WO2004006361A1

WO2004006361A1 - Method for preparing slurry composition for electrode of secondary cell

Info

Publication number: WO2004006361A1
Application number: PCT/JP2003/008401
Authority: WO
Inventors: Takao Suzuki; Masahiro Yamakawa; Katsuya Nakamura
Original assignee: Zeon Corporation
Priority date: 2002-07-02
Filing date: 2003-07-02
Publication date: 2004-01-15
Also published as: JP4470735B2; KR101083129B1; CN1290211C; KR20050016713A; CN1666360A; JPWO2004006361A1

Abstract

A method for preparing a slurry composition for an electrode of a secondary cell, which comprises kneading an electrode active material and a dispersion in a solvent (SA) of a polymer (A) containing 50 wt % or more of a portion insoluble in the solvent (SA), and then kneading the above-kneaded fluid and a solution of a polymer (B) in a solvent (SB). A slurry composition prepared by the method is reduced in the change of the viscosity thereof due to the elapse of time and exhibits good sticking property, and provides an electrode of a secondary cell having a mixed layer of a flat surface and a uniform thickness through applying the composition on a collector followed by drying.

Description

Description Method for producing slurry composition for secondary battery electrode

The present invention relates to a method for producing a slurry composition for a secondary battery electrode, and more particularly, to a secondary battery electrode that has a small change with time in viscosity and can be applied to a current collector to obtain an electrode with a smooth coating film surface. The present invention relates to a method for producing a slurry composition for use. Background art

Portable terminals such as notebook computers, mobile phones, and PDAs have become widespread, and lithium-ion secondary batteries are frequently used for these power supplies. Recently, there has been an increasing demand for extending the use time of a mobile terminal and shortening a charging time, and accordingly, there is a strong demand for higher performance of a battery, particularly, an increase in capacity and an improvement in charging speed (rate characteristics).

The lithium ion secondary battery has a structure in which a positive electrode and a negative electrode are arranged via a separator, and are housed in a container together with an electrolytic solution. Positive electrode and negative electrode (both collectively

“Secondary battery electrode” may be abbreviated as “electrode”. ) Is a binder polymer for a secondary battery electrode (hereinafter, simply referred to as “active material”) and a conductivity-imparting agent used as necessary. It may be referred to as “binder”.) It is bound to a current collector such as aluminum or copper. The electrode is usually prepared by dissolving or dispersing a binder in a liquid medium and mixing an active material, a conductivity imparting agent, and the like with the slurry composition for a secondary battery electrode (hereinafter, simply referred to as “slurry”).

It may be written as "slurry composition". ) Is applied to a current collector, the liquid medium is removed by drying or the like, and the mixture is bound as a mixed layer. .

However, there has been a problem that the dispersion of each component in the slurry composition is insufficient, or the viscosity of the slurry composition changes with time, so that the dispersion state of the slurry composition becomes uneven. When an electrode is made using a non-uniform slurry composition, the surface of the electrode does not become smooth and the battery performance decreases, or the binding of the active material deteriorates and the active material peels off from the current collector. Occurs. As a method for obtaining a highly dispersed slurry composition, JP-A-8-195201 discloses a method in which a binder obtained by dispersing a binder in a thickener solution is mixed with an active material and a conductivity-imparting agent. There has been proposed a method of adding, kneading and dispersing. However, this production method had problems such as insufficient dispersion of the conductivity-imparting agent and insufficient smoothness of the electrode surface.

Japanese Patent Application Laid-Open No. 9-204917 discloses a method for producing a slurry composition, in which a kneading step of each component and a slurry composition obtained by kneading are allowed to stand for a predetermined time to increase the viscosity. There has been proposed a method having a step and a step of re-kneading the viscous slurry composition. However, in this method, there are problems that the steps are complicated, and that the production of the slurry composition requires a long time and the productivity is reduced.

Further, Japanese Patent Application Laid-Open Publication No. 2000-348713 discloses that an active material and a conductivity-imparting agent are kneaded by adding a thickener at least twice or more and then kneading the binder. A method for producing a slurry composition using water as a medium has been proposed. However, even with this method, depending on the type of the binder, there is a problem that the dispersion of the binder itself is not sufficient, so that the viscosity changes with time or the binding property is reduced. Disclosure of the invention

Under such circumstances, an object of the present invention is to provide a slurry composition for a secondary battery electrode, which provides an electrode having a mixed layer in which the change in viscosity with time is small, the binding property is good, and the surface is smooth. It is to provide a manufacturing method.

The present inventors have intensively studied a method for obtaining a slurry composition in which the active material and the conductivity-imparting agent are highly dispersed, and as a result, kneaded the active material with a dispersion liquid in which a polymer binder that is difficult to dissolve in a solvent is dispersed. Then, by taking a procedure of mixing a solution in which a polymer binder soluble in the solvent is dissolved with the kneading liquid, a highly dispersed slurry composition is obtained. The present inventors have found that an electrode having a t-smooth mixed layer without agglomerates can be obtained when the electrode is manufactured, and further studies based on this finding have led to the completion of the present invention.

Thus, according to the present invention, a solvent (SA) dispersion of the polymer (A) containing at least 50% by weight of an insoluble content in the solvent (SA) is kneaded with the electrode active material, There is provided a method for producing a slurry composition for a secondary battery electrode, comprising kneading the obtained kneading liquid and a solvent (SB) solution of a polymer (B).

Further, according to the present invention, there is provided a method for producing a secondary battery electrode, which comprises applying the slurry composition produced as described above to a current collector and drying it. BEST MODE FOR CARRYING OUT THE INVENTION

In the method for producing a slurry composition for a secondary battery electrode according to the present invention, a solvent (SA) dispersion of a polymer (A) containing 50% by weight or more of an insoluble content in a solvent (SA) is kneaded with an electrode active material. Then, the obtained kneading liquid is kneaded with a solution of the polymer (B) in a solvent (SB).

First, the materials used in the present invention will be described.

As the solvent (S A) and the solvent (S B) used in the present invention, water and a non-aqueous solvent having a boiling point of 80 to 350 ° C. under atmospheric pressure are preferable. Examples of such non-aqueous solvents include: amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane, tetrauran; Alcohols such as 1-hexanol, 1-nonanol, and lauryl alcohol; ketones such as methylethyl ketone, cyclohexanone, holone, acetate phenone, and isophorone; benzyl acetate, isopentyl butyrate, and lactic acid Esters such as methyl, ethyl lactyl and butyl lactate; amines such as o-toluidine, m-toluidine, p-toluidine; lactones such as arptyrolactone, δ-z-tyrolactone; dimethyl sulfoxide And sulfoxides such as sulfolane and sulfones. Among these, water and amides are more preferred, and Ν-methylpyrrolidone is particularly preferred.

Each of these solvents (SA) and (SB) can be used alone or in combination of two or more. The solvent (SA) used for the dispersion of the polymer (A) and the solvent (SB) used for the solution of the polymer (B) preferably have the same composition. The polymer should be used if the insoluble content of the polymer (A) is 50% by weight or more and the polymer (B) is soluble in the solvent composition after mixing the dispersion and the polymer-(B) solution. Can be. In the present invention, two kinds of polymers are used as a binder. The type of the polymer (A), which is one component of the polymer binder, is not particularly limited, but a polymer containing 50% by weight or more of a component insoluble in a solvent (SA) is used. The component insoluble in the solvent (SA) of the polymer (A) is preferably at least 60% by weight, more preferably at least 70% by weight, and preferably 90% by weight or less, more preferably 87% by weight. % By weight or less. When the insoluble content in the solvent (SA) is in this range, the polymer (A) retains a particulate or fibrous state in the slurry composition, and as a result, the surface of the active material is covered with a film and the battery reaction is suppressed. Is assumed to be no longer hindered. If the amount of the insoluble component in the solvent (SA) is too small, the polymer (A) may be formed into a film, and the binding durability of the active material may be reduced, which may cause a decrease in capacity due to repeated charge and discharge. is there. Conversely, if the polymer (A) having an excessively large amount of insolubles in the solvent (SA) is used, there is a possibility that the binding property of the binder may be reduced.

Here, the amount of the insoluble component in the solvent (SA) was determined by immersing 0.2 g of the polymer in 20 ml of the solvent at a temperature of 60 ° C. for 72 hours, followed by filtration through an 80 mesh sieve. It is expressed as a percentage of the weight of the polymer determined by drying the above components relative to the weight of the polymer before immersion.

The polymer (A) containing a large amount of insolubles in the solvent (SA) as described above is a cross-linked copolymer of a monofunctional ethylenically unsaturated monomer and / or conjugated diene and a polyfunctional ethylenically unsaturated monomer. Preferably, there is.

Examples of the polyfunctional ethylenically unsaturated monomers include divinyl compounds such as divinylbenzene; dimethacrylates such as diethylene daricol dimethacrylate and ethylene glycol dimethacrylate; trimethylolpropane trimethacrylate and the like. Limethacrylic esters; diacrylic esters such as diethylene glycol diacrylate and 1,3-butylene glycol diacrylate; and triacrylic esters such as trimethylolpropane triacrylate. In addition, non-conjugated dienes such as 1,4-hexadiene, ethylidene norpolene, and dicyclopentene can also be used. These polyfunctional ethylenically unsaturated monomers can be used alone or in combination of two or more. The proportion of the polyfunctional ethylenically unsaturated monomer is usually from 0.3 to 5% by weight, preferably from 0.5 to 3% by weight, based on the total amount of the monomer for producing the polymer (A).

Monofunctional ethylenically unsaturated monomers used in the production of the polymer (A) include α-olefins such as ethylene, propylene, 、 -butene, isobutene and 3-methyl-1-butene; (meth) acrylonitrile ( Unsaturated nitrile compounds such as acrylonitrile or methacrylonitrile);

(Meth) methyl acrylate (Methyl acrylate or methyl methacrylate; the same applies hereinafter), (meth) ethyl acrylate, (meth) butyl acrylate, (meth) hexyl acrylate, (meth) acrylic acid (Meth) acrylic acid esters such as 2-ethylhexyl; crotonic acid esters such as methyl crotonate and 2-ethylhexyl crotonate and hydroxypropyl crotonate; (meth) acrylic acid ester (Meth) Acrylic esters containing alkoxy groups such as methoxyxyl and (meth) ethoxyxetyl acrylate; (meth) acrylic containing amino groups such as (meth) dimethylaminoethyl acrylate and (meth) getyl aminoethyl acrylate Acid esters; 2-hydroxypropyl (meth) acrylate, (meth) acrylic acid Hydroxy group-containing (meth) acrylates such as hydroxypropyl acid; (meth) acrylates having a phosphoric acid group, a sulfonic acid group, a boric acid group, etc. in an alkyl group; acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid And carboxyl group-containing vinyl compounds such as maleic acid and fumaric acid, and dicarboxylic anhydrides; and aromatic vinyl compounds such as styrene and α-methylstyrene.

Examples of the conjugated diene include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethylamine, 3-butadiene, and 1,3-pentadiene. These monofunctional ethylenically unsaturated monomers and conjugated diene can be used alone or in combination of two or more.

When a conjugated diene is used, a crosslinked polymer can be obtained by appropriately adjusting polymerization conditions such as polymerization temperature, polymerization conversion, and the amount of a molecular weight modifier even when a polyfunctional ethylenically unsaturated monomer is not used. .

The glass transition temperature (T g) of the polymer (Α) is preferably −80 to 0 ° C., and more preferably −60 to 15 ° C. If T g is too high, the flexibility of the electrode decreases, When charge and discharge are repeated, the active material is easily separated from the current collector. If τ g is too low, the battery capacity may decrease.

In order for the polymer (A) to have a T g in the above range, for example, 2-ethylhexyl acrylate (T g of a homopolymer is −85 ° C.), acrylic acid Monomers such as n-butyl (54 ° C), n-decyl methacrylate (65 ° C), 1,3-butadiene, isoprene, etc. whose homopolymer has a Tg of 0 ° C or less It is preferred to have a repeating unit of

Preferred examples of the polymer (A) include 2-ethylhexylnomethacrylate acrylate Zacrylonitrile / diethylene glycol dimethacrylate copolymer, butyl acrylate / acrylic acid / trimethylolpropane trimethacrylate copolymer. And acrylonitrile butadiene copolymer rubber.

The polymer (A) may be a mixture of polymers (A) having different monomer compositions. Further, the dispersion of the polymer (A) in the solvent (S A) may contain a small amount of a polymer having an insoluble content in the solvent (S A) of less than 50% by weight as long as the effects of the present invention are not impaired.

The average particle size of the polymer (A) is preferably from 0.005 to 1,000 m, more preferably from 0.01 to 100 m, particularly preferably from 0.05 to 10 m. If the average particle size is too large, the amount required for the binder will be too large, and the internal resistance of the electrode will increase. Conversely, if the average particle diameter is too small, the surface of the active material is covered and the battery reaction is hindered.

Here, the average particle diameter is a number average particle diameter calculated by measuring the diameter of 100 polymer particles randomly selected in a transmission electron micrograph and calculating the arithmetic average value. The method for producing the polymer (A) is not particularly limited. For example, the polymer (A) can be obtained by polymerization by a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, or a solution polymerization method. It is preferable to produce by the method described above because the particle diameter when dispersed in the solvent (SA) is easily controlled.

The other component of the polymer binder, polymer (B), is a polymer that is soluble in the solvent (SB) that is the medium of the slurry composition. Polymer (B) is a solvent The polymer binder is not limited as long as it does not contain a component insoluble in (SB). However, a polymer binder that increases the viscosity of the slurry so that a mixed layer is easily formed by applying the slurry composition to a current collector is preferable.

In the production of the polymer (B), a monofunctional ethylenically unsaturated monomer and / or a conjugated diene are used, and specific examples thereof include those exemplified as those used in the production of the polymer (A). . These monomers can be used alone or in combination of two or more.

Examples of the above polymer (B) include acrylonitrile butadiene copolymer and its hydride, ethylene / methyl acrylate copolymer, styrene / butadiene copolymer, butadiene rubber, ethylene / vinyl alcohol copolymer, acryloyl Examples thereof include nitrile / ethylene copolymer and acrylonitrile / methyl (meth) acrylate copolymer.

The polymer (B) may be a fluorine-containing polymer. The fluorine-containing polymer is a polymer containing 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more of fluorine-containing monofunctional ethylenic monomer units. Examples of the fluorine-containing monomer include vinylidene fluoride, tetrafluroethylene, hexafluene propylene, vinyl trifluoride, vinyl fluoride, and perfluoroalkyl vinyl ether. Is preferred. When a fluorine-containing monomer other than vinylidene fluoride is used, the amount of vinylidene fluoride is preferably 30 mol% or less, more preferably 20 mol% or less of the total fluorine-containing monomer. Used in conjunction with.

The fluorine-containing polymer may have a fluorine-free monomer unit of 50 mol% or less, preferably 30 mol% or less, more preferably 20 mol% or less. If the content of the non-fluorine-containing monomer unit is too large, the solvent resistance to the electrolytic solution is reduced, and the active material may easily fall off the electrode.

Monomers that can be copolymerized with the fluorine-containing monofunctional ethylenic monomer include ethylene, propylene, 1-butene and other olefins; methyl (meth) acrylate, methyl (meth) acrylate, and (meth) acryl. (Methyl) acrylates such as 2-ethylhexyl acid; styrene, α-methylstyrene, ρ-t-butyls Aromatic vinyl compounds such as ethylene; unsaturated methyl compounds such as (meth) acrylonitrile; (meth) acrylamide, (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, etc. Monofunctional ethylenically unsaturated monomers containing no fluorine, such as acrylamide compounds; In the present invention, the polymer (B) may be a mixture of polymers (B) having different compositions. The solvent (SB) solution of the polymer (B) may contain a small amount of a polymer insoluble in the solvent (SB) as long as the effect of the present invention is not impaired.

The method for producing the polymer (B) is not particularly limited. For example, it can be obtained by a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, and a solution polymerization method. The total amount of the polymer binder obtained by combining the polymer (A) and the polymer (B) is preferably from 0.1 to 5 parts by weight, more preferably from 0.2 to 3 parts by weight, especially from 100 parts by weight of the active material. Preferably it is 0.5 to 2 parts by weight. If the total amount of the binder is too small, the active material may fall off the electrode, and if the total amount is too large, the active material may be covered by the binder and the battery reaction may be inhibited.

The weight ratio of the polymer (A) to the polymer (B) is preferably 5/1 to 1 Z5, more preferably 31 to 13, and particularly preferably 2 / "! To 12. Polymer (A) If the ratio is too large, the binding property is improved, but the fluidity of the slurry composition is reduced, and the mixed layer obtained by coating the electrode may not be smooth. If the ratio is too small, the binder may obscure the surface of the active material and hinder the battery reaction.

The electrode active material used in the present invention varies depending on the type of the secondary battery.

In the case of a lithium ion secondary battery, any of a negative electrode active material and a positive electrode active material may be used as long as they are used for manufacturing a normal lithium ion secondary battery electrode.

Examples of the negative electrode active material of a lithium ion secondary battery include amorphous carbon, Daraphite, natural graphite, mesocarbon microbeads (MCM B), carbonaceous materials such as pitch-based carbon fibers, and conductive polymers such as polyacene. Is done.

As the positive electrode active _{material, L i C o 0 2,} L i N i 0 2, L i M n 0 2, L in 2 lithium-containing composite metal oxides such as _{_{o 4; τ is 2, τ}} is 3, amorphous M os ₃ of any transition metal _{_{_{sulfide; C u 2 V 2 0 3}}} , amorphous V _₂ 0- P ₂ 0 _{_{_{5, M o0 3, V 2}}} 0 5, ν 6 ο, transition metal oxides such as _3; and the like. Furthermore, polyacetylene, poly

Organic compounds such as a conductive polymer such as P-phenylene can also be used. In the case of a nickel-metal hydride secondary battery, both the negative electrode active material and the positive electrode active material can be used as long as they are used in a normal nickel-metal hydride secondary battery. The negative electrode active material is a hydrogen storage alloy. Can be used. In addition, as the positive electrode active material, nickel oxyhydroxide, nickel hydroxide, or the like can be used.

The solution of the polymer (B) in the solvent (SB) is preferably one containing a conductivity-imparting agent. Carbon is used as a conductivity-imparting agent in a lithium ion secondary battery. Examples of the conductivity imparting agent used in the nickel-hydrogen secondary battery include cobalt oxide for the positive electrode, nickel powder, cobalt oxide, titanium oxide, and carbon for the negative electrode.

In both of the above batteries, examples of the carbon as the conductivity-imparting agent include acetylene black, furnace black, graphite, carbon fiber, activated carbon, and fullerenes. Among them, acetylene black and furnace black are preferred. The amount of the conductivity-imparting agent to be used is generally about 20 to 20 parts by weight, preferably about 2 to 10 parts by weight, per 100 parts by weight of the active material.

Next, the manufacturing process of the slurry composition will be described. In the present invention, a solvent (SA) dispersion of a polymer (A) containing 50% by weight or more of an insoluble content in the solvent (SA) is kneaded with an electrode active material to prepare a mixed solution. It is important to separately prepare a solvent (SB) solution of the polymer (B) and then knead the two solutions. On the other hand, if the procedure of mixing the polymer (A) and the polymer (B) first, or the procedure of mixing the active material and the polymer (B) first, the change with time of the viscosity becomes large. Or the binding property may be reduced.

The amount of the solvent (SA) for preparing a mixed solution of the polymer (A) and the active material varies depending on the type of the active material, and is preferably 80 to the “liquid absorption amount” at which the active material can be adsorbed. To 120% by weight, more preferably 85 to 110% by weight, and particularly preferably 90 to 1% by weight. It is an amount to be 00% by weight. If the amount of the solvent in the mixed solution is less than 80% by weight of the absorbed amount of the active material, the active material becomes powdery at the time of kneading, so that the shearing does not work and the mixing of the active material and the polymer (A) is performed. May be uneven, which may result in a slurry composition having poor fluidity. Conversely, if the amount of the solvent in the mixed solution is more than 120% by weight of the absorbed amount of the active material, the viscosity of the mixed solution is low and the shearing does not work. As a result, the slurry composition having poor fluidity is obtained. There is a possibility of becoming a thing.

The liquid absorption of the active material can be measured by the following method according to ASTM D281. That is, while spinning 20 g of the active material collected in a petri dish with a spatula, add 0.5 ml of the solvent dropwise at a time, and determine the amount of the solvent in which the powder of the active material is collected into a hard cake. Convert to the weight of This measurement is performed three times, and the average value is taken as the liquid absorption.

In the method of the present invention, a mixer and a kneading time for dispersing the polymer (A) in the solvent (S A) and for dissolving the polymer (B) in the solvent (S B) are not particularly limited. As a mixer for performing these, for example, a mixing tank with a stirrer, a planetary mixer, and a repump blender are used.

As a method for dispersing the polymer (A), when the solvent (SA) is a non-aqueous solvent, the polymer (A) particles are dispersed in water by an ordinary method because of the high production efficiency and the like. It is preferable to prepare one aqueous dispersion and then replace the water in the aqueous dispersion of the polymer with a non-aqueous solvent. Examples of the substitution method include a method in which a non-aqueous solvent is added to an aqueous dispersion of the polymer (A), and then water in the dispersion medium is removed by, for example, a distillation method or a dispersion medium phase conversion method.

When using the conductivity-imparting agent, it is preferable to disperse the conductivity-imparting agent in the solution of the polymer (B) in advance and use the mixture as a mixture.

When preparing a mixed solution prepared by adding a conductivity-imparting agent to a solvent (SB) solution of the polymer (B), the solid content of the mixed solution is 30 to 40% by weight, particularly 33 to 38% by weight. It is preferable to adjust the amount of the solvent (SB) as described above and knead the mixture. Here, the solid content concentration is a ratio of the total amount of the polymer (B) and the conductivity-imparting agent to the total amount of the mixed solution. When the solid content is in this range, it becomes easy to mix the conductivity-imparting agent uniformly. In the production method of the present invention, a slurry composition is prepared by kneading a mixture obtained by kneading the dispersion of the polymer (A) and the active material prepared as described above, and a solution of the polymer (B). To manufacture. At the time of kneading, a solvent (SA) or (SB) may be added so as to have a viscosity suitable for coating, depending on the types of the binder, the electrode active material, and the conductivity imparting agent.

The optimum viscosity of the slurry composition depends on the type of coating machine applied to the current collector and the shape of the coating line, but at a temperature of 23 ° C, the rotor number is 4 using a Brookfie Id L-type viscometer. The viscosity after rotation for 1 minute at a rotation speed of 30 rpm is usually 1500 to 8000 mPas, preferably 2000 to 6000 mPas. If the viscosity of the slurry composition is excessively low, sedimentation of the slurry may occur over time, or liquid dripping may occur during coating. Conversely, if the viscosity is excessively high, the thickness of the coating film may be mixed. There is a possibility that the smoothness of the layer surface is reduced.

When kneading a mixed solution obtained by kneading a dispersion of the polymer (A) and the active material and a solution of the polymer (B), and kneading a dispersion of the solvent (SA) of the polymer (A) and the active material The mixer and the kneading time for preparing the mixed solution by mixing and for dispersing the conductivity-imparting agent in the solution of the polymer (B) in the solvent (SB) are not particularly limited. It is preferable to uniformly mix the particles of the substance or the conductivity-imparting agent and the polymer of the binder.

Examples of the high shear mixer include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Among them, a planetary mixer is preferable.

Mixing conditions in a high shear mixer are not particularly limited, but the mixing temperature is usually 15 to 50 ° C, and the mixing time is usually 60 to 180 minutes. The degree of dispersion can be measured by a grain gauge, but it is preferable to mix and disperse such that at least aggregates larger than 100 m are eliminated.

The slurry composition obtained by the method of the present invention provides a secondary battery electrode mixed layer having little change over time in viscosity, good binding properties, a smooth surface and a uniform thickness. The secondary battery electrode can be manufactured by a method in which the slurry composition for a secondary battery electrode obtained by the method of the present invention is applied to a current collector and dried. That is, the secondary battery The electrode is formed by binding a mixed layer containing a binder, an active material, and a conductive additive, a thickener, and the like added as needed to a current collector.

The secondary battery electrode obtained by the above method can be used for both a positive electrode and a negative electrode, but is preferably used for a positive electrode, and particularly preferably for a positive electrode of a lithium ion secondary battery.

The current collector is not particularly limited as long as it is made of a conductive material. Lithium secondary batteries are made of metal such as iron, copper, aluminum, nickel, and stainless steel.In particular, when aluminum is used for the positive electrode and copper is used for the negative electrode, the lithium secondary battery is manufactured by the method of the present invention. The effect of the slurry composition appears best. Examples of the nickel-metal hydride secondary battery include punched metal, expanded metal, wire mesh, foamed metal, reticulated metal fiber sintered body, and metal plating resin plate.

Although the shape of the current collector is not particularly limited, it is usually a sheet having a thickness of about 0.001 to 0.5 mm.

The method for applying the slurry composition to the current collector is not particularly limited. For example, methods such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and an eight-coating method can be used. The amount of the slurry composition to be applied is also not particularly limited, but the thickness of the dried mixed layer formed of the active material, the binder, and the like formed after drying and removing the liquid medium is usually 0.005 to 5 mm, preferably between 0.0 ° and 2 mm.

The method of drying the slurry composition applied to the current collector is not particularly limited. Examples of the method include drying with hot air, hot air, low-humidity air, vacuum drying, and irradiation with (far) infrared rays or electron beams. As an example.

Further, the density of the active material of the electrode may be increased by pressing the dried electrode by a method such as a roll press.

The secondary battery can be manufactured by using components such as the secondary battery electrode, the electrolyte solution, and the separator obtained by the above-described method, and manufacturing the secondary battery according to a conventional method. For example, a negative electrode and a positive electrode are overlapped with each other via a separator, rolled or folded according to the shape of the battery, placed in a battery container, filled with an electrolyte, and sealed. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like. The electrolyte may be in a liquid or gel form as long as it is used for a normal secondary battery, and an electrolyte that exhibits a function as a battery may be selected according to the type of the negative electrode active material and the positive electrode active material. .

As the electrolyte, a lithium ion secondary battery, also known lithium salt is any conventionally _{available, L i CI 0 4, L} i BF 4, L i PF have L i CF ₃ C0 _2, etc. can be mentioned.

The solvent in which this electrolyte is dissolved is not particularly limited. Specific examples include: carbonates such as ethylene carbonate, ethyl methyl carbonate, and propylene carbonate; lactones such as r-butyrolactone; 1,2-dimethoxetane, getyl ether, tetrahydrofuran, Ethers such as 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; and the like, and these can be used alone or as a mixed solvent of two or more kinds. In the nickel-metal hydride secondary battery, for example, a conventionally known aqueous solution of lithium hydroxide having a concentration of 5 mol / liter or more can be used.

Example

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto. The “parts” and “% J” described below are based on weight unless otherwise specified. The operations and tests in Examples and Comparative Examples were performed by the following methods.

(Characteristics of slurry component and slurry composition)

(1) Glass transition temperature (T g)

The Tg of the polymer was measured by a differential scanning calorimeter (DSC) at a heating rate of 1 o ° cz.

(2) N-methylpyrrolidone (NMP) insoluble content

The amount of polymer insoluble in NMP was determined by immersing 0.2 g of polymer in 20 ml of NMP at 60 ° C for 72 hours, filtering through an 80-mesh sieve, and drying the components on the sieve. Expressed as a percentage of the previous weight.

(3) Average particle size

The average particle diameter of the polymer is determined as the number average particle diameter calculated by measuring the diameter of 100 randomly selected polymer particles in a transmission electron micrograph and calculating the average value. Was. The unit is (m).

(4) Polymer composition

The content of each repeating unit constituting the polymer was determined by ¹ H— and ¹³ C—NMR measurements. The unit is (mol%).

(5) Liquid absorption of active material

While spinning 20 g of the active material collected in a Petri dish with a spatula, NMP was added dropwise in 0.5 ml increments, and the amount of NMP in which the powder of the active material was formed into a hard cake was measured, and the amount of NMP per 100 g of the active material was measured. Convert to weight. The average value of three measurements is taken as the liquid absorption.

(6) Slurry composition viscosity, slurry viscosity maintenance rate

The viscosity of the slurry composition was measured at 23 ° C after the preparation of the slurry composition, and after 1 hour and 24 hours, measured with a Br 0 kfie Id L-type viscometer at a temperature of 23 ° C. The measurement was performed after rotation for 1 minute at data number 4, rotation speed 30 rpm. The unit is (m P a ■ s). Also, the percentage of the viscosity value at 24 hours to the viscosity value at 1 hour was defined as slurry-one-viscosity maintenance rate (%).

[Characteristics of secondary battery electrode]

(7) Preparation of positive electrode for lithium ion secondary battery

The slurry composition for a lithium secondary battery positive electrode prepared in Examples and Comparative Examples was uniformly applied to aluminum foil (20 m thick) by a doctor blade method, and dried at a temperature of 120 ° C by a dryer. For 15 minutes. After further dried under reduced pressure for 2 hours at 0. 6 k P a, 1 20 ° C using a vacuum dryer, lithium and compressed so that the electrode density by roll press biaxial becomes 3. 2 GZC m ³ ions A secondary battery positive electrode was obtained.

(8) Arithmetic mean roughness (Ra)

The arithmetic average roughness (R a) of 20 μm square on the surface of the electrode mixed layer was observed with an atomic force microscope based on JIS B 0601.

(9) Peel strength

From the positive electrode of the lithium ion secondary battery obtained by the method described in (7) above, a rectangle having a length of 100 mm and a width of 25 mm is cut out so that the application direction is the long side, and is used as a test piece. After attaching cellophane tape to the entire mixed layer of the test piece, peel off the cellophane tape end of one end of the test piece and the current collector foil end in a vertical direction at a pulling speed of 50 mm / min. Measure the stress (NZcm) at the time of contact. The larger the stress, the higher the peel strength of the mixed layer.

[Characteristics of secondary battery]

(10) Manufacture of lithium ion secondary batteries

Metallic lithium was used as the negative electrode. The aluminum positive electrode and the lithium metal negative electrode obtained by the method described in (7) above were cut into a circular shape having a diameter of 15 mm, and a circular polypropylene porous film having a diameter of 18 mm and a thickness of 25 Aim was formed on the electrode layer side of the positive electrode. The lithium metal of the negative electrode is laminated in order, placed so that the aluminum foil of the positive electrode is in contact with the bottom of the outer container, expanded metal is placed on the negative electrode, and polypropylene packing is installed. It was housed in a stainless steel coin-shaped outer container (diameter 2 Omm, height 1.8 mm, stainless steel thickness 0.25 mm). The following electrolyte solution was injected into this container so that no air remained, and a 0.2 mm-thick stainless steel cap was placed over the outer container via polypropylene packing, and the battery can was sealed. A coin-type battery with a diameter of 20 mm and a thickness of about 2 mm was manufactured. Electrolytic solution was used a solution of ethylene carbonate Natick Bok / E chill methyl carbonate Natick Bok = 33/67 (volume ratio at 20 ° C) L i PF _s at a concentration of 1 mole / liter.

(1 1) Battery capacity

The battery capacity was measured at a charge / discharge rate of 0.1 C at 25 ° C, charged to 0.2 V by the constant current method (current density: 0.5 m AZg—active material), and charged to 3 V. Repeat charging and discharging 5 times each, and measure the battery capacity each time. The average value of the battery capacity measured repeatedly is used as the evaluation result. The unit is [mA hZg: per active material (hereinafter, the same applies to battery capacity)].

(1 2) Rate characteristics

Charge / discharge was performed by the constant current method in the same manner as in the measurement of the battery capacity, except that the measurement conditions were changed to a constant current of 1 C, and the discharge capacity at the third cycle (unit: mA hZg) was measured. The ratio of the discharge capacity at 1 C to the discharge capacity at 0.1 C in the third cycle was calculated as a percentage. The larger the value, the faster the charge / discharge is possible.

Table 1 shows the composition (unit: mol%) of each polymer used as a binder in Examples and Comparative Examples. Polymers A—1, 2 and B—1—3 are all milk It was produced by a chemical polymerization method. Commercially available polyvinylidene fluoride was used. Table 1

Note * 1: Polymer B-1 was obtained by hydrogenating the repeating unit derived from butadiene in an acrylonitrile / butadiene copolymer. Example 1

0.4 parts of polymer A- 1 to NM P 1 5. dispersion and lithium cobalt oxide dispersed in 6 parts (L i C o 0 _2, the active material (is, liquid absorption amount 1 5. 6 g) 1 The mixture (100 parts) was kneaded with a planetary mixer having two pairs of spiral hook type stirring blades for 60 minutes to prepare a mixture a.The solid content concentration of the mixture a was 86.6%. Acetylene black, a conductivity-imparting agent, in a solution prepared by dissolving 0.2 part of polymer B-1 and 0.2 part of polymer B-3 in 3 parts of NMP (Denka Black granules, manufactured by Denki Kagaku Kogyo KK) 3 parts were added and kneaded with a planetary mixer of the same type as above at a solid content concentration of 35.1%, and 1.8 parts of NMP was added to prepare a mixed solution b having a solid content concentration of 29.6%. The mixed liquid a was added to the mixed liquid a using the planetary mixer, and kneaded for 30 minutes to obtain a slurry composition for a positive electrode of a lithium ion secondary battery. The solids concentration of one composition was 81.4%. The slurry viscosity was 2200 mPa ■ s at the first hour, 2270 mPa as at the 24th hour, and the slurry-viscosity change rate was 103%.

Table 2 shows the results of testing the characteristics of the secondary battery electrode and the secondary battery manufactured using the slurry composition after 24 hours.

Examples 2 to 6

A slurry composition was prepared in the same manner as in Example 1 with the components and amounts shown in Table 2. Of the NMP amounts indicated in the preparation of mixed solution b, 6.3 parts were used for dissolving polymer (B), and the remaining amount was added after mixing the conductivity-imparting agent. However, in Example 3, all the indicated amounts were used for dissolving the polymer (B). The characteristics of the slurry composition and the secondary battery electrode and the secondary battery produced using the slurry composition were tested. Table 2 shows the test results.

1

18

Table 2

* 1 i C o 0 _2, liquid-absorbing amount of 1 5. 6 g

11 ■ i C o 0 _2, the liquid-absorbent amount of 1 3 · 1 g

111. I C o O _2, liquid absorption amount 1 7 · 9 g * 2 PVDF: polyvinylidene fluoride

(# 1100, manufactured by Kureha Chemical Co., Ltd., NMP insoluble content less than 0.1%) As shown in Table 2, it is possible to use a polymer that is hardly soluble in a solvent with respect to three types of active materials with different liquid absorptions. The slurry composition produced according to the method of the present invention using both the soluble polymer and the binder exhibited a low and stable viscosity (small change with time) both 1 hour and 24 hours after production. The electrode mixed layer produced by applying the slurry composition had a smooth surface, a sufficiently high peel strength, and good binding properties. In addition, lithium ion secondary batteries using these batteries had high capacity and high rate characteristics (Examples 1 to 6). Comparative Example 1

23. Dissolve 0.2 part of polymer B-Ί and 0.2 part of polymer B-3 in 7 parts of NMP, disperse 0.4 part of polymer A-1 and further disperse acetylene black 3 parts and 100 parts of the active material (i) were added, and the mixture was kneaded with a planetary mixer having two pairs of spiral hook-type stirring blades for 90 minutes to obtain a lithium secondary battery positive electrode slurry composition. . The solid content of the slurry composition was 81.4%. The slurry viscosity was 3400 mPa · s at the first hour and 20Ί0 mPa-s at the 24th hour, and the slurry viscosity change rate was 15%.

Table 3 shows the results of testing the characteristics of the secondary battery electrode and the secondary battery produced using the slurry composition after the elapse of 24 hours.

Comparative Example 2

1. Dissolve 0.2 part of polymer B-1 and 0.2 part of polymer B-3 in 6.9 parts of NMP, and then add and disperse 0.4 part of polymer A-1. The liquid, 3 parts of acetylene black and 100 parts of the active material (i) are kneaded for 60 minutes with a planetary mixer having two pairs of spiral hook-type stirring blades, 6.8 parts of NMP are added, and the mixture is further kneaded for 30 minutes Thus, a slurry composition for a lithium ion secondary battery positive electrode was obtained. The solid concentration of the slurry composition was 81.4%. The slurry viscosity was 1800 mPa · s at the first hour, and 2120 mPa · s at the 24th hour, and the slurry-viscosity change rate was 17%. Table 3 shows the results of testing the characteristics of the secondary battery electrode and the secondary battery produced using the slurry composition after the elapse of 24 hours.

Comparative Example 3

NM P 16.1 Dissolve 0.1 part of polymer B-1 and 0.1 part of polymer B-3 in 6.1 parts, and add this solution, 3 parts of acetylene black and 100 parts of active material (i). Kneading with a planetary mixer having two pairs of spiral hook type stirring blades for 30 minutes, dissolving 0.1 part of polymer B-1 and 0.1 part of polymer B-3 in 3 parts of NMP The undulated solution was added and kneaded for another 30 minutes. Here, a dispersion liquid in which 0.4 part of polymer A-1 was dispersed in 4.6 parts of NMP was added and kneaded for 30 minutes to obtain a slurry composition for a positive electrode of a lithium ion secondary battery. The solid content concentration of the slurry composition was 81.4%. The slurry viscosity was 8400 mPa ■ s at the first hour and 2050 mPa as at the 24th hour, and the slurry-viscosity change rate was 11%. Table 3 shows the results of testing the characteristics of the secondary battery electrode and the secondary battery produced using the slurry composition after 24 hours.

Comparative Example 4

NM P 1 Dissolve 0.2 part of polymer B-1 and 0.2 part of polymer B-3 in 5.8 parts, and mix this solution with 100 parts of active material (i) in two pairs of spirals The mixture was kneaded for 60 minutes with a planetary mixer having hook-type stirring blades to prepare a mixed solution c. The solid content concentration of the mixed solution c was 86.4%. Separately, add 3 parts of acetylene black to a dispersion of 0.4 parts of Polymer A-1 dispersed in 7.9 parts of NMP, and disperse with a planetary mixer to mix at a solids concentration of 30.0%. Liquid d was prepared. The mixed solution d was added to the mixed solution c using the above-mentioned brine mixer, and the mixture was further kneaded for 30 minutes to obtain a slurry composition for a positive electrode of a lithium ion secondary battery. The solid concentration of the slurry composition was 8.4%. The slurry viscosity was 8950 mPa · s at the first hour and 1980 mPa · s at the 24th hour, and the slurry viscosity change rate was 22%. Table 3 shows the results of testing the characteristics of the secondary battery electrode and the secondary battery produced using the slurry composition after 24 hours. Table 3

As shown in Table 3, even when the same components were used in the same amounts as in the above invention examples (Examples 1 to 6), any of the slurry compositions produced by a procedure different from that of the present invention exhibited defects. That is, it is obtained by a method in which all components other than the solvent are sequentially added to the entire amount of the solvent and kneaded, or a method in which the remaining components are added to the remaining amount of the solvent by sequentially adding and kneading about 70% of the solvent. The resulting slurry composition has a high initial value of viscosity and then drops rapidly and is not stable, and the electrode mixture layer has a rough surface and a remarkably low peel strength. Both capacity and rate characteristics were low (Comparative Examples 1 and 2).

The slurry composition prepared by a method of adding a liquid in which the polymer (A) is dispersed to a liquid mixture in which the polymer (B), the conductivity-imparting agent, and the active material are mixed first has an initial viscosity value. It was as high as 8 to 9 times and decreased sharply with time. The electrode and the secondary battery obtained using this slurry composition exhibited the same defects as Comparative Examples 1 and 2 (Comparative Example 3).

Furthermore, a separately prepared solution in which the polymer (A) and the conductivity-imparting agent are dispersed is added to a mixed solution in which the active material is dispersed by dissolving the polymer (B), and the mixture is kneaded. When the reverse blending procedure is adopted, the viscosity of the slurry composition shows an initial value about four times as large as that of the present invention, and then drops significantly, and the electrodes and the secondary batteries have the same disadvantages as Comparative Examples 1 to 3. (Comparative Example 4). Industrial applicability

The slurry composition obtained by the method of the present invention has little change in viscosity over time and good binding properties. When this composition is applied to a current collector and dried, the mixture has a smooth surface and a uniform thickness. A secondary battery electrode having a layer is formed.

The above-mentioned secondary battery electrode can be used for both the positive electrode and the negative electrode, but is preferably used for the positive electrode, and is particularly preferably used for the positive electrode of the lithium ion secondary battery.

Claims

The scope of the claims

1. A solvent (SA) dispersion of a polymer (A) containing 50% by weight or more of an insoluble content in a solvent (SA) is kneaded with an electrode active material, and then the obtained kneaded liquid is mixed with a polymer (A). A method for producing a slurry composition for a secondary battery electrode, which comprises kneading a solvent (B) solution of B).

2. The method for producing a slurry composition according to claim 1, wherein an insoluble content of the polymer (A) in the solvent (S A) is 50% by weight or more and 90% by weight or less.

3. The method for producing a slurry composition according to claim 1, wherein an insoluble content of the polymer (A) in the solvent (S A) is 50% by weight or more and 87% by weight or less.

4. The polymer according to claims 1 to 3, wherein the polymer (A) is a crosslinked copolymer of at least one monomer selected from a monofunctional ethylenically unsaturated monomer and a conjugated diene and a polyfunctional ethylenically unsaturated monomer. The method for producing a slurry composition according to any one of the above.

5. The method for producing a slurry composition according to any one of claims 1 to 4, wherein the glass transition temperature (T g) of the polymer (A) is in the range of −80 ° C. to 0 ° C.

6. The method for producing a slurry composition according to any one of claims 1 to 5, wherein the average particle size of the polymer (A) is in the range of 0.05 xm to 1 and Ο Ο Ι.

7. The slurry composition according to any one of claims 1 to 6, wherein the polymer (Β) is a polymer of at least one monomer selected from a monofunctional ethylenically unsaturated monomer and a conjugated diene. Manufacturing method.

8. The production of the slurry composition according to any one of claims 1 to 7, wherein the polymer (Β) contains a fluorine-containing polymer containing 50 mol% or more of one unit of a fluorine-containing monofunctional ethylenic monomer. Method.

9. The method according to any one of claims 1 to 8, wherein the total amount of the polymer (Α) and the polymer (Β) is in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the active material. A method for producing the slurry composition according to the above.

10. The slurry composition according to any one of claims 1 to 9, wherein the weight ratio of the polymer (Α) to the polymer (ポリマー) [(A) / (Β)] is in the range of 51-1/5. Made of Construction method.

11. The solvent according to claim 1, wherein the solvent (SA) and the solvent (SB) are selected from water and a non-aqueous solvent having a boiling point of 80 ° C. to 350 ° C. under atmospheric pressure. 0. The method for producing a slurry composition according to any one of [0].

1 2. The method for producing a slurry composition according to any one of claims 1 to 11, wherein the solvent (S A) and the solvent (S B) have the same composition.

1 3. The method for producing a slurry composition according to any one of claims 1 to 12, wherein the solvent (SB) solution of the polymer (B) further contains a conductivity-imparting agent.

1 4. The solvent (SB) solution of the polymer (B) containing the conductivity-imparting agent is obtained by kneading at a solids concentration of 30 to 40% by weight. A method for producing a slurry composition according to the above item.

1 5. The method for producing a slurry composition according to claim 13 or 14, wherein the amount of the conductivity-imparting agent is 1 to 20 parts by weight per 100 parts by weight of the active material.

1 6. The amount of the solvent (SA) in the kneading of the solvent (SA) dispersion of the polymer (A) and the electrode active material is 80 to 120% by weight of the absorbed amount of the electrode active material. 16. The method for producing a slurry composition according to any one of ranges 1 to 15.

1 7. A slurry composition for a secondary battery electrode produced by the production method according to any one of claims 1 to 16.

1 8. A method for producing a secondary battery electrode, comprising applying the slurry composition according to claim 17 to a current collector and drying.

19. The method for producing a secondary battery electrode according to claim 18, wherein a mixed layer derived from the slurry composition and having a thickness of 0.005 mm to 5 mm is formed on the current collector.