional components. In the present invention, the chelate compound may be added when the unreacted monomer is removed by distillation under heating under reduced pressure, or may be added simultaneously when the isothiazoline compound is added. The chelating agent may be added in the form of sodium salt, potassium salt or ammonium salt.

  The viscosity of the slurry for the porous membrane 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.

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

  Secondary batteries include lithium ion secondary batteries and nickel metal hydride secondary batteries, etc., but safety improvement is most demanded and the effect of introducing a porous film is the highest, and in addition, improvement of rate characteristics is cited as an issue Therefore, a lithium ion secondary battery is preferable. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

(Positive electrode and negative electrode)
The positive electrode and the negative electrode are generally formed by attaching an electrode active material layer containing an electrode active material as an essential component to a current collector.

<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. -50 μm, preferably 1-20 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 the electrode active material (negative electrode active material) for the negative electrode of a lithium ion secondary battery include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based filaments, 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 also be used. The particle size of the negative electrode active material is appropriately selected in consideration of other constituent elements 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 active material layer>
In the present invention, the electrode active material layer contains a binder (hereinafter sometimes referred to as “binder for active material layer”) in addition to the electrode active material. By including the binder for the active material layer, the binding property of the electrode active material layer in the electrode is improved, the strength against mechanical force applied during the process of winding the electrode is increased, Since the electrode active 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 binder for the active material layer. 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 active material layers.

Furthermore, the soft polymer exemplified below can also be used as the binder for the active material layer.
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 binder for the active material layer in the electrode active material layer is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, particularly preferably 100 parts by mass of the electrode active material. 0.5 to 3 parts by mass. When the amount of the binder for the active material layer in the electrode active material layer is in the above range, it is possible to prevent the active material from dropping from the electrode without inhibiting the battery reaction.

  The binder for the active material layer is prepared as a solution or a dispersion for producing 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.

<Other optional additives>
In the present invention, the electrode active material layer may contain any additive such as a conductivity-imparting material and a reinforcing material in addition to the electrode active material and the binder for the active material layer. 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 usage-amount of an electroconductivity imparting material or a reinforcing material is 0-20 mass parts normally with respect to 100 mass parts of electrode active materials, Preferably it is 1-10 mass parts. Further, the isothiazoline-based compound or chelate compound used in the present invention may be included in the electrode active material layer.

<Formation of electrode active material layer>
The electrode active material layer can be formed by attaching a slurry containing an electrode active material, a binder for the active material layer, and a solvent (hereinafter sometimes referred to as “mixture slurry”) to a current collector. .

  Any solvent may be used as long as it can dissolve or disperse the binder for the active material layer in the form of particles. When a solvent that dissolves the binder for the active material layer is used, the binder for the active material layer is adsorbed on the surface of the electrode active material or any additive, thereby stabilizing the dispersion of the electrode active material.

  As a solvent used for the mixture slurry, either water or an organic solvent can be used. Examples of the organic solvent 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 mixture 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 mixture slurry is used. Specifically, the thickener exemplified in the porous film of the present invention can be used. As for the usage-amount of a thickener, 0.5-1.5 mass parts is preferable with respect to 100 mass parts of electrode active materials. When the use amount of the thickener is within the above range, the coating property of the mixture slurry and the adhesion with the current collector are good.

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

  The amount of the solvent in the mixture slurry is adjusted so as to have a viscosity suitable for coating according to the type of the electrode active material, the binder for the active material layer, and the like. Specifically, the concentration of solid content in the mixture slurry, which is a combination of arbitrary additives such as the electrode active material, the binder for the active material layer, and the conductivity-imparting material, is preferably 30 to 90% by mass, More preferably, the amount is adjusted to 40 to 80% by mass.

  The mixture slurry is obtained by mixing an electrode active material, a binder for the active material layer, an optional additive such as a conductivity-imparting material 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 the electrode active material, the binder for the active material layer, the conductivity-imparting material, and the thickener as the constituent components of the mixture slurry, the conductivity-imparting material and the thickener are mixed in a solvent to conduct electricity. It is preferable to disperse the property-imparting material in the form of fine particles, and then add the binder for the active material layer and the electrode active material and further mix them, because 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 mixture slurry is preferably 35 μm or less, and 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.

  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 mixture, 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 current collector surface in order to increase the adhesive strength and conductivity of the electrode mixture 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 side, preferably both sides of the current collector. For example, the mixture slurry is applied to a current collector, 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 mixture 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. The 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.

(separator)
As a separator for a lithium ion secondary battery, a known separator such as a polyolefin resin such as polyethylene or polypropylene or a separator containing an aromatic polyamide resin is used.

  As the separator used in the present invention, a porous membrane having a fine pore size, having no electronic conductivity, ionic conductivity, high resistance to organic solvents, and, for example, polyolefin-based materials (polyethylene, polypropylene, polybutene, polyvinyl chloride) is used. ), And a microporous film made of a resin such as a mixture or copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, etc. Examples thereof include a microporous membrane made of the above resin 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 properties of the aforementioned slurry for porous membranes are excellent, the thickness of the entire separator can be reduced, the active material ratio in the battery can be increased, and the capacity per volume can be increased. A microporous membrane is preferred.

  The thickness of a separator is 0.5-40 micrometers normally, Preferably it is 1-30 micrometers, More preferably, it is 1-10 micrometers. Within this range, the resistance due to the separator in the battery is reduced. Moreover, the workability | operativity at the time of coating the slurry for porous films mentioned above to a separator is good.

  In the present invention, examples of the polyolefin-based resin used as the separator material 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 or more and 12 million or less, more preferably 200,000 or more and 3 million or less. 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 separator, a publicly known one is used. For example, after forming a melt-extruded film of polypropylene or polyethylene, annealing is performed at a low temperature to grow a crystal domain, and stretching is performed in this state. A dry process for 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 collecting the solvent or low molecular weight in the amorphous phase A wet method in which a microporous film is formed by removing a film that has started to form an island phase by using this solvent or low molecular weight 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 separator used in the present invention may contain any filler or fiber compound for the purpose of controlling strength, hardness, and heat shrinkage. In addition, when laminating the porous membrane of the present invention, a low molecular weight compound or a high molecular weight compound may be used in advance for the purpose of improving the adhesion between the separator and the porous membrane or improving the liquid impregnation property by lowering the surface tension against the electrolytic solution. A coating treatment with a molecular compound, electromagnetic radiation treatment such as ultraviolet rays, or 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.

(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 density | concentration of the supporting electrolyte in electrolyte solution is 1-30 mass% normally, Preferably it is 5-20 mass%. Further, it is usually used at a concentration of 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.

(Method for manufacturing secondary battery)
As a specific method for producing a lithium ion secondary battery, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the shape of the battery. The method of injecting and sealing is mentioned. The porous film of the present invention is formed on any one of a positive electrode, a negative electrode, and a separator. The method for forming the porous film of the present invention on the positive electrode, the negative electrode, and the 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 a separator independently as the method of the above-mentioned (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 formed on the surface of the electrode active material layer of the positive electrode or the negative electrode. By forming the porous film of the present invention on the surface of the electrode active material layer, even if the separator shrinks due to heat, a short circuit between the positive electrode and the negative electrode does not occur, and high safety is maintained. In addition, by forming the porous membrane of the present invention on the surface of the electrode active material layer, the porous membrane can function as a separator even without a separator, making it possible to produce a secondary battery at low cost. Become. Further, even when a 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 the examples and comparative examples, various physical properties are evaluated as follows.

<Flexibility of electrode with porous film or separator with porous film>
An electrode or a separator is cut into a rectangle having a width of 1 cm and a length of 5 cm to obtain a test piece. Stainless steel with a diameter of 1 mm on the surface in the middle of the length (2.5 cm from the end) and on the non-coated surface Set the stick in a lateral direction. The test piece is bent 180 degrees around the stainless steel bar so that the porous membrane layer is on the outside. Ten test pieces are tested, and the bent portion of the porous film layer of each test piece is observed for cracking or peeling, and determined according to the following criteria. It shows that a porous film is excellent in a softness | flexibility, so that there are few cracks or peeling.
A: Cracking or peeling is not observed in all 10 sheets.
B: Cracking or peeling is observed in 1 to 2 of 10 sheets.
C: Cracking or peeling is observed on 3 to 4 of 10 sheets.
D: Cracking or peeling is observed on 5 to 6 sheets out of 10 sheets.
E: Cracking or peeling is observed in 7 to 9 sheets out of 10 sheets.
F: Cracking or peeling is observed in all 10 sheets.

<Storage stability of slurry for porous membrane>
According to JIS Z8803: 1991, the viscosity is measured with a single cylindrical rotational viscometer (25 ° C., rotational speed = 60 rpm, spindle shape: 4), a value of 1 minute is obtained after the start of measurement, and this is used as the slurry viscosity. . A value obtained by dividing the value of the slurry viscosity 14 days after the slurry production by the value of the slurry viscosity 1 hour after the slurry production is defined as the rate of viscosity change, and is evaluated according to the following criteria. It shows that it is excellent in slurry stability, so that a viscosity change rate is low.
A: Less than 5% B: 5% or more and less than 10% C: 10% or more and less than 15% D: 15% or more and less than 20% E: 20% or more and less than 25% F: 25% or more

<High temperature cycle characteristics>
A 10-cell full-cell coin-type battery was charged to 4.3 V by a constant current method of 0.2 C in an atmosphere of 50 ° C., and the electric capacity was repeatedly measured by charging and discharging to 3.0 V. Using the average value of 10 cells as a measured value, the charge / discharge capacity retention ratio represented by the ratio (%) of the electric capacity at the end of 50 cycles and the electric capacity at the end of 5 cycles is obtained, and this is used as an evaluation criterion for cycle characteristics. To do. Higher values indicate better high temperature cycle characteristics.
A: 80% or more B: 70% or more and less than 80% C: 60% or more and less than 70% D: 50% or more and less than 60% E: 40% or more and less than 50% F: Less than 40%

Example 1
<Preparation of binder>
In a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate and 0.3 part of potassium persulfate were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was changed to 60 ° C. The temperature rose. On the other hand, in another container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate, and 77.7 parts of 2-ethylhexyl acrylate, 20 parts of acrylonitrile, 2 parts of methacrylic acid, 0. 3 parts were mixed to obtain a monomer mixture. The monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to obtain an aqueous dispersion (binder dispersion) containing a binder. The polymerization conversion rate was 99% or more.

<Addition of isothiazoline compounds and chelate compounds>
After cooling the obtained binder dispersion to 25 ° C., aqueous ammonia was added to adjust the pH to 7, and then steam was introduced to remove unreacted monomers. Immediately thereafter, 0.025 parts of BIT, 0.025 part of MIT, and 0.25 part of EDTA are added to and mixed with 100 parts of the solid content of the binder, and the solid content concentration is further adjusted with ion-exchanged water. The mixture was filtered through a 200-mesh (mesh size of about 77 μm) stainless steel wire mesh to obtain a binder composition having a solid content of 40%. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 5/5.

<Preparation of slurry for porous membrane>
As a thickener, 1% aqueous solution was prepared using 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. Prepared.

  Non-conductive particles (manufactured by Sekisui Plastics Co., Ltd., cross-linked polystyrene SBX, average particle size 1.0 μm, iron content: less than 13 ppm): carboxymethylcellulose: solid content mass ratio of binder is 100: 4: 5 The mixture was mixed and dispersed in water using a bead mill to prepare a slurry for a porous membrane. In addition, content of raw materials other than water (total solid content) in the slurry was set to 50% by mass. Table 1 shows the evaluation results of the storage stability of this porous membrane slurry.

<Production of negative electrode composition and negative electrode>
98 parts of graphite having a particle diameter of 20 μm and a specific surface area of 4.2 m ² / g as a negative electrode active material, and 5 parts (corresponding to a solid content) of PVDF (polyvinylidene fluoride) as a binder for the active material layer are mixed. -Methylpyrrolidone was added and mixed with a planetary mixer to prepare a slurry-like electrode composition for negative electrode (mixture slurry for negative electrode). This negative electrode composition was applied to one side of a 10 μm thick copper foil, dried at 110 ° C. for 3 hours, and then roll pressed to obtain a negative electrode having a negative active material layer having a thickness of 60 μm.

<Production of electrode composition for positive electrode and positive electrode>
92 parts of lithium manganate having a spinel structure as a positive electrode active material, 5 parts of acetylene black, and 3 parts of PVDF (polyvinylidene fluoride) (corresponding to solid content) as a binder for the active material layer are added, and further solid content is obtained with NMP. After adjusting the concentration to 87%, the mixture was mixed for 60 minutes with a planetary mixer. Furthermore, after adjusting to solid content concentration 84% with NMP, it mixed for 10 minutes and prepared the electrode composition for positive electrodes for positive electrodes (mixture slurry for positive electrodes). This positive electrode composition was applied to 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 thickness of 50 μm.

<Preparation of separator with porous membrane>
Using a wire bar so that the thickness of the porous membrane after drying the slurry for porous membrane is 5 μm on a single-layer polypropylene separator (porosity 55%, thickness 25 μm) produced by a dry method. The porous film was formed by coating and then drying at 90 ° C. for 10 minutes to obtain a separator with a porous film. Table 1 shows the evaluation results of the flexibility of this separator with a porous membrane.

<Production of secondary battery>
Next, the positive electrode obtained was cut into a circle having a diameter of 13 mm, the negative electrode having a diameter of 14 mm, and the separator with a porous film having a diameter of 18 mm. The separator is interposed on the positive electrode active material layer side of the positive electrode so that the porous membrane surface of the separator faces, and the negative electrode is placed so that the electrode active material layer faces each other and the positive electrode aluminum foil contacts the bottom of the outer container Furthermore, an expanded metal was put on the copper foil of the negative electrode, and it was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. . The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A full-cell coin cell having a thickness of 20 mm and a thickness of about 3.2 mm was manufactured (coin cell CR2032). In addition, as an electrolytic solution, LiPF ₆ was added at 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.). A solution dissolved at a concentration was used.
Table 1 shows the evaluation results of the high-temperature cycle characteristics of this full-cell coin cell.

(Example 2)
<Preparation of binder>
In a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate and 0.3 part of potassium persulfate were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was changed to 60 ° C. The temperature rose. On the other hand, in another container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate, and 93.7 parts of 2-ethylhexyl acrylate, 5 parts of acrylonitrile, 1 part of methacrylic acid, 0. 3 parts were mixed to obtain a monomer mixture. The monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was terminated by further stirring at 70 ° C. for 3 hours to obtain a binder dispersion. The polymerization conversion rate was 99% or more.

  Except having used said binder dispersion liquid, operation similar to Example 1 was performed, the isothiazoline type compound and the chelate compound were added, and the slurry for porous films was obtained and evaluated. The results are shown in Table 1.

<Preparation of negative electrode with porous film>
On the negative electrode active material layer of the negative electrode prepared in Example 1, the slurry for porous film was applied using a wire bar so that the thickness of the porous film after drying was 5 μm, and then at 90 ° C. for 10 minutes. By drying, a porous film was formed, and a negative electrode with a porous film was obtained and evaluated. The results are shown in Table 1.

<Production of secondary battery>
In place of the separator with porous membrane of Example 1, a single-layer polypropylene separator (porosity 55%, thickness 25 μm) produced by a dry method was used, and the porous membrane was replaced with the negative electrode of Example 1. A secondary battery was fabricated and evaluated in the same manner as in Example 1 except that the attached negative electrode was used. The results are shown in Table 1.

(Example 3)
Except that the amount of EDTA added was 0.01 parts, the same operation as in Example 1 was performed, and a binder, a slurry for a porous film, and a secondary battery were produced and evaluated. The results are shown in Table 1.

Example 4
Example 1 except that high purity alumina AHP200 made by Nippon Light Metal (average particle size: 0.4 μm) was used in place of the crosslinked polystyrene particles as non-conductive particles, and the amount of EDTA added was 0.4 parts. The same operation was performed to produce a binder, a slurry for a porous film, and a secondary battery, and evaluated. The results are shown in Table 1.

(Example 5)
A binder, a slurry for a porous film, and a secondary battery were prepared and evaluated by performing the same operations as in Example 1 except that DCTA was used instead of EDTA. The results are shown in Table 1.

(Example 6)
Example 1 except that titanium oxide CR-EL (average particle size: 0.3 μm) manufactured by Ishihara Sangyo Co., Ltd. was used instead of crosslinked polystyrene particles as non-conductive particles, and HEDTA was used instead of EDTA. The same operation was performed to prepare a binder and a slurry for a porous film, and evaluated. The results are shown in Table 1.

<Preparation of positive electrode with porous film>
On the positive electrode active material layer of the positive electrode produced in Example 1, the slurry for porous film was applied using a wire bar so that the thickness of the porous film after drying was 5 μm, and then at 90 ° C. for 10 minutes. By drying, a porous film was formed, and a positive electrode with a porous film was obtained and evaluated. The results are shown in Table 1.

<Production of secondary battery>
Instead of the separator with porous membrane of Example 1, a single-layer polypropylene separator (porosity 55%, thickness 25 μm) produced by a dry method was used, and the porous membrane described above was used instead of the positive electrode of Example 1. A secondary battery was produced and evaluated by performing the same operation as in Example 1 except that the attached positive electrode was used. The results are shown in Table 1.

(Example 7)
A binder, a slurry for a porous film, and a secondary battery were prepared and evaluated by performing the same operations as in Example 1 except that HEDP was used instead of EDTA. The results are shown in Table 1.

(Example 8)
A binder, a slurry for a porous membrane, and a secondary battery were prepared and evaluated by performing the same operations as in Example 6 except that citric acid was used instead of HEDTA. The results are shown in Table 1.

Example 9
Except that the addition amount of BIT was 0.04 part and the addition amount of MIT was 0.04 part, the same operation as in Example 1 was performed to prepare a binder, a slurry for porous film, and a secondary battery. And evaluated. The results are shown in Table 1. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 5/5.

(Example 10)
The same procedure as in Example 6 was performed except that BIT was added in an amount of 0.15 parts, MIT was added in an amount of 0.15 parts, and EDTA was used instead of HEDTA. Slurry and secondary battery were prepared and evaluated. The results are shown in Table 1. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 5/5.

(Example 11)
Except that the addition amount of BIT was 0.005 part and the addition amount of MIT was 0.045 part, the same operation as in Example 1 was performed to prepare a binder, a slurry for porous film, and a secondary battery. And evaluated. The results are shown in Table 1. In addition, the mass ratio (BIT / MIT) of the isothiazoline-based compound was 1/9.

(Example 12)
Except that the addition amount of BIT was 0.0125 part and the addition amount of MIT was 0.0375 part, the same operation as in Example 1 was performed to prepare a binder, a slurry for porous film, and a secondary battery. And evaluated. The results are shown in Table 1. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 2.5 / 7.5.

(Example 13)
Except that the addition amount of BIT was 0.035 part and the addition amount of MIT was 0.015 part, the same operation as in Example 10 was performed to prepare a binder, a slurry for porous film, and a secondary battery. And evaluated. The results are shown in Table 1. In addition, the mass ratio (BIT / MIT) of the isothiazoline-based compound was 7/3.

(Example 14)
Except that the amount of BIT added was 0.05 parts and MIT was not added, the same operation as in Example 10 was performed, and a binder, a slurry for a porous film, and a secondary battery were produced and evaluated. . The results are shown in Table 1. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 10/0.

(Example 15)
A binder, a slurry for a porous film, and a secondary battery were produced by performing the same operation as in Example 10 except that 0.025 part of CIT and 0.025 part of OIT were added instead of BIT and MIT. Evaluation was performed. The results are shown in Table 1.

(Example 16)
A binder, a slurry for a porous film, and a secondary battery were prepared and evaluated in the same manner as in Example 1 except that 0.05 part of OIT was added instead of BIT and MIT. The results are shown in Table 1.

(Comparative Example 1)
Instead of titanium oxide CR-EL (average particle size: 0.3 μm) manufactured by Ishihara Sangyo Co., Ltd. as cross-linked polymethyl methacrylate particles (average particle size: 1.0 μm) manufactured by Sekisui Plastics Co., Ltd. Except that BIT and MIT were not added, the same operations as in Example 10 were performed, and a binder, a slurry for a porous film, and a secondary battery were produced and evaluated. The results are shown in Table 1.

(Comparative Example 2)
Except that the addition amount of BIT was 2 parts and the addition amount of MIT was 2 parts, the same operation as in Example 10 was performed, and a binder, a slurry for a porous film, and a secondary battery were produced and evaluated. It was. The results are shown in Table 1. The mass ratio (BIT / MIT) of the isothiazoline-based compound was 5/5.

(Comparative Example 3)
Except that EDTA was not added, the same operation as in Example 1 was performed, and a binder, a slurry for a porous membrane, and a secondary battery were produced and evaluated. The results are shown in Table 1.

(Comparative Example 4)
Except that the amount of EDTA added was 4 parts, the same operation as in Example 4 was performed, and a binder, a slurry for a porous film, and a secondary battery were produced and evaluated. The results are shown in Table 1.

(Comparative Example 5)
<Preparation of binder>
In a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate and 0.3 part of potassium persulfate were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was changed to 60 ° C. The temperature rose. On the other hand, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate, and 39.7 parts of 2-ethylhexyl acrylate, 60 parts of acrylonitrile, and 0.3 part of allyl methacrylate were mixed in a separate container. To obtain a monomer mixture. The monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 99% or more.

  Except that the aqueous dispersion containing the above binder was used, the same operation as in Example 1 was performed, and the isothiazoline-based compound and the chelate compound were added to prepare a slurry for a porous film and a secondary battery, and evaluation Went. The results are shown in Table 1.

From the results in Table 1, the following can be said.
Binder comprising polymer units of (meth) acrylic acid ester monomers, polymer units of vinyl monomers having acidic groups, and polymer units of α, β-unsaturated nitrile monomers, non-conductive particles, and isothiazoline compounds And a chelate compound, the content of the isothiazoline-based compound is 0.001 to 1.0 part by mass with respect to 100 parts by mass of the binder, and the content of the chelate compound is 0 with respect to 100 parts by mass of the binder. The electrodes or separators on which the porous membranes (Examples 1 to 16) having 0.001 to 1.0 parts by mass have good flexibility. Moreover, the secondary battery using the electrode or separator on which the porous film is formed has good high-temperature cycle characteristics. Furthermore, the slurry for porous film for forming the porous film has good storage stability.
In particular, a specific chelate compound is included, the content of the chelate compound is in the range of 0.01 to 0.3 parts by mass with respect to 100 parts by mass of the binder, and the content of the isothiazoline-based compound is 100 parts by mass of the binder. On the other hand, in the case of 0.01 to 0.1 parts by mass and containing BIT and MIT as an isothiazoline-based compound and the mass ratio (BIT / MIT) is within a predetermined range (Examples 1 to 3, 5 to 5) Nos. 7, 9, and 13) have good storage stability of the slurry for the porous membrane, and the obtained secondary battery exhibits excellent high-temperature cycle characteristics.
On the other hand, when a predetermined amount of the isothiazoline-based compound is not included (Comparative Examples 1 and 2), when a predetermined amount of the chelate compound is not included (Comparative Examples 3 and 4), and a vinyl monomer having an acidic group in the polymerization unit of the binder When not included (Comparative Example 5), the flexibility, slurry storage stability, and high-temperature cycle characteristics are inferior, and the high-temperature cycle characteristics are particularly inferior to those of Examples 1-16.

Claims (6)

Binder comprising polymer units of (meth) acrylic acid ester monomers, polymer units of vinyl monomers having acidic groups, and polymer units of α, β-unsaturated nitrile monomers, non-conductive particles, and isothiazoline compounds And a chelate compound,
The content of the isothiazoline-based compound is 0.001 to 1.0 parts by mass with respect to 100 parts by mass of the binder,
The secondary battery porous membrane whose content of the said chelate compound is 0.001-1.0 mass part with respect to 100 mass parts of said binders. The isothiazoline compound comprises a benzoisothiazoline compound and 2-methyl-4-isothiazolin-3-one;
2. The secondary battery porous membrane according to claim 1, wherein a mass ratio of the benzoisothiazoline-based compound to the 2-methyl-4-isothiazolin-3-one is in a range of 2/8 to 8/2.   The content ratio of the polymerization unit of the (meth) acrylic acid ester monomer is 50 to 98 mass%, the content ratio of the polymerization unit of the vinyl monomer having an acidic group is 1.0 to 3.0 mass%, 3. The secondary battery porous membrane according to claim 1, wherein the content of polymerization units of the α, β-unsaturated nitrile monomer is 1.0 to 50% by mass. The binder further comprises a polymerized unit having crosslinkability;
The secondary battery porous membrane according to any one of claims 1 to 3, wherein a content ratio of the polymerized units having crosslinkability is 0.01 to 2.0 mass%. Binder comprising polymer units of (meth) acrylic acid ester monomers, polymer units of vinyl monomers having acidic groups, and polymer units of α, β-unsaturated nitrile monomers, non-conductive particles, and isothiazoline compounds And a chelate compound and a solvent,
The content of the isothiazoline-based compound is 0.001 to 1.0 parts by mass with respect to 100 parts by mass of the binder,
The slurry for secondary battery porous films whose content of the said chelate compound is 0.001-1.0 mass part with respect to 100 mass parts of said binders. A secondary battery including a positive electrode, a negative electrode, a separator and an electrolyte solution,
The secondary battery by which the secondary battery porous film in any one of Claims 1-4 is laminated | stacked in any one of the said positive electrode, the said negative electrode, and the said separator.