JP2014149936A - Secondary battery separator, method for manufacturing secondary battery separator, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery separator good in heat resistance and high in adhesiveness with an electrode active material layer laminated on a collector.SOLUTION: A secondary battery separator includes: an organic separator; a heat resistant layer formed adjacent to at least one surface of the organic separator and including non-conductive particles and a binder; and an adhesive layer formed on the heat resistant layer and including a vinylidene fluoride copolymer having a melting point in the range of 70-150°C. The amount of coating per one surface of the heat resistance layer to the organic separator is in the range of 2-10 g/m, and the amount of coating per one surface of the adhesive layer to the heat resistant layer is in the range of 0.1-1.5 g/m.

Description

  The present invention relates to a separator for a secondary battery used in a secondary battery such as a lithium ion secondary battery, a method for producing the separator for a secondary battery, and a secondary battery using the separator for a secondary battery.

  In recent years, mobile terminals such as notebook computers, tablet terminals, and mobile phones such as smartphones have been widely used. As a secondary battery used for the power source of these portable terminals, a lithium ion secondary battery or the like is frequently used. Because more comfortable portability is required for mobile terminals, miniaturization, thinning, weight reduction, and high performance are rapidly progressing. As a result, mobile terminals are used in various places. It has become. In addition, the battery is required to be smaller, thinner, lighter, and higher in performance as in the case of the portable terminal.

  In the lithium ion secondary battery, lithium is dissolved from the positive electrode active material of the positive electrode into the electrolyte in the organic separator as lithium ions during charging and enters the negative electrode active material of the negative electrode, and enters the negative electrode active material of the negative electrode during discharge. The charge / discharge operation is performed by releasing lithium ions into the electrolytic solution and returning again into the positive electrode active material of the positive electrode.

  Usually, as an organic separator used for a lithium ion secondary battery, for example, a microporous film made of a polyolefin-based resin is used. The organic separator melts and closes the micropore when the temperature inside the battery reaches around 130 ° C, thereby preventing the movement of lithium ions and shutting down the current. Has a role to hold. However, when the battery temperature exceeds, for example, 150 ° C. due to instantaneous heat generation, the organic separator contracts rapidly, and the positive electrode and the negative electrode may be in direct contact with each other, thereby expanding the location where the short circuit occurs. In this case, the battery temperature may reach a state where it is abnormally overheated to several hundred degrees Celsius or higher.

  For this reason, non-aqueous separators and the like in which a heat-resistant porous film layer (hereinafter sometimes referred to as “heat-resistant layer”) is laminated on the surface of an organic separator such as a polyethylene microporous film have been studied. . The porous membrane layer is a membrane having a large number of linked micropore structures inside, and binds non-conductive particles, non-conductive particles, and non-conductive particles to an organic separator or a current collector. Therefore, it contains a polymer binder (hereinafter sometimes referred to as “binder”). Further, the porous membrane layer can be used by being laminated on an electrode, or can be used as an organic separator itself.

Patent Document 1 describes a secondary battery separator in which a heat resistant layer containing a heat resistant resin is provided on an organic separator. Patent Document 1 describes a secondary battery separator in which an adhesive layer containing a vinylidene fluoride resin is provided on an organic separator.
Patent Document 2 describes that an adhesive layer is provided between the organic separator and the heat-resistant layer.

Japanese Patent No. 4806735 JP 2012-89346 A

  However, in patent document 1, the separator which provided the heat-resistant layer on the organic separator, and the separator which provided the adhesive bond layer on the organic separator were separately disclosed, and according to examination of this inventor, on an organic separator. When a separator provided with a heat-resistant layer is used, the adhesiveness between the heat-resistant layer and the electrode active material layer of the electrode is insufficient. It was found that desorption (powder removal) of substances and the like could not be prevented sufficiently, and the danger of short-circuiting between electrodes due to the desorption was increased.

In addition, when a separator having an adhesive layer provided on an organic separator is used, sufficient heat resistance cannot be obtained as a separator. Therefore, the separator generally tends to shrink even at a temperature of 150 ° C. or less, and a short circuit of the battery is likely to occur. I found out.
Also in Patent Document 2, sufficient adhesive strength between the heat-resistant layer and the electrode active material layer of the electrode cannot be obtained.
That is, in Patent Documents 1 and 2, the shutdown function and the adhesiveness between the separator and the electrode cannot be sufficiently achieved.

  The present invention has been made in view of the above problems, and has good heat resistance and high adhesion to an electrode active material layer laminated on a current collector. Secondary battery separator and secondary battery separator It aims at providing the manufacturing method of. Furthermore, an object of this invention is to provide the secondary battery which has this separator for secondary batteries.

  As a result of intensive studies, the inventors have found that the above object can be achieved by forming a specific heat-resistant layer on the organic separator and further forming a specific adhesive layer on the heat-resistant layer. It came to be completed.

That is, according to the present invention,
(1) An organic separator, a heat-resistant layer formed adjacent to at least one surface of the organic separator, including non-conductive particles and a binder, and formed on the heat-resistant layer and having a melting point of 70 to 150 ° C. An adhesive layer containing a vinylidene copolymer, the coating amount of the heat-resistant layer per side to the organic separator is ² to 10 g / m ² , and the adhesive layer per side of the heat-resistant layer to the heat-resistant layer A separator for a secondary battery, wherein the coating amount is 0.1 to 1.5 g / m ² ;
(2) The secondary battery separator according to (1), wherein the degree of swelling of the vinylidene fluoride copolymer with respect to the electrolyte is 110 to 200%,
(3) The separator for secondary batteries according to (1) or (2), wherein the adhesive layer further contains an acrylic polymer,
(4) A heat-resistant layer forming step of forming a heat-resistant layer by applying a slurry for a heat-resistant layer containing non-conductive particles and a binder on an organic separator and drying, and a vinylidene fluoride copolymer on the heat-resistant layer. A method for producing a separator for a secondary battery, comprising: an adhesive layer forming step of forming an adhesive layer by applying and drying a slurry for an adhesive layer,
(5) A secondary battery comprising the separator for a secondary battery according to any one of (1) to (3), a positive electrode, a negative electrode, and an electrolytic solution is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the separator for secondary batteries which has favorable heat resistance and high adhesiveness with the electrode active material layer laminated | stacked on the electrical power collector, and a separator for secondary batteries is provided. In addition, according to the present invention, there is provided a secondary battery including a secondary battery separator having good heat resistance and high adhesion to an electrode active material layer laminated on a current collector.

Hereinafter, the secondary battery separator and the secondary battery according to the present invention will be described. The separator for a secondary battery according to the present invention is formed adjacent to at least one surface of the organic separator, the organic separator, a heat resistant layer containing non-conductive particles and a binder, and formed on the heat resistant layer, and has a melting point of 70. An adhesive layer containing a vinylidene fluoride copolymer having a temperature of ˜150 ° C., the coating amount of the heat-resistant layer on one side of the organic separator being ² to 10 g / m ² , and the adhesive layer The coating amount per one side to the heat-resistant layer is 0.1 to 1.5 g / m ² . Hereinafter, the organic separator, the heat-resistant layer, and the adhesive layer will be described in detail in this order.

(Organic separator)
As the organic separator used in the present invention, a porous membrane having a fine pore diameter, which has no electron conductivity and ion conductivity and high resistance to an organic solvent is used. For example, a polyolefin film (polyethylene, polypropylene, polybutene, polyvinyl chloride), a microporous film made of a resin such as a mixture or copolymer thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, Examples thereof include a microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like. Among these, since the coating property of the slurry for the heat-resistant layer is excellent, the thickness of the secondary battery separator can be reduced, and the capacity per volume can be increased by increasing the ratio of the electrode active material layer in the battery. A microporous membrane made of polyolefin resin is preferred.

  The thickness of the organic separator is usually from 0.5 to 40 μm, preferably from 1 to 30 μm, from the viewpoint that the resistance due to the organic separator in the battery is reduced and the workability during battery production is excellent. More preferably, it is 1-20 micrometers.

  The organic separator used in the present invention may contain fillers and fiber compounds other than non-conductive particles for the purpose of controlling strength, hardness, and heat shrinkage. In addition, when laminating a heat-resistant layer on the surface of the organic separator, a low molecular compound or a polymer compound is previously prepared for the purpose of improving adhesion or improving the liquid impregnation property by lowering the surface tension with the electrolytic solution. The surface of the organic separator may be subjected to coating treatment, electromagnetic radiation treatment such as ultraviolet rays, or plasma treatment such as corona discharge / plasma gas. In particular, those coated with a polymer compound containing a polar group such as a carboxylic acid group, a hydroxyl group, and a sulfonic acid group are preferable from the viewpoint of high impregnation of the electrolytic solution and easy adhesion to the heat-resistant layer.

  The organic separator used in the present invention may have a multilayer structure between the organic separators for the purpose of increasing the tear strength and the piercing strength. Specific examples include a laminate of a polyethylene microporous membrane and a polypropylene microporous membrane, and a laminate of a nonwoven fabric and a polyolefin separator.

(Heat resistant layer)
The heat resistant layer constituting the separator for a secondary battery of the present invention contains non-conductive particles and a binder. The heat-resistant layer has a structure in which non-conductive particles are bound via a binder and voids between the non-conductive particles are formed. This void is a hole in the heat-resistant layer.

(Non-conductive particles)
As a material constituting the non-conductive particles, it is desired that the material is stably present in an environment where the lithium ion secondary battery is used and is electrochemically stable. For example, various non-conductive inorganic particles and organic particles can be used.

As the material of the inorganic particles, a material that is electrochemically stable and suitable for preparing a slurry composition for a heat-resistant layer by mixing with other materials, for example, a viscosity adjusting agent described later is preferable. From this point of view, the inorganic particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ ), bakelite, magnesium oxide, magnesium hydroxide, iron oxide, Silicon oxide, titanium oxide (titania), oxides such as calcium oxide, nitrides such as aluminum nitride and silicon nitride, silica, barium sulfate, barium fluoride, calcium fluoride, etc. Among these, in electrolyte Oxides are preferred from the standpoint of stability and potential stability at high temperatures, and titanium oxide, alumina, boehmite, magnesium oxide and magnesium hydroxide are particularly preferred from the standpoint of low water absorption and excellent heat resistance (eg, resistance to high temperatures of 180 ° C. or higher). Alumina, boehmite, magnesium oxide and water Magnesium reduction is particularly preferred.

  As the organic particles, polymer (polymer) particles are usually used. The organic particles can control the affinity for water by adjusting the type and amount of functional groups on the surface, and thus can control the amount of water contained in the heat-resistant layer of the present invention. Preferred examples of the organic material for the non-conductive particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer compound forming the particles may be a homopolymer or a copolymer. In the case of a copolymer, any of a block copolymer, a random copolymer, a graft copolymer, and an alternating copolymer is used. it can. Furthermore, it may be at least partially modified or a crosslinked product. And a mixture of these may be sufficient. In the case of a cross-linked product, the cross-linking agent includes a cross-linked product having an aromatic ring such as divinylbenzene, a polyfunctional acrylate cross-linked product such as ethylene glycol dimethacrylate, and a cross-linked product having an epoxy group such as glycidyl acrylate and glycidyl methacrylate. Can be mentioned. The organic particles may be formed of a mixture of two or more polymer compounds.

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

  The volume average particle diameter D50 of the non-conductive particles is usually 0.1 μm or more, preferably 0.2 μm or more, and usually 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less. By using such non-conductive particles having a volume average particle diameter D50, a uniform porous film can be obtained even if the thickness of the porous film is thin, so that the capacity of the battery can be increased. Here, the volume average particle diameter D50 represents the particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle size distribution measured by the laser diffraction method.

In addition, the BET specific surface area of these non-conductive particles is specifically 0.9 to ²⁰⁰ m ² / g from the viewpoint of suppressing particle aggregation and optimizing the fluidity of the heat-resistant layer slurry. It is preferably 1.5 to 150 m ² / g. The BET specific surface area of the nonconductive particles is measured by a BET measurement method by adsorbing nitrogen gas to the nonconductive particles using a specific surface area measuring device (Gemini 2310: manufactured by Shimadzu Corporation).

  In the present invention, examples of the shape of the nonconductive particles include a spherical shape, an elliptical spherical shape, a polygonal shape, a tetrapod (registered trademark) shape, a plate shape, and a scale shape. Among these, from the viewpoint of increasing the porosity of the porous membrane and suppressing the decrease in ionic conductivity due to the porous membrane separator, a tetrapod (registered trademark) shape, a plate shape, and a scale shape are preferable.

  The content ratio of the nonconductive particles in the heat-resistant layer is such that the gap between the nonconductive particles can be formed to such an extent that the nonconductive particles have contact portions and the movement of ions is not inhibited. It is preferable that it is mass%, and it is more preferable that it is 80-95 mass%.

(binder)
The heat-resistant layer in the present invention contains a binder. The binder plays a role of maintaining the mechanical strength of the heat-resistant layer. Usually, various binders can be used as long as they have binding properties. For example, a polymer containing a conjugated diene polymer, an acrylate monomer unit and / or a methacrylic acid ester monomer unit (hereinafter, referred to as “(meth) acrylic polymer”. ) “Acryl” means acrylic and / or methacrylic), fluoropolymers, silicon polymers and the like.

  Among them, a styrene-butadiene copolymer (SBR) described later is preferable because it is easy to obtain a battery having excellent non-conductive particle retention and flexibility in the obtained heat-resistant layer, and being stable in oxidation and reduction and having excellent life characteristics. ), Hydrides of acrylonitrile-butadiene copolymer (NBR) (H-NBR) and (meth) acrylic polymers are preferred, (meth) acrylic polymers are more preferred, and among (meth) acrylic polymers, ( In addition to a (meth) acrylic acid ester monomer unit, an acrylonitrile / (meth) acrylic acid ester copolymer containing a (meth) acrylonitrile monomer unit is more preferable.

The conjugated diene polymer is a polymer containing a conjugated diene monomer unit and a hydride thereof. The conjugated diene monomer unit is a repeating unit obtained by polymerizing a conjugated diene monomer.
Examples of the conjugated diene monomer constituting the conjugated diene monomer unit include 1,3-butadiene, isoprene, chloroprene and the like.
In addition to the conjugated diene monomer unit, the conjugated diene polymer can contain a monomer unit of a monomer copolymerizable with the conjugated diene as an optional component.

Monomers constituting the monomer unit copolymerizable with the conjugated diene include non-conjugated diene monomers such as 1,2-butadiene; α-olefins such as ethylene, propylene, and isobutylene; Aromatic vinyl monomers; vinyl cyanide monomers such as acrylonitrile and methacrylonitrile;
These copolymerizable monomers can be used alone or in combination of two or more.

  Specific examples of the conjugated diene polymer include conjugated diene homopolymers such as polybutadiene and polyisoprene; styrene / butadiene copolymer (SBR), styrene / butadiene / styrene block copolymer (SBS), styrene / isoprene / styrene. Aromatic vinyl / conjugated diene copolymer such as block copolymer (SIS) and its hydride; aromatic vinyl / conjugated such as styrene / butadiene / methacrylic acid copolymer and styrene / butadiene / itaconic acid copolymer And copolymers of diene / carboxylic acid group-containing monomers; vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR) and hydrides thereof; and the like.

  The acrylic ester monomer unit is a repeating unit obtained by polymerizing an acrylic ester monomer, and the methacrylic ester monomer unit is a repeating unit obtained by polymerizing a methacrylate monomer. Unit.

  As acrylic acid ester and / or methacrylic acid ester, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2- Acrylic acid alkyl esters such as ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate , Pentyl methacrylate, hexyl methacrylate, Heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Among these, acrylic acid alkyl ester is preferable, and at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate is preferable, and butyl acrylate is more preferable.

  The content ratio of the monomer units of the (meth) acrylic acid ester in the (meth) acrylic polymer is preferably 50 to 98% by mass, more preferably 60 to 97.5% by mass, and 70 to It is particularly preferably 95% by mass.

  The (meth) acrylic polymer preferably contains a (meth) acrylonitrile monomer unit in addition to the (meth) acrylic acid ester monomer unit. When the (meth) acrylic polymer contains the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit, a battery having a long life and stable in redox can be obtained. In addition, by using a (meth) acrylic polymer containing these repeating units as a binder, the flexibility of the heat-resistant layer is improved, so that non-conductive particles are removed from the heat-resistant layer during cutting (slit) processing or winding. Desorption can be suppressed.

  The (meth) acrylonitrile monomer unit is a repeating unit obtained by polymerizing (meth) acrylonitrile. The binder may contain only an acrylonitrile monomer unit as a (meth) acrylonitrile monomer unit, or may contain only a methacrylonitrile monomer unit, and an acrylonitrile monomer unit and a methacrylonitrile monomer unit. Both nitrile monomer units may be included in combination at any ratio.

  In the present invention, the ratio of (meth) acrylonitrile monomer unit to (meth) acrylic acid ester monomer unit in (meth) acrylic polymer (= (meth) acrylonitrile monomer unit / (meth) acrylic acid) The ester monomer unit) is preferably in the range of 1/99 to 30/70, more preferably in the range of 5/95 to 25/75. When the ratio of the (meth) acrylonitrile monomer unit in the (meth) acrylic polymer is too low, the binder is swollen in the electrolytic solution, so that ionic conductivity is lowered and rate characteristics are lowered. Moreover, since the intensity | strength of a binder will fall when the said ratio is too high, the intensity | strength of a heat-resistant layer falls. Usually, the ratio of the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit contained in the binder is the (meth) acrylonitrile monomer occupying in all monomers used to produce the binder and It becomes the same as the ratio (preparation ratio) of the (meth) acrylic acid ester monomer.

The (meth) acrylic polymer preferably contains another monomer unit in addition to the (meth) acrylic acid ester monomer unit and the (meth) acrylonitrile monomer unit.
Examples of other monomer units include a monomer unit of a vinyl monomer having an acidic group, a monomer unit of a monomer having a crosslinkable group, and the like.

Examples of the vinyl monomer having an acidic group include a monomer having a —COOH group (carboxylic acid group), a monomer having an —OH group (hydroxyl group), and a monomer having an —SO ₃ H group (sulfonic acid group). , A monomer having a —PO ₃ H ₂ group, a monomer having a —PO (OH) (OR) group (R represents a hydrocarbon group), and a monomer having a lower polyoxyalkylene group. It is done. Moreover, the acid anhydride which produces | generates a carboxylic acid group by a hydrolysis can be used similarly.

  Examples of the monomer having a carboxylic acid group include monocarboxylic acid, dicarboxylic acid, dicarboxylic acid anhydride, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. 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, acrylic acid-2 - hydroxypropyl, alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl methacrylate; to the general formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m -H (m 2 to 9 , N is an integer of 2 to 4, and R ¹ represents hydrogen or a methyl group). An ester of (meth) acrylic acid and 2-hydroxyethyl-2 ′-(meth) Dihydroxy esters of dicarboxylic acids such as acryloyloxyphthalate and 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate Mono (meth) acrylic acid esters; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) Mono (meth) allyl ethers of alkylene glycols such as allyl-3-hydroxypropyl ether; polyoxyalkylene glycols (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether Glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether, (poly) al; Mono (meth) allyl ether of halogenated and hydroxy-substituted products of xylene glycol; mono (meth) allyl ether of polyhydric phenols such as eugenol and isoeugenol and halogen-substituted products thereof; (meth) allyl-2-hydroxyethylthioether ( And (meth) allylthioethers of alkylene glycol such as (meth) allyl-2-hydroxypropylthioether.

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

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 phosphate -2- (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, the vinyl monomer having an acidic group is a monomer having a carboxylic acid group because of its excellent adhesion to an organic separator and the efficient capture of transition metal ions eluted from the positive electrode active material layer. Among them, monocarboxylic acids having 5 or less carbon atoms having carboxylic acid groups such as acrylic acid and methacrylic acid, and dicarboxylic acids having 5 or less carbon atoms having two carboxylic acid groups such as maleic acid and itaconic acid are preferable. . Furthermore, acrylic acid, methacrylic acid, and itaconic acid are preferred from the viewpoint of high storage stability of the prepared heat-resistant layer slurry.

  The content ratio of the vinyl monomer having an acidic group in the (meth) acrylic polymer is preferably 1 to 3% by mass, and more preferably 1.5 to 2.5% by mass.

  The crosslinkable monomer unit is a structural unit obtained by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or energy ray irradiation. As an example of the crosslinkable monomer, a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional crosslinkable monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule; a polyfunctional monomer having two or more olefinic double bonds per molecule. A functional crosslinkable monomer is mentioned.

  Examples of the thermally crosslinkable group include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and a combination thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate Unsaturated carboxylic acids such as sidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Examples include glycidyl esters of acids.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline is mentioned.

Examples of crosslinkable monomers having two or more olefinic double bonds per molecule include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth). Acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane -Diallyl ether, allyl or vinyl ether of polyfunctional alcohols other than those mentioned above, triallylamine, methylenebisacrylamide, and divinylbenzene That.
Among these, as the crosslinkable monomer, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are particularly preferable.
As the crosslinkable monomer unit, one kind of the above crosslinkable monomers may be used alone, or two or more kinds may be used in combination at any ratio.

  The content ratio of the crosslinkable monomer unit in the (meth) acrylic polymer is preferably 0.1 to 10% by mass, and more preferably 0.1 to 5% by mass. By setting the content ratio of the crosslinkable monomer unit in the (meth) acrylic polymer to the above range, the deformation of the heat-resistant layer due to the elution of the (meth) acrylic polymer into the electrolytic solution is suppressed, and the secondary battery Cycle characteristics can be improved.

  The (meth) acrylic polymer suitably used in the present invention may contain monomer units copolymerizable with these in addition to the monomer units described 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; methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether Vinyl ethers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone and the like; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole; acrylamide; Is mentioned.

  The content ratio of the copolymerizable monomer unit in the (meth) acrylic polymer is preferably 0.1 to 30% by mass from the viewpoint of excellent temporal stability of the heat-resistant layer slurry described later. More preferably, it is 1-20 mass%. A secondary battery having a heat-resistant layer containing a (meth) acrylic polymer as a binder is excellent in cycle characteristics and rate characteristics.

  The method for producing the binder is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method may be used. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and used as they are as a material for the heat-resistant layer slurry.

  The method for initiating polymerization is not particularly limited, but it is preferable to use a polymerization initiator. 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. Although it does not specifically limit, It is preferable that the usage-amount of a polymerization initiator is the range of 0.01-10 mass parts with respect to 100 mass parts of monomers used for manufacture of a binder.

  Moreover, when manufacturing a binder, it is preferable to include a dispersing agent in the reaction system. As the dispersant, those used in usual synthesis may be used. Specific examples include benzene sulfonates such as sodium dodecylbenzene sulfonate and sodium dodecyl phenyl ether sulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate. Acid salts; Fatty acid salts such as sodium laurate; Ethoxysulfate salts such as polyoxyethylene lauryl ether sulfate sodium salt and polyoxyethylene nonylphenyl ether sulfate sodium salt; Alkane sulfonate; Alkyl ether phosphate sodium salt; Ethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, polyoxyethylene-polyoxypropylene Nonionic emulsifiers such as block copolymers; gelatin, maleic anhydride-styrene copolymers, polyvinylpyrrolidone, sodium polyacrylate, water-soluble polymers such as polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more And so on. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Among these, benzene sulfonates such as sodium dodecylbenzene sulfonate and sodium dodecyl phenyl ether sulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate are preferable, and dodecyl benzene sulfone is excellent in oxidation resistance. Benzene sulfonates such as sodium acid and sodium dodecylphenyl ether sulfonate are more preferred. The amount of the dispersant can be arbitrarily set, and is preferably about 0.01 to 10 parts by mass with respect to 100 parts by mass of the total amount of monomers.

  The weight average molecular weight of the binder is appropriately selected depending on the purpose of use, but is a cyclohexane solution (toluene solution if the polymer does not dissolve) from the viewpoint of easily improving the strength of the heat-resistant layer and the dispersibility of the nonconductive particles. It is preferably 10,000 to 500,000, more preferably 20,000 to 200,000, in terms of polystyrene-equivalent weight average molecular weight (Mw) measured by gel permeation chromatography.

  The binder is usually prepared and stored as a dispersion in a state of being dispersed in a dispersion medium (water or organic solvent), and this is used as a material in the production of the slurry for the heat-resistant layer. In the present invention, it is preferable to use water as a dispersion medium from the viewpoint that the load on the environment is small and the drying speed is fast. 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 volume average particle diameter D50 of the binder dispersed in the form of particles is preferably 0.01 to 0.7 μm, preferably 0.01 to 0.00. More preferably, it is 5 μm. When the volume average particle diameter D50 of the binder is too small, the porosity of the heat-resistant layer is lowered, so that the resistance of the heat-resistant layer is increased and the battery characteristics are deteriorated. On the other hand, if the volume average particle diameter D50 of the binder is too large, the bonding points between the non-conductive particles and the binder are reduced and the binding property is lowered. Here, the volume average particle diameter D50 of the binder is obtained by measuring the dispersed particle diameter of the binder in the dispersion medium using a laser diffraction particle size distribution measuring device.

  The solid content concentration in the dispersion liquid in which the binder is dispersed in the dispersion medium in the form of particles is usually 15 to 70% by mass, preferably 20 to 65% by mass, and preferably 30 to 60% by mass. Further preferred. When the solid content concentration is within this range, workability in producing a heat-resistant layer slurry described later is good.

  The glass transition temperature (Tg) of the binder is preferably -50 to 20 ° C, more preferably -40 to 15 ° C, and particularly preferably -30 to 5 ° C. When the glass transition temperature (Tg) is within the above range, the flexibility of the heat-resistant layer of the present invention is improved, the flex resistance of the organic separator is improved, and the defect rate due to the cracking of the heat-resistant layer can be reduced. In addition, cracks, chipping, and the like can be suppressed when the secondary battery separator of the present invention is wound around a roll or wound. The glass transition temperature of the binder can be adjusted by combining various monomers.

  The content of the binder in the heat-resistant layer is 0.1 to 20 parts by mass with respect to 100 parts by mass of the non-conductive particles from the viewpoint of improving the adhesion between the heat-resistant layer and the organic separator and reducing the internal resistance. It is preferable that it is 0.2-15 mass parts, and it is especially preferable that it is the range of 0.5-10 mass parts.

(Other optional ingredients)
In addition to the components described above, the heat-resistant layer may further contain an arbitrary component. Examples of such optional components include a viscosity modifier, a surfactant, an antifoaming agent, and an electrolytic solution additive having a function of suppressing electrolytic decomposition. The optional component is not particularly limited as long as it does not exert an excessively unfavorable influence on the battery reaction in the secondary battery using the secondary battery separator of the present invention. These contain the component added for the stability improvement of the slurry for heat-resistant layers mentioned later, and the component added for the battery performance improvement. Moreover, the kind of arbitrary component may be one, and two or more kinds may be sufficient as it.

  As the viscosity modifier, cellulose derivatives such as carboxymethylcellulose (CMC); poly (meth) acrylates such as sodium poly (meth) acrylate; polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinylpyrrolidone, polycarboxylic acid, Examples thereof include oxidized starch, phosphate starch, casein, various modified starches, chitin, and chitosan derivatives. Among these, cellulose derivatives are particularly preferable.

  The cellulose derivative is a compound obtained by etherifying or esterifying at least a part of the hydroxyl group of cellulose, and is preferably water-soluble. Cellulose derivatives usually do not have a glass transition point. Specific examples include carboxymethyl cellulose, carboxymethyl ethyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. Moreover, these ammonium salt and alkali metal salt are mentioned. Among these, a salt of carboxymethyl cellulose is preferable, and an ammonium salt of carboxymethyl cellulose is particularly preferable. The degree of etherification of the cellulose derivative is preferably 0.5 to 2, and more preferably 0.5 to 1.5. Here, the degree of etherification is a value representing how many hydroxyl groups contained per 3 glucose units of cellulose are etherified on average. When the degree of etherification is within this range, the stability of the heat-resistant layer slurry is high, and solid matter sedimentation and aggregation are unlikely to occur. Furthermore, the coating property and fluidity | liquidity of a coating material improve by using a cellulose derivative.

  The viscosity when the solid content concentration of the viscosity modifier is 1% is preferably 10 to 8,000 mPa · s. By using a viscosity modifier having a viscosity in this range, the uniform coating property of the heat-resistant layer slurry described later is excellent, and the high-speed coating property and the temporal stability of the heat-resistant layer slurry are also excellent. For this reason, the thickness of the heat-resistant layer can be reduced, whereby the ionic conductivity of the secondary battery separator and the rate characteristics of the secondary battery can be further improved. The viscosity when the solid content concentration of the viscosity modifier is 1% is a value when measured after 60 seconds at 25 ° C. and a rotational speed of 60 rpm using a B-type viscometer.

The content of the viscosity modifier in the heat-resistant layer is 0.01 to 5 parts by mass with respect to 100 parts by mass of the non-conductive particles in that the flexibility and strength of the obtained heat-resistant layer can be further improved. Is preferable, it is more preferable that it is 0.05-4 mass parts, and it is especially preferable that it is the range of 0.05-3 mass parts.
Examples of the surfactant include an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant.

  The content of the surfactant in the heat-resistant layer is preferably within a range that does not affect the battery characteristics. Particularly when the heat-resistant layer slurry is applied to the organic separator, the penetration force of the heat-resistant layer slurry to the organic separator is appropriate. Specifically, it is 0.01 to 3 parts by mass with respect to 100 parts by mass of the nonconductive particles in that the wettability between the organic separator and the slurry for the heat-resistant layer can be further improved. It is preferable that it is 0.03-1.5 mass parts, and it is especially preferable that it is 0.05-1 mass part.

  Other additives include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the heat-resistant layer slurry can be controlled, and the leveling property of the resulting heat-resistant layer can be improved.

(Adhesive layer)
The adhesive layer in the present invention contains a vinylidene fluoride copolymer having a melting point of 70 to 150 ° C. Moreover, the adhesive layer may contain non-conductive particles contained in the heat-resistant layer as necessary. The adhesive layer has a large number of micropores inside, and these micropores are connected from one surface of the adhesive layer to the other surface. Accordingly, the adhesive layer can pass liquid or gas.

(Vinylidene fluoride copolymer)
As the vinylidene fluoride copolymer contained in the adhesive layer, a copolymer of at least one of hexafluoropropylene, chlorotrifluoroethylene, hexafluoroethylene and ethylene and vinylidene fluoride can be used. From the viewpoint of sufficiently ensuring the adhesion between the electrode and the separator for the secondary battery, a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-HFP) is preferable. As PVDF-HFP, KANAR 2850/2851, KANAR 2800/2801, KANAR 2820/2821, KYNAR2750 /, KYNAR7201, KYNAR9301 (all manufactured by ARKEM) or the like can be used.

  Further, the melting point of the vinylidene fluoride copolymer is 70 to 150 ° C. from the viewpoint of sufficiently maintaining the adhesive strength between the organic separator and the electrode.

  Moreover, the swelling degree with respect to the electrolyte solution mentioned later of the vinylidene fluoride copolymer is 110 to 200%. If the degree of swelling of the vinylidene fluoride copolymer is too large, the thickness of the adhesive layer containing the vinylidene fluoride copolymer increases and the ion diffusion distance becomes long. Therefore, the resistance increases. On the other hand, if the degree of swelling of the vinylidene fluoride copolymer is too small, the diffusion of ions is inhibited, so that the resistance increases.

(Acrylic polymer)
The adhesive layer in the present invention may further contain an acrylic polymer in addition to the above-mentioned vinylidene fluoride copolymer. Including an acrylic polymer is preferable because the binding property of the adhesive layer to the heat-resistant layer may be further improved. As the acrylic polymer, a (meth) acrylic polymer that can be used for the binder of the above-described heat-resistant layer may be used, but a nitrile group-containing acrylic polymer is preferably used.

(Nitrile group-containing acrylic polymer)
The nitrile group-containing acrylic polymer is a polymer containing a monomer unit having a nitrile group and a (meth) acrylate monomer unit. A monomer unit having a nitrile group is a structural unit formed by polymerizing a monomer having a nitrile group, and a (meth) acrylate monomer unit is a (meth) acrylate ester unit. A structural unit formed by polymerizing a monomer. The nitrile group-containing acrylic polymer may further contain a monomer unit derived from another monomer such as an ethylenically unsaturated acid monomer unit and a crosslinkable monomer, if necessary. These monomer units are structural units formed by polymerizing the monomers. For example, a monomer unit having a nitrile group is formed by polymerizing a nitrile group-containing monomer. A structural unit. Here, the content ratio of each monomer is usually the same as the content ratio of the repeating unit in the nitrile group-containing acrylic polymer.

  Specific examples of the nitrile group-containing monomer include acrylonitrile and methacrylonitrile. Among them, acrylonitrile is preferable in that the binding property of the adhesive layer to the heat resistant layer can be improved.

  The content ratio of the monomer unit having a nitrile group in the nitrile group-containing acrylic polymer is preferably 5 to 35% by mass, more preferably 10 to 30% by mass, and particularly preferably 15 to 25% by mass. When the amount of the monomer unit having a nitrile group is within this range, the binding strength of the resulting adhesive layer to the heat-resistant layer is improved.

The (meth) acrylic acid ester monomer unit has the general formula (1): CH ₂ ═CR ¹ —COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group or a cycloalkyl group. It is a monomer unit derived from the compound represented by.

  Specific examples of the compound represented by the general formula (1) include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, Acrylate such as isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate; ethyl acrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, meta Metaacrylates such as isobutyl acrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate And the like. Among these, acrylate is preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the obtained electrode can be improved.

  A (meth) acrylic acid ester monomer may be used individually by 1 type, and may combine two or more types by arbitrary ratios. Therefore, the nitrile group-containing acrylic polymer may contain only one type of (meth) acrylic acid ester monomer, or may contain two or more types in combination at any ratio.

  The content ratio of the (meth) acrylic acid ester monomer unit in the nitrile group-containing acrylic polymer is preferably 35 to 85% by mass, more preferably 45 to 75% by mass, and particularly preferably 15 to 25% by mass. . When a nitrile group-containing acrylic polymer in which the content ratio of the (meth) acrylic acid ester monomer unit is in the above range is used, the heat resistance becomes higher.

  The nitrile group-containing acrylic polymer may contain an ethylenically unsaturated acid monomer unit in addition to the monomer unit having the nitrile group and the (meth) acrylic acid ester monomer unit.

The ethylenically unsaturated acid monomer unit is a structural unit formed by polymerizing an ethylenically unsaturated acid monomer. The ethylenically unsaturated acid monomer is an ethylenically unsaturated monomer having an acid group such as a carboxyl group, a sulfonic acid group, or a phosphinyl group, and is not limited to a specific monomer.
Specific examples of the ethylenically unsaturated acid monomer include an ethylenically unsaturated carboxylic acid monomer, an ethylenically unsaturated sulfonic acid monomer, and an ethylenically unsaturated phosphoric acid monomer.

Specific examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof.
Examples of ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.

Examples of ethylenically unsaturated monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, And β-diaminoacrylic acid.
Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

  Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

  Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; and diphenyl maleate, nonyl maleate And maleate esters such as decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate.

  Specific examples of the ethylenically unsaturated sulfonic acid monomer include vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth) acryl sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamide- 2-hydroxypropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and the like.

Specific examples of the ethylenically unsaturated phosphate monomer include (meth) acrylic acid-3-chloro-2-phosphate propyl, (meth) acrylic acid-2-ethyl phosphate, 3-allyloxy-2-hydroxypropane Such as phosphoric acid.
Moreover, the alkali metal salt or ammonium salt of the said ethylenically unsaturated acid monomer can also be used.

  The said ethylenically unsaturated acid monomer may be used individually by 1 type, and may combine 2 or more types by arbitrary ratios. Therefore, the nitrile group-containing acrylic polymer may contain only one type of ethylenically unsaturated acid monomer, or may contain two or more types in combination at any ratio.

  Among these, from the viewpoint of improving the dispersibility of the nitrile group-containing acrylic polymer, the ethylenically unsaturated acid monomer may be an ethylenically unsaturated carboxylic acid monomer or an ethylenically unsaturated sulfonic acid monomer. Are preferably used alone or in combination with an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer, and the ethylenically unsaturated carboxylic acid monomer and the ethylenically unsaturated sulfonic acid monomer are preferred. Is more preferable.

  Among ethylenically unsaturated carboxylic acid monomers, from the viewpoint of expressing good dispersibility in the nitrile group-containing acrylic polymer, ethylenically unsaturated monocarboxylic acid is preferable, and acrylic acid or methacrylic acid is more preferable. Particularly preferred is methacrylic acid.

  Of the ethylenically unsaturated sulfonic acid monomers, 2-acrylamido-2-hydroxypropanesulfonic acid, 2-acrylamido-2 are preferable from the viewpoint of expressing good dispersibility in the nitrile group-containing acrylic polymer. -Methylpropanesulfonic acid, more preferably 2-acrylamido-2-methylpropanesulfonic acid.

  The content ratio of the ethylenically unsaturated acid monomer unit in the nitrile group-containing acrylic polymer is high in dispersibility of the nitrile group-containing acrylic polymer when slurried, and can form a highly uniform active material layer. From the viewpoint of reducing the resistance of the electrode layer, the range is preferably 10 to 30% by mass, more preferably 12 to 28% by mass, and particularly preferably 14 to 26% by mass.

  Moreover, when using together an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer as the ethylenically unsaturated acid monomer, the ethylenically unsaturated carboxylic acid in the nitrile group-containing acrylic polymer The content ratio of the monomer is preferably 10 from the viewpoint of high dispersibility of the nitrile group-containing acrylic polymer when slurried, a highly uniform active material layer can be formed, and the resistance of the electrode layer can be reduced. It is -30 mass%, More preferably, it is 12-28 mass%, Preferably the content rate of an ethylenically unsaturated sulfonic acid monomer is 0.1-10 mass%.

  The nitrile group-containing acrylic polymer may further contain a crosslinkable monomer unit as long as it does not affect the THF-insoluble content of the nitrile group-containing acrylic polymer in addition to each of the above structural units. The crosslinkable monomer unit is a structural unit capable of forming a crosslinked structure during or after polymerization by heating or energy irradiation of the crosslinkable monomer. As an example of the crosslinkable monomer, a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

  Examples of thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

  Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl. Unsaturated glycidyl ethers such as ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate Glycidyl crotonate, Unsaturated carboxylic acids such as glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Examples include glycidyl esters of acids.

  Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

  Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl ) -4-trifluoromethyloxetane.

  Examples of the crosslinkable monomer having an oxazoline group as a thermally crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline is mentioned.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Ethers, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylene bisacrylamide, and divinylbenzene.

  As the crosslinkable monomer, in particular, allyl (meth) acrylate, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate can be preferably used.

  The said crosslinking | crosslinked monomer may be used individually by 1 type, and may combine 2 or more types by arbitrary ratios. Therefore, the nitrile group-containing acrylic polymer may contain only one type of crosslinkable unsaturated acid monomer, or may contain two or more types in combination at any ratio.

  When the crosslinkable monomer unit is contained in the nitrile group-containing acrylic polymer, the content ratio is preferably 0.1% by mass or more, more preferably 0.2% by mass, from the viewpoint of improving dispersibility. % Or more, particularly preferably 0.5% by mass or more, preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less. When too large, the dispersibility of a nitrile group containing acrylic polymer will deteriorate.

Further, in addition to the above, the nitrile group-containing acrylic polymer may contain an aromatic vinyl monomer unit, an ethylenically unsaturated carboxylic acid amide monomer unit, and the like.
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, chlorostyrene, and hydroxymethylstyrene.

  Examples of the ethylenically unsaturated carboxylic acid amide monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide and the like.

  These monomer units may be contained in a proportion of 10% by mass or less.

  Here, the content ratio of each monomer is usually a repeating unit in a nitrile group-containing acrylic polymer (for example, (meth) acrylic acid ester monomer unit, ethylenically unsaturated acid monomer unit, and crosslinkability). The content ratio of the monomer unit is the same.

  Next, the degree of swelling of the nitrile group-containing acrylic polymer with respect to the non-aqueous electrolyte and the amount of the nitrile group-containing acrylic polymer insoluble in tetrahydrofuran (THF) will be described.

  The degree of swelling of the nitrile group-containing acrylic polymer with respect to the non-aqueous electrolyte is such that the volume of the polymer is not significantly changed in the electrolyte, and even if the charge / discharge cycle is repeated, From the viewpoint of maintaining the binding property and improving the cycle characteristics, it is preferably 100 to 300%, more preferably 100 to 280%, and particularly preferably 100 to 260%. Here, the nonaqueous electrolytic solution is an electrolytic solution constituting the lithium ion secondary battery of the present application. The degree of swelling with respect to the nonaqueous electrolytic solution can be controlled by, for example, the content ratio of each monomer unit described above. Specifically, it increases when the content ratio of the nitrile group-containing monomer unit is increased. Moreover, it decreases when the content of the ethylenically unsaturated monomer unit is increased.

  Further, the tetrahydrofuran (THF) insoluble amount of the nitrile group-containing acrylic polymer is 30% by mass or less, preferably 25% by mass or less, and more preferably, in order to appropriately dissolve the polymer in the slurry dispersion medium. Is in the range of 20% by weight or less. The THF-insoluble matter is an index of the amount of gel, and if the amount of THF-insoluble matter is large, it exists in the form of particles in a slurry using an organic solvent such as N-methylpyrrolidone (hereinafter sometimes referred to as NMP). The dispersibility in a slurry may be impaired. As described later, the THF-insoluble content can be controlled by the polymerization reaction temperature, the monomer addition time, the polymerization initiator amount, and the like. Specifically, the amount of insoluble matter is reduced by increasing the polymerization reaction temperature, increasing the polymerization initiator, and the chain transfer agent.

  Although the manufacturing method of a nitrile group containing acrylic polymer is not specifically limited, As mentioned above, the monomer mixture containing the monomer which comprises a nitrile group containing acrylic polymer can be obtained by emulsion polymerization. The method for emulsion polymerization is not particularly limited, and a conventionally known emulsion polymerization method may be employed. The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

  Examples of the polymerization initiator used for emulsion polymerization include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide Organic peroxides such as oxide and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, etc. Is .

  Among these, inorganic peroxides can be preferably used. These polymerization initiators can be used alone or in combination of two or more.

  In order to adjust the amount of THF-insoluble matter in the copolymer obtained, it is preferable to use a chain transfer agent during emulsion polymerization. Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfides; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide; phenols such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol Compounds; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; thioglycolic acid, Oringo acid, 2-ethylhexyl thioglycolate, diphenylethylene, etc. α- methylstyrene dimer.

Among these, alkyl mercaptans are preferable, and t-dodecyl mercaptan can be more preferably used. These chain transfer agents can be used alone or in combination of two or more.
The amount of the chain transfer agent used is preferably 0.05 to 2 parts by mass, more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the monomer mixture.

A surfactant may be used during the emulsion polymerization. The surfactant may be any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. Specific examples of the anionic surfactant include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium octyl sulfate, sodium decyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate and the like. Sulfuric acid ester salts of higher alcohols; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, sodium lauryl benzene sulfonate, sodium hexadecyl benzene sulfonate; fats such as sodium lauryl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfonate Group sulfonates; and the like.
The amount of the surfactant used is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the monomer mixture.

  Further, in the emulsion polymerization, various additives such as a pH adjusting agent such as sodium hydroxide and ammonia; a dispersing agent, a chelating agent, an oxygen scavenger, a builder, and a seed latex for adjusting the particle size can be appropriately used. . In particular, emulsion polymerization using a seed latex is preferred. Seed latex refers to a dispersion of fine particles that becomes the nucleus of the reaction during emulsion polymerization. The fine particles often have a particle size of 100 nm or less. The fine particles are not particularly limited, and general-purpose polymers such as diene polymers are used. According to the seed polymerization method, copolymer particles having a relatively uniform particle diameter can be obtained.

  Although the polymerization temperature at the time of performing a polymerization reaction is not specifically limited, Usually, 0-100 degreeC, Preferably you may be 40-80 degreeC. Emulsion polymerization is performed in such a temperature range, and the polymerization reaction is stopped at a predetermined polymerization conversion rate by adding a polymerization terminator or cooling the polymerization system. The polymerization conversion rate at which the polymerization reaction is stopped is preferably 93% by mass or more, more preferably 95% by mass or more, from the viewpoint that the amount of THF-insoluble matter in the resulting copolymer can be appropriately adjusted.

  After stopping the polymerization reaction, if necessary, the unreacted monomer is removed, the pH and solid content concentration are adjusted, and the copolymer is dispersed in a dispersion medium (latex) in a nitrile group-containing acrylic polymer Is obtained. Thereafter, if necessary, the dispersion medium may be replaced, or the dispersion medium may be evaporated to obtain a particulate copolymer in powder form.

  Addition of known dispersants, thickeners, anti-aging agents, antifoaming agents, antiseptics, antibacterial agents, anti-blistering agents, pH adjusting agents, etc., to the nitrile group-containing acrylic polymer dispersion You can also

(Method for producing secondary battery separator)
The method for producing the secondary battery separator of the present invention is not particularly limited as long as the heat-resistant layer and the adhesive layer are formed in this order on the organic separator, but the non-conductive particles and the binder are formed on the organic separator. A heat-resistant layer forming step of forming a heat-resistant layer by applying and drying a slurry for heat-resistant layer, and applying and drying a slurry for an adhesive layer containing a vinylidene fluoride copolymer on the heat-resistant layer The method which has an adhesive bond layer formation process which forms an adhesive bond layer by this is preferable. Below, this method is demonstrated as a manufacturing method of the separator for secondary batteries of this invention.

(Method for forming heat-resistant layer)
In the production method of the present invention, first, a heat-resistant layer slurry containing non-conductive particles and a binder is applied onto an organic separator and dried to form a heat-resistant layer. The heat-resistant layer may be formed on only one side of the organic separator or on both sides.
The heat-resistant layer slurry is produced by mixing the dispersion medium with the aforementioned non-conductive particles, binder, and optional components that are solid components.
In the present invention, by using the above components, a slurry for a heat-resistant layer in which non-conductive particles are highly dispersed can be obtained regardless of the mixing method and mixing order.
The dispersion medium is not particularly limited as long as it can uniformly disperse the solids (non-conductive particles, binder and the optional component).

  As the dispersion medium used in the slurry for the heat-resistant layer, 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 dispersion media may be used alone, or two or more of these dispersion media may be mixed and used as a mixed dispersion medium. Among these, a dispersion medium 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 dispersion medium thereof is preferable.

  In particular, when the (meth) acrylic polymer described above is used as a binder, it is possible to use an aqueous dispersion medium such as water as a dispersion medium and obtain a slurry for a heat-resistant layer as an aqueous dispersion, thereby reducing the manufacturing process and process load. This is particularly preferable because it can be performed.

  The solid content concentration of the heat-resistant layer slurry can be appropriately adjusted to a concentration that allows the heat-resistant layer slurry to be applied and has a fluid viscosity, but is generally about 10 to 50% by mass. It is.

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

  Since the heat-resistant layer slurry is for forming a heat-resistant layer, the non-conductive particles, binder, and optional components (components described above as optional components of the heat-resistant layer) in the total solid content of the heat-resistant layer slurry. The content ratio of can be the ratio as described above for the heat-resistant layer.

  The mixing apparatus 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. However, it is particularly preferable to use a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix that can add a high dispersion share.

  The viscosity of the slurry for the heat-resistant layer is sufficient as long as it is suitable for coating, but is preferably 10 to 300 mPa · s. By adjusting the viscosity of the heat-resistant layer slurry to the above range, it is possible to produce a uniform heat-resistant layer without thinning of the heat-resistant layer, uneven distribution of binders or non-conductive particles in the heat-resistant layer, and further uniform coating. Excellent in workability, high-speed coating property, and heat storage layer slurry storage stability. In the present invention, the viscosity of the heat-resistant layer slurry is more preferably 10 to 200 mPa · s, and particularly preferably 20 to 100 mPa · s. The viscosity of the heat-resistant layer slurry is a value (η60) when measured after 60 seconds at 25 ° C. and a rotation number of 60 rpm using an E-type viscometer.

  There is no restriction | limiting in the method of forming the coating film of the slurry for heat-resistant layers on an organic separator, For example, you may carry out by the apply | coating method, the immersion method, etc. Among these, the coating method is preferable because the thickness of the heat-resistant layer can be easily controlled. Examples of the coating method include a doctor blade coating method, a dip coating method, a reverse roll coating method, a direct roll coating method, a gravure coating method, an extrusion coating method, and a brush coating method. Among them, the dip coating method and the gravure coating method are preferable in that a uniform heat-resistant layer can be obtained.

  There is no limitation on the method for drying the heat-resistant slurry slurry formed on the organic separator. For example, drying with warm air, hot air, low-humidity air, etc., vacuum drying, irradiation with (far) infrared rays, electron beams, etc. And the like.

  The drying temperature may be a temperature at which the dispersion medium is vaporized and removed from the coating film. However, when the binder has a thermally crosslinkable group, the drying is performed at a temperature higher than the temperature at which the thermally crosslinkable group causes a crosslinking reaction. Preferably it is done. By simultaneously removing the dispersion medium from the coating film and crosslinking, the number of steps can be reduced and the production efficiency can be improved. Usually, it is dried at 30 to 100 ° C.

  When manufacturing the heat-resistant layer, another process may be performed in addition to the application process and the drying process described above. For example, the pressing process may be performed using a mold press, a roll press, or the like. Thereby, the adhesiveness of an organic separator and a heat-resistant layer can be improved. What is necessary is just to control appropriately the pressure and pressurization time of a pressurization process in the range which does not impair the porosity of a heat-resistant layer.

Moreover, the coating amount per one side to the organic separator of a heat-resistant layer is 2-10 g / m < ² >. If the coating amount of the heat-resistant layer is too large, the resistance increases, so that the cycle characteristics of the obtained secondary battery are deteriorated. Moreover, when there are too few application | coating amounts of a heat-resistant layer, the heat resistance of the separator for secondary batteries obtained will become low.

  The thickness of the heat-resistant layer is 0.1 to 20 μm in that a decrease in ionic conductivity can be suppressed and a sufficient heat-resistant layer with an organic separator can be formed because it has sufficient binding properties. Is preferably 0.2 to 15 μm, particularly preferably 0.3 to 10 μm.

(Adhesive layer formation method)
In the production method of the present invention, the adhesive layer slurry is applied by applying a slurry for an adhesive layer containing a vinylidene fluoride copolymer on the heat-resistant layer formed on one or both sides of the organic separator by the above-described steps, and drying. Form. Here, the melting point of the vinylidene fluoride copolymer contained in the slurry for the adhesive layer is preferably 70 to 150 ° C. Moreover, it is preferable that the swelling degree with respect to the electrolyte solution mentioned later of the vinylidene fluoride copolymer contained in the slurry for adhesive layers is 110 to 200%.

The slurry for the adhesive layer is produced by mixing the dispersion medium, the above-described particulate polymer, and optional components. As a dispersion medium and a mixing apparatus, the thing equivalent to what was used with the slurry for heat-resistant layers mentioned above can be used.
In the present invention, by using the above components, a slurry for an adhesive layer in which the particulate polymer is highly dispersed can be obtained regardless of the mixing method and the mixing order.

  The method for applying the slurry for the adhesive layer is not particularly limited. For example, the doctor blade method, the dip coating method, the reverse roll coating method, the direct roll coating method, the spray coating method, the gravure coating method, the extrusion coating method, the brushing method. Examples thereof include a coating method.

  Examples of the method for drying the coating film of the adhesive layer slurry include drying with warm air, hot air, low-humidity air, and the like, vacuum drying, drying method by irradiation with (far) infrared rays, electron beams, and the like. . The drying temperature can be changed depending on the type of medium used. In order to completely remove the medium, for example, when a low-volatility medium such as N-methylpyrrolidone is used, the medium is preferably dried at a high temperature of 120 ° C. or higher with a blower-type dryer. Conversely, when a highly volatile medium is used, it can be dried at a low temperature of 100 ° C. or lower.

Moreover, the coating amount per side to the heat-resistant layer of the adhesive layer is 0.1 to 1.5 g / m ² . If the coating amount of the heat-resistant layer is too large, the resistance increases, so that the cycle characteristics of the obtained secondary battery are deteriorated. Moreover, when there are too few application | coating amounts of a heat-resistant layer, the adhesiveness of an electrode and a separator will be low and the cycling characteristics of the secondary battery obtained will deteriorate.

  The thickness of the adhesive layer is preferably 0.1 to 5 μm from the viewpoint of achieving both moderate ion permeability and good adhesion between the electrode active material layer and the heat-resistant layer after electrode production, More preferably, it is 0.3-4 micrometers, and it is especially preferable that it is 0.3-3 micrometers.

(Secondary battery)
The secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and the above-described separator for a secondary battery. Secondary batteries include lithium metal batteries, lithium ion secondary batteries, etc., but the most important is to improve performance such as long-term cycle characteristics and output characteristics. A battery is preferred. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

(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 inorganic compounds used for the positive electrode active material include lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ ; 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 other constituent elements of the battery, but a secondary battery having a large charge / discharge capacity and a viewpoint of improving battery characteristics such as load characteristics and cycle characteristics is obtained. The volume average particle diameter D50 is preferably from 0.1 to 50 [mu] m, more preferably from 1 to 20 [mu] m, from the viewpoint of being easy to handle and making the electrode slurry and electrode easy to handle. The volume average particle diameter D50 of the positive electrode active material can be obtained by measuring the particle diameter of the positive electrode active material using a laser diffraction particle size distribution analyzer.

  Examples of electrode active materials (negative electrode active materials) for negative electrodes of lithium ion secondary batteries include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, pitch-based carbon fibers, and high conductivity such as polyacene. Examples include molecules. 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, load characteristics, and cycle characteristics, the volume average particle diameter of the negative electrode active material is used. D50 is preferably 1 to 50 μm, and more preferably 15 to 30 μm. The volume average particle diameter D50 of the negative electrode active material is measured by the same method as that for the positive electrode active material.

(Binder for active material layer)
In the present invention, the electrode active material layer preferably contains an active material layer binder 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.
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 that is a homopolymer of a methacrylic acid derivative or a copolymer with a monomer copolymerizable therewith; isobutylene soft such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer Polymer: Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, Acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene / butadiene / styrene / block copolymer, isoprene / styrene / block copolymer, styrene / isoprene / styrene / block copolymer, etc. Diene-based soft polymer; silicon-containing soft polymer such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane; liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin Olefin-based soft polymers such as copolymers, ethylene / propylene / diene copolymers (EPDM), ethylene / propylene / styrene copolymers; polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / Vinyl-based soft polymers such as ethylene copolymers; 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; Natural rubber And other soft polymers such as polypeptides, proteins, polyester-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and the like. 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 usually 0. 10 parts by mass with respect to 100 parts by mass of the electrode active material from the viewpoint of preventing the active material from falling off the electrode without inhibiting the battery reaction. 1 to 5 parts by mass, preferably 0.2 to 4 parts by mass, and more preferably 0.5 to 3 parts by mass.

  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.

  In the secondary battery of the present invention, the electrode active material layer may contain a conductivity imparting material or a reinforcing material. 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. 0-20 mass parts is preferable with respect to 100 mass parts of electrode active materials, and, as for the usage-amount of an electroconductivity imparting material, it is more preferable that it is 1-10 mass parts.

  The electrode active material layer may be present alone, but is usually present in a form attached to the current collector. The electrode active material layer can be formed by attaching a mixture slurry containing an electrode active material and a dispersion medium to a current collector.

  As the dispersion medium, when the electrode active material layer contains the binder for the active material layer, any material can be used as long as it can be dissolved or dispersed in the form of particles. When a dispersion medium that dissolves the binder for the active material layer is used, the dispersion of the electrode active material and the like is stabilized by the binding of the binder for the active material layer to the surface.

  The mixture slurry contains a dispersion medium and disperses the electrode active material, the binder for the active material layer, and the conductivity-imparting material. It is preferable to use a dispersion medium that can dissolve the binder for the active material layer because the dispersibility of the electrode active material and the conductivity-imparting material is excellent. By using the active material layer binder dissolved in the dispersion medium, it is assumed that the binder for the active material layer is adsorbed on the surface of the electrode active material and the like, and the dispersion is stabilized by the volume effect. Is done.

  Examples of the dispersion medium used for the mixture slurry include the same dispersion medium used for the heat-resistant layer. These dispersion media may be used alone or in admixture of two or more and may be appropriately selected from the viewpoint of drying speed and environment. Among them, in the present invention, it is preferable to use a non-aqueous solvent from the viewpoint of the electrode expansion property to water.

The mixture slurry may further contain additives that exhibit various functions such as a thickener. As the thickener, a polymer soluble in the dispersion medium used for the mixture slurry is used.
Specifically, acrylonitrile-butadiene copolymer hydride or the like is used.

  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 organic solvent in the mixture slurry is adjusted so as to have a viscosity suitable for coating depending on the type of the electrode active material, the binder for the active material layer, and the like. Specifically, it is preferable to adjust the solid content concentration of the electrode active material, the binder for the active material layer, and other additives in the mixture slurry to 30 to 90% by mass, More preferably, the amount is adjusted to 80% by mass.

  The mixture slurry is obtained by mixing an electrode active material, an active material layer binder added as necessary, a conductivity imparting material, other additives, and a dispersion medium using a mixing device. The mixing may be performed by supplying the above components all at once to a mixing apparatus. When using an electrode active material, a binder for an active material layer, a conductivity-imparting material, and a thickener as components of the mixture slurry, the conductivity-imparting material and the thickener are mixed in a dispersion medium. It is preferable to disperse the conductivity-imparting material in the form of fine particles, and then add and mix the binder for the active material layer and the electrode active material, since the dispersibility of the mixture slurry is improved. As the mixing device, those described above can be used, and a ball mill is preferable because aggregation of the conductivity imparting material and the electrode active material can be suppressed.

  The particle size of the mixture slurry is preferably 35 μm or less, and more preferably 25 μm or less, from the viewpoint of high dispersibility of the conductivity imparting material and obtaining a homogeneous electrode.

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

  The method for producing the electrode active material layer may be any method in which the electrode active material layer is bound in layers on at least one 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, and the same method as the method for applying the heat-resistant layer slurry or the method for applying the adhesive layer slurry can be used.

Next, it is preferable to lower the porosity of the electrode mixture by pressurization 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 mixture is easily peeled off and a defect is likely to occur. 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 and preferably 10 to 250 μm for both the positive electrode and the negative electrode.

(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 an organic 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 organic 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 organic solvent used decreases, the lithium ion conductivity can be adjusted depending on the type of the organic solvent.

  The density | concentration of the supporting electrolyte in electrolyte solution is 1-30 mass% normally, and it is preferable that 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.

(Production method)
As a specific method for producing a lithium ion secondary battery, for example, a laminated body in which a positive electrode and a negative electrode are superposed via the secondary battery separator of the present invention is obtained, and this is wound and folded according to the battery shape. For example, it may be put into a battery container, and an electrolytic solution is injected into the battery container and sealed.

  When obtaining the said laminated body, it is preferable to heat-press a laminated body. Hot pressing is a method in which heating and pressing are performed simultaneously. The pressing is performed using a roll press machine using a metal roll, an elastic roll or the like, a flat plate press machine, or the like. Examples of the press method include a batch type press and a continuous type roll press, and a continuous type roll press is preferable in terms of enhancing productivity. The temperature of the hot press is not particularly limited as long as the structure of the electrode constituting the laminate and the separator for the secondary battery is not destroyed, but preferably 60 to 110 ° C, more preferably 70 to 105 ° C, particularly preferably. 80-100 ° C.

  From the viewpoint of firmly bonding the electrode and the secondary battery separator while maintaining the porosity of the secondary battery separator, the pressure of the hot press is usually 0.1 to 10 MPa, preferably 0.3 to 5 MPa, More preferably, it is 0.5-3 MPa. Moreover, the time which performs a hot press is 2-60 second normally from a viewpoint which can adhere | attach an electrode active material layer and the separator for secondary batteries firmly, and ensures high productivity, and is 5-40 second. It is preferable that it is 8 to 20 seconds.

  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 placed in the battery container to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples shown below, and may be arbitrarily changed without departing from the gist of the present invention and its equivalent scope. May be implemented. Further, in the following description, “%” and “part” representing the amount are based on mass unless otherwise specified. Further, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Heat shrinkage]
A separator for a secondary battery was cut into a square having a width of 5 cm and a length of 5 cm to obtain a test piece. The test piece was placed in a thermostatic bath at 150 ° C. and allowed to stand for 1 hour, and then the square area change was determined as the heat shrinkage rate. Moreover, it evaluated by the following reference | standard and the result was shown in Table 1. The smaller the heat shrinkage rate, the better the heat shrinkability of the secondary battery separator.
A: The heat shrinkage rate is less than 1% B: The heat shrinkage rate is 1% or more and less than 5% C: The heat shrinkage rate is 5% or more and less than 10% D: The heat shrinkage rate is 10% or more

[Adhesiveness of adhesive layer]
A secondary battery separator and a negative electrode having an electrode active material layer were cut into squares each having a width of 3 cm and a length of 3 cm. The adhesive layer of the secondary battery separator and the electrode active material layer of the negative electrode are overlapped, and at 90 ° C. and 10 kg / cm ² using a hot press machine (SA-501 high precision hot press machine manufactured by Tester Sangyo Co., Ltd.). The laminate was obtained by hot pressing for 10 seconds under the conditions.

  With the negative electrode surface of the obtained laminate fixed to the test stand, one end of the secondary battery separator is pulled off in the vertical direction at a pulling rate of 50 mm / min, and the secondary battery separator and the negative electrode active material layer The adhesion was evaluated according to the following criteria. The results are shown in Table 1. When peeled off at the negative electrode active material layer / current collector interface, the adhesive layer has the highest adhesiveness, indicating excellent adhesion between the secondary battery separator and the negative electrode active material layer.

The same adhesive evaluation as described above was performed for a laminate of a separator for a secondary battery and a positive electrode having an electrode active material layer. When the adhesion evaluation between the secondary battery separator and the positive electrode active material layer is the same as the negative electrode evaluation result, only the negative electrode test result is shown in Table 1.
In all of the laminates obtained in the examples and comparative examples, no peeling occurred at the interface between the heat-resistant layer and the organic separator.
A: Peeling at the negative electrode active material layer / current collector interface B: Peeling at the heat-resistant layer / adhesive layer interface or Peeling at the adhesive layer / negative electrode active material layer interface C: Secondary battery separator Adhesive layer does not adhere to the negative electrode active material layer

[Adhesiveness of adhesive layer in electrolyte]
The laminated body of the separator for secondary batteries and the negative electrode which has an electrode active material layer was cut | disconnected to 10 mm width, and it was immersed in the same electrolyte solution used for manufacture of the battery mentioned later at the temperature of 60 degreeC for 3 days. Then, this was taken out and the separator for secondary batteries was peeled off in a wet state. The adhesiveness at this time was evaluated according to the following criteria. The results are shown in Table 1.
It shows that the holding | maintenance characteristic of the adhesive force of the adhesive bond layer in electrolyte solution is so high that there exists resistance when peeling the separator for secondary batteries from the electrode active material layer of a negative electrode.

Furthermore, the adhesive evaluation similar to the above was performed also about the laminated body of the separator for secondary batteries, and the positive electrode which has an electrode active material layer. When the adhesion evaluation between the secondary battery separator and the positive electrode active material layer is the same as the negative electrode evaluation result, only the negative electrode test result is shown in Table 1.
A: Resistance when peeled (excellent adhesion)
B: Almost no resistance when peeled (poor adhesion)
C: already peeled off from the electrolyte

[High temperature cycle characteristics]
A 10-cell lamellar battery was charged to 4.2 V by a constant current method of 0.2 C in an atmosphere of 60 ° C., and charging / discharging to 3 V was repeated 200 times (= 200 cycles), and the electric capacity was measured. Using the average value of 10 cells as a measured value, the ratio of the electric capacity at the end of 200 cycles to the electric capacity at the end of 5 cycles was calculated as a percentage to obtain the charge / discharge capacity retention rate, and evaluated according to the following criteria. The results are shown in Table 1. Higher values indicate better high temperature cycle characteristics.
A: The charge / discharge capacity retention is 80% or more.
B: The charge / discharge capacity retention is 70% or more and less than 80%.
C: The charge / discharge capacity retention is 60% or more and less than 70%.
D: The charge / discharge capacity retention is less than 60%.

[Example 1]
(Manufacture of heat-resistant binder)
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (product name “Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate, The gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ° C.

  On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94.8 parts of butyl acrylate (BA) and 2 parts of acrylonitrile (AN) as polymerizable monomers Then, 1 part of methacrylic acid (MAA), 1.2 parts of N-methylolacrylamide (NMA) and 1 part of allyl glycidyl ether (AGE) were mixed to obtain a monomer mixture. This 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 produce an aqueous dispersion containing a (meth) acrylic polymer as a binder for the heat resistant layer.

  The content ratio of the crosslinkable monomer unit in the obtained (meth) acrylic polymer was 2.2%. The volume average particle diameter D50 of the (meth) acrylic polymer was 0.36 μm, and the glass transition temperature was −45 ° C.

(Manufacture of slurry for heat-resistant layer)
Alumina particles (AKP-3000 manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter D50 = 0.45 μm, tetrapot-like particles) were prepared as non-conductive particles.

  As the viscosity modifier, an etherification degree of 0.8 to 1.0 carboxymethyl cellulose (manufactured by Daicel Finechem, product name D1200) was used. In addition, the viscosity of the 1% aqueous solution of the viscosity modifier was 10 to 20 mPa · s.

  100 parts of non-conductive particles, 1.5 parts of a viscosity modifier, and ion-exchanged water were mixed and dispersed so that the solid content concentration was 40% by mass. Further, an aqueous dispersion containing the (meth) acrylic polymer as a binder is mixed in an amount of 4 parts by solid content, and 0.2 part of a polyethylene glycol type surfactant (San Nopco SN wet 366) is mixed, and a slurry for a heat-resistant layer Manufactured.

(Manufacture of slurry 1 for adhesive layer)
To 100 parts of vinylidene fluoride copolymer (KYNAR 2821-00, manufactured by ARKEM), N-methylpyrrolidone was mixed so that the solid content concentration would be 8%, whereby an adhesive layer slurry 1 was obtained.

(Manufacture of secondary battery separators)
An organic separator (thickness 16 μm, Gurley value 210 s / 100 cc) made of a polyethylene porous substrate was prepared. The slurry for heat-resistant layer was applied to both surfaces of the prepared organic separator and dried at 50 ° C. for 3 minutes. Thereby, an organic separator provided with a heat-resistant layer having a coating amount of 8 g / m ² was obtained.

Next, on each heat-resistant layer, the adhesive layer slurry 1 is applied by spray coating, dried at 50 ° C. for 1 minute, and provided with an adhesive layer having an application amount of 0.5 g / m ² . A separator was obtained. The degree of swelling of the vinylidene fluoride copolymer constituting the adhesive layer with respect to the indicator solution was 135%.
About the obtained separator for secondary batteries, heat shrinkability was evaluated.

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

(Manufacture of negative electrode)
98 parts of graphite having a particle size of 20 μm and a BET specific surface area of 4.2 m ² / g are mixed as a negative electrode active material, and 1 part of solid content equivalent of SBR (styrene-butadiene rubber, glass transition temperature: −10 ° C.) is mixed as a binder. Then, 1 part of carboxymethylcellulose was further mixed with this mixture, water was further added as a solvent, and these were mixed with a planetary mixer to obtain a mixture slurry for a negative electrode. This negative electrode mixture slurry was applied to one side of a 18 μm thick copper foil, dried at 120 ° C. for 3 hours, and then roll pressed to obtain a negative electrode having an electrode active material layer with a total thickness of 60 μm. .

(Preparation of negative electrode / secondary battery separator / positive electrode laminate)
The positive electrode was cut into a 4 × 4 cm ² square to obtain a positive electrode. The negative electrode was cut into a square of 4.2 × 4.2 cm ² to obtain a negative electrode. The secondary battery separator was cut into a square of 5 × 5 cm ² to obtain a secondary battery separator.

  Square secondary battery separator, with the positive electrode on the surface and the negative electrode on the back, and then heated and pressed at 80 ° C. and 0.5 MPa for 10 seconds to separate the positive and negative electrodes into a secondary battery separator The negative electrode / secondary battery separator / positive electrode laminate was prepared by bonding the positive electrode and the negative electrode to the adhesive layer of the secondary battery separator.

  In addition, after placing only the negative electrode or the positive electrode on one side of the square secondary battery separator, the sample is subjected to hot pressing in the same manner as the method for manufacturing the secondary battery separator, and the sample for evaluating the adhesiveness of the adhesive layer Was made. About the obtained sample for adhesive evaluation, the adhesiveness of the adhesive bond layer and the adhesiveness of the adhesive bond layer in electrolyte solution were evaluated.

(Lithium ion secondary battery)
As the battery exterior, an aluminum wrapping exterior was prepared, and a negative electrode / secondary battery separator / positive electrode laminate was installed and housed. The electrolyte was injected so that no air remained. The solvent of this electrolytic solution is a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5 (volume ratio)), and the electrolyte is LiPF having a concentration of 1M. It was ₆ . Further, in order to seal the opening of the aluminum wrapping material, heat sealing at 150 ° C. was performed to close the aluminum exterior, thereby producing a ramice-type lithium ion secondary battery.

[Example 2]
(Manufacture of acrylic binder for adhesive layer)
In an autoclave equipped with a stirrer, 164 parts by mass of ion-exchanged water, 59.5 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of methacrylic acid, 20 parts by mass of acrylonitrile, 0.5 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid After adding 0.3 parts of potassium persulfate as a polymerization initiator and 1.6 parts of sodium lauryl sulfate as an emulsifier, the mixture was stirred thoroughly and then heated at 70 ° C for 3 hours and then at 80 ° C for 2 hours for polymerization. An aqueous dispersion of a nitrile group-containing acrylic polymer was obtained. The polymerization conversion rate determined from the solid content concentration was 96%. Further, 500 parts of N-methylpyrrolidone was added to 100 parts of this aqueous dispersion, and after evaporating all of water and residual monomers under reduced pressure, 81 parts of N-methylpyrrolidone was evaporated to obtain 8% by mass of the acrylic polymer. Of NMP was obtained. The swelling degree of the non-aqueous electrolyte at this time was 1.7 times, and the amount of THF-insoluble matter was 10% or less.

(Production of slurry 2 for adhesive layer)
20 parts of the above acrylic binder is added to 80 parts of vinylidene fluoride copolymer (KYNAR 2821-00, manufactured by ARKEM), and N-methylpyrrolidone is mixed so that the solid content concentration becomes 8%, and bonded. A slurry 2 for the agent layer was obtained. A secondary battery separator and a secondary battery were produced in the same manner as in Example 1 except that the adhesive layer slurry 2 was used instead of the adhesive layer slurry 1.

Example 3
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that the coating amount of the heat-resistant layer was 10 g / m ² and the coating amount of the adhesive layer was 0.9 g / m ² .

Example 4
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that the coating amount of the heat-resistant layer was 5 g / m ² and the coating amount of the adhesive layer was 0.1 g / m ² .

Example 5
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that a heat-resistant layer and an adhesive layer were provided only on the negative electrode side of the organic separator.

Example 6
Secondary in the same manner as in Example 1 except that boehmite (APYRAL AOH 60, manufactured by Nabaltec, volume average particle diameter D50 = 0.9 μm, plate-like particles) was used as non-conductive particles in the production of the heat-resistant layer slurry. Battery separators and secondary batteries were produced.

Example 7
(Manufacture of organic fine particles)
In a reactor equipped with a stirrer, 95 parts of styrene, 5 parts of acrylic acid, 1 part of sodium dodecylbenzenesulfonate, 100 parts of ion-exchanged water and 0.5 part of potassium persulfate are placed and polymerized at 80 ° C. for 8 hours. It was. Thereby, an aqueous dispersion of seed polymer particles A having a number average particle diameter of 58 nm was obtained.

  In a reactor equipped with a stirrer, 2 parts of the aqueous dispersion of the seed polymer particles A based on the solid content (ie, based on the mass of the seed polymer particles A), 0.2 parts of sodium dodecylbenzenesulfonate, and potassium persulfate were added. 0.5 part and 100 parts of ion exchange water were added and mixed to obtain a mixture A, which was heated to 80 ° C. Meanwhile, 82 parts of styrene, 15.3 parts of methyl methacrylate, 2 parts of itaconic acid, 0.7 part of acrylamide, 0.5 part of sodium dodecylbenzenesulfonate, and 100 parts of ion-exchanged water were mixed in another container. A dispersion of monomer mixture C was prepared.

This dispersion of the monomer mixture C was continuously added and polymerized in the mixture A obtained above over 4 hours. The temperature of the reaction system during the continuous addition of the dispersion of the monomer mixture C was maintained at 80 ° C., and the reaction was performed. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours. As a result, an aqueous dispersion of seed polymer particles B having a number average particle diameter of 198 nm was obtained.

Next, in a reactor equipped with a stirrer, 20 parts of the aqueous dispersion of the seed polymer particles B on the basis of solid content (ie, based on the mass of the seed polymer particles B) and a monomer mixture D (divinylbenzene and ethylvinylbenzene). , Monomer mixing ratio: divinylbenzene / ethylvinylbenzene = 60/40, manufactured by Nippon Steel Chemical Co., Ltd., product name: DVB-570), 100 parts, sodium dodecylbenzenesulfonate 0.5 parts, polymerized As an initiator, 4 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O), 540 parts of ion-exchanged water and 60 parts of ethanol were added and stirred at 35 ° C. for 12 hours. Then, the monomer mixture D and the polymerization initiator were completely absorbed in the seed polymer particles B. Thereafter, this was polymerized at 90 ° C. for 7 hours. Thereafter, steam was introduced to remove unreacted monomers and ethanol to obtain an aqueous dispersion of polymer particles. Here, the polymer particles were spherical, and the volume average particle diameter D ₅₀ was 0.45 μm.

  Production of separator for secondary battery and secondary battery in the same manner as in Example 1 except that the polymer particles (abbreviated as “organic fine particles A”) were used as non-conductive particles when producing the slurry for the heat-resistant layer. Went.

Example 8
In the production of the slurry for the heat-resistant layer, the same as in Example 2 except that boehmite (APYRAL AOH 60, manufactured by Nabaltec, volume average particle diameter D ₅₀ = 0.9 μm, plate-like particles) was changed as non-conductive particles. A separator for a secondary battery and a secondary battery were produced.

Example 9
In producing the slurry for the heat-resistant layer, the separator for the secondary battery and the secondary battery were produced in the same manner as in Example 2 except that the polymer particles (organic fine particles A) produced in Example 7 were used as the non-conductive particles. It was.

[Comparative Example 1]
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that the adhesive layer was not provided on the organic separator.

[Comparative Example 2]
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that the heat-resistant layer was not provided on the separator.

[Comparative Example 3]
A separator for a secondary battery and a secondary battery were produced in the same manner as in Example 1 except that polyvinylidene fluoride was used instead of PVDE-HFP.

As shown in Table 1, an organic separator and a heat-resistant layer containing non-conductive particles and a binder are formed adjacent to at least one surface of the organic separator, and the melting point is 70 to 150 ° C. on the heat-resistant layer. When the adhesive layer containing the vinylidene copolymer is formed, the coating amount per side of the heat-resistant layer to the organic separator is ² to 10 g / m ² , and the coating amount per side of the adhesive layer to the heat-resistant layer is 0 When set to 0.1 to 1.5 g / m ² , all of the heat shrinkability, adhesiveness, and battery characteristics (high temperature cycle characteristics) were good.

Claims (5)

An organic separator;
A heat-resistant layer formed adjacent to at least one surface of the organic separator and comprising non-conductive particles and a binder;
An adhesive layer comprising a vinylidene fluoride copolymer formed on the heat-resistant layer and having a melting point of 70 to 150 ° C.
The coating amount per one side of the heat-resistant layer to the organic separator is ² to 10 g / m ² ,
A secondary battery separator, wherein an amount of the adhesive layer applied to one side of the heat-resistant layer is 0.1 to 1.5 g / m ² .   The secondary battery separator according to claim 1, wherein the degree of swelling of the vinylidene fluoride copolymer with respect to the electrolyte is 110 to 200%.   The secondary battery separator according to claim 1, wherein the adhesive layer further contains an acrylic polymer. A heat-resistant layer forming step of forming a heat-resistant layer by applying a slurry for a heat-resistant layer containing non-conductive particles and a binder on an organic separator, and drying;
A separator for a secondary battery comprising: an adhesive layer forming step of forming an adhesive layer by applying a slurry for an adhesive layer containing a vinylidene fluoride copolymer on the heat-resistant layer and drying the slurry. Manufacturing method.   A secondary battery comprising the separator for a secondary battery according to any one of claims 1 to 3, a positive electrode, a negative electrode, and an electrolytic solution.