KR102310732B1 - Binder composition for secondary cell - Google Patents

Abstract

A binder composition for a secondary battery containing thermal gas expandable particles and a binder resin, wherein the volume change of a cast film formed by the binder composition for a secondary battery is V (150° C.)/V (25° C.) = 2 to 30 (V) (150 degreeC) shows the volume of the said cast film in 150 degreeC, V (25 degreeC) shows the volume of the said cast film in 25 degreeC.) The binder composition for secondary batteries which is.

Description

Binder composition for secondary batteries {BINDER COMPOSITION FOR SECONDARY CELL}

This invention relates to the binder composition for secondary batteries used in order to form the electrode mixture layer of secondary batteries, such as a lithium ion secondary battery.

A lithium ion secondary battery that is small, lightweight, has high energy density, and can be repeatedly charged and discharged is expected to increase in demand in the future also in environmental response. Lithium ion secondary batteries have high energy density and are used in fields such as mobile phones and notebook computers. However, with the expansion and development of applications, further improvements in performance such as lower resistance and higher capacity are required.

A separator plays an important function of preventing an electrical short circuit between the positive electrode and the negative electrode of a lithium ion secondary battery, and normally, as a separator used for a lithium ion secondary battery, it consists of polyolefin resin, for example. The sclera is used. In addition, the separator usually melts when the temperature inside the battery reaches a high temperature, such as around 130 ° C., and blocks micropores, thereby preventing lithium ions from moving and shutting off the current. It is responsible for maintaining the safety of the battery. However, when the battery temperature further exceeds the melting point of the resin due to instantaneous heat generation, the separator abruptly contracts, the positive electrode and the negative electrode come into direct contact with each other, and the short-circuiting point may expand. In this case, the battery temperature may reach a state in which it is abnormally overheated to several hundred degrees C or more.

Therefore, in Patent Document 1, the electrode mixture layer contains a conductive material that increases resistance in a temperature range of 90 to 160°C, and electrical insulation can be maintained even at a temperature higher than 160°C, and once the temperature is 160°C or higher A lithium ion secondary battery using a separator made of a material that exhibits ion conductivity even when cooled to 100° C. or lower after rising has been proposed.

Japanese Laid-Open Patent Publication No. 2004-327183

In Patent Document 1, an electrode mixture layer containing a predetermined conductive material and a separator made of a predetermined material are used in combination. It is also desired to form an electrode mixture layer capable of ensuring corresponding safety.

An object of the present invention is to provide a binder composition for a secondary battery from which an electrode mixture layer capable of improving the safety of a secondary battery is obtained.

As a result of intensive studies, the present inventors have found that the above object can be achieved by using heat-sensitive gas expandable particles that expand with gas at a predetermined temperature or higher, and have completed the present invention.

That is, according to the present invention,

(1) A binder composition for a secondary battery containing thermal gas expandable particles and a binder resin, wherein the volume change of a cast film formed by the binder composition for a secondary battery is V (150° C.)/V (25° C.) = 2 to 30 (V (150 ° C.) represents the volume of the cast film at 150 ° C., V (25 ° C.) represents the volume of the cast film at 25 ° C.) Binder composition for secondary batteries,

(2) the volume change of the thermal gas expandable particles is v (150° C.)/v (25° C.) = 3 to 60 (v (150° C.) represents the volume of the thermal gas expandable particles at 150° C., v (25°C) represents the volume of the thermal gas expandable particles at 25°C), the binder composition for secondary batteries according to (1),

(3) The binder composition for secondary batteries according to (1) or (2), wherein the ratio of the thermal gas expandable particles to the binder resin is thermal gas expandable particles/binder resin = 97/3 to 3/97 (weight ratio). ,

(4) The binder composition for secondary batteries according to any one of (1) to (3), wherein the thermal gas expandable particles have a particle diameter of 0.1 to 10 µm;

(5) The binder composition for secondary batteries according to any one of (1) to (4), wherein the thermal gas expandable particles have a core-shell structure, and the core material of the thermal gas expandable particles is a hydrocarbon having a boiling point of 10 to 150°C;

(6) The binder for secondary batteries according to any one of (1) to (5), wherein the thermal gas expandable particles have a core-shell structure, and the shell material of the thermal gas expandable particles is a polymer containing a polymer unit having a nitrile group. composition

this is provided

ADVANTAGE OF THE INVENTION According to this invention, the binder composition for secondary batteries from which the electrode mixture layer which can improve the safety|security of a secondary battery is obtained can be provided.

Hereinafter, the binder composition for secondary batteries of this invention is demonstrated. The binder composition for secondary batteries of the present invention is a binder composition for secondary batteries containing thermal gas expandable particles and a binder resin, wherein the volume change of the cast film formed by the binder composition for secondary batteries is V (150 ° C.) / V ( 25 degreeC) =2-30 (V(150 degreeC) represents the volume of the said cast film in 150 degreeC, and V(25 degreeC) represents the volume of the said cast film in 25 degreeC.).

(thermal gas intumescent particles)

The thermal gas expandable particle used for the binder composition for secondary batteries of this invention is a particle|grain which expands with gas when it becomes a predetermined|prescribed temperature or more. The thermal gas expandable particles preferably have a core-shell structure including a shell material formed of a resin, an elastomer, or the like, and a core material containing a low-boiling point solvent.

The method for producing the core-shell structure is not particularly limited, but thermal gas expandable particles having a core-shell structure can be prepared using, for example, a low-boiling solvent and a polymer monomer forming a core portion and a polymer monomer forming a shell portion, A method of polymerizing stepwise by changing the ratio of these monomers over time, or by mixing and polymerizing a hydrophobic low-boiling solvent and lipophilic monomer that can be core particles with a monomer corresponding to a shell material with high hydrophilicity can

Here, high hydrophilicity means that the solubility of water at a temperature of 20°C is 1 or more (unit: g/100 g), and it is preferably 3 or more, more preferably 4 or more, from the viewpoint that the boundary of the core-shell structure becomes clearer. do. Although there is no especially upper limit, it is preferable that it is 30 or less. In addition, the water solubility in the temperature of 20 degreeC can be measured by the EPA method (EPA Chemical Fate testing Guideline CG-1500 Water Solubility).

When the water solubility (unit: g/100g) in the temperature of 20 degreeC of a typical monomer and a solvent is shown in parentheses, it will be as follows. Acrylonitrile (7), methyl acrylate (6), ethyl acrylate (2), butyl acrylate (2), styrene (0.03), butadiene (0.07), isooctane (insoluble), isopentane (insoluble).

The material of the shell material is not particularly limited as long as it has electrolyte resistance and flexibility enough to prevent cracks when the thermal gas expandable particles are expanded. do.

Examples of the polymerization unit having a nitrile group include an α,β-ethylenically unsaturated nitrile monomer unit. Said "monomer unit" is a structural unit formed by superposing|polymerizing a monomer.

The monomer forming the α,β-ethylenically unsaturated nitrile monomer unit is not limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, acrylonitrile; α-chloroacrylonitrile, α-bromoacrylonitrile ?-halogenoacrylonitrile, such as; ?-alkylacrylonitrile, such as methacrylonitrile, etc. are mentioned, Acrylonitrile and methacrylonitrile are preferable. As an α,β-ethylenically unsaturated nitrile monomer, a plurality of these types may be used in combination.

The polymer containing the polymer unit which has a nitrile group may be a copolymer of the monomer which forms the polymer unit which has a nitrile group, and the monomer copolymerizable. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; 2 or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate -Carboxylic acid esters having a carbon double bond; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, di Styrenic monomers such as vinylbenzene; Amide-based monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid; Olefins such as ethylene and propylene; Diene-based monomers such as butadiene and isoprene; Chloride Halogen atom-containing monomers such as vinyl and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; methyl vinyl ketone; vinyl ketones such as ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; As the said copolymerizable monomer, you may use these multiple types together.

Although there will be no restriction|limiting in particular as long as the core material as an inclusion material of the shell material of a thermal gas expandable particle vaporizes when a secondary battery becomes high temperature, A hydrocarbon with a boiling point of 10-150 degreeC is preferable.

As a hydrocarbon with a boiling point of 10-150 degreeC, isopentane, isooctane, n-pentane, n-hexane, isohexane, heptane, petroleum ether etc. are mentioned, for example.

In addition, the volume change of the thermal gas expandable particle is v (150 degreeC)/v (25 degreeC) = 3-60 (v (150 degreeC) represents the volume of the thermal gas expandable particle at 150 degreeC, v (25 degreeC) ) represents the volume of thermal gas expandable particles at 25°C). Here, the volume change of the thermal gas expandable particle can be calculated|required as a volume change of the cast film formed of the thermal gas expandable particle|grains, for example.

Moreover, it is preferable that it is 0.1-10 micrometers, as for the particle diameter of thermal gas expandable particle|grains, it is more preferable that it is 0.3-3 micrometers, It is especially preferable that it is 0.3-1 micrometer. By making a particle diameter into the said range, the expansion balance of a volume change can be adjusted suitably. The particle diameter can be obtained from the average value by calculating (a + b)/2 by performing electron microscopy observation and making the longest side a and the shortest side b as the longest side of the particle image for 100 or more particles. have.

(Binder resin)

As binder resin used for the binder composition for secondary batteries of this invention, a diene type polymer, an acryl type polymer, a fluorine type polymer, a silicone type polymer, etc. are mentioned, for example.

Among these, since it is excellent in the binding force between electrode active materials, a diene polymer or an acrylic polymer is preferable.

(Diene-based polymer)

A diene-type polymer is a polymer containing the monomeric unit formed by superposing|polymerizing conjugated dienes, such as a butadiene and an isoprene. The ratio of the monomer unit formed by superposing|polymerizing the conjugated diene in a diene polymer is 40 weight% or more normally, Preferably it is 50 weight% or more, More preferably, it is 60 weight% or more. Examples of the polymer include homopolymers of conjugated dienes such as polybutadiene and polyisoprene; copolymers of conjugated dienes and copolymerizable monomers. Examples of the copolymerizable monomer include α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinyl Styrenic monomers such as benzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; Olefins such as ethylene and propylene; Halogen atoms such as vinyl chloride and vinylidene chloride Containing monomers; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl Vinyl ketones, such as vinyl ketone and isopropenyl vinyl ketone; Heterocyclic-containing vinyl compounds, such as N-vinyl pyrrolidone, a vinyl pyridine, and vinylimidazole, are mentioned.

(Acrylic polymer)

An acrylic polymer is a polymer containing the monomeric unit formed by superposing|polymerizing an acrylic acid ester and/or a methacrylic acid ester. The ratio of the monomer unit formed by superposing|polymerizing the acrylic acid ester and/or methacrylic acid ester in an acrylic polymer is 40 weight% or more normally, Preferably it is 50 weight% or more, More preferably, it is 60 weight% or more. As a polymer, the homopolymer of acrylic acid ester and/or methacrylic acid ester, and the copolymer of this and the monomer copolymerizable are mentioned. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; 2 or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate -Carboxylic acid esters having a carbon double bond; styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, di Styrenic monomers such as vinylbenzene; Amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid; α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Olefins such as ethylene and propylene; Diene-based monomers such as butadiene and isoprene; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; methyl vinyl ether Vinyl ethers such as , ethyl vinyl ether and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; N-vinylpyrrolidone, vinylpyridine, Heterocyclic containing vinyl compounds, such as vinylimidazole, are mentioned.

(Fluorine-based polymer)

A fluorine-type polymer is a polymer containing the monomeric unit containing a fluorine atom. Specific examples of the fluorine-based polymer include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene/perfluoroalkylvinyl ether copolymer, ethylene/tetrafluoroethylene copolymer, ethylene/chlorotrifluoroethylene copolymer, A perfluoroethylene propene copolymer is mentioned.

(Binder composition for secondary battery)

The binder composition for secondary batteries of this invention contains the above-mentioned thermo-sensitive gas expandable particle|grains and binder resin. The mixing ratio of the heat-sensitive gas-expandable particles and the binder resin is preferably 97/3 to 3/97 (weight ratio), more preferably 40/60 to 60/40.

The volume change of the cast film formed with the binder composition for secondary batteries of this invention is V (150 degreeC)/V (25 degreeC) = 2-30 (V (150 degreeC) is the volume of the cast film in 150 degreeC It shows, and V (25 degreeC) represents the volume of the cast film in 25 degreeC.), and 15-25 are preferable.

When the volume change of the cast film formed by the binder composition for secondary batteries of this invention is too large, the adhesive force and cohesion force of the binder composition for secondary batteries will fall, and the cycling characteristics of the secondary battery obtained will fall. Moreover, since the distance between electrode active materials cannot fully be extended when the volume change of the cast film formed with the binder composition for secondary batteries of this invention is too small, there exists a possibility that desired safety|security may not be acquired.

In addition, the method of mixing the thermal gas expandable particles and the binder resin is not particularly limited, and examples thereof include a method using a mixing device such as a stirring type, a shaking type, and a rotary type.

(electrode for secondary battery)

The binder composition of this invention can be used for the electrode for secondary batteries. The electrode for secondary batteries is obtained by forming an electrode mixture layer on a collector, and an electrode mixture layer contains an electrode active material, the binder composition of this invention, the thickener used as needed, a conductive material, etc. Moreover, content of the binder composition in an electrode mixture layer is 0.1-20 weight part with respect to 100 weight part of electrode mixture layer, Preferably it is 0.2-15 weight part, More preferably, it is 0.3-10 weight part.

An electrode mixture layer is formed by apply|coating and drying the slurry composition for electrodes containing an electrode active material, the binder composition of this invention, the thickener used as needed, and an electrically conductive material on an electrical power collector.

The method of apply|coating the slurry composition for electrodes on an electrical power collector is not specifically limited. For example, methods, such as the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, a comma direct coat, a slide die coat, and the brush application method, are mentioned. As a drying method, the drying method by irradiation of a hot air, a hot air, dry by low-humidity wind, vacuum drying, (far) infrared rays, an electron beam, etc. is mentioned, for example. Drying time is 1-60 minutes normally, and drying temperature is 40-180 degreeC normally. You may form an electrode mixture layer by repeating application|coating and drying of the slurry composition for electrodes in multiple times.

Here, the slurry composition for electrodes can be obtained by mixing solvents, such as an electrode active material, a binder, the thickener and electrically conductive material used as needed, and water, etc. further.

Although limitation in particular is not carried out as for the mixing method, For example, the method using mixing apparatuses, such as a stirring type, a shaking type, and a rotary type, is mentioned. Moreover, the method using dispersion-kneading apparatuses, such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader, is mentioned.

(current collector)

The material of the current collector is, for example, a metal, carbon, a conductive polymer or the like, and a metal is preferably used. As a metal for an electrical power collector, aluminum, platinum, nickel, tantalum, titanium, stainless steel, copper, another alloy, etc. are used normally. Among them, it is preferable to use copper, aluminum or an aluminum alloy from the viewpoint of conductivity and voltage resistance.

The thickness of the current collector is preferably 5 to 100 µm, more preferably 8 to 70 µm, still more preferably 10 to 50 µm.

(electrode active material)

As an electrode active material (positive electrode active material) of the positive electrode for lithium ion secondary batteries in case a secondary battery is a lithium ion secondary battery, the metal oxide which can dope/dedope lithium ion reversibly is mentioned. As such a metal oxide, lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, etc. are mentioned, for example. In addition, the positive electrode active material illustrated above may be used independently according to a use suitably, and may be used in mixture of multiple types.

Moreover, as an active material (negative electrode active material) of a negative electrode as a counter electrode of the positive electrode for lithium ion secondary batteries, For example, low crystalline carbon (amorphous carbon), such as graphitizable carbon, non-graphitizable carbon, pyrolytic carbon, graphite, (natural graphite, artificial graphite), alloy-type materials, such as tin and silicon, oxides, such as a silicon oxide, a tin oxide, and lithium titanate, etc. are mentioned. In addition, the negative electrode active material illustrated above may be used independently according to a use suitably, and may be used in mixture of multiple types.

As for the shape of the electrode active material of the electrode for lithium ion secondary batteries, it is preferable that it was established in a granular form. When the shape of the particles is granular, a higher density electrode can be formed at the time of electrode molding.

As for the volume average particle diameter of the electrode active material of the electrode for lithium ion secondary batteries, a positive electrode and a negative electrode are 0.1-100 micrometers normally, Preferably it is 0.5-50 micrometers, More preferably, it is 0.8-30 micrometers.

(conductive material)

The electrode mixture layer of the present invention may contain a conductive material as needed. The conductive material is not particularly limited as long as it is a material having conductivity, and a particulate material having conductivity is preferable, for example, conductive carbon black such as furnace black, acetylene black, and Ketjen black; natural graphite, artificial graphite, etc. of graphite; and carbon fibers such as polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, and vapor-grown carbon fibers. The average particle diameter when the conductive material is a particulate material is not particularly limited, but it is preferably smaller than the average particle diameter of the electrode active material, and from the viewpoint of expressing sufficient conductivity with a smaller amount, preferably 0.001 to 10 μm, More preferably, it is 0.05-5 micrometers, More preferably, it is 0.1-1 micrometer.

(thickener)

The electrode mixture layer of the present invention may contain a thickener as needed. Examples of the thickener include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and ammonium salts and alkali metal salts thereof; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohol; Polyvinyl alcohols such as acrylic acid or a copolymer of acrylate and vinyl alcohol, maleic anhydride or a copolymer of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, and starch oxide , phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. Among these, it is preferable to use the ammonium salt and alkali metal salt of carboxymethylcellulose and carboxymethylcellulose. In the present invention, "(modified) poly" means "unmodified poly" or "modified poly".

The content of the thickener in the electrode mixture layer is preferably in a range that does not affect the battery characteristics, and is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 4 parts by weight, further preferably 0.1 to 5 parts by weight based on 100 parts by weight of the electrode mixture layer. is 0.3 to 3 parts by weight.

(secondary battery)

As a usage aspect of the electrode for electrochemical elements of this invention, the lithium ion secondary battery etc. which used such an electrode are mentioned. For example, a lithium ion secondary battery uses the electrode for electrochemical elements with an electrode mixture layer containing the binder composition of this invention for at least one of a positive electrode and a negative electrode, and is further equipped with a separator and electrolyte solution.

As the separator, for example, a microporous film or nonwoven fabric containing a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder, etc. can be used.

The thickness of the separator is preferably 0.5 to 40 µm, more preferably 1 µm, from the viewpoint of reducing resistance by the separator in the lithium ion secondary battery and excellent in workability in manufacturing the lithium ion secondary battery. It is 30 micrometers, More preferably, it is 1-25 micrometers.

(electrolyte)

Although the electrolyte solution is not specifically limited, For example, what melt|dissolved lithium salt in the non-aqueous solvent as a supporting electrolyte can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF _{6 , LiAlCl 4} , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ and lithium salts such as NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO _{2 )NLi. In particular, LiPF 6} , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and exhibit a high degree of dissociation, are preferably used. These can be used individually or in mixture of 2 or more types. The amount of the supporting electrolyte is usually 1 wt% or more, preferably 5 wt% or more, and usually 30 wt% or less, preferably 20 wt% or less with respect to the electrolyte solution. Even if the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered and the charging and discharging characteristics of the battery are lowered.

The solvent used in the electrolytic solution is not particularly limited as long as it dissolves the supporting electrolyte, but usually dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate ( BC) and alkyl carbonates such as methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane, and Sulfur-containing compounds, such as dimethyl sulfoxide, are used. Since it is easy to obtain especially high ionic conductivity and the operating temperature range is wide, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable. These can be used individually or in mixture of 2 or more types. Moreover, it is also possible to make electrolyte solution contain an additive, and to use it. Moreover, as an additive, carbonate type compounds, such as vinylene carbonate (VC), are preferable.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte in which an electrolytic solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as _{lithium sulfide, LiI, Li 3} N, Li ₂ SP ₂ S _{5 glass ceramic.} can be heard

A lithium ion secondary battery is obtained by overlapping a negative electrode and a positive electrode with a separator interposed therebetween, winding this according to the shape of the battery, folding it, etc., put it in a battery container, injecting an electrolyte into the battery container, and sealing it. In addition, if necessary, an overcurrent protection element such as an expanded metal, a fuse, or a PTC element, a lead plate, or the like may be inserted to prevent a rise in pressure inside the battery and overcharge/discharge. The shape of the battery may be any of a laminate cell type, a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat shape.

ADVANTAGE OF THE INVENTION According to this invention, the binder composition for secondary batteries from which the electrode mixture layer which can improve the safety|security of a secondary battery is obtained can be provided.

Example

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples, and may be arbitrarily changed and implemented without departing from the gist and equivalent scope of the present invention. . In addition, in the following description, "%" and "part" which show a quantity are a weight basis, unless otherwise indicated.

In an Example and a comparative example, the volume change of a binder composition, high temperature cycling characteristics of a lithium ion secondary battery, and evaluation of the safety test were performed as follows, respectively.

[Volume Change of Binder Composition]

By pouring the dispersion liquid of the binder composition into a Teflon (registered trademark) container, forming a film in an environment of 23 ° C. and 50% RH, and vacuum drying at 25 ° C. for 24 hours, a film of the binder composition having a thickness of 1 mm got This film was cut into the size of 10 cm long x 1 cm wide, and it was set as the test piece. In a 25 degreeC environment, V (25 degreeC) (volume of the cast film of the binder composition in 25 degreeC) was computed by immersing the test piece in the scalpel cylinder filled with liquid paraffin. Moreover, V (150 degreeC) (the volume of the cast film of the binder composition in 150 degreeC) was computed by leaving the scalpel cylinder into which the test piece was put in 150 degreeC oven for 10 minutes. And the volume change (V(150 degreeC)/V(25 degreeC)) of the cast film was calculated|required.

In addition, in the following examples and comparative examples, the volume change (v (150°C)/v (25°C)) of the cast film of the thermal gas expandable particles was calculated in the same manner as the volume change of the binder composition. That is, by pouring a dispersion of thermal gas expandable particles into a Teflon (registered trademark) container, forming a film in an environment of 23 ° C. and 50% RH, and vacuum drying at 25 ° C. for 24 hours, a thickness of 1 mm A film of thermal gas expandable particles was obtained. This film was cut into the size of 10 cm long x 1 cm wide, and it was set as the test piece. In a 25 degreeC environment, v (25 degreeC) (volume of the cast film of thermal gas expandable particle at 25 degreeC) was computed by immersing a test piece in the scalpel cylinder filled with liquid paraffin. Moreover, v (150 degreeC) (volume of the cast film of thermal gas expandable particle in 150 degreeC) was computed by leaving the scalpel cylinder into which the test piece was put in 150 degreeC oven for 10 minutes. Then, the volume change (v (150°C)/v (25°C)) of the cast film of the thermal gas expandable particles (hereinafter, sometimes referred to as “volume change of the thermal gas expandable particles”) was calculated.

In addition, the volume change of the binder resin was calculated in the same manner as the volume change of the binder composition, but the volume change of the cast film of the binder resins a to d used in Examples and Comparative Examples was 1.0.

[High Temperature Cycle Characteristics]

After standing still for 24 hours, the pouch-type lithium ion secondary batteries produced in Examples and Comparative Examples were charged to 4.2 V at a charge/discharge rate of 0.2 C and discharged to 3.0 V, and the initial capacity C ₀ was measured. Further, in a 45°C environment, charging and discharging at 4.35 V at a charging/discharging rate of 1.0 C and discharging to 3.0 V are repeated _{to measure the capacity C 1} after 100 cycles, ΔC = C ₁ /C ₀ × 100 The capacity retention rate represented by (%) was calculated|required. This capacity retention rate was evaluated according to the following criteria, and the results are shown in Table 1. It shows that the fall of the discharge capacity is small, and it is excellent in cycling characteristics, so that the value of this capacity retention ratio is high.

A: 80% or more

B: 75% or more and less than 80%

C: 70% or more and less than 75%

D: less than 70%

[Safety Test]

After leaving still for 24 hours, the pouch-shaped lithium ion secondary battery manufactured by the Example and the comparative example was charged to 4.2V at a charge/discharge rate of 0.2C, and operation which discharges to 3.0V was performed. Then, it charged to 4.35V at 25 degreeC at the charge rate of 0.2C. A voltage measurement terminal was connected to this pouch-shaped lithium ion secondary battery, and it was placed inside the heating test apparatus. Then, at a rate of 5°C/min, the temperature was raised to 150°C and maintained at 150°C. The elapsed time from reaching 150 degreeC until short circuit was measured was measured. This elapsed time was evaluated by the following reference|standard, and the result was shown in Table 1. The longer the elapsed time, the higher the safety of the battery.

A: More than 30 minutes

B: 20 minutes or more and less than 30 minutes

C: 10 minutes or more and less than 20 minutes

D: less than 10 minutes

[Example 1]

(Preparation of thermal gas expandable particle A)

In a reactor equipped with a stirrer, 94.0 parts of acrylonitrile as a monomer, 5.0 parts of methacrylic acid, 1.0 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. "Light Ester EG"), 20.0 parts of isopentane as an expanding agent, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 1.0 part of t-butylperoxy-2-ethylhexanoate ("Perbutyl O" manufactured by Nichiyo Co., Ltd.) as a polymerization initiator, 0.5 part of hydroquinone as an aqueous polymerization inhibitor , and 400 parts of ion-exchanged water were added, and the mixture was stirred until no coarse droplet could be visually confirmed. This was subjected to high-speed shearing and stirring for 1 minute at a rotation speed of 15,000 rpm using an in-line emulsion disperser (“Cavitron” manufactured by Pacific Machinery Co., Ltd.) to obtain a dispersion of a polymerizable monomer composition. In addition, stirring temperature was managed at 5-10 degreeC. The dispersion liquid of this polymerizable monomer composition was poured into a 5 MPa pressure vessel equipped with a stirrer, and it was made to react at the reaction temperature of 70 degreeC for 12 hours. The pressure at the time of reaction was implemented at 0.5 MPa. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Thus, an aqueous dispersion of thermal gas expandable particles A having a number average particle diameter of 600 nm was obtained. The volume change of this thermal gas expandable particle A was 33.0.

(Preparation of binder resin a)

In a 5 MPa pressure vessel equipped with a stirrer, 62.0 parts of styrene as an aromatic vinyl monomer, 33.0 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 4.0 parts of itaconic acid as an ethylenically unsaturated carboxylic acid monomer, 2- as a hydroxyl group-containing monomer 1.0 parts of hydroxyethyl acrylate, 0.3 parts of t-dodecyl mercaptan as a molecular weight modifier, 1.0 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and 1.0 parts of potassium persulfate as a polymerization initiator, After stirring, the mixture was heated to 55°C to initiate polymerization. When the monomer consumption reached 95.0%, it was cooled and the reaction was stopped. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Then, the unreacted monomer was removed by heating and vacuum distillation. After that, it was cooled down to 30°C or less. Thereby, binder resin a with a number average particle diameter of 150 nm was obtained.

(Preparation of binder composition 1)

50 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 50 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 1 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 1 was 17.0.

(Preparation of the slurry composition for negative electrodes)

In a planetary mixer, 97.0 parts of natural graphite as a carbon-based active material, 1.0 parts of sodium carboxymethylcellulose (CMCNa; "MAC-350HC" manufactured by Nippon Paper Co., Ltd.) as a thickener as a thickener, as a binder, the aqueous dispersion of the binder composition 1 as a solid equivalent The slurry composition for negative electrodes was obtained by injecting 2.0 parts, and adding and mixing ion-exchange water so that solid content concentration might be set to 52%.

(Production of negative electrode)

The above-mentioned slurry composition for negative electrodes was apply|coated with the comma coater so that an application amount might be 9.8-10.2 mg/cm<2> on a 20-micrometer-thick copper foil (current collector). The slurry composition on copper foil is dried by conveying the inside of 80 degreeC oven for 2 minutes, and the inside of 120 degreeC oven again over 2 minutes for the copper foil to which this slurry composition for negative electrodes was apply|coated at a speed|rate of 0.3 m/min, and a negative electrode got the fabric.

Then, the obtained negative electrode fabric is pressed with a roll press so that the density of the mixture layer is 1.45 to 1.55 g/cm 3 made The negative electrode sheet was cut into a predetermined size, processed, and the negative electrode lead was welded to obtain a negative electrode.

(Production of positive electrode)

_{In a planetary mixer, 96.0 parts of LiCoO 2} as a positive electrode active material, 2.0 parts of acetylene black (AB; "HS-100" manufactured by Denki Chemical Industries, Ltd.) as a conductive material, PVDF (polyvinylidene fluoride, Co., Ltd.) as a binder 2.0 parts of Kureha Chemicals "KF-1100"), and N-methylpyrrolidone was added and mixed so that total solid content concentration might be 67%, and the slurry composition for positive electrodes was prepared.

The obtained slurry composition for positive electrodes was apply|coated on the 20-micrometer-thick aluminum foil with the comma coater, and it was dried. In addition, this drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for aluminum foil at the speed|rate of 0.5 m/min. Then, it heat-processed at 120 degreeC for 2 minute(s), and the positive electrode original fabric was obtained.

After drying the obtained positive electrode original fabric, press with a roll press so that the density of the composite material layer after pressing becomes 3.40 to 3.50 g/cm 3 A positive electrode sheet formed by forming a positive electrode mixture layer thereon was produced. The positive electrode sheet was cut to a predetermined size, processed, and a positive electrode lead was welded to obtain a positive electrode.

(Manufacture of lithium ion secondary battery)

The negative electrode and the positive electrode manufactured above were wound on a jelly roll with the single-layer polypropylene separator (25 micrometers in thickness, 55% of porosity) manufactured by the dry method, and the electrode group was produced. After inserting this electrode group into a pouch-shaped battery case and injecting a nonaqueous electrolyte, the opening of the battery case was sealed with a heat sealer to complete a lithium ion secondary battery. The design capacity of the battery was set to 2000 mAh. Here, as the non-aqueous electrolyte, a solution obtained by adding 2% by volume of VC (vinylene carbonate) to _{a LiPF 6 solution having a concentration of 1.0 M was used.} The solvent of the LiPF ₆ solution is a mixed solvent of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) (EC/EMC = 3/7 weight ratio).

[Example 2]

(Preparation of binder composition 2)

5 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 95 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 2 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 2 was 2.6.

Except having used the binder composition 2, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of a lithium ion secondary battery were performed similarly to Example 1.

[Example 3]

(Preparation of binder composition 3)

85 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 15 parts of binding resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 3 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 3 was 28.2.

Except having used the binder composition 3, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Example 4]

(Preparation of thermal gas expandable particles B)

In a reactor equipped with a stirrer, 93.0 parts of methacrylonitrile as a monomer, 5.0 parts of acrylic acid, 2.0 parts of divinylbenzene, 20.0 parts of isopentane as an expanding agent, 1.0 parts of sodium dodecylbenzenesulfonate as an emulsifier, t- as a polymerization initiator 1.0 parts of butylperoxy-2-ethylhexanoate ("Perbutyl O" manufactured by Nichi Oil Corporation), 0.5 parts of hydroquinone as an aqueous polymerization inhibitor, and 400 parts of ion-exchanged water were added, and coarse droplets were visually confirmed. It was stirred until it became impossible. This was subjected to high-speed shearing and stirring for 1 minute at a rotation speed of 15,000 rpm using an in-line emulsion disperser (“Cavitron” manufactured by Pacific Machinery Co., Ltd.) to obtain a dispersion of a polymerizable monomer composition. In addition, stirring temperature was managed at 5-10 degreeC. The dispersion liquid of this polymerizable monomer composition was poured into a 5 MPa pressure vessel equipped with a stirrer, and it was made to react at the reaction temperature of 70 degreeC for 12 hours. The pressure at the time of reaction was implemented at 0.5 MPa. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Thus, an aqueous dispersion of thermal gas expandable particles B having a number average particle diameter of 600 nm was obtained. The volume change of this thermal gas expandable particle B was 25.0.

(Preparation of binder composition 4)

50 parts of thermosensitive gas expandable particle|grains B by solid content equivalent, 50 parts of binding resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 4 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 4 was 13.0.

Except having used the binder composition 4, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Example 5]

(Preparation of thermal gas expandable particles C)

In a reactor equipped with a stirrer, 50.0 parts of acrylonitrile and 44.0 parts of methacrylonitrile as monomers, 5.0 parts of methacrylic acid, 1.0 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. "Light Ester EG"), and a swelling agent 20.0 parts of isooctane as an emulsifier, 0.3 parts of sodium dodecylbenzenesulfonate as an emulsifier, 1.0 parts of t-butylperoxy-2-ethylhexanoate ("Perbutyl O" manufactured by Nichiyu Corporation) as a polymerization initiator, polymerization of water phase is prohibited As an agent, 0.5 parts of hydroquinone and 400 parts of ion-exchange water were put, and it stirred until it became impossible to confirm a coarse droplet with the naked eye. This was subjected to high-speed shearing and stirring for 1 minute at a rotation speed of 15,000 rpm using an in-line emulsion disperser (“Cavitron” manufactured by Pacific Machinery Co., Ltd.) to obtain a dispersion of a polymerizable monomer composition. In addition, stirring temperature was managed at 5-10 degreeC. The dispersion liquid of this polymerizable monomer composition was poured into a 5 MPa pressure vessel equipped with a stirrer, and it was made to react at the reaction temperature of 70 degreeC for 12 hours. The pressure at the time of reaction was implemented at 0.5 MPa. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Thereby, the aqueous dispersion of the thermal gas expandable particle|grains C with a number average particle diameter of 2000 nm was obtained. The volume change of this thermal gas expandable particle C was 18.0.

(Preparation of binder composition 5)

50 parts of thermosensitive gas expandable particle|grains C by solid content equivalent, 50 parts of binding resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 5 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 5 was 9.5.

Except having used the binder composition 5, manufacture of a negative electrode, manufacture of a positive electrode, and manufacture of a lithium ion secondary battery were performed similarly to Example 1.

[Example 6]

(Preparation of binder resin b)

In a 5 MPa pressure vessel equipped with a stirrer, as monomers, 45.0 parts of butyl acrylate, 52.0 parts of ethyl acrylate, 2.0 parts of methacrylic acid, 1.0 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. "Light Ester EG") , 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water as a solvent, and 1.0 part of potassium persulfate as a polymerization initiator were put and thoroughly stirred, followed by heating to 55°C to initiate polymerization. When the monomer consumption reached 95.0%, it was cooled and the reaction was stopped. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Then, the unreacted monomer was removed by heating and vacuum distillation. Moreover, it cooled to 30 degrees C or less after that. Thereby, binder resin b with a number average particle diameter of 150 nm was obtained.

(Preparation of binder composition 6)

50 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 50 parts of binding resin b by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 6 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 6 was 17.0.

Except having used the binder composition 6, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Example 7]

(Preparation of binder resin c)

In a 5 MPa pressure vessel equipped with a stirrer, 19.9 parts of acrylonitrile as a monomer, 80.0 parts of acrylic acid, 0.1 parts of ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd. "Light Ester EG"), 150 parts of ion-exchanged water as a solvent , and 1.0 part of potassium persulfate as a polymerization initiator, and after stirring sufficiently, the polymerization was initiated by heating to 55°C. When the monomer consumption reached 95.0%, it was cooled and the reaction was stopped. Sodium hydroxide aqueous solution was added 5% to the aqueous dispersion containing the polymer obtained in this way, and it adjusted to pH 8. Then, the unreacted monomer was removed by heating and vacuum distillation. Moreover, it cooled to 30 degrees C or less after that. Thereby, water-soluble binder resin c was obtained.

(Preparation of binder composition 7)

50 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 50 parts of binding resin c by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 7 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 7 was 17.0.

Except having used the binder composition 7, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Example 8]

(Preparation of binder composition 8)

An aqueous dispersion of the thermal gas expandable particle A and PVDF (polyvinylidene fluoride, "KF-1100" manufactured by Kureha Chemical Co., Ltd.) as the binder resin d are mixed in a weight-solids ratio of 1:1, and further NMP (N -methyl-2-pyrrolidone) was added. By removing water|moisture content from this by vacuum distillation, the binder composition 8 which uses NMP as a solvent was prepared. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 8 was 17.0.

(Preparation of the slurry composition for positive electrodes)

_{In a planetary mixer, 96.0 parts of LiCoO 2} as a positive electrode active material, 2.0 parts of acetylene black as a conductive material ("HS-100" manufactured by Denki Chemical Industry Co., Ltd.), 4.0 parts of binder composition 8 as a solid equivalent, as a binder, and N-methylpyrrolidone was added and mixed so that total solid content concentration might be 67 %, and the slurry composition for positive electrodes was prepared.

(Production of positive electrode)

The obtained slurry composition for positive electrodes was apply|coated on the 20-micrometer-thick aluminum foil with the comma coater, and it was dried. In addition, this drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for aluminum foil at the speed|rate of 0.5 m/min. Then, it heat-processed at 120 degreeC for 2 minute(s), and the positive electrode original fabric was obtained.

After drying the obtained positive electrode fabric, it is pressed with a roll press so that the density of the composite material layer after pressing becomes 3.40 to 3.50 g/cm 3 , and for the purpose of removing moisture, it is placed in an environment of 120° C. under vacuum conditions for 3 hours, and the current collector A positive electrode sheet formed by forming a positive electrode mixture layer thereon was manufactured. The positive electrode sheet was cut to a predetermined size, processed, and a positive electrode lead was welded to obtain a positive electrode.

(Production of negative electrode)

In a planetary mixer, 97.0 parts of natural graphite as a carbon-based active material, 1.0 parts of sodium carboxymethylcellulose as a thickener ("MAC-350HC" manufactured by Nippon Paper Co., Ltd.) 1.0 parts as a binder, and 1.0 parts of binder resin a as a solid equivalent, Furthermore, the slurry composition for negative electrodes was obtained by adding and mixing ion-exchange water so that solid content concentration might be set to 52 %.

The above-mentioned slurry composition for negative electrodes was apply|coated with the comma coater so that an application amount might be 9.8-10.2 mg/cm<2> on a 20-micrometer-thick copper foil (current collector). The slurry composition on copper foil is dried by conveying the inside of 80 degreeC oven for 2 minutes, and the inside of 120 degreeC oven again over 2 minutes for the copper foil to which this slurry composition for negative electrodes was apply|coated at a speed|rate of 0.3 m/min, and a negative electrode got the fabric.

Then, the obtained negative electrode fabric is pressed with a roll press so that the density of the mixture layer is 1.45 to 1.55 g/cm 3 Manufactured. The negative electrode sheet was cut into a predetermined size, processed, and the negative electrode lead was welded to obtain a negative electrode.

(Manufacture of lithium ion secondary battery)

The negative electrode and the positive electrode manufactured above were wound on a jelly roll with the single-layer polypropylene separator (25 micrometers in thickness, 55% of porosity) manufactured by the dry method, and the electrode group was produced. After inserting this electrode group into a pouch-shaped battery case and injecting a nonaqueous electrolyte, the opening of the battery case was sealed with a heat sealer to complete a lithium ion secondary battery. The design capacity of the battery was set to 2000 mAh. Here, as the non-aqueous electrolyte, a solution obtained by adding 2% by volume of VC (vinylene carbonate) to _{a LiPF 6 solution having a concentration of 1.0 M was used.} The solvent of the LiPF ₆ solution is a mixed solvent of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) (EC/EMC = 3/7 weight ratio).

[Comparative Example 1]

(Preparation of binder composition 9)

2 parts of thermosensitive gas expandable particle|grains A by solid content equivalent, 98 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment in 25 degreeC environment. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 9 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 9 was 1.6.

Except having used the binder composition 9, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Comparative Example 2]

(Preparation of thermal gas expandable particles D)

Thermosensitive gas expandable particles were manufactured under the same conditions as in Example 1 except that the amount of isopentane used in Example 1 (production of thermosensitive gas expandable particles A) was 1.8 parts, and the number average particle diameter An aqueous dispersion of 600 nm thermal gas expandable particles D was obtained. The volume change of this thermal gas expandable particle D was 2.7.

(Preparation of binder composition 10)

50 parts of thermosensitive gas expandable particle|grains D by solid content equivalent, 50 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 10 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 10 was 1.9.

Except having used the binder composition 10, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Comparative Example 3]

(Preparation of binder composition 11)

98 parts of thermal gas expandable particle|grains A by solid content equivalent, 2 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 11 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 11 was 32.4.

Except having used the binder composition 11, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Comparative Example 4]

(Preparation of thermal gas expandable particles E)

Thermosensitive gas expandable particles were manufactured under the same conditions as in Example 1, except that the amount of isopentane used in Example 1 (production of thermosensitive gas expandable particles A) was 40.0 parts, and the number average particle diameter An aqueous dispersion of 600 nm thermal gas expandable particles E was obtained. The volume change of this thermal gas expandable particle E was 65.0.

(Preparation of binder composition 12)

50 parts of thermosensitive gas expandable particle|grains E by solid content equivalent, 50 parts of binder resin a by solid content equivalent, and ion-exchange water were stirred in 25 degreeC environment for 1 hour. Thereby, solid content concentration obtained the aqueous dispersion of the binder composition 12 of 30 weight%. The volume change (V(150 degreeC)/V(25 degreeC)) of the cast film formed with this binder composition 12 was 33.0.

Except having used the binder composition 12, manufacture of the negative electrode, manufacture of the positive electrode, and manufacture of the lithium ion secondary battery were performed similarly to Example 1.

[Comparative Example 5]

(Production of positive electrode)

What was kneaded into pellets by 60 parts of carbon black and 40 parts of polyethylene was grind|pulverized by the jet mill method, and the PTC electroconductive material with an average particle diameter of 1 micrometer was obtained.

In a planetary mixer, _{96.0 parts of LiCoO 2} as a positive electrode active material, 2.0 parts of a PTC conductive material as a conductive material, 2.0 parts of PVDF (polyvinylidene fluoride; "KF-1100" manufactured by Kureha Chemical Co., Ltd.), and a total solid content concentration N-methylpyrrolidone was added and mixed so that it might become 67 %, and the slurry composition for positive electrodes was prepared.

The obtained slurry composition for positive electrodes was apply|coated on the 20-micrometer-thick aluminum foil with the comma coater, and it was dried. In addition, this drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for aluminum foil at the speed|rate of 0.5 m/min. Then, it heat-processed at 120 degreeC for 2 minute(s), and the positive electrode original fabric was obtained.

After drying the obtained positive electrode fabric, it is pressed with a roll press so that the density of the composite material layer after pressing becomes 3.40 to 3.50 g/cm 3 , and for the purpose of removing moisture, it is placed in an environment of 120° C. under vacuum conditions for 3 hours, and the current collector A positive electrode sheet formed by forming a positive electrode mixture layer thereon was manufactured. The positive electrode sheet was cut to a predetermined size, processed, and a positive electrode lead was welded to obtain a positive electrode.

(Production of negative electrode)

In a planetary mixer, 97.0 parts of natural graphite as a carbon-based active material, 1.0 parts of carboxymethylcellulose (CMCNa; "MAC-350HC" manufactured by Nippon Paper Co., Ltd.) as a thickener, and 1.0 parts of a binder resin a as a solid content equivalent to 1.0 parts were added Furthermore, the slurry composition for negative electrodes was obtained by adding and mixing ion-exchange water so that solid content concentration might be 52.0 %.

The obtained slurry composition for negative electrodes was apply|coated with the comma coater so that an application amount might be 9.8-10.2 mg/cm<2> on a 20-micrometer-thick copper foil (current collector). The slurry composition on copper foil is dried by conveying the inside of 80 degreeC oven for 2 minutes, and the inside of 120 degreeC oven again over 2 minutes for the copper foil to which this slurry composition for negative electrodes was apply|coated at a speed|rate of 0.3 m/min, and a negative electrode got the fabric.

Then, the obtained negative electrode fabric is pressed with a roll press so that the density of the mixture layer is 1.45 to 1.55 g/cm 3 made The negative electrode sheet was cut into a predetermined size, processed, and the negative electrode lead was welded to obtain a negative electrode.

A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the positive electrode and the negative electrode obtained above were used.

As shown in Table 1, as a binder composition for secondary batteries containing thermosensitive gas expandable particles and a binder resin, the volume change of the cast film formed by the binder composition for secondary batteries is V (150 ° C.) / V (25 ° C.) = 2-30 (V (150 ° C.) represents the volume of the cast film at 150 ° C., and V (25 ° C.) represents the volume of the cast film at 25 ° C.) The binder composition for secondary batteries The high-temperature cycle characteristics and safety|security of the lithium ion secondary battery obtained using it were favorable.

Claims (6)

A binder composition for secondary batteries comprising thermal gas expandable particles and a binder resin, the binder composition comprising:
The volume change of the cast film formed by the binder composition for secondary batteries
V (150 ℃)/V (25 ℃) = 2 ~ 30
(V (150°C) represents the volume of the cast film at 150°C, and V (25°C) represents the volume of the cast film at 25°C.) The binder composition for secondary batteries. The method of claim 1,
The volume change of the thermal gas expandable particle is,
v (150 ℃)/v (25 ℃) = 3 ~ 60
(v (150°C) represents the volume of the thermosensitive gas expandable particles at 150°C, and v (25°C) represents the volume of the thermosensitive gas expandable particles at 25°C). 3. The method according to claim 1 or 2,
The binder composition for secondary batteries, wherein the ratio of the thermal gas expandable particles to the binder resin is thermal gas expandable particles/binder resin = 97/3 to 3/97 (weight ratio). 3. The method according to claim 1 or 2,
A binder composition for a secondary battery, wherein the thermal gas expandable particles have a particle diameter of 0.1 to 10 µm. 3. The method according to claim 1 or 2,
The said thermosensitive gas expandable particle|grains have a core-shell structure, The binder composition for secondary batteries whose core material of the said thermosensitive gas expandable particle is a hydrocarbon with a boiling point of 10-150 degreeC. 3. The method according to claim 1 or 2,
The thermal gas expandable particle has a core-shell structure, and the shell material of the thermal gas expandable particle is a polymer containing a polymer unit having a nitrile group, the binder composition for a secondary battery.