TW201832397A - Aqueous resin composition for lithium ion secondary battery binders and separator for lithium ion secondary batteries - Google Patents

Abstract

An aqueous resin composition for lithium ion secondary battery binders, which contains: (A) core-shell particles, each of which has a core part composed of a polymer (a1) and a shell part composed of a polymer (a2); and (B) an aqueous medium. This aqueous resin composition for lithium ion secondary battery binders is characterized in that: the amount of styrene in a monomer starting material of the polymer (a1) is 60% by mass or more; the amount of methyl methacrylate in a monomer starting material of the polymer (a2) is 45-97.5% by mass; and the amount of a (meth)acrylate having an alkyl group with 4 or more carbon atoms in the monomer starting material of the polymer (a2) is 2-40% by mass. This aqueous resin composition has excellent film forming properties at low temperatures and exhibits excellent adhesion to an electrode and a porous body that constitutes a separator. Consequently, this aqueous resin composition is suitable for use as a binder.

Description

 Lithium ion secondary battery bonding water-based resin composition, and lithium ion secondary battery separator  

The present invention relates to an aqueous resin composition which can be used for a binder of a lithium ion secondary battery separator.

In the case of a separator for producing a lithium ion secondary battery, generally, a porous body obtained by using a polyolefin resin or the like is used. A lithium ion secondary battery generally functions as a battery by moving ions in an electrolytic solution through pores constituting a separator.

On the other hand, when the output of the lithium ion secondary battery is increased, there is a concern that the lithium ion secondary battery may have a possibility of occurrence of ignition or the like due to abnormal heat generation. In the method of preventing the above-mentioned igniting or the like, for example, a method in which the microporous separator of the separator can be made non-porous due to the influence of the heat is known when the lithium ion secondary battery is heated.

However, this separator is remarkably shrunk due to the influence of the heat, and as a result, the conduction of ions in the electrolytic solution cannot be stopped, and there is a possibility that a short circuit of the lithium ion secondary battery is caused.

On the other hand, as a separator which can reduce heat shrinkage, it is proposed to provide a heat-resistant layer on the surface of a porous body obtained by using a polyolefin resin or the like to further improve the adhesion of the separator and the electrode having the heat-resistant layer. An adhesive comprising a particulate polymer having a specific degree of swelling to an electrolytic solution (see, for example, Patent Documents 1 and 2). However, this adhesive has a problem that the film forming property at low temperature is insufficient.

Therefore, a material for forming an adhesive layer is obtained, which is excellent in adhesion to a separator and an electrode even when dried at a low temperature.

 [Previous Technical Literature]    [Patent Literature]  

[Patent Document 1] International Publication No. 2011/040474

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2015-28842

An object of the present invention is to provide an aqueous resin composition which is excellent in low-temperature film-forming property and which is excellent in adhesion to a porous body and an electrode constituting a separator.

In order to solve the above problems, the present inventors have conducted intensive studies and found that the above problems can be solved by using a core-shell type particle having a specific polymer and an aqueous resin composition having an aqueous medium. this invention.

That is, the present invention relates to a water-based resin composition for bonding a lithium ion secondary battery, which comprises a core-shell type particle having a core portion composed of a polymer (a1) and a shell portion composed of a polymer (a2). (A) A water-based resin composition which is bonded to a lithium ion secondary battery of an aqueous medium (B), wherein the styrene in the monomer raw material of the polymer (a1) is 60% by mass or more, (a2) The methyl methacrylate in the monomer raw material is 45 to 97.5% by mass, and the (meth) acrylate having an alkyl group having 4 or more carbon atoms is 2 to 40% by mass.

The water-based resin composition for bonding a lithium ion secondary battery of the present invention is excellent in low-temperature film-forming property and excellent in adhesion to a separator and an electrode, and is suitable for use as a binder for a lithium ion secondary battery.

 [Formation of the Invention]  

The aqueous resin composition for bonding lithium ion secondary batteries of the present invention contains core-shell type particles (A) having a core portion composed of a polymer (a1) and a shell portion composed of a polymer (a2), and an aqueous medium. (B) A lithium ion secondary battery bonded aqueous resin composition, wherein styrene in the monomer raw material of the polymer (a1) is 60% by mass or more, and methyl methacrylate in the monomer raw material of (a2) The (meth) acrylate having an alkyl group having 4 or more carbon atoms is from 4 to 40% by mass, and is from 4 to 40% by mass.

First, the core-shell type particles (A) will be described. The core-shell type particle (A) has a plurality of layers of a core portion of the polymer (a1) constituting particles and a shell portion of the polymer (a2) constituting particles, but may be stably present in the aqueous medium ( In B), the polymer (a1) may constitute a part of the shell portion, and the polymer (a2) may constitute a part of the core portion.

The styrene in the monomer raw material of the polymer (a1) is 60% by mass or more, and is preferably 80% by mass or more from the viewpoint of maintaining the shape of the adhesive layer.

As the monomer raw material of the polymer (a1), a monomer other than styrene can be used. For example, various monomers described later as a monomer raw material of the polymer (a2) can be used.

The methyl methacrylate in the monomer raw material of the polymer (a2) is 45 to 97.5% by mass, and is preferably 55 to 95% by mass from the viewpoint of further improving the balance between lithium ion permeability and heat resistance.

The (meth) acrylate having an alkyl group having 4 or more carbon atoms in the monomer raw material of the polymer (a2) is 2 to 40% by mass, but it is preferably 4 in terms of adhesion improvement. ~20% by mass.

The (meth) acrylate having an alkyl group having 4 or more carbon atoms may, for example, be n-butyl (meth)acrylate, isobutyl (meth)acrylate or tertiary (meth)acrylate. Butyl ester, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and the like. These (meth) acrylates may be used singly or in combination of two or more.

In the present invention, the term "(meth)acryl fluorenyl" means one or both of acryloyl and methacryloyl; "(meth) acrylate" By methacrylic and methacrylic, it means one or both of acrylate and methacrylate; the term "(meth)acrylic" refers to acrylic and methacrylic) One or both of them.

In the monomer raw material of the polymer (a2), a monomer other than (meth) acrylate having a methyl group having 4 or more carbon atoms can be used, and for example, for example, An alkyl (meth)acrylate having an alkyl group having 3 or less carbon atoms such as ethyl (meth)acrylate or propyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate; ) 3-hydroxypropyl acrylate, 4-hydroxy-n-butyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-n-butyl (meth) acrylate, 3-(meth)acrylic acid Hydroxy-n-butyl ester, 1,4-cyclohexanedimethanol mono(meth)acrylate, N-(2-hydroxyethyl)(meth)acrylamide, glycerol mono(meth)acrylate, Polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-(methyl) propylene fluorenyl oxygen Ethyl-2-hydroxyethyl phthalate, a monomer having a hydroxyl group such as a lactone-modified (meth) acrylate having a hydroxyl group at the terminal; N,N-dimethylaminoethyl (methyl) Acrylate, N,N-diethylaminoethyl (meth) acrylate N,N-dimethylaminopropyl (meth) acrylate, N,N-diethylaminopropyl (meth) acrylate, etc. having an amine group (meth) acrylate; N-hydroxyl group a monomer having an N-hydroxymethylguanamine group such as methyl (meth) acrylamide; a monomer having an N-alkoxymethyl guanamine group such as N-butoxymethyl acrylamide (meth) acrylate having a glycidyl group such as (meth)acrylic acid propyl acrylate; vinyl trimethoxy decane, vinyl triethoxy decane, vinyl methyl dimethoxy decane, 3-(Meth)acryloyloxypropyltrimethoxydecane, 3-(methyl)propenyloxypropyltriethoxydecane, 3-(methyl)propenyloxypropylmethyldi a monomer having an alkoxyalkyl group such as methoxydecane; polyethylene glycol (meth) acrylate, methoxy polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, Polyalkylene glycol (meth) acrylate such as methoxypolypropylene glycol (meth) acrylate, polybutylene glycol (meth) acrylate, methoxy polybutylene glycol (meth) acrylate ; (meth)acrylic acid, crotonic acid, etc. Carboxylic acid; unsaturated dicarboxylic acid such as itaconic acid (anhydride), maleic acid (anhydride), fumaric acid, etc.; styrene, α-methylstyrene, p-methylstyrene, chloromethylbenzene a vinyl monomer such as ethylene, vinyl acetate or (meth)acrylonitrile; tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate; ethylene glycol di(meth)acrylate, propylene glycol A di(meth)acrylate such as di(meth)acrylate. These monomers may be used singly or in combination of two or more.

Further, from the viewpoint of further improving the balance between the shape of the adhesive layer and the ion permeability, the mass ratio (a1/a2) of the polymer (a1) to the polymer (a2) is preferably 100/3 to 100/ 200, more preferably 100/10~100/150.

In the method for producing the core-shell type particle (A), various methods are mentioned. However, from the viewpoint of easily obtaining the core-shell type particle (A), an emulsion polymerization method is preferred.

In the method of obtaining the core-shell type particle (A) by the emulsion polymerization method, for example, a method in which a monomer which is a raw material of the polymer (a1) is used in an aqueous medium, an emulsifier, and In the presence of a polymerization initiator, radical polymerization is carried out at a temperature of from 50 to 100 ° C to obtain the monomer (a1), and then a monomer which is a raw material of the polymer (a2) is further added, and the polymerization is carried out.

Examples of the emulsifier include sulfuric acid esters of higher alcohols and salts thereof, alkylbenzenesulfonates, polyoxyethylene alkylphenylsulfonates, and polyoxyethylene alkyl diphenyl ethersulfonates. An anionic emulsifier such as a sulfuric acid half-ester of a polyoxyethylene alkyl ether, an alkyl diphenyl ether disulfonate or a dialkyl sulfonate sulfonate; a polyoxyethylene alkyl ether or a polyoxyethylene a nonionic emulsifier such as an alkylphenyl ether, a polyoxyethylene diphenyl ether, a polyoxyethylene-polyoxypropylene block copolymer or an acetylene glycol; a cationic emulsifier such as an alkylammonium salt; A two-ionic emulsifier such as a base (decylamine) betaine or an alkyldimethylamine oxide. Further, these emulsifiers may be used singly or in combination of two or more. Further, the emulsifier is preferably used in an amount of from 0.5 to 5.0% by mass based on the total of the monomers which are raw materials of the polymer.

Examples of the aforementioned polymerization initiator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), and azobiscyanopentane. An azo compound such as acid; tributyl butyl peroxyacetate, butyl benzoate benzoate, butyl peroxy-2-ethylhexanoate, di-tertiary butyl peroxide, An organic peroxide such as cumene hydroperoxide, benzoyl peroxide, or a tertiary butyl hydroperoxide; an inorganic peroxide such as hydrogen peroxide, ammonium persulfate, potassium persulfate or sodium persulfate; . Further, these polymer initiators may be used singly or in combination of two or more. Further, the polymerization initiator is preferably used in an amount of 0.1 to 10% by mass based on the total of the monomers which are raw materials of the polymer.

In view of further improving the dispersion stability of the core-shell type particle (A), it is preferred to adjust the pH by a basic compound and/or an acidic compound; and as the basic compound, for example, methylamine, Organic amines such as dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, 2-aminoethanol, 2-dimethylaminoethanol; ammonia (water), sodium hydroxide, potassium hydroxide, etc. Inorganic basic compound; tetramethylammonium hydroxide, tetra-n-butylammonium hydroxide, quaternary ammonium hydroxide of trimethylbenzylammonium hydroxide, and the like. Among these, it is preferred to use an organic amine and ammonia (water). Further, these basic compounds may be used singly or in combination of two or more.

The acidic compound is, for example, a carboxylic acid compound such as formic acid, acetic acid, propionic acid or lactic acid; a monoester or a diester of phosphoric acid such as monomethyl phosphate or dimethyl phosphate; methanesulfonic acid or benzenesulfonate; An organic sulfonic acid compound such as an acid or dodecylbenzenesulfonic acid; an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid. Among these, a carboxylic acid compound is preferred. Further, these acidic compounds may be used singly or in combination of two or more.

Examples of the aqueous medium (B) include water, an organic solvent mixed with water, and the like. Examples of the organic solvent to be mixed with water include alcohols such as methanol, ethanol, n-propanol and isopropanol; ketones such as acetone and methyl ethyl ketone; ethylene glycol, diethylene glycol and propylene glycol. Such as polyalkylene glycol; polyalkylene glycol alkyl ether; N-methyl-2-pyrrolidone and other internal guanamine. In the present invention, water alone or a mixture of water and an organic solvent mixed with water may be used, and only an organic solvent mixed with water may be used. From the viewpoint of safety and environmental load, it is preferred to use only water or a mixture of water and an organic solvent mixed with water, and it is particularly preferred to use only water.

The aqueous medium (B) is preferably used as it is convenient to use an aqueous medium which is used in the production of the core-shell type particles (A) by an emulsion polymerization method.

The aqueous resin composition for bonding a lithium ion secondary battery of the present invention contains the core-shell type particles (A) and the aqueous medium (B), but is preferably dispersed by a core-shell type particle (A) obtained by an emulsion polymerization method. For aqueous media (B).

Further, the solvent removal step is carried out as needed, whereby the amount of the organic solvent in the aqueous resin composition of the present invention can be lowered.

In view of the improvement in coating workability, the aqueous resin composition of the present invention obtained by the above method preferably contains the core shell in a range of 5 to 60% by mass based on the total amount of the aqueous resin composition. In the case of the type particle (A), the core-shell type particle (A) is more preferably contained in an amount of 10 to 50% by mass.

In addition, the aqueous resin composition of the present invention preferably contains the aqueous medium (B) in an amount of from 95 to 40% by mass based on the total amount of the aqueous resin composition. More preferably, the aqueous medium (B) is contained in an amount of from 90 to 50% by mass.

The aqueous resin composition of the present invention may be used in combination with a curing agent, a curing catalyst, a lubricant, a filler, a thixotropic imparting agent, an adhesion-imparting agent, a wax, a heat stabilizer, a light stabilizer, and a fluorescent whitening. Additives such as agents and foaming agents, pH adjusters, leveling agents, gelation inhibitors, dispersion stabilizers, antioxidants, radical scavengers, heat-resistant imparting agents, inorganic fillers, organic fillers, plasticizing agents Agent, reinforcing agent, catalyst, antibacterial agent, antifungal agent, corrosion inhibitor, thermoplastic resin, thermosetting resin, pigment, dye, conductivity imparting agent, antistatic agent, moisture permeability promoter, hydrophobic agent, oleophobic Agent, hollow foam, compound containing crystal water, flame retardant, water absorbing agent, moisture absorbent, deodorant, foam stabilizer, antifoaming agent, antifungal agent, preservative, algicide, pigment dispersant , anti-adhesives, hydrolysis inhibitors, pigments.

The aqueous resin composition of the present invention is excellent in adhesion to a separator and an electrode, and can be suitably used as a binder for a lithium ion secondary battery.

In addition, by adding a polymer emulsion having a low glass transition temperature (hereinafter, abbreviated as "low Tg polymer emulsion") to the aqueous resin composition of the present invention, the low-temperature film forming property is further improved.

 [Examples]  

Hereinafter, the present invention will be described in more detail by way of specific examples. In addition, the glass transition temperature (Tg) was calculated by measuring 10 mg of the sample in an aluminum pan, using a differential thermal analysis measuring device ("QA-100" manufactured by TA Instulments), using an empty aluminum pan as a reference, and measuring the temperature range. The DSC curve was measured between -100 ° C and 500 ° C at a heating rate of 10 ° C / min under normal temperature and humidity. During the temperature rise, the differential signal (DDSC) becomes the intersection of the baseline before the end of the endothermic peak of the DSC curve of 0.05 mW/min/mg or more, and the tangent of the DSC curve at the inflection point which initially appears after the endothermic peak. The glass transition temperature (Tg) was determined.

[Synthesis of Low Tg Polymer Emulsion (1)]

In a reaction vessel of 2 L in which a stirrer, a thermometer, and a cooler were attached, 180 parts by mass of ion-exchanged water was charged, and the mixture was heated to 80 ° C, and styrene (hereinafter, abbreviated as "ST") was added dropwise thereto for 2 hours. 21 parts by mass of n-butyl acrylate (hereinafter abbreviated as "BA") 75 parts by mass of methyl methacrylate (hereinafter, abbreviated as "MMA"), and 4 parts by mass of sodium dodecylbenzenesulfonate ( 3 parts by mass of an emulsion obtained by emulsifying 3 parts by mass of 0.5 parts by mass of ion-exchanged water with 0.5 parts by mass of ammonium persulfate, and after emulsification polymerization, it is kept for 2 hours, then cooled to 40 ° C or lower, and pH is adjusted with ammonia water. Adjust to 7~8 and adjust the non-volatile content to 40~42% with ion exchange water. The obtained low Tg polymer emulsion (1) was a nonvolatile component of 40.4%, a viscosity of 25 mPa‧s, a pH of 7.4, and a Tg of -25 °C.

[Preparation of slurry for porous film (1)]

99 parts by mass of alumina (manufactured by Showa Denko Co., Ltd. "AL-163"), which is a heat-resistant inorganic component, and 1 part by mass of carboxymethylcellulose ("DN-800H" manufactured by DAICEL Chemical Co., Ltd.) as a dispersion component 150 parts by mass of water was dispersed by a bead mill to prepare an alumina dispersion having a solid content of 40% by mass. Thereafter, 100 parts by mass of the present alumina dispersion and 5 parts by mass of the low Tg polymer emulsion (1) obtained above were stirred and mixed in a disperser to obtain a slurry (1) for a porous film.

(Example 1: Preparation and evaluation of aqueous resin composition (1) for lithium ion secondary battery bonding)

In a 2 L reaction vessel equipped with a stirrer, a thermometer, and a cooler, 300 parts by mass of ion-exchanged water was charged, heated to 80 ° C, and 85 parts by mass of ST 85 parts by weight of 2-ethylhexyl acrylate was added dropwise thereto for 2 hours. (hereinafter, abbreviated as "2EHA".) 13 parts by mass and methacrylic acid (hereinafter, abbreviated as "MAA".) 2 parts by mass of 3 parts by mass of sodium dodecylbenzenesulfonate and 0.4 parts by mass of ammonium persulfate. The emulsion obtained by emulsification of 40 parts by mass of the ion-exchanged water was subjected to emulsion polymerization, and after 0.2 parts by mass of ammonium persulfate was added, 15.8 parts by mass of MMA, 3 parts by mass of 2EHA, and 1 part by mass of MAA were added dropwise thereto for further 1 hour. And a mixture of 0.2 parts by mass of ethylene glycol dimethacrylate (hereinafter abbreviated as "EDM"), and polymerized for 2 hours, and then cooled to 40 ° C or lower, and the pH was adjusted to 7 to 8 with ammonia water. The non-volatile content was adjusted to 24 to 26% with ion-exchanged water. The obtained aqueous resin composition (1) for lithium ion secondary battery bonding was a nonvolatile component of 25.0%, a viscosity of 4 mPa ‧ and a pH of 7.6.

[Modulation of Adhesive Liquid for Adhesive Layer]

The adhesive layer for the adhesive layer is prepared by mixing 100 parts by mass of the aqueous resin composition (1) obtained by the above-mentioned lithium ion secondary battery bonding and 5 parts by mass of the low Tg polymer emulsion (1) obtained above ( 1).

[Manufacture of insulation materials]

An organic porous substrate (having a thickness of 16 μm and a Gurley value of 210 s/100 cc) made of polyethylene was prepared as a separator substrate. The slurry (1) for a porous film obtained above was applied to both surfaces of the prepared separator substrate, and dried at 50 ° C for 3 minutes to form a porous film on both surfaces of the separator substrate. The thickness of each layer of the porous film was 3 μm. Next, the adhesive layer (1) obtained as described above was applied onto each porous film by a spray coating method, and dried at 60 ° C for 10 minutes. Thereby, an adhesive layer having a thickness of 2 μm per layer was provided on the aperture film to obtain a spacer (1).

[Evaluation of low temperature film forming property]

The separator (1) obtained above was rubbed by a black cloth at a pressure of 4903 Pa for 10 times, and the low-temperature film-forming property was evaluated from the peeled state of the black cloth of the adhesive layer according to the following criteria.

○: not peeled off

△: partial peeling

×: Fully stripped

[Manufacture of positive electrode]

95 parts by mass of LiCoO _{2 was prepared} as a positive electrode active material, and PVDF (polyvinylidene fluoride; KF-1100 manufactured by Kureha Chemical Co., Ltd.) was added as a positive electrode binder in an amount of 3 parts by mass in terms of solid content. Further, 2 parts by mass of acetylene black and 20 parts by mass of N-methylpyrrolidone were further added, and these were mixed in a planetary mixer to obtain a slurry for a positive electrode. This slurry for positive electrodes was applied to one surface of an aluminum foil having a thickness of 18 μm, and dried at 120 ° C for 3 hours. Thereafter, rolling was performed to obtain a positive electrode having a positive electrode mixture layer having a thickness of 100 μm.

[Manufacture of negative electrode]

98 parts by mass of graphite having a particle diameter of 20 μm and a specific surface area of 4.2 m ² /g was prepared as a negative electrode active material. This was mixed with SBR (styrene-butadiene rubber, glass transition point -10 ° C) as a binder for a negative electrode in an amount of 1 part by mass in terms of solid content. Further, 1.0 part by mass of carboxymethylcellulose was added to the mixture, and the mixture was mixed by a planetary mixer to prepare a slurry for a negative electrode. This slurry for negative electrodes was applied to one surface of a copper foil having a thickness of 18 μm, and dried at 120 ° C for 3 hours. Thereafter, rolling was performed to obtain a negative electrode having a negative electrode mixture layer having a thickness of 100 μm.

[Manufacture of laminated body with electrode and separator]

The positive electrode obtained above was cut into a circular shape having a diameter of 13 mm to obtain a circular positive electrode. Further, the negative electrode obtained above was cut into a circular shape having a diameter of 14 mm to obtain a circular negative electrode. Further, the separator obtained above was cut into a circular shape having a diameter of 18 mm to obtain a circular separator. Further, the direction in which the negative electrode or the positive electrode is brought into contact with the separator by the surface on the side of the electrode active material layer is along one side of the circular separator. Thereafter, the laminate was subjected to a hot press treatment at a temperature of 80 ° C and a pressure of 0.5 MPa for 10 seconds, and the positive electrode and the negative electrode were pressure-bonded to a separator to obtain a laminate including a positive electrode and a separator, and a laminate including a negative electrode and a separator.

[Evaluation of adhesion]

The laminate having the positive electrode and the separator and the laminate including the negative electrode and the separator were cut into a width of 10 mm to obtain a test piece. The test piece was immersed in an electrolytic solution at 60 ° C for 3 days. At this time, in the case of the electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used (volume mixing ratio EC/DEC = 50.0/50.0, relative to the solvent of 1 mol/L). the concentration of LiPF ₆ were dissolved.

Thereafter, the test piece was taken out and the electrolyte adhered to the surface was wiped. Thereafter, the test piece was attached to the surface of the electrode with the surface of the electrode (positive or negative electrode) facing downward. At this time, as for the celluloid tape, the one specified in JIS Z1522 is used. In addition, the celluloid tape is pre-fixed to a horizontal test stand. Thereafter, the stress when the one end of the separator was stretched vertically upward at a tensile speed of 50 mm/min and peeled off was measured. The laminate including the positive electrode and the separator, and the laminate including the negative electrode and the separator, were subjected to the measurement three times in total, and the measurement was performed six times in total, and the average value of the stress was obtained, and the average value was used as the peel strength to evaluate the adhesion. Sex.

(Example 2: Preparation and evaluation of aqueous resin composition (2) for lithium ion secondary battery bonding)

In a 2 L reaction vessel equipped with a stirrer, a thermometer, and a cooler, 300 parts by mass of ion-exchanged water was charged, and the mixture was heated to 80 ° C, and 85 parts by mass of ST, 13 parts by mass of BA, and MAA were added dropwise thereto for 2 hours. 2 parts by mass of an emulsion obtained by emulsifying 3 parts by mass of sodium dodecylbenzenesulfonate and 40 parts by mass of ion-exchanged water of 40 parts by mass of ammonium persulfate, and emulsifying and polymerizing, and then introducing ammonium persulfate 0.2 mass After the mixture, a mixture of 15.8 parts by mass of MMA, 3 parts by mass of BA, 1 part by mass of MAA, and 0.2 parts by mass of EDM was added dropwise for 1 hour, and polymerization was carried out for 2 hours, and then cooled to 40 ° C or lower to adjust the pH with ammonia water. In 7~8, the non-volatile content is adjusted to 24~26% with ion exchange water. The obtained aqueous lithium ion resin composition (1) was a nonvolatile component of 25.0%, a viscosity of 4 mPa·s, and a pH of 7.6.

The lithium ion secondary battery bonding aqueous resin composition (1) used in the first embodiment was changed to the lithium ion secondary battery bonding aqueous resin composition (2), and the same operation as in the first embodiment was carried out. After the blending liquid (2) was prepared for the adhesive layer, the separator (2) was produced, and the low-temperature film-forming property and the adhesion were evaluated.

(Example 3: Preparation and evaluation of aqueous resin composition (3) for lithium ion secondary battery bonding)

In a 2 L reaction vessel equipped with a stirrer, a thermometer, and a cooler, 300 parts by mass of ion-exchanged water was charged, and the mixture was heated to 80 ° C, and 51 parts by mass of ST, 7.8 parts by mass of 2EHA, and MAA were added dropwise thereto for 2 hours. 1.2 parts by mass of an emulsion obtained by emulsifying 3 parts by mass of sodium dodecylbenzenesulfonate and 40 parts by mass of ion-exchanged water of ammonium persulfate, and emulsifying polymerization, and then introducing ammonium persulfate 0.3 mass After the mixture, a mixture of 47.5 parts by mass of MMA, 9 parts by mass of 2EHA, 3 parts by mass of MAA, and 0.5 parts by mass of EDM was added dropwise for 1 hour, and polymerization was carried out for 2 hours, and then cooled to 40 ° C or lower to adjust the pH with ammonia water. In 7~8, the non-volatile content is adjusted to 24~26% with ion exchange water. The obtained water-based resin composition (3) for lithium ion secondary battery bonding was 25.1% nonvolatile matter, viscosity 7 mPa‧s, and pH 7.5.

The same procedure as in Example 1 was carried out except that the aqueous resin composition (1) for lithium ion secondary battery bonding used in Example 1 was changed to the aqueous resin composition (3) for lithium ion secondary battery bonding. After the blending liquid (3) was prepared for this adhesive layer, the separator (3) was produced, and the low-temperature film-forming property and the adhesion were evaluated.

(Comparative Example 1: Preparation and evaluation of aqueous resin composition (R1) for lithium ion secondary battery bonding)

In a 2 L reaction vessel equipped with a stirrer, a thermometer, and a cooler, 300 parts by mass of ion-exchanged water was charged, and the mixture was heated to 80 ° C, and 85 parts by mass of ST, 13 parts by mass of MMA, and MAA were added dropwise thereto for 2 hours. 2 parts by mass of an emulsion obtained by emulsification of 3 parts by mass of sodium dodecylbenzenesulfonate and 40 parts by mass of ion-exchanged water of 0.3 parts by mass of ammonium persulfate, followed by emulsion polymerization, and then ammonium persulfate 0.2 mass After the mixture, a mixture of 18.8 parts by mass of MMA, 1 part by mass of MAA, and 0.2 parts by mass of EDM was added dropwise thereto for 1 hour, and polymerization was carried out for 2 hours, and then cooled to 40 ° C or lower, and the pH was adjusted to 7 to 8 with ammonia water. The non-volatile content was adjusted to 24 to 26% with ion-exchanged water. The obtained aqueous lithium ion resin composition (R1) was a nonvolatile component of 25.7%, a viscosity of 4 mPa·s, and a pH of 7.8.

The same procedure as in Example 1 was carried out except that the aqueous resin composition (1) for lithium ion secondary battery bonding used in Example 1 was changed to the aqueous resin composition (R1) for lithium ion secondary battery bonding. After the blending liquid (R1) was prepared for this adhesive layer, a separator (R1) was produced, and low-temperature film-forming property and adhesion were evaluated.

The evaluation results of the above Examples 1 to 3 and Comparative Example 1 are shown in Table 1.

In the examples 1 to 3 which are the aqueous resin compositions of the present invention, it was confirmed that the low-temperature film forming property and the adhesiveness were excellent.

On the other hand, in Comparative Example 1, the (meth) acrylate having an alkyl group having 4 or more carbon atoms was not contained in the monomer raw material of the polymer (a2) constituting the shell portion, and the low-temperature film forming property was confirmed. And poor adhesion.

Claims (3)

 An aqueous resin composition for bonding a lithium ion secondary battery, comprising a core-shell type particle (A) having a core portion composed of a polymer (a1) and a shell portion composed of a polymer (a2), and an aqueous medium (B) A water-based resin composition for bonding a lithium ion secondary battery, characterized in that styrene in the monomer raw material of the polymer (a1) is 60% by mass or more, and A in the monomer raw material of (a2) The methyl acrylate is 45 to 97.5% by mass, and the (meth) acrylate having an alkyl group having 4 or more carbon atoms is 2 to 40% by mass.    The lithium ion secondary battery adhesive aqueous composition according to claim 1, wherein the mass ratio (a1/a2) of the polymer (a1) to the polymer (a2) is from 100/3 to 100/200.    A separator for a lithium ion secondary battery, comprising: an adhesive layer obtained by using an aqueous resin composition for bonding a lithium ion secondary battery according to claim 1 or 2.