JP4748439B2 - Binder resin composition for lithium battery electrode, electrode and battery - Google Patents

Description

  The present invention relates to a binder resin composition for a lithium battery electrode, an electrode slurry, an electrode, and a battery.

Advances in electronic technology have improved the performance of electronic devices, making them smaller and more portable, and secondary batteries with high energy density are desired as the power source. Conventional secondary batteries include lead-acid storage, nickel-cadmium batteries, and the like, which are insufficient in terms of high energy density batteries. Therefore, as an alternative to these batteries, in recent years, an organic electrolyte lithium secondary battery (hereinafter simply referred to as “lithium battery”) that can greatly improve the energy density has been developed and rapidly spread.
Lithium-containing metal composite oxides such as lithium-cobalt composite oxide are mainly used as the active material for the positive electrode of the lithium battery, and lithium ions are mainly inserted between the layers as the active material (lithium intercalation compound). Carbon materials having a multilayer structure capable of forming and releasing lithium ions from the interlayer are used. For the positive and negative electrodes, a slurry obtained by dispersing these active materials and a binder resin composition in a solvent such as N-methyl-2-pyrrolidone or water is applied on the surface of a metal foil as a current collector. Then, after the solvent is removed by drying, a mixture layer is formed, and this is compression-molded with a roll press. As the binder resin composition, polyvinylidene fluoride (hereinafter simply referred to as “PVDF”) is generally used for both electrodes.

  However, when PVDF is used as the binder resin composition, the adhesion at the interface between the current collector and the mixture layer and the adhesion between the active materials in the mixture layer are poor. In particular, because the former adhesion is inferior, (1) a part or all of the mixture layer is collected during the battery manufacturing process such as cutting the electrode plates of each electrode or winding the electrodes of both electrodes in a spiral shape through a separator. (2) Since the carbon material of the negative electrode active material expands / shrinks as lithium ions are inserted / released due to charging / discharging of the battery, a part or all of the mixture layer is repeatedly charged / discharged. Has a problem that it peels off from the current collector, and such inadequate adhesion causes a decrease in battery capacity.

As a fluorine-containing binder resin composition capable of solving the above-mentioned adhesion problem of PVDF, for example, JP-A-6-172252 discloses a vinylidene fluoride as a main component and a small amount of an unsaturated dibasic monoester. It has been proposed to use a vinylidene fluoride copolymer obtained by copolymerization of a polymer, but when such a vinylidene fluoride copolymer is used as a binder resin composition, a current collector and a mixture While the adhesion at the interface with the layer is greatly improved, (1) the electrolyte is injected after winding due to a decrease in crystallinity (mediates the exchange of lithium ions between the positive and negative electrodes due to charge / discharge) Liquid) (hereinafter referred to as “electrolytic solution resistance”) is reduced, and it tends to swell, and contact between the current collector and the mixture layer and contact between the active materials in the mixture layer Become loose. This leads to the collapse of the conductive network of the entire electrode, and the capacity of the battery decreases. (2) Under high voltage, decomposition accompanied by desorption / generation of highly corrosive hydrogen fluoride occurs easily, and the internal pressure is reduced. It has been pointed out that the battery does not function due to a rise, and has not yet solved the essential problem.
In addition, these fluorine-containing binder resin compositions are used in a form dissolved in an organic solvent such as N-methyl-2-pyrrolidone (NMP), but this NMP has problems in terms of cost and environmental load. .

  On the other hand, as a binder resin composition other than fluorine-containing binders such as PVDF, for example, JP-A-5-74461 uses a diene synthetic rubber such as styrene-butadiene rubber (hereinafter abbreviated as “SBR”). Has been proposed. The diene rubber is in the form of an aqueous dispersion, and has a lower environmental impact than the case where an organic solvent is used, so that a battery can be manufactured at a low cost. Further, when such a diene synthetic rubber is used as a binder resin, the adhesion at the interface between the current collector and the mixture layer is relatively good. However, since diene rubber also has low electrolysis resistance and easily swells, it leads to the collapse of the conductive network of the electrode due to repeated charging and discharging, and when lithium batteries are repeatedly charged and discharged, it is a cause that capacity decreases with time. It was.

Moreover, there exists a nitrile group containing resin as binder resin composition which was excellent in the electrolyte solution resistance and swelling resistance with low solubility to electrolyte solution by binder resin compositions other than the above. Among them, JP-A No. 2003-132893 discloses a repeating unit derived from acrylonitrile or methacrylonitrile and a formula (I): CH ₂ = CR ¹ -COOR ² (wherein R ¹ is a hydrogen atom or a methyl group, R ² discloses a slurry composition for an electrode containing a repeating unit derived from a monomer having an alkyl group having 3 or less carbon atoms. However, (meth) acrylonitrile is inherently a polymer that forms a rigid molecular structure. Therefore, in formula (I), a monomer having a short chain length in which R ² is an alkyl group having 3 or less carbon atoms is used. When polymerized, the flexibility and flexibility of the electrode containing the resulting copolymer are not sufficiently improved. If the flexibility and flexibility of the electrode are insufficient, the mixture layer will crack in roll press molding in the production of lithium battery electrodes, or in the process of winding the positive electrode and the negative electrode in a spiral through a separator, etc. There was a concern about the occurrence of defects.

Japanese Patent Laid-Open No. 6-175252 JP-A-5-74461 JP 2003-132893 JP

An object of the present invention is to provide a binder resin composition for a lithium battery electrode (hereinafter simply referred to as “binder resin composition”) having a low degree of swelling with respect to an electrolyte solution (that is, having an electrolyte solution resistance) and excellent adhesion and flexibility. Is sometimes provided).
Another object of the present invention is to provide an electrode for a lithium battery excellent in electrolytic solution resistance and adhesion produced using a slurry comprising the binder resin composition and an active material.
Another object of the present invention is to provide a lithium battery that can significantly reduce capacity reduction in a charge / discharge cycle by using the lithium battery electrode as a positive electrode and / or a negative electrode.

（式中、Ｒ₁は、H又はCH₃；Ｒ₂は、炭素数4〜100のアルキル基である）
で表される単量体由来の繰り返し単位とを含む共重合体を含有することを特徴とする、リチウム電池電極用バインダ樹脂組成物に関する。また、本発明は、集電体と、該集電体の少なくとも１面に設けられた合剤層とを有し、該合剤層が、活物質を含む上記リチウム電池電極用バインダ樹脂組成物からなる、リチウム電池用電極に関する。更に本発明は、上記リチウム電池用電極を含む、リチウム電池に関する。 As a result of intensive studies, the present inventors use a copolymer of a nitrile group-containing monomer and a monomer having a relatively long chain length at the end as a binder resin composition for a lithium battery electrode. Thus, it has been found that a binder resin composition excellent in adhesion of the electrode to the current collector, hardly swelled with respect to the electrolytic solution, and excellent in flexibility and flexibility can be provided.
That is, the present invention relates to a repeating unit derived from a nitrile group-containing monomer and a formula (式)

(Wherein R ₁ is H or CH ₃ ; R ₂ is an alkyl group having 4 to 100 carbon atoms)
The binder resin composition for lithium battery electrodes characterized by containing the copolymer containing the repeating unit derived from the monomer represented by these. Moreover, this invention has a collector and the mixture layer provided in the at least 1 surface of this collector, and this mixture layer contains the active material, The said binder resin composition for lithium battery electrodes The present invention relates to an electrode for a lithium battery. Furthermore, this invention relates to the lithium battery containing the said electrode for lithium batteries.

  The binder resin composition of the present invention is excellent in electrolytic solution resistance, adhesiveness and flexibility. The electrode for a lithium battery using the binder resin composition of the present invention is excellent in electrolytic solution resistance, adhesiveness and flexibility. By using the electrode for a lithium battery using the binder resin composition of the present invention, it is possible to reduce a decrease in discharge capacity in a charge / discharge cycle, and a long-life lithium battery can be provided.

（式中、Ｒ₁は、H又はCH₃、Ｒ₂は、炭素数4〜100のアルキル基である） (1) Binder resin composition for lithium battery electrode The binder resin composition for lithium battery of the present invention is represented by (1) a repeating unit derived from a nitrile group-containing monomer, and (2) represented by the following formula (I): A copolymer containing a repeating unit derived from a monomer and (3) a repeating unit derived from any other monomer is contained.

(In the formula, R ₁ is H or CH ₃ , and R ₂ is an alkyl group having 4 to 100 carbon atoms)

(1-1) Nitrile group-containing monomer The nitrile group-containing monomer of the present invention includes, for example, acrylic monomers such as acrylonitrile and methacrylonitrile; methyl α-cyanoacrylate, ethyl α-cyanoacrylate Α-cyanoacrylate monomers such as these; vinyl monomers such as dicyanovinylidene and fumaronitrile. In particular, the nitrile group-containing monomer of the present invention is preferably acrylonitrile and / or methacrylonitrile in terms of ease of polymerization, flexibility and flexibility of the electrode, and the like. These nitrile group-containing monomers are used alone or in combination of two or more. When acrylonitrile and methacrylonitrile are used as the nitrile group-containing monomer of the present invention, acrylonitrile is, for example, 20 to 95% by mass, preferably 40 to 90%, based on the total amount of the nitrile group-containing monomer. It is suitable to contain the mass%.

(1-2) monomer represented by the formula (iota) of the monomer present invention represented by the formula (I), In the formula, R ₁ is H or CH _3; R ₂ is A monomer that is an alkyl group having 4 to 100 carbon atoms. Examples of such a monomer represented by the formula (I) include n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl. Acrylate compounds such as acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, tridecyl acrylate, hexadecyl acrylate, stearyl acrylate, isostearyl acrylate, cyclohexyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate , Isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate , T-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, hexadecyl methacrylate, stearyl methacrylate, There are methacrylate compounds such as isostearyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate.
In general formula (Ι), the alkyl group represented by R ₂ may be partially substituted with fluorine, silicon, or the like. For example, R ₂ may be a fluoroalkyl group having 4 to 100 carbon atoms. Examples of the monomer represented by the general formula (I) having such a fluoroacryl group include 1,1-bis (trifluoromethyl) -2,2,2-trifluoroethyl acrylate, 2,2 , 3,3,4,4,4-heptafluorobutyl acrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, nonafluoroisobutyl acrylate, 2,2,3,3,4,4, 5,5-octafluoropentyl acrylate, 2,2,3,3,4,4,5,5,5-nonafluoropentyl acrylate, 2,2,3,3,4,4,5,5,6, 6,6-undecafluorohexyl acrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl acrylate, 3,3, 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl acrylate, 2,2,3,3,4,4,5, 5,6,6,7,7,8,8,9,9,10,10,10-acrylate compounds such as nonadecafluorodecyl acrylate, nonafluoro-t-butyl methacrylate 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2,3,3,4 , 4,5,5,6,6,7,7-dodecafluoroheptyl methacrylate, heptadecafluorooctyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7, 8,8,8-pentadecafluorooctyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluorononyl methacrylate, etc. There are methacrylate compounds.
In the monomer represented by the general formula (Ι), the carbon number of R ₂ is usually 4 to 100, preferably 6 to 50, and more preferably 8 to 15. If the number of carbon atoms is 4 or more, sufficient flexibility of the electrode including the binder resin composition can be obtained, and if the number of carbon atoms is 100 or less, sufficient electrolytic solution resistance and swelling resistance can be obtained. it can. These monomers represented by the general formula (I) may be used alone or in combination of two or more.

(1-3) Repeating units of other monomers In addition to the repeating unit derived from the nitrile group-containing monomer and the repeating unit of the monomer represented by the formula (I), the binder resin composition includes: It can contain repeating units of other monomers copolymerizable with these monomers.
Examples of the other monomers include unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid, maleic acid, fumaric acid, citraconic acid, metaconic acid, glutaconic acid, adipic acid, itaconic acid, tetrahydro Unsaturated dicarboxylic acids such as phthalic acid, crotonic acid, isocrotonic acid, nadic acid, acrylamide monomers such as acrylamide, N-methylolacrylamide, N-butoxymethylacrylamide, methacrylamide, N-methylolmethacrylamide, N-butoxy Methacrylamide monomers such as methyl methacrylamide, glycidyl group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, acryl glycidyl ether, styrene, α-methyl styrene, vinyl toluene, pt-butyl styrene, chloro Styrene, etc. Examples thereof include conjugated diene monomers such as a thylene monomer, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and piperylene.

  From the viewpoint of resistance to electrolytic solution, a small amount of a crosslinkable monomer may be added to the binder resin composition of the present invention for polymerization. Crosslinkable monomers include divinyl compounds such as divinylbenzene, polyfunctional dimethacrylates such as diethylene glycol dimethacrylate and ethylene glycol dimethacrylate, polyfunctional trimethacrylates such as trimethylolpropane trimethacrylate, and diacrylic. Examples thereof include polyfunctional diacrylic acid esters such as polyethylene glycol acid and 1,3-butylene glycol diacrylate, and polyfunctional triacrylic acid esters such as trimethylolpropane triacrylate.

(1-4) Content of nitrile group-containing monomer and monomer represented by formula (I) The repeating unit derived from acrylonitrile and / or methacrylonitrile in the binder resin composition of the present invention is When the total mass of the binder resin composition is 100 parts by mass, it is preferably 70 to 95 parts by mass, more preferably 80 to 95 parts by mass, and still more preferably 85 to 95 parts by mass. If it is 70 parts by mass or more, good electrolytic solution resistance can be maintained, and if it is 95 parts by mass or less, the adhesiveness and flexibility of the binder resin composition of the present invention can be sufficiently maintained, which is preferable. .
On the other hand, the repeating unit derived from the monomer represented by the general formula (I) is preferably 5 to 30 parts by mass when the total mass of the binder resin composition of the present invention is 100 parts by mass. It is more preferable to set it as -20 mass parts, and it is still more preferable to set it as 5-15 mass parts. If it is 30 parts by mass or less, good electrolytic solution resistance can be maintained, and if it is 5 parts by mass or more, the adhesiveness and flexibility of the binder resin composition of the present invention can be sufficiently maintained, which is preferable.
The above-mentioned other monomers are used in a proportion of 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, when the total mass of the binder resin composition of the present invention is 100 parts by mass.
The crosslinkable monomer is used in a proportion of 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, when the total mass of the binder resin composition of the present invention is 100 parts by mass.

(2) Method for producing binder resin composition for lithium battery electrode The binder resin composition for a lithium battery electrode of the present invention is represented by (1) the nitrile group-containing monomer and (2) the formula (I). It is produced by polymerizing a monomer and (3) any of the above other monomers. As a polymerization method for producing the binder resin composition of the present invention, existing methods such as bulk suspension polymerization, suspension polymerization, dispersion polymerization, and emulsion polymerization can be applied.
(2-1) Radical polymerization initiator In order to produce the binder resin composition of the present invention, a radical polymerization initiator can be used. Examples of the radical polymerization initiator include benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, di-t-butyl peroxyhexahydroterephthalate, t-butyl peroxy-2-ethylhexanoate, 1 , 1-t-butylperoxy-3,3,5-trimethylcyclohexane, organic peroxides such as t-butylperoxyisopropyl carbonate, azobisisobutyronitrile, azobis-4-methoxy-2,4-dimethylvalero Nitrile, azobiscyclohexanone-1-carbonitrile, azodibenzoyl, 2,2'-azobis (2-methylpropionamide) dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) Propane] Hydrogen dichloride, 2,2'-azobis (2-methylpropionamide) dihydrochloride, 4,4'-azobi Azo compounds such as (4-cyanovaleric acid), 2,2′-azobis [2- (N- (2-carboxyethyl) amino) propane], persulfates such as potassium persulfate and ammonium persulfate, and peroxides Or what can be used for normal radical polymerization, such as a redox catalyst by the combination of a persulfate and a reducing agent, can be used. 2,2'-azobis (2-methylpropionamide) dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis (2- Methylpropionamide) dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis [2- (N- (2-carboxyethyl) amino) propane] and other azo compounds, persulfuric acid Particularly preferred are persulfates such as potassium and ammonium persulfate. The binder resin composition synthesized using these radical polymerization initiators can improve the adhesion between the binder resin composition and the mixture layer containing the active material and the current collector.
The radical polymerization initiator is preferably used in an amount of 0.01 to 5 mol% based on the total amount of monomers used for the synthesis of the binder resin composition. If the amount of the radical polymerization initiator is 0.01 mol% or more, the reaction proceeds rapidly, and if the amount of the radical polymerization initiator is 5 mol% or less, the mixture containing the obtained binder resin composition It is preferable because good adhesion and flexibility of the layer can be obtained.

(2-2) Molecular weight regulator In the production of the binder resin composition of the present invention, a molecular weight regulator can be added as necessary. Examples of the molecular weight modifier include mercaptan compounds, thioglycol, carbon tetrachloride, α-methylstyrene dimer, and the like.
(2-3) Emulsifier / Dispersant When water is used as the solvent in the production of the binder resin composition of the present invention, an emulsifier / dispersant can be used as necessary.
Examples of the emulsifier include benzene sulfonates such as sodium octylbenzene sulfonate and sodium dodecylbenzene sulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate; lauric acid Fatty acid salts such as sodium; ethoxy sulfate salts such as sodium polyoxyethylene lauryl ether sulfate and polyoxyethylene nonylphenyl ether sulfate sodium salts; and nonionic emulsifiers such as polyoxyethylene-polyoxypropylene block copolymers.
Examples of the dispersant include methyl cellulose, polyethylene oxide, gelatin, and polyvinyl alcohol.
These may be used alone or in combination of two or more. The addition amount of the emulsifier / dispersant is suitably 0.01 to 10 parts by weight, preferably 0.05 to 3 parts by weight, based on 100 parts by weight of the entire binder resin composition of the present invention. is there.
(2-4) Polymerization conditions The polymerization temperature can be appropriately selected from 0 to 100 ° C, preferably 30 to 90 ° C. If the polymerization temperature is 0 ° C. or higher, the polymerization rate does not decrease, and if the polymerization temperature is 100 ° C. or lower, even when water is used as the solvent, the water evaporates and the polymerization becomes difficult. It is preferable because there is nothing.
The polymerization time is suitably 0.5 to 24 hours, preferably 3 to 12 hours.
The shape of the obtained copolymer is preferably particulate. The particle size is, for example, 0.01 to 5 μm, preferably 0.05 to 2 μm.

(3) Lithium Battery Electrode The lithium battery electrode of the present invention has a current collector and a mixture layer provided on at least one surface of the current collector. This mixture layer is composed of the binder resin composition of the present invention containing an active material and an active material. The mixture layer is obtained by applying a slurry containing the binder resin composition of the present invention, a solvent, an active material, and the like to the current collector and removing the solvent.

(3-1) Current Collector The current collector of the present invention may be any material having electrical conductivity. For example, aluminum, copper, nickel, iron, stainless steel, titanium, or the like can be used as the metal. Further, the shape of the current collector is not particularly limited, but a thin film shape is preferable from the viewpoint of increasing the energy density of the lithium battery. The thickness of the current collector is, for example, 3 to 50 μm, preferably 8 to 20 μm.

(3-2) Mixture Layer The mixture layer of the present invention is composed of the binder resin composition containing an active material. The mixture layer is prepared by preparing a slurry containing the binder resin composition, a solvent, an active material, and other additives, applying the slurry to at least one surface of the current collector, and further removing the solvent. can get.
(3-2-1) Active Material The active material used in the present invention is not particularly limited as long as it can reversibly insert and release lithium ions by charging and discharging a lithium battery. However, the positive electrode has a function of releasing lithium ions at the time of charging and receiving lithium ions at the time of discharging, while the negative electrode has a function opposite to that of the positive electrode of receiving lithium ions at the time of charging and releasing lithium ions at the time of discharging. Therefore, it is preferable that the active materials used in the positive electrode and the negative electrode are different types of active materials in accordance with the respective functions.
The positive electrode active material may be any transition metal oxide capable of reversibly inserting and releasing lithium ions by charge and discharge, and may be lithium cobalt composite oxide, lithium, nickel composite oxide, or a mixture thereof. Also, in the lithium nickel composite oxide, lithium nickel or lithium site substituted with at least one metal selected from Al, V, Cr, Fe, Co, Sr, Mo, W, Mn, B, and Mg. A complex may also be used. Further, in the lithium manganese composite oxide, the manganese site or the lithium site is substituted with at least one metal selected from Al, V, Cr, Fe, Co, Sr, Mo, W, Mn, B, and Mg. A composite oxide may be used. Note that the positive electrode active material may be used in combination with a conductive additive. Examples of the conductive assistant include graphite, carbon black, acetylene black, and the like. These conductive assistants may be used alone or in combination of two or more.
On the other hand, as the active material of the negative electrode, for example, carbon materials such as amorphous carbon, graphite, carbon fiber, coke, activated carbon and the like are preferable. These oxides can be used. These active materials are used alone or in combination of two or more.

(3-2-2) Solvent The solvent used in the production of the mixture layer is not particularly limited as long as it can dissolve or disperse the binder composition uniformly. For example, various solvents such as water and organic solvents can be used. For example, N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) or glyme solvents (diglyme, triglyme, tetraglyme) Etc.) is preferred. These solvents may be used alone or in combination of two or more.

(3-2-3) Other additives A thickener can be added to the slurry for producing the mixture layer of the present invention in order to improve the dispersion stability and coating property of the slurry. Thickeners include celluloses such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and ammonium salts or alkali metal salts thereof, polyacrylic acid and alkali metal salts thereof, polyvinyl alcohol, ethylene / vinyl alcohol copolymer Examples thereof include polyvinyl alcohol copolymers such as coalescence.

(3-3) Electrode Production Method The electrode of the present invention can be produced without any particular limitation using a known electrode production method. For example, a slurry containing the binder resin composition, the solvent, and the active material. Is applied to at least one surface of the current collector, then the solvent is removed, and rolling is performed as necessary to form a mixture layer on the surface of the current collector.
Here, application | coating can be performed using a comma coater etc., for example. The application is suitably performed so that the active material utilization rate per unit area is not less than negative electrode / positive electrode = 1 in the opposing electrode. In the case of the negative electrode, for example, the slurry coating amount is such that the dry mass of the mixture layer is, for example, 50 to 200 g / m ² , preferably 100 to 150 g / m ² . The removal of the solvent is performed, for example, by drying at 60 to 150 ° C., preferably 80 to 130 ° C. for 1 to 120 minutes, preferably 5 to 60 minutes. Rolling is performed, for example, using a roll press machine, the bulk density of the mixture layer, when the negative electrode, for example, 0.7~2.0g / cm ^3, preferably 1.0~1.7g / cm ³ It is preferable to be pressed so that Further, in order to remove the residual solvent and adsorbed water in the electrode, for example, vacuum drying may be performed at 120 ° C. for 10 hours.

(4) Battery The electrode of the present invention can be further combined with an electrolytic solution to produce a lithium battery.
(4-1) Electrolytic Solution The electrolytic solution used in the present invention is not particularly limited as long as it exhibits the battery function, but a solution in which an electrolyte is dissolved in an organic solvent can be used.
Examples of the organic solvent include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, lactones such as γ-butyrolactone, trimethoxymethane, 1,2-dimethoxyethane, and diethyl. Ethers, ethers such as 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, sulfoxides such as dimethyl sulfoxide, oxolanes such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, acetonitrile, nitromethane, N -Nitrogens such as methyl-2-pyrrolidone, esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, phosphate triester, diglyme Glymes such as triglyme and tetraglyme, ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone, sulfolanes such as sulfolane, oxazolidinones such as 3-methyl-2-oxazolidinone, 1,3-propanesultone, Examples include sultone such as 1,4-butane sultone and naphtha sultone. The organic solvent of the electrolytic solution is used alone or in combination of two or more.
As the electrolyte, for _{example, LiCl, LiBF 4, LiI,} LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH 3 SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and the like can be mentioned. Among these, an electrolytic solution in which LiPF ₆ is dissolved in carbonates is preferable.

(4-2) Method for Producing Lithium Battery The method for producing the lithium battery of the present invention is not particularly limited, but known methods can be used. For example, first, the electrode is wound through a separator made of a polyethylene microporous membrane. The obtained spiral wound group is inserted into a battery can, and a tab terminal previously welded to a negative electrode current collector is welded to the bottom of the battery can. Inject the electrolyte into the resulting battery can, weld the tab terminal that was previously welded to the positive electrode current collector to the battery lid, and place the lid on the top of the battery can via an insulating gasket A battery is obtained by caulking and sealing the part where the lid and the battery can are in contact.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited to this.
<Preparation of binder resin composition>
Example 1
In a 1.0 liter separable flask equipped with a stirrer, thermometer, and cooling tube, 45.0 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a nitrile group-containing monomer under a nitrogen atmosphere, a single unit represented by the formula (I) Lauryl acrylate (manufactured by Aldrich) 5.0 g as a polymer, potassium persulfate (manufactured by Wako Pure Chemical Industries) 0.235 mg as a radical polymerization initiator, α-methylstyrene dimer (manufactured by Wako Pure Chemical Industries) 135 mg as a molecular weight regulator, solvent As a reaction solution, 450 ml of purified water (Wako Pure Chemical Industries, Ltd.) was added. While the reaction solution was vigorously stirred, the reaction was terminated by stirring at 60 ° C. for 3 hours and at 80 ° C. for 8 hours (resin solid content 49 g, yield 98%). Thereafter, the unreacted monomer was distilled off under reduced pressure at 60 ° C. and 133 hPa (100 Torr) for 30 minutes and cooled to room temperature to obtain an aqueous dispersion of the binder resin composition of Example 1.
Example 2
35.0 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a nitrile group-containing monomer, 15.0 g of lauryl acrylate (manufactured by Aldrich) as a monomer represented by formula (I), potassium persulfate (Japanese sum) as a radical polymerization initiator An aqueous dispersion of the binder resin composition of Example 2 was obtained in the same manner as in Example 1 except that the amount was 0.194 mg.

Example 3
As the monomer represented by the formula (I), 5.0 g of perfluorooctylethyl acrylate (Kyoeisha Chemical Co., Ltd. Light Acrylate FA-108) is used instead of lauryl acrylate, and potassium persulfate ( An aqueous dispersion of the binder resin composition of Example 3 was obtained in the same manner as in Example 1 except that 0.232 mg of Wako Pure Chemical Industries, Ltd. was used.
Example 4
As a monomer represented by the formula (I), 10.0 g of perfluorooctylethyl acrylate (Kyoeisha Chemical Co., Ltd. Light Acrylate FA-108) is used instead of lauryl acrylate, and potassium persulfate ( An aqueous dispersion of the binder resin composition of Example 4 was obtained in the same manner as in Example 1 except that 0.209 mg (manufactured by Wako Pure Chemical Industries, Ltd.) was used.
Example 5
As a monomer represented by the formula (I), instead of lauryl acrylate, perfluorooctylethyl acrylate (Kyoeisha Chemical Co., Ltd., Light Acrylate FA-108) 15.0 g, potassium persulfate (Wako Pure Chemical Industries, Ltd.) 0.186 mg Except that, an aqueous dispersion of the binder resin composition of Example 5 was obtained in the same manner as Example 1.

Comparative Example 1
50 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) is used as a nitrile group-containing monomer, does not contain the monomer represented by formula (I), and potassium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) as a radical polymerization initiator An aqueous dispersion of the binder resin composition was obtained in the same manner as in Example 1 except that 1.27 g was used. In addition, this comparative example 1 is a reference example of this invention which does not contain the monomer represented by a formula (I).
Comparative Example 2
40.0 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) is used as the nitrile group-containing monomer, and 10.0 g of ethyl acrylate (manufactured by Aldrich) is used as the equivalent of the monomer represented by formula (I). An aqueous dispersion of the binder resin composition of the present invention was obtained in the same manner as in Example 1 except that 0.82 g of potassium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the polymerization initiator. This Comparative Example 2 is a reference example of the present invention because R ₂ in formula (I) is an alkyl group having 2 carbon atoms.

Comparative Example 3
A commercially available polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution (solid content 12% by mass, manufactured by Kureha Chemical, KF-1120) was used. In addition, since this comparative example 3 does not include the repeating unit derived from the nitrile group-containing monomer and the repeating unit derived from the monomer represented by the formula (I), it is a reference example of the present invention.
Comparative Example 4
A commercially available styrene-butadiene rubber (SBR) latex (solid content 40% by mass, manufactured by Nippon Zeon Co., Ltd., BM400) was prepared as Comparative Example 4. In addition, since this comparative example 4 does not include the repeating unit derived from the nitrile group-containing monomer and the repeating unit derived from the monomer represented by the formula (I), it is a reference example of the present invention.

<Evaluation of binder resin composition>
Evaluation of swelling degree (electrolytic solution resistance), adhesiveness and flexibility of each binder resin composition with respect to the electrolytic solution by the following methods using the binder resin compositions of Examples 1 to 5 and Comparative Examples 1 to 4 Went. The results are summarized in Table 1.
(1) Evaluation of degree of swelling (electrolytic solution resistance) with respect to electrolyte solution The aqueous dispersions of the binder resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were suction filtered, and the recovered solid content was acetone. The resin was isolated by vacuum drying at 60 ° C. for 24 hours. Next, the isolated resin was dissolved in N-methyl-2-pyrrolidone (NMP), and samples of Examples 1 to 5 and Comparative Examples 1 and 2 were prepared as NMP solutions containing 10% by mass of the resin content. Comparative Examples 3 and 4 were used as samples as they were.
Each sample was coated on a glass substrate so that the film thickness after drying was about 10 μm, dried for 2 hours with a 120 ° C blower-type dryer, and 10 minutes with a vacuum dryer (120 ° C / 133 Pa (1 torr)). The film was dried for a time to form a binder resin composition film. The obtained film was cut into a 2 cm square in a glove box having an argon atmosphere of about 100 μm, and the mass was measured. Membrane cut into a container that can be sealed and a sufficient amount of electrolyte to immerse the membrane (ethylene carbonate / diethyl carbonate / dimethyl carbonate in which LiPF ₆ is dissolved at a concentration of 1M = 1/1/1 (volume ratio) The mixed solution) was added, the membrane was immersed in an electrolytic solution, and the container was sealed. The sealed container containing the membrane and the electrolyte was placed in a constant temperature bath at 25 ° C. and 50 ° C. and left for 24 hours. The sealed container was again put in a glove box in an argon atmosphere, the membrane was taken out, the electrolytic solution adhering to the membrane surface was wiped off with filter paper, and the mass of the membrane after immersion was measured. The degree of swelling was calculated from the following formula, and the results are summarized in Table 1.
Swelling degree = [(film mass after immersion−film mass before immersion) / (film mass before immersion)] × 100
If the degree of swelling is usually 3 or less, preferably 2 or less, more preferably less than 1, it is evaluated that the swellability with respect to the electrolytic solution is low.

(2) Evaluation of adhesiveness 2 parts by mass each of the aqueous dispersions of the binder resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 and 2 and the solid content of the styrene-butadiene rubber latex of Comparative Example 4 96 parts by mass of mesocarbon microbeads (MCMB) with an average particle diameter of 15 μm as the active material and 2 parts by mass of carboxymethylcellulose aqueous solution as a thickener with carboxymethylcellulose solid content, and well mixed and dispersed to slurry Was made. The polyvinylidene fluoride NMP solution of Comparative Example 3 was prepared by mixing 4 parts by mass of a polyvinylidene fluoride solid content with 96 parts by mass of MCMB having an average particle size of 15 μm, and further adding 37 parts by mass of NMP to adjust the viscosity. Produced.
The slurry mixture thus prepared was applied on one side of a current collector (rolled copper foil, thickness 14 μm) so as to be 12 to 13 mg / cm ^2, and dried at 80 ° C. for 1 hour with a blow-type dryer. After forming the mixture layer, the mixture layer was pressed by a roll press so that the bulk density of the mixture layer was 1.5 g · cm ³ . Further, this electrode was vacuum-dried at 120 ° C. for 12 hours to obtain a 4.5 × 9 cm test piece. What was cut out from this test piece to 2 × 2 cm was an electrolyte (mixed solution of ethylene carbonate / dimethyl carbonate / diethyl carbonate = 1/1/1 (volume ratio) in which LiPF ₆ was dissolved at a concentration of 1M) ) At 50 ° C. for 72 hours to evaluate the adhesion at the interface between the mixture layer and the current collector. The adhesion between the mixture layer and the current collector was visually observed. As the evaluation criteria, a case where interfacial peeling between the mixture layer and the current collector was not observed was good, and a case where interfacial peeling was observed was regarded as poor.

(3) Flexibility evaluation (2) Cut the same test piece as used for the adhesive evaluation above into a 1x5cm strip and wrap it around a 4mmφ stainless steel rod with the surface of the mixture layer on the outside. Both ends were overlapped and a 100 g weight was attached. This state was maintained for 1 minute, and the appearance of the surface of the mixture layer was visually observed. The evaluation criteria for the flexibility were good when no defects such as cracks and wrinkles were observed on the surface of the mixture layer, and when the defect was observed. In addition, a result repeats the same test 5 times and represents the number of defects (number of defects / 5) among the five tests. If the number of defects is 2, preferably 1, and more preferably 0, it is determined that the product has good flexibility.

Table 1

From Table 1, it was found that the binder resin compositions used in Examples 1 to 5 had a lower degree of swelling with respect to the electrolytic solution than PVDF and SBR of Comparative Examples 3 and 4. The mixture layers of Examples 1 to 5 were found to have good adhesiveness and flexibility.
Further, the binder resin composition of Comparative Example 1 which is only acrylonitrile and does not have the monomer component of the general formula (I) has a low degree of swelling with respect to the electrolytic solution, but the adhesiveness and flexibility of the mixture layer are poor. Become. Further, the binder resin composition of Comparative Example 2 using a monomer having 3 or less carbon atoms of R _{2 in} the general formula (I) has a low degree of swelling with respect to the electrolyte solution, but the adhesiveness of the mixture layer is Slightly inferior and poor flexibility.

<Evaluation of battery characteristics>
(1) Production Example 1 of Electrode for Negative Electrode 1
3 parts by mass of the binder resin composition aqueous dispersion of Example 1 in terms of binder resin composition solids, 95 parts by mass of artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG) having an average particle size of 35 μm as a negative electrode active material, and 2 parts by mass of carboxymethylcellulose aqueous solution as a thickener is blended so that the total amount of the binder resin composition solid, negative electrode active material and thickener solids is 100 parts by mass, and kneaded. To prepare a slurry. The obtained slurry was applied on both sides of a current collector (rolled copper foil) having a thickness of 10 μm by adjusting the gap of the transfer roll so that the coating amount was 130 g / m ² on one side by the dry mass of the mixture layer. It dried and the mixture layer was formed. Next, the obtained mixture layer was rolled with a roll press so that the bulk density of the mixture layer was 1.5 g / cm ^3, and cut into 425 mm × 56 mm to prepare a strip-shaped electrode sheet for negative electrode. An aluminum current collector tab was ultrasonically welded to the end of the obtained negative electrode sheet, and vacuum-dried at 120 ° C. for 16 hours to completely remove residual moisture in the electrode sheet. An electrode was obtained.

Production examples 2-5
Instead of the aqueous dispersion of the binder resin composition of Example 1, the aqueous dispersion of the binder resin composition of Examples 2 to 5 was used in the same manner as in Production Example 1 for the negative electrodes of Production Examples 2 to 5 An electrode was produced.

Reference creation examples 1 and 2
Negative electrodes of Reference Preparation Examples 1 and 2 in the same manner as Preparation Example 1 except that the aqueous dispersion of the binder resin composition of Comparative Examples 1 and 2 was used instead of the aqueous dispersion of the binder resin composition of Example 1. An electrode was prepared. The reference preparation examples 1 and 2 are reference examples of the present invention because the binder resin compositions of comparative examples 1 and 2 are used.
Reference creation example 3
The NMP solution of polyvinylidene fluoride (PVDF) of Comparative Example 3 was 6 parts by mass with a polyvinylidene fluoride solid content, and 94 parts by mass of artificial graphite having an average particle diameter of 35 μm as a negative electrode active material, and the above-mentioned polyvinylidene fluoride solid content and The total amount of the negative electrode active material was blended to be 100 parts by mass, and further kneaded while adding 56 parts by mass of NMP to prepare a slurry. The step of obtaining the negative electrode for Reference Preparation Example 3 from the slurry was the same as in Preparation Example 1. This Reference Preparation Example 3 is a reference example of the present invention because the polyvinylidene fluoride of Comparative Example 3 is used.

Reference creation example 4
3 parts by mass of styrene / butadiene / rubber (SBR) latex of Comparative Example 4 in terms of solid content of styrene / butadiene / rubber, 95 parts by mass of artificial graphite having an average particle diameter of 35 μm as a negative electrode active material, and an aqueous carboxymethylcellulose solution as a thickener. 2 parts by mass in terms of solid content were blended so that the total of the styrene / butadiene / rubber solid content, the negative electrode active material and the thickener solid content was 100 parts by mass, and kneaded to prepare a slurry. The step of obtaining the negative electrode for Reference Preparation Example 4 from the slurry mixture was the same as in Preparation Example 1. This Reference Preparation Example 4 is a reference example of the present invention because the styrene-butadiene rubber of Comparative Example 4 is used.

(2) Production example 6 of positive electrode
The aqueous dispersion of the binder resin composition of Example 3 was 2.5 parts by mass of the binder resin composition solid content, 87 parts by mass of lithium cobalt oxide having an average particle diameter of 10 μm as the positive electrode active material, and the average particle diameter of 3 μm as the conductive auxiliary agent. 8.5 parts by mass of artificial graphite and 2 parts by mass of carboxymethylcellulose aqueous solution as a thickener, the binder resin composition solids, the positive electrode active material, the conductive assistant and the thickener solids It mix | blended so that it might become 100 mass parts, knead | mixed, and prepared the slurry. The obtained slurry was applied to both sides of a current collector (aluminum foil) having a thickness of 20 μm by adjusting the gap of the transfer roll so that the coating amount was 330 g / m ² on one side by the dry mass of the mixture layer. It dried and the mixture layer was formed. Next, the obtained mixture layer was rolled with a roll press so that the bulk density of the mixture layer was 3.2 g / cm ^3, and cut into 385 mm × 54 mm to produce a strip-like electrode sheet for positive electrode. An aluminum current collector tab was ultrasonically welded to the end of the obtained electrode sheet for positive electrode, and then vacuum-dried at 120 ° C. for 16 hours in order to completely remove residual moisture in the electrode sheet. The positive electrode was obtained.

Reference creation example 5
The NMP solution of polyvinylidene fluoride (PVDF) of Comparative Example 3 is 4.5 parts by mass in terms of polyvinylidene fluoride solids, 87 parts by mass of lithium cobaltate having an average particle size of 10 μm as a positive electrode active material, and an average particle size of 3 μm as a conductive additive. 8.5 parts by weight of artificial graphite was blended so that the total of the above-mentioned polyvinylidene fluoride solid content, the positive electrode active material and the conductive additive was 100 parts by weight, and kneaded while adding 50 parts by weight of NMP to prepare a slurry mixture did. This slurry mixture was applied to both sides of a current collector (aluminum foil) having a thickness of 20 μm by adjusting the gap of the transfer roll so that the coating amount was 290 g / m ² on one side by the dry mass of the binder resin composition layer. And dried to form a mixture layer. Next, the obtained mixture layer was rolled with a roll press so that the bulk density of the mixture layer was 3.2 g / cm ^3, and cut into 385 mm × 54 mm to produce a strip-shaped electrode sheet for a positive electrode. . Vacuum welding at 120 ° C for 16 hours to ultrasonically weld an aluminum current collector tab to the end of the resulting positive electrode sheet and completely remove volatile components such as residual solvent and adsorbed moisture in the electrode sheet The electrode for positive electrodes of Reference Preparation Example 5 was obtained by drying.

(3) Production of lithium secondary battery The positive electrode and the negative electrode of the combination preparation examples or reference preparation examples shown in Table 2 below are wound through a separator made of a polyethylene microporous film having a thickness of 25 μm and a width of 58 mm. A spiral wound group was prepared. This wound group was inserted into a battery can, and a tab terminal previously welded to the negative electrode current collector was welded to the bottom of the battery can. Next, 5 ml of an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / l in a solution mixed with ethylene carbonate / dimethyl carbonate = 1/2 (volume ratio) was poured into the battery can. After that, the tab terminal that has been previously welded to the positive electrode current collector is welded to the battery lid, and the lid is placed on the top of the battery can via an insulating gasket, and the battery can and the lid are crimped and sealed. Thus, a cylindrical lithium secondary battery having a diameter of 18 mm and a height of 65 mm was produced.

The lithium secondary batteries of the batteries 1 to 7 and the reference batteries 1 to 4 obtained above were charged at a constant current to a limit voltage of 4.2 V at a charging current of 400 mA at an ambient temperature of 50 ° C. (charging). Thereafter, constant current discharge was performed at a discharge current of 800 mA until the discharge end voltage reached 2.7 V (discharge). The initial discharge capacity at this time was measured. Next, charging / discharging was repeated at an ambient temperature of 50 ° C with the above charging / discharging as one cycle, and the number of cycles when the discharge capacity reached 70% of the initial discharge capacity was determined as the life cycle number (high-temperature life expired). Judgment line). The results are shown in Table 2.
Table 2

  From Table 2, as the binder resin composition, batteries (reference batteries 3 and 4) consisting only of electrodes using PVDF or SBR having a large degree of swelling with respect to the electrolyte, and electrodes having poor adhesion and flexibility of the electrode mixture layer It can be seen that the batteries using the battery (reference batteries 1 and 2) have reached the end of their life in 180 to 250 cycles. On the other hand, it can be seen that the batteries (batteries 1 to 7) using the electrode of the present invention have a long life of 400 cycles or more. In particular, it can be seen that the battery (battery 6) using the electrode of the present invention for both electrodes has the longest lifetime.

Claims (3)

A repeating unit derived from a nitrile group-containing monomer and the formula (I)

(Wherein R ₁ is H or CH ₃ ; R ₂ is an alkyl group having 4 to 100 carbon atoms)
A binder resin composition for a lithium battery electrode containing a copolymer containing a repeating unit derived from a monomer represented by :
The repeating unit derived from the nitrile group-containing monomer is 70 to 95 parts by mass when the total mass of the binder resin composition is 100 parts by mass, and the repeating unit derived from the monomer represented by the formula (I) Is 5-30 parts by mass when the total mass of the binder resin composition is 100 parts by mass,
The nitrile group-containing monomer is acrylonitrile and / or methacrylonitrile.
A binder resin composition for a lithium battery electrode, characterized in that A current collector, and a mixture layer provided on at least one surface of the current collector,該合adhesive layer, a lithium battery electrode binder resin composition of claim 1 comprising an active material , Electrodes for lithium batteries. A lithium battery comprising the electrode for a lithium battery according to claim 2 .