CN1290211C - Method for preparing slurry composition for electrode of secondary cell - Google Patents

Abstract

Mixing the solvent ( _SA ) dispersion of the polymer (A) containing 50% by weight or more of the insoluble component of the solvent ( _SA ) and the electrode active material, and then mixing the resulting mixed solution with the polymer (B ) of the solvent (S _B ) solution is kneaded, thereby constituting the preparation method of the slurry composition for secondary battery electrodes. The slurry composition obtained by this method has little change in viscosity with time and good adhesiveness. After the composition is applied to a current collector and dried, a secondary battery electrode having a mixed layer with a smooth surface and a uniform thickness can be formed.

Description

Preparation method of slurry composition for secondary battery electrode

technical field

The invention relates to a preparation method of a slurry composition for secondary battery electrodes. More specifically, it relates to a method for producing a slurry composition for secondary battery electrodes, which has little change in viscosity over time, and which can be applied to a current collector to obtain an electrode with a smooth coating film surface.

Background technique

Mobile terminal devices such as notebook computers, mobile phones, and PDAs are widely used, and most of their power sources are lithium-ion secondary batteries. Recently, higher demands have been placed on mobile terminal devices, such as extending the operating time and shortening the charging time. Along with this, there is also a strong demand for higher performance of batteries, especially increased capacity and improved charging speed (speed characteristics).

A lithium ion secondary battery is provided with a separator interposed between a positive electrode and a negative electrode, and has a structure contained in a container together with an electrolytic solution. The positive electrode and the negative electrode (the two are collectively referred to as "secondary battery electrodes" and can be referred to as "electrodes" for short) are electrode active materials (hereinafter referred to as "active materials") and conductivity-imparting agents used when necessary, etc., through two The secondary battery electrode is formed by adhering a binder polymer (hereinafter simply referred to as "binder") to a current collector such as aluminum or copper. Usually, the binder is dissolved or dispersed in a liquid medium, and mixed with an active material, a conductivity-imparting agent, etc. to obtain a slurry composition for secondary battery electrodes (hereinafter referred to as "slurry composition"), and then This is applied to the current collector, and the liquid medium is removed by drying or the like, and the mixed layer is adhered to form an electrode.

However, since the dispersion of each component in the slurry composition is insufficient, the viscosity of the slurry composition changes with time, and there is a problem that the dispersion state of the slurry composition is not uniform enough. If an uneven slurry composition is used to make an electrode, it will lead to problems such as poor battery performance due to uneven electrode surface, and peeling of the active material from the current collector due to a decrease in the adhesion of the active material.

As a method of obtaining a highly dispersed slurry composition, JP-A-8-195201 discloses adding an active material and a conductivity-imparting agent to a mixed solution of a binder dispersed in a tackifier solution and performing mixing and dispersing methods. However, due to insufficient dispersion of the conductivity-imparting agent in this preparation method, there are still problems such as insufficient smoothness of the electrode surface.

In addition, as a slurry composition preparation method, JP-A-9-204917 discloses a step of kneading various components, a thickening step of leaving the kneaded slurry composition for a certain period of time, and a thickening step. The subsequent mixing step of the slurry composition. However, the process of this method is cumbersome, and there are also problems such as the preparation of the slurry composition takes too long, and the production efficiency is low.

In Japanese Patent Application Laid-Open No. 2000-348713, it is disclosed that the tackifier is divided into two or more times and added to the active material and the conductivity-imparting agent for kneading, and then the binder is added for mixing, and water is used as the medium. The preparation method of feed composition. However, this method also has the problem of insufficient adhesive dispersion due to different types of adhesives, resulting in excessive changes in viscosity over time and low adhesiveness.

Contents of the invention

Based on the above-mentioned circumstances, an object of the present invention is to provide a method for preparing a slurry composition for secondary battery electrodes capable of obtaining an electrode having a mixed layer having a smooth surface with little change in viscosity over time and good adhesion.

The present inventors, on the basis of in-depth studies on the method of preparing a highly dispersed slurry composition of the active material and the conductivity-imparting agent, found that the dispersion liquid in which the polymer binder that is hardly soluble in the solvent is dispersed and the active material are mixed. kneading, followed by mixing the solution of dissolving the soluble polymer binder in the solvent into the kneading liquid, a highly dispersed slurry composition can be obtained, and when the slurry composition is used to manufacture electrodes, it can be obtained with Electrodes with a smooth mixed layer without clots. On the basis of the above cognition, further in-depth research, complete the present invention.

The invention provides a preparation method of a slurry composition for secondary battery electrodes, the method comprising adding a solvent (S) of a polymer ( _A ) containing 50% by weight or more of a solvent (SA) insoluble _A ) The dispersion liquid is kneaded with the electrode active material, and then the obtained kneaded liquid is kneaded with the solvent (S B ) solution of the polymer ( _B ).

In addition, the present invention also provides a method for manufacturing a secondary battery electrode, the method comprising coating the slurry composition prepared by the above method on a collector and drying.

Detailed ways

The preparation method of the slurry composition for secondary battery electrodes of the present invention comprises: the solvent ( _SA ) dispersion liquid of polymer (A) containing solvent ( _SA ) insoluble component 50% by weight or more than 50% by weight and The electrode active material is kneaded, and then the obtained kneaded solution is kneaded with a polymer (B) solution in a solvent (S _B ).

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

As the solvent ( _SA ) and the solvent ( _SB ) used in the present invention, water and non-aqueous solvents having a boiling point of 80 to 350°C under atmospheric pressure are preferable. The non-aqueous solvent can be exemplified, for example, amides such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane, tetrahydronaphthalene; 2- Ethyl-1-hexanol, 1-nonanol, lauryl alcohol and other alcohols; methyl ethyl ketone, cyclohexanone, phorone, acetophenone, isophorone and other ketones; benzyl acetate, butyl Esters such as isoamyl lactate, methyl lactate, ethyl lactate, butyl lactate; o-toluidine, m-toluidine, p-toluidine and other amines; γ-butyrolactone, δ-butyrolactone and other lactones ; Dimethyl sulfoxide, sulfolane and other sulfoxides and sulfones, etc. Among them, water and amides are preferred, and N-methylpyrrolidone is particularly preferred.

These solvents (S _A ) and (S _B ) can be used singly or in combination. In addition, it is preferable that the solvent (S _A ) used for the dispersion of the polymer (A) and the solvent (S B ) used for the solution of the polymer ( _B ) have the same composition, but even if they are different from each other, as long as the polymer ( The composition of the solvent after mixing the dispersion of A) and the solution of the polymer (B) is such that the insoluble component of the polymer (A) is 50% by weight or more, and the polymer (B) is soluble. can use.

In the present invention, two polymers are used as binders. The kind of polymer A as a component of the polymer binder is not particularly limited, but a polymer containing 50% by weight or more of a solvent ( _SA ) insoluble component is used. The solvent (SA) insoluble component of the polymer ( _A ) is preferably 60% by weight or more, more preferably 70% by weight or more, and preferably 90% by weight or less, preferably 87% by weight or 87% by weight or less. It is speculated that when the solvent ( _SA ) insoluble component content is within this range, the polymer (A) remains granular or fibrous in the slurry composition, and as a result, does not cover the surface of the active material in a film and hinder the progress of the battery reaction. When the insoluble component of the solvent (S _A ) is too small, the polymer (A) will form a film, the adhesion durability of the active material will be reduced, and there will be a problem that the battery capacity will decrease when charging and discharging are repeated. On the contrary, when the polymer ( _A ) having too much solvent (SA) insoluble component is used, problems such as a reduction in adhesiveness of the adhesive may arise.

The amount of the insoluble component of the solvent ( _SA ) here is obtained by immersing 0.2 g of the polymer in 20 ml of solvent at a temperature of 60°C for 72 hours, filtering through a 80-mesh sieve, and drying the components on the sieve. It is expressed as a percentage of the weight of the material to the weight of the polymer before impregnation.

The polymer ( _A ) containing a large amount of solvent (SA) insoluble components as described above is preferably a cross-linked copolymer of a monofunctional ethylenically unsaturated monomer and/or a conjugated diene and a polyfunctional ethylenically unsaturated monomer .

As polyfunctional ethylenically unsaturated monomers, divinyl compounds such as divinylbenzene; dimethacrylates such as diethylene glycol dimethacrylate and ethylene glycol dimethacrylate; trimethylol Trimethacrylates such as propane trimethacrylate; diacrylates such as diethylene glycol diacrylate and 1,3-butanediol diacrylate; triacrylates such as trimethylolpropane triacrylate wait. In addition, non-conjugated dienes such as 1,4-hexadiene, ethylidene norbornene, and dicyclopentadiene can 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 0.3 to 5% by weight, preferably 0.5 to 3% by weight, relative to the total amount of monomers used in the preparation of the polymer.

As the monofunctional ethylenically unsaturated monomer used to prepare the polymer (A), α-olefins such as ethylene, propylene, 1-butene, isobutylene, 3-methyl-1-butene; base) unsaturated nitrile compounds such as acrylonitrile (meaning acrylonitrile or methacrylonitrile);

Methyl (meth)acrylate (represents methyl acrylate or methyl methacrylate, the same below.), ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylate base) (meth)acrylates such as 2-ethylhexyl acrylate; crotonate such as methyl crotonate, 2-ethylhexyl crotonate, hydroxypropyl crotonate, etc.; ) Methoxyethyl acrylate, ethoxyethyl (meth)acrylate and other (meth)acrylates containing alkoxy groups; dimethylaminoethyl (meth)acrylate, diethyl (meth)acrylate Acrylic esters containing amino groups such as amino ethyl esters; (meth)acrylates containing hydroxyl groups such as 2-hydroxypropyl (meth)acrylate and hydroxypropyl (meth)acrylate; (meth)acrylic acid esters such as acid groups and boric acid groups; vinyl compounds and dicarboxylic anhydride compounds containing carboxyl groups such as acrylic acid, methacrylic acid, crotonic acid, methacrylic acid, maleic acid, fumaric acid, etc.; styrene, Aromatic vinyl compounds such as α-methylstyrene, etc.

Examples of conjugated dienes include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butane ene, 1,3-pentadiene, etc. These monofunctional ethylenically unsaturated monomers and conjugated dienes may be used alone or in combination of two or more.

When using a conjugated diene, even without using a polyfunctional ethylenically unsaturated monomer, a crosslinked copolymer can be obtained by appropriately adjusting polymerization conditions such as polymerization temperature, polymerization conversion rate, and amount of a molecular weight modifier.

The glass transition temperature (T _g ) of the polymer (A) is preferably -80 to 0°C, more preferably -60 to -5°C. When the _Tg is too high, the flexibility of the electrode decreases, and the active material tends to be peeled off from the current collector during repeated charging and discharging. In addition, when T _g is too low, the battery capacity may decrease.

In order to make the _Tg of the polymer (A) fall within the above range, it is preferable to have, for example, 2-ethylhexyl acrylate (homopolymer _Tg : -85°C), n-butyl acrylate, etc., as repeating units in the molecular structure of the polymer. T _g change of ester (homopolymer T _g -54°C), n-decyl methacrylate (homopolymer T _g -65°C), 1,3-butadiene, isoprene and other homopolymers It is a monomeric repeating unit at or below 0°C.

Preferred polymers (A) include 2-ethylhexyl acrylate/methacrylic acid/acrylonitrile/diethylene glycol dimethacrylate copolymer, butyl acrylate/acrylic acid/trimethylolpropanetrimethacrylate Propylene rubber such as acrylate copolymer, acrylonitrile/butadiene copolymer rubber, etc.

Polymer (A) may also be a mixture of polymers (A) composed of different monomers. In addition, the solvent (SA) dispersion of the polymer ( _A ) may contain a small amount of a polymer having a solvent ( _SA ) insoluble component of less than 50% by weight within the range that does not affect the effect of the present invention.

The average particle diameter of the polymer (A) is preferably 0.005 to 1000 μm, more preferably 0.01 to 100 μm, particularly preferably 0.05 to 10 μm. If the average particle diameter is too large, the required amount of the binder becomes too large, and the internal resistance of the electrode increases. On the contrary, if the average particle size is too small, the surface of the active material will be covered and the battery reaction will be hindered.

The measurement of the average particle diameter here is to measure the diameters of 100 randomly selected polymer particles through a transmission electron microscope photograph, and take the arithmetic mean value as the calculated average particle diameter of each particle.

The preparation method of the polymer (A) is not particularly limited, for example, it can be obtained by polymerization using known polymerization methods such as emulsion polymerization, suspension polymerization, dispersion polymerization or solution polymerization. When the emulsion polymerization method is used, it is preferable to use this method because it is easy to control the particle diameter when dispersed in the solvent ( _SA ).

The polymer (B), which is another component of the polymer binder, is a polymer soluble in the solvent (S _B ) which is the medium of the slurry composition. For the polymer (B), there is no limitation as long as it does not contain solvent (S _B ) insoluble components. In order to make it easier to form a mixed layer after the slurry composition is coated on the collector, it is preferable to use a slurry composition that can increase Viscosity polymer binder.

When preparing the polymer (B), a monofunctional ethylenically unsaturated monomer and/or a conjugated diene can be used, and specific examples thereof include those used in the preparation of the above-mentioned polymer (A). These monomers can be used alone or in combination of multiple kinds.

Examples of the aforementioned polymer (B) include acrylonitrile/butadiene copolymers and their hydrogenated products, ethylene/methyl acrylate copolymers, styrene/butadiene copolymers, butadiene rubber, ethylene/ethylene Alcohol copolymer, acrylonitrile/ethylene copolymer, acrylonitrile/methyl methacrylate copolymer, etc.

Polymer (B) may also be a fluoropolymer. The fluorine-containing polymer is a polymer containing 50 mol% or more of fluorine-containing monofunctional ethylenic monomer units, preferably 70 mol% or more, more preferably 80 mol% or more. Examples of the fluorine-containing polymer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chloroethylene trifluoride, vinyl fluoride, perfluoroalkyl vinyl ether, etc., preferably vinylidene fluoride. When using fluorine-containing monomers other than vinylidene fluoride, vinylidene fluoride is used in combination, preferably the total amount of fluorine-containing monomers other than vinylidene fluoride is 30 mol% or less of all fluorine-containing monomers, more preferably It is 20 mol% or less.

The non-fluorine-containing monomer unit in the above-mentioned fluoropolymer is 50 mol% or less, preferably 30 mol% or less, more preferably 20 mol% or less. When the content of the non-fluorine-containing monomer unit is too high, the solvent resistance of the polymer to the electrolyte decreases, causing the problem that the active material is easy to fall off from the electrode.

As monomers that can be copolymerized with fluorine-containing monofunctional ethylenic monomers, 1-olefins such as ethylene, propylene, and 1-butene; methyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylate base) (meth)acrylic esters such as 2-ethylhexyl acrylate; aromatic vinyl compounds such as styrene, α-methylstyrene, p-tert-butylstyrene, etc.; (meth)acrylonitrile and other unsaturated Nitrile compounds; (meth)acrylamide compounds such as (meth)acrylamide, N-methylol(meth)acrylamide, N-butoxy(meth)acrylamide, etc., fluorine-free monofunctional vinyl Sexually unsaturated monomers.

The polymer (B) in the present invention may also be a mixture of polymers (B) of different compositions. In addition, the solvent (S _B ) solution of the polymer (B) may contain a small amount of a solvent (S _B ) insoluble polymer within the range that does not impair the effects of the present invention.

There is no particular limitation on the preparation method of the above-mentioned polymer (B). For example, it can be obtained by polymerization using known polymerization methods such as emulsion polymerization, suspension polymerization, dispersion polymerization, and solution polymerization.

With respect to 100 parts by weight of the active material, the total amount of the polymer binder composed of the polymer (A) and the polymer (B) is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 3 parts by weight, particularly preferably 0.5 to 2 parts by weight share. If the total amount of the binder is too small, the active material is likely to fall off from the electrode. On the contrary, if it is too much, the active material will be covered by the binder, which may hinder the battery reaction.

The weight ratio of the polymer (A) to the polymer (B) is preferably 5/1 to 1/5, more preferably 3/1 to 1/3, particularly preferably 2/1 to 1/2. When the ratio of the polymer (A) is too large, the adhesiveness will be improved but the fluidity of the slurry composition will be reduced, and the mixed layer obtained by coating on the electrode will become rough. Conversely, if the proportion of the polymer (A) is too small, the binder may cover the surface of the active material and hinder the battery reaction.

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

In the case of a lithium ion secondary battery, the same materials as those used for electrodes of general lithium ion batteries can be used for both the negative electrode active material and the positive electrode active material.

As the negative electrode active material of the lithium ion secondary battery, carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon micro gaskets (Mesoka-bon microbiosis, MCMB), pitch-based carbon fibers, polyacetylene (Polyasen) and other conductive polymers.

As the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ and other lithium-containing composite metal oxides; TiS ₂ , TiS ₃ , amorphous MoS ₃ and other transition metal sulfides; Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ and other transition metal oxides, etc. In addition, conductive polymeric organic compounds such as polyacetylene and polyparaphenylene can also be used.

For the nickel-metal hydride secondary battery, the negative electrode active material and the positive electrode active material can be the materials used in common nickel-hydrogen secondary batteries. A hydrogen storage alloy can be used as the negative electrode active material. As the positive electrode active material, basic nickel hydroxide, nickel hydroxide, and the like can be used.

The solvent (S _B ) solution of the polymer (B) preferably contains a conductivity-imparting agent. Carbon is used as a conductivity imparting agent in lithium ion secondary batteries. As the conductivity-imparting agent used in the nickel-hydrogen secondary battery, cobalt oxide can be used for the positive electrode, and nickel powder, cobalt oxide, titanium oxide, carbon, etc. can be used for the negative electrode.

In the above-mentioned two types of batteries, the carbon used as the conductivity-imparting agent includes acetylene black, furnace black, graphite, carbon fiber, activated carbon, flalens, and the like. Among them, acetylene black and furnace black are preferable.

The usage-amount of a conductivity imparting agent is 1-20 weight part normally per 100 weight part of active materials, Preferably it is 2-10 weight part.

The preparation process of the slurry composition is explained below. In the present invention, the solvent (SA) dispersion of the polymer ( _A ) containing 50% by weight or more than 50% by weight of the solvent ( _SA ) insoluble component and the electrode active material are mixed to prepare a mixed solution, and separately The order of preparing polymer (B) in solvent (S _B ) and then mixing the two liquids is very important. On the contrary, if the order of mixing the polymer (A) and the polymer (B) is adopted first, or the order of mixing the active material and the polymer (B) first, it will cause problems such as a large change in viscosity over time or a decrease in adhesion. .

In order to prepare the mixed solution of polymer (A) and active substance, the amount of solvent ( _SA ) varies with the type of active substance, and is preferably 80 to 120% by weight relative to the "liquid absorption" that the active substance may adsorb , more preferably 85 to 110% by weight, most preferably 90 to 100% by weight. When the solvent amount of the mixed solution is less than 80% by weight of the liquid absorption of the active material, the active material becomes powdery during mixing, the shearing effect is poor, and the mixing of the active material and the polymer (A) is not uniform, resulting in the prepared The resulting slurry composition has poor fluidity. Conversely, when the amount of solvent in the mixed liquid is more than 120% by weight of the liquid absorption amount of the active material, the viscosity of the mixed liquid will decrease, shearing will be ineffective, and a slurry composition with poor fluidity will also be formed.

Active substance adsorption can be determined by the following method according to ASTM D 281. That is, put 20 grams of the active substance taken in the vessel, drop 0.5 milliliters of solvent at a time while stirring with a spatula, measure the amount of solvent when the active substance powder is consolidated into a cake, and then convert it into an equivalent of 100 The amount of solvent corresponding to gram of active substance. After three determinations, the average value was taken as the liquid absorption volume.

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

In addition, as a method for dispersing the polymer (A), when the solvent ( _SA ) is a non-aqueous solvent, it is preferable to disperse the particles of the polymer (A) in water according to a usual method in view of excellent production efficiency. After the aqueous polymer dispersion is formed, the water in the aqueous polymer dispersion is replaced with a non-aqueous solvent. The replacement method is a method of removing water in the dispersion medium by, for example, distillation or phase inversion of the dispersion medium after adding a non-aqueous solvent to the aqueous dispersion of the polymer (A).

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

When preparing a mixed liquid containing a conductivity-imparting agent in a solvent (S _B ) solution of the polymer (B), it is preferable to adjust the amount of the solvent (S _B ) so that the solid content concentration of the mixed liquid is 30 to 40% by weight, particularly preferably 33% by weight. ~38% by weight and mixed. Here, the concentration of solid content refers to the ratio of the total amount of the polymer (B) and the conductivity-imparting agent to the total amount of the liquid mixture. When the solid content concentration is in the above-mentioned range, it is easy to mix the conductivity-imparting agent uniformly.

In the preparation method of the present invention, the mixed liquid obtained by kneading the dispersion liquid of the polymer (A) prepared as above and the active substance is then kneaded with the solution of the polymer (B) to make a slurry composition . During kneading, in order to obtain a viscosity suitable for coating, an additional solvent (S _A ) or (S _B ) may be added depending on the type of binder, electrode active material, and conductivity-imparting agent.

The optimum viscosity of the slurry composition varies with the type of coating machine coated on the collector and the shape of the coating line. At a temperature of 23°C, use a Brookfield L-type viscometer, No. 4 impeller, and a rotation speed of 30rpm The viscosity after rolling for 1 minute is usually 1500 to 8000 mPa·S, preferably 2000 to 6000 mPa·S. When the viscosity of the slurry composition is too low, sedimentation will occur in the slurry after a period of time, or the phenomenon of liquid hanging (liquid grey) will occur during coating. On the contrary, when the viscosity is too high, uneven coating thickness or mixing will occur. The smoothness of the layer surface is low.

When mixing the mixed solution formed by kneading the dispersion of polymer (A) and the active substance with the solution of polymer (B), and mixing the dispersion of polymer (A) with the solvent (S _A ) When kneading the active material to prepare a liquid mixture, and when dispersing the conductivity-imparting agent in the solvent (S _{B ) solution of the polymer (B} ), the mixer and kneading time are not particularly limited. Preferably, the particles of the active material or the conductivity-imparting agent and the binder polymer are uniformly kneaded together using a high-shear type mixer.

Examples of high-shear type mixers include ball mills, sand mills, pigment dispersers, attritors, ultrasonic dispersers, homogenizers, and planetary mixers, among which planetary mixers are preferred.

The mixing conditions of the high-shear mixer are not particularly specified, and the mixing temperature is usually 15-50° C., and the mixing time is usually 60-180 minutes. The degree of dispersion can be measured by a particle size meter, and it is preferred to mix and disperse until at least no aggregates larger than 100 μm exist.

The slurry composition obtained by the method of the present invention has little change in viscosity over time, good adhesion, and can obtain a secondary battery electrode mixed layer with smooth surface and uniform thickness.

A secondary battery electrode can be produced by applying the slurry composition for secondary battery electrodes obtained by the method of the present invention to a current collector and then drying it. That is, the secondary battery electrode is formed by adhering a mixed layer uniformly containing a binder, an active material, and, if necessary, a conductivity-imparting agent, a thickener, and the like on a current collector.

The secondary battery electrode obtained by the above method can be used for any one of the positive electrode and the negative electrode, preferably suitable for the positive electrode, particularly preferably suitable for the positive electrode of the lithium ion secondary battery.

The current collector is not particularly limited as long as it is composed of a conductive material. Metal products such as iron, copper, aluminum, nickel, and stainless steel are used in lithium-ion secondary batteries, especially when aluminum is used for the positive electrode and copper is used for the negative electrode, the effect of the slurry composition prepared by the method of the present invention is the most obvious. Examples of the nickel-hydrogen secondary battery include punched metal, expanded metal, metal mesh, foamed metal, mesh-shaped metal fiber sintered body, metal-coated resin plate, and the like.

The shape of the current collector is not particularly limited, and is usually a sheet-like object with a thickness of about 0.001 to 0.5 mm.

There is no particular limitation on the method of applying the slurry composition to the current collector. For example, doctor blade method (doctor-braid method), dip method (dipper method), reverse rolling method (river-roll method), same-direction rolling method (guirect method), gravure printing method ( grabia method), extrusion method (extroll-junction method), brushing method (hake coating method) and the like. There is no specific limitation on the amount of the slurry composition to be coated. It is generally formed after the liquid medium is removed by drying. The thickness of the dried mixed layer composed of active materials, binders, etc. is usually 0.005-5mm , preferably an amount of 0.01 to 2 mm.

The drying method of the slurry composition coated on the current collector is not particularly limited, for example, drying with warm air, hot air, low humidity air, vacuum drying, (far) infrared rays and electron beam irradiation drying methods can be mentioned.

In addition, the density of the electrode active material can be increased by applying pressure to the dried electrode by a method such as roll pressing.

Using the secondary battery electrodes, electrode solution, separators and other parts prepared according to the above method, the secondary battery can be manufactured according to the usual method. For example, the positive electrode and the negative electrode are overlapped through the separator, and the battery container is folded according to the shape of the battery, and the electrolyte solution is injected into the battery container and then sealed. The shape of the battery is coin-shaped, button-shaped, sheet-shaped, cylindrical, angular, flat and so on.

As the electrolytic solution, those commonly used in secondary batteries can be used, and either liquid or gel may be used. Any electrolytic solution may be selected according to the types of the negative electrode active material and the positive electrode active material and can function as a battery.

As the electrolyte, any conventionally known lithium salt can be used in the lithium ion secondary battery, such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO ₂ , etc. can be used.

The solvent for dissolving the electrolyte is not particularly limited. Specific examples include carbonates such as ethylene carbonate, ethyl methyl carbonate, and propylene carbonate; lactones such as γ-butyrolactone; 1,2-dimethoxyethane, diethyl ether, tetrahydrofuran, etc. , 2-methyltetrahydrofuran and other ethers; dimethyl sulfoxide and other sulfoxides, etc. These may be used alone or in the form of a mixture of two or more of the above solvents.

In addition, in the nickel-hydrogen secondary battery, a conventionally known potassium hydroxide aqueous solution having a concentration of 5 mol/liter or more can be used.

Example

The following examples are given to describe the present invention, but the present invention is not limited thereto.

In addition, "parts" and "%" described below are based on weight unless otherwise specified.

The operations and tests in Examples and Comparative Examples were performed by the following methods.

[Slurry Components and Properties of Slurry Composition]

(1) Glass transition temperature (T _g )

The _Tg of the polymer was measured by a differential scanning calorimeter (DSC) at a temperature increase rate of 10°C/min.

(2) Amount of N-methylpyrrolidone (NMP) insoluble components

The amount of the NMP-insoluble component of the polymer is expressed as a percentage of the weight obtained after immersing 20 g of the polymer in 20 ml of NMP at 60° C. for 72 hours, filtering with an 80 mesh sieve, and drying the components on the sieve relative to the weight before immersion.

(3) Average particle size

The average particle diameter of the polymer is that 100 polymer particles are randomly selected from the transmission micrograph and their diameters are measured, and the average value is calculated as the average particle diameter per particle, and the unit is (μm).

(4) Composition of the polymer

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

(5) Liquid absorption of active substances

Put 20g of the active substance into the vessel, add 0.5ml of NMP each time while stirring with a spatula, measure the amount of NMP added when the active substance is consolidated into a cake, and then convert it into the equivalent of 100g of active substance Solvent volume. The average value of three determinations was taken as the liquid absorption volume.

(6) Viscosity of slurry composition, slurry viscosity maintenance rate

The viscosity of the slurry composition is, the slurry composition is stored at 23°C after preparation, and after 1 hour and 24 hours, when the temperature is 23°C, use a Brookfield L-type viscometer and No. 4 impeller to rotate at a speed of 30rpm Measure the viscosity respectively after 1 minute, and the unit is (mPa·S). In addition, the percentage of the viscosity value after 24 hours and the viscosity value after 1 hour was used as the viscosity maintenance rate of a slurry.

[Characteristics of secondary battery electrodes]

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

The slurry composition for positive electrodes of lithium ion secondary batteries prepared in Examples and Comparative Examples was evenly coated on aluminum foil (thickness 20 μm) with a doctor blade method, and dried at a temperature of 120° C. for 15 minutes with a drier. After drying under reduced pressure in a vacuum dryer at 0.6 kPa and 120° C. for 2 hours, it was compressed with a biaxial roller press until the electrode density reached 3.2 g/cm ³ , and the positive electrode of the lithium ion secondary battery was obtained.

(8) Arithmetic mean roughness (Ra)

Based on JIS B0601, the arithmetic mean roughness (Ra) of the 20 μm square range on the surface of the electrode mixed layer was observed with an atomic force microscope.

(9) Peel strength

From the positive electrode of the lithium ion secondary battery obtained by the method described in the above (7), cut out a test piece with a length of 100 mm and a width of 25 mm and a test piece whose coating direction is the long side. After pasting the cellophane tape on the entire surface of the mixed layer of the test piece, the end of the cellophane tape at one end of the test piece and the end of the current collector foil are torn and peeled off at a tearing speed of 50 mm/min in the vertical direction. The stress (N/cm). The greater the stress, the greater the peel strength of the mixed layer can be judged.

[Characteristics of secondary batteries]

(10) Manufacture of lithium-ion secondary batteries

Lithium metal is used as the negative electrode. Cut the aluminum positive electrode and metal lithium negative electrode prepared according to the method described in (7) into a circular shape with a diameter of 15 mm, and sequentially stack circular polypropylene porous membranes with a diameter of 18 mm and a thickness of 25 μm on the electrode layer side of the positive electrode. The separator and negative electrode metal lithium are arranged so that the bottom surface of the outer container is in contact with the positive electrode aluminum foil, the expanded metal is put on the negative electrode, and they are put into a stainless steel coin-shaped outer container ( diameter 20mm, height 1.8mm, stainless steel thickness 0.25mm). Inject the electrolyte into the container, and be careful not to leave any air. Cover the outer container with a stainless steel top cover with a thickness of 0.2 mm through the polypropylene gasket and fix it. Close the battery cylinder and make a coin shape with a diameter of 20 mm and a thickness of about 2 mm. Battery. The electrolytic solution was a solution in which 1 mol/liter of LiPF ₆ was dissolved in ethylene carbonate/ethyl methyl carbonate=33/67 (volume ratio at 20° C.).

(11) Battery capacity

The measurement of battery capacity is to charge and discharge at 25°C at a rate of 0.1C, charge to 1.2V with a constant current method (current density: 0.5mA/g-active material), discharge to 3V, and repeat charge and discharge 5 times each. Each time the battery capacity is measured, the average value of the repeatedly measured battery capacity is taken as the evaluation result. The unit is [mAh/g: active material (the description of the battery capacity below is the same as this)].

(12)Charge and discharge speed characteristics

Except changing the measurement condition to a constant flow rate of 1C, charge and discharge were carried out by the constant current method as in the measurement of the battery capacity, and the discharge capacity [unit = mAh/g] at the third cycle was measured. The percentage of the discharge capacity at 1C relative to the discharge capacity at 0.1C at the third cycle was calculated. The larger the value, the more likely it is to charge and discharge at a high rate.

Table 1 shows the composition (unit: mole %) of each polymer used as a binder in Examples and Comparative Examples. Polymers A-1, 2 and polymers B-1-3 are all prepared by emulsification polymerization. As polyvinylidene fluoride, a commercially available product was used.

Table 1 polymer A-1 A-2 B-1 B-2 B-3 Composition (mol%) Vinyl - - - 35 - Butadiene - - 70*1 - - Acrylonitrile 20 16 30 - 80 Methyl acrylate - - - 65 - Butyl acrylate - 80 - - - 2-Ethylhexyl Acrylate 77 - - - 20 Methacrylate 2 3 - - - Diethylene glycol dimethacrylate 1 1 - - - characteristic T _g (°C) -50 -38 -10 -6 twenty two Amount of NMP insoluble components (%) 85 87 <0.1 <0.1 <0.1 Average particle size (μm) 0.15 0.12 - - -

Note ^* 1: Polymer B-1 was used after partially hydrogenating the repeating unit of butadiene derived from an acrylonitrile/butadiene copolymer.

Example 1

Disperse 0.4 parts of polymer A-1 in 15.6 parts of NMP dispersion, and 100 parts of lithium cobaltate (LiCoO ₂ , active material (i), liquid absorption 15.6g), with two pairs of spiral stirring blades Planetary mixer kneaded for 60 minutes to prepare mixed solution a. The solid component concentration of the mixed solution a was 86.6%. In addition, to a solution in which 0.2 parts of polymer B-1 and 0.2 parts of polymer B-3 were dissolved in 6.3 parts of NMP, 3 parts of a conductivity-imparting agent, acetylene carbon black (denka black granular form manufactured by Denki Kagaku Kogyo Co., Ltd.) was added. , the solid component concentration was 35.1%, mixed with the same planetary mixer as above, and 1.8 parts of NMP was added to make a mixed solution b with a solid component concentration of 29.6%. Add the mixed solution b to the mixed solution a with the planetary mixer, and knead for 30 minutes to prepare the slurry composition for the positive electrode of the lithium ion secondary battery. The solid content concentration of the slurry composition was 81.4%. The viscosity of the slurry was 2200 mPa·S in the first hour and 2270 mPa·S in the 24th hour, and the viscosity change rate of the slurry was 103%.

In Table 2, the secondary battery electrode and the characteristic test result of the secondary battery produced using the slurry composition after 24 hours passed are described.

Embodiment 2～6

According to composition and quantity shown in table 2, the same method as embodiment 1 prepares slurry composition. When preparing the mixed solution b, among the NMP amounts recorded in the table, 6.3 parts were first added when dissolving the polymer (B), and the remaining amount was added after mixing with the conductivity-imparting agent. However, in Example 3, the entire amount recorded in the table was added when dissolving the polymer (B). The characteristics of the slurry composition, the secondary battery electrode made with the slurry composition, and the secondary battery were tested. The test results are shown in Table 2.

Table 2 Example 1 2 3 4 5 6 active substance Type ^* 1 Addition amount (part) i100 i100 i100 ii100 iii100 i100 Polymer (A) Addition amount of species (parts) A-10.4 A-10.4 A-10.4 A-10.4 A-10.4 A-20.4 Mixed solution a Mixing condition Concentration of solid components (%) Acetylene carbon black (parts) Solvent amount (parts) Solvent amount (to active material liquid absorption %) 86.6-15.6100 88.6-12.983 84.5-18.4118 88.5-1399 85.0-17.799 86.6-15.6100 Polymer (B) Type 1 Type 1 addition amount (parts) B-10.2 B-10.2 B-10.2 B-10.2 B-10.2 B-20.2 Type 2 Addition amount of type 1 (parts) B-30.2 B-30.2 B-30.2 B-30.2 B-30.2 PVDF ^* 20.2 Mixed liquid b Mixing conditions Solvent amount (parts) Acetylene carbon black (parts) Solid component concentration (%) 8.1329.6 10.8323.9 5.3339.1 8.3329.1 7.4331.5 8.1329.6 slurry composition Solvent amount (per 100 parts of active substance corresponding parts) solid component concentration (%) 23.781.4 23.781.4 23.781.4 21.383.0 25.180.5 23.781.4 slurry composition Slurry viscosity at the first hour (mPa·S) Slurry viscosity at the 24th hour (mPa·S) Slurry viscosity maintenance rate (%) 22002270103 19401980102 2320220095 3560348098 3600350097 3940386098 Secondary battery electrode Arithmetic mean roughness Ra(μm)Peel strength(N/cm) 0.80.24 0.70.26 0.90.27 0.90.23 0.80.22 0.80.25 secondary battery Battery capacity (mAh/g) Charge and discharge rate characteristics (%) 14794 14593 14694 14495 14893 14593

Note ^* 1 i: LiCoO ₂ , liquid absorption 15.6g,

ii: LiCoO ₂ , liquid absorption 13.1g,

iii: LiCoO ₂ , liquid absorption 17.9g

^* 2PVDF: polyvinylidene fluoride (#1100, manufactured by Kureha Chemical Co., Ltd., less than 0.1% of NMP insoluble components)

As shown in Table 2, for three kinds of active substances with different liquid absorption, the binder of two kinds of polymers that are insoluble and soluble in the solvent is used, and the slurry composition prepared by the method of the present invention is prepared After 1 hour and 24 hours, it showed low and stable (less change over time) viscosity. The electrode mixed layer made after coating these slurry compositions has a smooth surface, high peel strength, and good adhesion. good. In addition, lithium ion secondary batteries using these electrodes had high capacity and high charge and discharge rate characteristics (Examples 1-6).

Comparative example 1

Add 0.2 parts of polymer B-1 and 0.2 parts of polymer B-3 to 23.7 parts of NMP to dissolve it, disperse 0.4 parts of polymer A-1 in it, then add 3 parts of acetylene carbon black and 100 parts of active substances (i), kneading for 90 minutes with a planetary mixer having two pairs of helical stirring blades to obtain a slurry composition for positive electrodes of lithium ion secondary batteries. The solid content concentration of the slurry composition was 81.4%. The viscosity of the slurry was 13400 mPa·S in the first hour and 2010 mPa·S in the 24th hour, and the viscosity change rate of the slurry was 15%.

Table 3 shows the secondary battery electrodes and the results of the characteristic test of the secondary battery using the slurry composition after 24 hours.

Comparative example 2

Add 0.2 parts of polymer B-1 and 0.2 parts of polymer B-3 to 16.9 parts of NMP to dissolve it, then add 0.4 parts of polymer A-1 to disperse, mix this dispersion with 3 parts of acetylene carbon black and 100 parts The active material (i) was kneaded for 60 minutes with a planetary mixer having two pairs of helical stirring blades, 6.8 parts of NMP were added, and kneaded for another 30 minutes to obtain a slurry composition for positive electrodes of lithium ion secondary batteries. The solid content concentration of the slurry composition was 81.4%. The viscosity of the slurry was 12800 mPa·S in the first hour and 2120 mPa·S in the 24th hour, and the viscosity change rate of the slurry was 17%.

Table 3 shows the secondary battery electrodes and the results of the characteristic test of the secondary battery using the slurry composition after 24 hours.

Comparative example 3

Add 0.1 part of polymer B-1 and 0.1 part of polymer B-3 to 16.1 parts of NMP to dissolve it, and mix this solution with 3 parts of acetylene carbon black and 100 parts of active material (i) with two pairs of helical stirring blades A planetary mixer was used for kneading for 30 minutes, a solution of 0.1 part of polymer B-1 and 0.1 part of polymer B-3 dissolved in 3 parts of NMP was added thereto, and kneading was continued for 30 minutes. A dispersion liquid in which 0.4 parts of polymer A-1 was dispersed in 4.6 parts of NMP was added thereto, and mixed again 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 viscosity of the slurry was 18400 mPa·S in the first hour and 2050 mPa·S in the 24th hour, and the rate of change in viscosity of the slurry was 11%.

Table 3 shows the secondary battery electrodes and the results of the characteristic test of the secondary battery using the slurry composition after 24 hours.

Comparative example 4

Dissolve 0.2 part of polymer B-1 and 0.2 part of polymer B-3 in 15.8 parts of NMP, this solution and 100 parts of active substance (i) are mixed with the planetary mixer machine that has two pairs of spiral type stirring blades for 60 Minutes to make a mixture c. The solid component concentration of the mixed liquid c was 86.4%. Separately, 3 parts of acetylene black was added to a dispersion in which 0.4 parts of polymer A-1 was dispersed in 7.9 parts of NMP, and dispersed with a planetary mixer to prepare a mixed solution d with a solid content concentration of 30.0%. Add the mixed liquid d to the mixed liquid c with the above-mentioned planetary mixer, knead for 30 minutes, and prepare the slurry composition for lithium ion secondary battery cathode. The solid content concentration of the slurry composition was 81.4%. The viscosity of the slurry was 8950 mPa·S in the first hour and 1980 mPa·S in the 24th hour, and the rate of change in viscosity of the slurry was 22%.

Table 3 shows the secondary battery electrodes and the results of the characteristic test of the secondary battery using the slurry composition after 24 hours.

table 3 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Components of the first mixed solution (parts) B-1B-3A-1 Acetylene carbon black active material (refer to Table 2 note) solvent 0.20.20.4310023.7 0.20.20.4310016.9+6.8 (supplement added) 0.10.1-310016.1 0.20.2--10015.8 Mixing conditions of the first mixed solution Solid component concentration (%) Solvent amount when active substance is dispersed (liquid absorption of active substance %) 81.4147 86.0 added after adding (81.4) 108 86.5103 86.4101 Components of the second mixture (parts) B-1B-3A-1 Acetylene Carbon Black Solvent ----- ----- 0.10.1--3 --0.437.9 Mixing conditions of the second mixed solution Solid component concentration (%) - - 6.3 30 Components of the third mixed solution (parts) A-1 solvent -- -- 0.44.6 -- Mixing conditions of the third mixed solution Solid component concentration (%) - - 8 - slurry composition Solvent amount (corresponding number of parts per 100 active substances) solid component concentration (%) 23.781.4 23.781.4 23.781.4 23.781.4 Viscosity of pulp at 1st hour (mPa·S) Viscosity of pulp at 24th hour (mPa·S) Viscosity maintenance rate of pulp (%) 13400201015 12800212017 18400205011 8850198022 Secondary battery electrode Arithmetic mean roughness Ra(μm)Peel strength(N/cm) 160.07 0.40.1 1.50.06 1.80.05 secondary battery Battery capacity (mAh/g) Charge and discharge rate characteristics (%) 14076 14178 13976 13868

As shown in Table 3, even if the same components as the above-mentioned inventive examples (Examples 1-6) are used in the same amount, the slurry compositions prepared in different order steps from the present invention all show poor results . That is, according to the method of sequentially adding all the ingredients except the solvent to the total amount of solvent for mixing, or adopting the method of sequentially adding about 70% of the amount of solvent, and then adding the remaining amount of solvent after mixing, the resulting The initial value of the viscosity of the slurry composition is high, and then sharply decreases and is very unstable. The surface of the electrode mixed layer is very rough, and the peeling strength is obviously too small. The secondary battery made of such an electrode has a battery Both capacity and charge-discharge rate characteristics were inferior (Comparative Examples 1 and 2).

In addition, the initial value of the viscosity of the slurry composition obtained by adding the dispersion of the polymer A to the mixed solution of the polymer (B), the conductivity-imparting agent and the active material in advance is 8 to 9 times higher. , but decreases rapidly with time. The electrodes and secondary batteries produced using this slurry composition exhibited the same disadvantages as Comparative Examples 1 and 2 (Comparative Example 3).

In addition, if the dispersion liquid of the polymer (A) and the conductivity-imparting agent prepared separately is added to the mixed liquid in which the polymer (B) is dissolved and the active substance is dispersed, and kneaded, the preparation opposite to the present invention is adopted. Step, the slurry composition viscosity initial value that it makes is four times of the embodiment of the present invention, but then greatly reduces, and the electrode that obtains and secondary battery have the same shortcoming as comparative example 1～3 (comparative example 4 ).

Industry Applicability

The slurry composition prepared by the method of the present invention has little change in viscosity over time and good adhesion. After the composition is applied to a current collector and dried, a two-layer mixed layer with a smooth surface and uniform thickness can be formed. secondary battery electrodes.

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

Claims (19)

1. A preparation method of a slurry composition for secondary battery electrodes, the method comprising the solvent _SA dispersion of the polymer A comprising 50% by weight or more than 50% by weight of the solvent _SA insoluble component and electrode active The materials are kneaded, and then the obtained kneaded liquid and the solvent S _B solution of the polymer B are kneaded, thereby forming a slurry composition for secondary battery electrodes. 2. The preparation method of the slurry composition according to claim 1, wherein the solvent S _A insoluble component of the polymer A is 50% by weight to 90% by weight. 3. The preparation method of the slurry composition according to claim 1, wherein the solvent S _A insoluble component of the polymer A is 50% by weight to 87% by weight. 4. The preparation method of the slurry composition according to any one of claims 1 to 3, wherein said polymer A is at least one selected from monofunctional ethylenically unsaturated monomers and conjugated dienes A cross-linked copolymer of monomers and polyfunctional ethylenically unsaturated monomers. 5. The method for preparing the slurry composition according to any one of claims 1 to 3, wherein the glass transition temperature _Tg of the polymer A is in the range of -80°C to 0°C. 6. The method for preparing the slurry composition according to any one of claims 1 to 3, wherein the average particle diameter of the polymer A is in the range of 0.005 μm to 1000 μm. 7. The preparation method of the slurry composition according to any one of claims 1 to 3, wherein the polymer B is at least one monomer selected from monofunctional ethylenically unsaturated monomers and conjugated dienes of polymers. 8. The method for preparing the slurry composition according to any one of claims 1 to 3, wherein the polymer B comprises a fluorine-containing polymer containing 50 mol% or more of fluorine-containing monofunctional ethylenic monomer units. things. 9. The preparation method of the slurry composition described in any one of claims 1 to 3, wherein relative to 100 parts by weight of the active substance, the total amount of the polymer A and the polymer B is 0.1 to 5 parts by weight scope. 10. The preparation method of the slurry composition according to any one of claims 1-3, wherein the weight ratio A/B of the polymer A to the polymer B is in the range of 5/1-1/5. 11. The method for preparing the slurry composition according to any one of claims 1 to 3, wherein the solvent _SA and the solvent S _B are selected from water and non-aqueous solvents with a boiling point of 80°C to 350°C under atmospheric pressure. 12. The method for preparing the slurry composition according to any one of claims 1 to 3, wherein the solvent _SA and the solvent _SB have the same composition. 13. The method for producing the slurry composition according to any one of claims 1 to 3, wherein the solvent SB solution of the polymer _B further contains a conductivity imparting agent. 14. The method for preparing the slurry composition according to claim 13, wherein the solvent _SB solution of the polymer B containing the conductivity-imparting agent is prepared by kneading at a solid concentration of 30 to 40% by weight. 15. The method for preparing the slurry composition according to claim 13, wherein the amount of the conductivity-imparting agent is 1 to 20 parts by weight per 100 parts by weight of the active material. 16. The preparation method of the slurry composition described in any one of claims 1 to 3, when the solvent S _A dispersion liquid of the polymer A and the electrode active material were mixed, the amount of the solvent S _A was the electrode active material 80 to 120% by weight of the liquid absorption. 17. The slurry composition for secondary battery electrodes, which is prepared according to the preparation method of the slurry composition according to any one of claims 1-3. 18. 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.