KR20170129732A - METHOD FOR PRODUCING SLIDE COMPOSITION FOR SECONDARY CELL FOR SECONDARY BATTERY, - Google Patents

Abstract

An object of the present invention is to provide a method for producing a slurry composition for a secondary battery positive electrode that exhibits excellent high-voltage durability on a positive electrode. The method for producing the positive electrode slurry composition of the present invention comprises the steps of dry mixing the polymer particles for the positive electrode of the secondary battery, the positive electrode active material and the conductive material to obtain a dry mixture, and mixing the dry mixture and the dispersion medium, Thereby obtaining a slurry composition. Here, the polymer particles contain a copolymer containing a nitrile group-containing monomer unit and a hydrophilic group-containing monomer unit, and the volume average particle diameter D50 thereof is 1 占 퐉 or more. The ratio of the volume average particle diameter D50 of the polymer particles to the volume average particle diameter D50 of the positive electrode active material is 0.1 or more.

Description

METHOD FOR PRODUCING SLIDE COMPOSITION FOR SECONDARY CELL FOR SECONDARY BATTERY,

The present invention relates to a method for producing a slurry composition for a secondary battery positive electrode, a positive electrode for a secondary battery, and a secondary battery.

BACKGROUND ART [0002] A secondary battery such as a lithium ion secondary battery is small and light in weight, has a high energy density, and is capable of repeatedly charging and discharging, and is used in a wide variety of applications. For this reason, in recent years, improvement of battery members such as electrodes has been studied for the purpose of achieving higher performance of the secondary battery.

Here, a positive electrode used in a secondary battery such as a lithium ion secondary battery generally has a current collector and an electrode composite layer (positive electrode composite layer) formed on the current collector. The positive electrode composite material layer is formed, for example, by dispersing and / or dissolving a positive electrode active material and a binder in a dispersion medium to prepare a slurry composition, coating the slurry composition on the current collector, and drying the dispersion.

In recent years, therefore, an attempt has been made to improve the method of forming the positive electrode composite material layer on the current collector in order to achieve the performance improvement of the secondary battery.

For example, in Patent Document 1, a positive electrode active material and a particulate binding material each having a predetermined average particle size are dry-mixed at a predetermined ratio, and mixed powder obtained is fixed on the current collector to form a positive electrode mixture layer There has been proposed a method of forming a thin film transistor. It has been reported that by forming the positive electrode composite material layer by this method, it is possible to increase the active material density in the positive electrode composite material layer and to suppress cycle deterioration while increasing the capacity of the secondary battery.

Japanese Patent Publication No. 4778034

In recent years, secondary batteries have been required to exhibit battery characteristics such as excellent lifetime characteristics even when they are exposed for a long time on a high voltage in accordance with diversification of applications. However, when the positive electrode formed by forming the positive electrode composite material layer on the current collector by the above-described conventional method is exposed to a high potential over a long period of time, battery characteristics may be significantly deteriorated due to deterioration of the surface of the positive electrode active material. Therefore, a new technique for improving the battery characteristics of the secondary battery by increasing the high potential durability of the positive electrode has been desired.

It is therefore an object of the present invention to provide a method for producing a slurry composition for a secondary battery positive electrode that exhibits excellent high-voltage durability on a positive electrode.

Another object of the present invention is to provide a secondary battery having excellent high-durability durability and a positive electrode for the secondary battery, and to provide a secondary battery having excellent battery characteristics.

The present inventors have conducted intensive studies in order to achieve the above object. The inventors of the present invention found that when a slurry composition for a secondary battery positive electrode is prepared by dry blending polymer particles having a predetermined composition and properties with a positive electrode active material and a conductive material and then mixing the resultant mixture with a dispersion medium, And it is possible to improve the high-potential durability of the positive electrode formed from the composition, thereby completing the present invention.

That is, the object of the present invention is to solve the above problems advantageously, and a method for producing a slurry composition for a secondary battery positive electrode of the present invention is a method for manufacturing a secondary battery positive electrode slurry composition, And a step of mixing the dry mix and the dispersion medium to obtain a slurry composition for a secondary battery positive electrode, wherein the polymer particles for a secondary battery positive electrode comprise a nitrile group-containing monomer unit and a hydrophilic group-containing monomer Unit and a volume average particle diameter D50 of 1 占 퐉 or more and a ratio of a volume average particle diameter D50 of the secondary battery positive electrode polymer particles to a volume average particle diameter D50 of the positive electrode active material is 0.1 or more . As described above, when the slurry composition for a secondary battery positive electrode prepared by dry mixing the polymer particles, the positive electrode active material, and the conductive material having the above-described predetermined composition and properties and then mixing the dispersion medium is used, Can be prepared.

Further, in the present invention, the term "the polymer includes a monomer unit" means that "a polymer obtained by using the monomer contains a structural unit derived from a monomer".

In the present invention, the " volume average particle diameter D50 " is a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in a dry particle size distribution measurement using a laser diffraction / scattering particle size distribution measuring apparatus .

In the present invention, the term " dry mixing " means that the solid content concentration of the mixture at the time of mixing exceeds 90% by mass.

Here, in the method for producing the slurry composition for a secondary battery positive electrode of the present invention, it is preferable that the secondary battery positive electrode polymer particles have a volume average particle diameter D50 of 2000 mu m or less and a volume average particle diameter D50 of the positive electrode active material It is preferable that the ratio of the volume average particle diameter D50 of the polymer particles for use is 200 or less. This is because the internal resistance of the secondary battery can be reduced if the ratio of the volume average particle diameter D50 of the polymer particles and the volume average particle diameter D50 of the polymer particles to the volume average particle diameter D50 of the positive electrode active material are respectively not more than the above-mentioned values.

In the method for producing a slurry composition for a secondary battery positive electrode according to the present invention, the copolymer contains 80% by mass or more and 99.9% by mass or less of the nitrile group-containing monomer units, and 0.1% By mass or less and 20% by mass or less. The use of the copolymer containing the nitrile group-containing monomer unit and the hydrophilic group-containing monomer unit in the above-mentioned respective proportions can improve the high-strength durability while improving the peel strength of the positive electrode, It is possible to reduce it.

Further, in the method for producing the slurry composition for a secondary battery positive electrode of the present invention, it is preferable that the molecular weight distribution (Mw / Mn) of the copolymer is 10 or less. This is because using a copolymer having a molecular weight distribution of 10 or less can reduce the internal resistance of the secondary battery.

In the present invention, "molecular weight distribution (Mw / Mn)" refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). In the present invention, "number average molecular weight (Mn)" and "weight average molecular weight (Mw)" can be measured using gel permeation chromatography.

In addition, in the method for producing a slurry composition for a secondary battery positive electrode of the present invention, it is preferable that the glass transition temperature of the copolymer is 60 占 폚 or more and 170 占 폚 or less. When a copolymer having a glass transition temperature of 60 ° C or more and 170 ° C or less is used, it is possible to further improve high-voltage durability while reducing the internal resistance of the secondary battery while increasing the peak strength of the positive electrode.

In the present invention, " glass transition temperature " can be measured in accordance with JIS K7121.

The positive electrode for a secondary battery of the present invention comprises a current collector and a positive electrode composite material layer formed on at least one surface of the current collector, Wherein the positive electrode composite layer is formed from a slurry composition for a secondary battery positive electrode obtained by the method for producing a slurry composition for a secondary battery positive electrode as described above. The positive electrode formed from the slurry composition for a secondary battery positive electrode obtained by the above-described method for producing a slurry composition for a secondary battery positive electrode is excellent in high-potential durability.

It is another object of the present invention to solve the above problems in an advantageous manner. The secondary battery of the present invention is characterized by comprising a positive electrode, a negative electrode, an electrolytic solution and a separator, wherein the positive electrode is the above- . By using the above-described positive electrode for a secondary battery, a secondary battery having excellent battery characteristics such as life characteristics can be obtained even when exposed to a high voltage for a long time.

According to the present invention, it is possible to provide a method for producing a slurry composition for a secondary battery positive electrode that exhibits excellent high-potential durability on a positive electrode.

According to the present invention, it is possible to provide a secondary battery having a positive electrode for a secondary battery excellent in high-potential durability and a positive electrode for the secondary battery and having excellent battery characteristics.

Hereinafter, embodiments of the present invention will be described in detail.

Here, the method for producing a slurry composition for a secondary battery positive electrode of the present invention is used for preparing a slurry composition for a secondary battery positive electrode. The positive electrode for a secondary battery of the present invention is characterized by being manufactured using the slurry composition for a secondary battery positive electrode obtained by the method for producing a slurry composition for a secondary battery positive electrode of the present invention. The secondary battery of the present invention is characterized by including the positive electrode for a secondary battery of the present invention.

(Method for producing slurry composition for secondary battery positive electrode)

A method for producing a slurry composition for a secondary battery positive electrode according to the present invention is a method for producing a slurry composition for a secondary battery positive electrode by mixing at least a polymer particle for a secondary battery positive electrode, a positive electrode active material, a conductive material and a dispersion medium in a predetermined order .

Here, the secondary battery positive electrode polymer particles used in the method for producing the slurry composition for a secondary battery positive electrode of the present invention contain a copolymer containing both a nitrile group-containing monomer unit and a hydrophilic group-containing monomer unit, Wherein the average particle diameter D50 is 1 占 퐉 or more and the ratio of the volume average particle diameter D50 of the positive electrode active material to the particle diameter ratio of the polymer particles to the positive electrode active material is 0.1 or more. The method for producing a slurry composition for a secondary battery positive electrode according to the present invention comprises the steps of dry-mixing the aforementioned polymer particles for a positive electrode for a positive electrode, a positive electrode active material and a conductive material to obtain a dry mixture, To obtain a slurry composition for a positive electrode for a secondary battery.

Here, when the method for producing a slurry composition for a secondary battery positive electrode of the present invention is used, the predetermined polymer particles for a secondary battery positive electrode are dry-mixed with a positive electrode active material and a conductive material, and then the obtained dry mixture is mixed with a dispersion medium , It is possible to prepare a slurry composition for a secondary battery positive electrode capable of sufficiently increasing the high potential durability of the positive electrode. By using the positive electrode, it is possible to obtain a secondary battery exhibiting battery characteristics such as excellent life characteristics even when exposed to a high voltage for a long time.

Further, by preliminarily mixing the predetermined polymer particles for positive electrode with the positive electrode active material and the conductive material prior to the addition of the dispersion medium, it is possible to sufficiently increase the high-potential durability of the positive electrode and to exhibit excellent battery characteristics in the secondary battery The reason for this is unclear, but it is assumed to be due to the following reasons. That is, by uniformly dispersing the conductive material by the premixing of the polymer particles, the positive electrode active material, and the conductive material having the above-described composition and properties, the conductive paths in the positive electrode composite material layer are well formed, By adsorbing on the surface of the positive electrode active material, the surface of the positive electrode active material can be sufficiently protected by the copolymer in the obtained positive electrode. It is therefore presumed that deterioration of the surface of the positive electrode active material on the high potential is suppressed.

Hereinafter, the components to be mixed with the slurry composition and the preparation procedure of the slurry composition using the components will be described.

≪ Polymer particle for positive electrode of secondary battery >

The secondary battery positive electrode polymer particles are components including a copolymer which functions as a binder. This copolymer keeps the components contained in the positive electrode mixture layer from being removed from the positive electrode mixture layer in the positive electrode produced by using the slurry composition obtained by the method for producing a slurry composition of the present invention. The copolymer contained in the polymer particles for the positive electrode of the secondary battery needs to include both a nitrile group-containing monomer unit and a hydrophilic group-containing monomer unit. The copolymer may optionally contain a monomer unit other than the nitrile group-containing monomer unit and the hydrophilic group-containing monomer unit, as long as the effect of the present invention is not impaired.

[Composition of copolymer]

[[Nitrile group-containing monomer unit]]

The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer.

Here, examples of the nitrile group-containing monomer capable of forming a nitrile group-containing monomer unit include an?,? - ethylenically unsaturated nitrile monomer. Specifically, the?,? - ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an?,? - ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile,? -Chloroacrylonitrile, ? -Halogenoacrylonitrile such as methacrylonitrile,? -Halogenoacrylonitrile such as methacrylonitrile,? -Alkylacrylonitrile such as methacrylonitrile and? -Ethyl acrylonitrile, and the like. Of these, acrylonitrile and methacrylonitrile are preferable as the nitrile group-containing monomer from the viewpoint of enhancing the binding force of the copolymer, and acrylonitrile is more preferable.

These may be used alone or in combination of two or more.

The content of the nitrile group-containing monomer units in the copolymer is preferably 80% by mass or more, more preferably 82% by mass or more, and more preferably 85% by mass or more, based on 100% by mass of the total repeating units in the copolymer. More preferably 90% by mass or more, particularly preferably 99.9% by mass or less, more preferably 99% by mass or less, and even more preferably 98.5% by mass or less. When the content of the nitrile group-containing monomer units in the copolymer is within the above-mentioned range, the binder strength of the copolymer and the dispersibility of the slurry composition obtained are improved, the peak strength of the positive electrode can be sufficiently increased, Durability can also be increased. Therefore, it is possible to prevent the separation of the positive electrode composite material layer, reduce the internal resistance of the secondary battery, and obtain a secondary battery excellent in battery characteristics such as life characteristics even when exposed to a high voltage for a long time.

[[Hydrophilic group-containing monomer unit]]

The hydrophilic group-containing monomer unit is a repeating unit derived from a hydrophilic group-containing monomer.

Examples of the hydrophilic group-containing monomer include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and a monomer having a hydroxyl group.

Examples of the monomer having a carboxylic acid group include a monocarboxylic acid and a derivative thereof, a dicarboxylic acid and an acid anhydride thereof, and derivatives thereof.

Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

Examples of the monocarboxylic acid derivative include 2-ethyl acrylic acid, isocrotonic acid,? -Acetoxy acrylic acid,? -Trans-aryloxy acrylic acid,? -Chloro-? -E-methoxy acrylic acid,? -Diamino acrylic acid, .

Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like.

Examples of the dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenylmaleic acid maleate, maleic acid dicylate, Maleic acid dodecyl maleate, octadecyl maleate, and maleic acid esters such as maleic acid fluoroalkyl.

Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic acid anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

As the monomer having a carboxylic acid group, an acid anhydride which generates a carboxyl group by hydrolysis can also be used.

In addition, there may be mentioned monoethyl maleate, monoethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, Monoesters and diesters of?,? - ethylenically unsaturated polycarboxylic acids such as monobutylsuccinic acid, monobutylsuccinic acid, monoethylsuccinic acid, diethyl itaconate, monobutyl itaconate and dibutyl itaconate.

Examples of the monomer having a sulfonic acid group include vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylate-2-sulfonate, -Hydroxypropanesulfonic acid and the like.

In the present invention, "(meth) allyl" means allyl and / or methallyl. In the present invention, "(meth) acryl" means acryl and / or methacryl.

Examples of the monomer having a phosphoric acid group include (meth) acryloyloxyethyl phosphate, methyl 2- (meth) acryloyloxyethyl phosphate and ethyl- (meth) acryloyloxyethyl phosphate.

In the present invention, "(meth) acryloyl" means acryloyl and / or methacryloyl.

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol and 5-hexen-1-ol; Hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di- St. alkanol ester of unsaturated carboxylic acid and the like; the formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m -H ( in the formula, m represents an integer of 2 to 9, n is an integer of 2-4 , R ¹ represents a hydrogen or a methyl group) which is a polyalkylene glycol with (meth) acrylic acid esters represented by; 2-hydroxyethyl-2 '- oxy one (meth) acrylate phthalate, 2-hydroxyethyl - 2 '- (meth) acryloyloxysuccinate, and the like. The mono (meth) acrylic acid of the dihydroxy ester of the dicarboxylic acid (Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-2-hydroxypropyl ether, (Meth) allyl-3-hydroxybutyl ether, (meth) allyl-2-hydroxybutyl ether, Mono (meth) allyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; alkylene glycol mono (Meth) allyl-2-chloro-3-hydroxypropyl ether and (meth) allyl-2-hydroxy-3-chloropropyl ether, such as glycerin mono (meth) allyl ether, The halogen and hydroxy substituents of alkylene glycol mono (Meth) allyl-2-hydroxyethyl thioether, (meth) allyl-2-hydroxy (meth) allyl ether, (Meth) allylthioethers of alkylene glycols such as propylthioether and the like.

The above-mentioned hydrophilic group-containing monomers may be used singly or in combination of two or more. Of these, methacrylic acid, acrylic acid and itaconic acid are more preferable from the viewpoint of enhancing the peel strength and high-potential durability of the positive electrode. That is, it is more preferable that the copolymer includes a monomer unit derived from at least one kind selected from the group consisting of methacrylic acid, acrylic acid, and itaconic acid as the hydrophilic group-containing monomer unit.

The content of the hydrophilic group-containing monomer units in the copolymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, and more preferably 2% by mass or more based on 100% by mass of the total repeating units in the copolymer More preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 15% by mass or less, particularly preferably 10% by mass or less. When the content of the hydrophilic group-containing monomer units in the copolymer is 0.1 mass% or more, the adhesive strength of the copolymer is improved, so that the peel strength of the positive electrode is increased and the copolymer can cover the positive electrode active material more satisfactorily The high potential durability of the positive electrode can be enhanced. On the other hand, when the content of the hydrophilic group-containing monomer units in the copolymer is 20 mass% or less, the positive electrode active material in the positive electrode composite material layer is not overcoated with the copolymer, and the increase in internal resistance can be suppressed.

- other monomer units -

The copolymer may contain a monomer unit other than a nitrile group-containing monomer unit and a hydrophilic group-containing monomer unit. As such other monomer units, there may be mentioned (meth) acrylic acid ester monomer units.

Examples of the (meth) acrylic acid ester monomer capable of forming the (meth) acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, Acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, n-butyl methacrylate, Butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methane But are not limited to, acrylate, methacrylate, acrylate, acrylate, acrylate, acrylate, isoleucyl acrylate, Methacrylic acid alkyl esters such as stearyl methacrylate; and the like.

The monomers capable of forming other monomer units may be used alone or in combination of two or more.

Incidentally, the content ratio of other monomer units is not particularly limited, but is preferably 20% by mass or less when the total repeating units in the copolymer is 100% by mass from the viewpoint of sufficiently obtaining the desired effect of the present invention, More preferably 15 mass% or less, and further preferably 10 mass% or less.

[Properties of Copolymer]

[[Weight average molecular weight (Mw)]]

The copolymer preferably has a weight average molecular weight of 500,000 or more, more preferably 1,000,000 or more, more preferably 2,500,000 or less, and still more preferably 2,000,000 or less. If the weight-average molecular weight of the copolymer is 500,000 or more, the internal resistance of the secondary battery can be reduced without increasing the amount of the low-molecular-weight component and thereby excessively coating the positive electrode active material with the copolymer. When the polymer has a weight average molecular weight of 2,500,000 or less, the positive electrode composite material layer having a uniform thickness can be formed without increasing the viscosity of the slurry composition obtained by using the polymer particles. Therefore, the internal resistance of the secondary battery can be reduced while enhancing the high potential durability of the positive electrode.

[[Molecular weight distribution (Mw / Mn)]]

The copolymer preferably has a molecular weight distribution of 10 or less, more preferably 9 or less, further preferably 8 or less, particularly preferably 7 or less. If the molecular weight distribution of the copolymer is 10 or less, the internal resistance of the secondary battery can be reduced without an excessive coating of the positive electrode active material with the copolymer due to an increase in the low molecular weight component.

[[Glass Transition Temperature (Tg)]]

The copolymer preferably has a glass transition temperature of 60 占 폚 or higher, more preferably 80 占 폚 or higher, more preferably 100 占 폚 or higher, 170 占 폚 or lower, more preferably 160 占 폚 or lower, and 150 占 폚 or lower More preferable. When the glass transition temperature of the copolymer is 60 占 폚 or higher, the blocking of the particles during dry mixing is suppressed, and the polymer particles, the positive electrode active material, and the conductive material can be uniformly dispersed. Therefore, in the positive electrode composite material layer, the copolymer can cover the positive electrode active material more satisfactorily, and the internal resistance of the secondary battery can be reduced while increasing the high potential durability of the positive electrode. When the glass transition temperature of the copolymer is 170 DEG C or less, the flexibility of the positive electrode can be ensured and the fill strength can be increased.

[Preparation of Polymer Particles Containing Copolymer]

The method of preparing the polymer particles is not particularly limited as long as the polymer particles include the above-mentioned copolymer. The polymer particles containing the copolymer can be prepared, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent to form a copolymer in the form of particles, and then obtaining the polymer particles by coagulation, filtration, Or may be obtained by polymerizing a monomer composition containing the above-mentioned monomer in an arbitrary polymerization solvent to obtain a copolymer, followed by spray drying.

Here, in the present invention, the content of each monomer in the monomer composition can be determined in accordance with the content of each monomer unit in the copolymer constituting the polymer particles.

The polymerization is not particularly limited, and any of a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsion polymerization method and the like can be used. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used.

Among them, from the standpoint of narrowing the molecular weight distribution while increasing the weight average molecular weight of the copolymer, and furthermore, from the viewpoint of satisfactorily producing polymer particles having a predetermined volume average particle diameter D50, by radical polymerization using a suspension polymerization method, It is preferred to polymerize the composition. In this radical polymerization, known additives such as dispersants and polymerization initiators can be used. Examples of such a known additive include those described in Japanese Patent No. 5573966.

[Volume average particle diameter D50 of polymer particles]

The volume average particle diameter D50 of the polymer particles obtained as described above needs to be 1 占 퐉 or more, preferably 10 占 퐉 or more, more preferably 50 占 퐉 or more, further preferably 100 占 퐉 or more, particularly preferably 200 占 퐉 or more, More preferably 1800 占 퐉 or less, further preferably 1000 占 퐉 or less, and particularly preferably 500 占 퐉 or less. If the volume average particle diameter D50 of the polymer particles is less than 1 占 퐉, the high-potential durability of the positive electrode can not be ensured because the layer of the copolymer covering the positive electrode active material in the positive electrode mixture layer becomes excessively thin, . On the other hand, if the volume average particle diameter D50 of the polymer particles is 2000 m or less, the internal resistance of the secondary battery can be reduced without increasing the thickness of the copolymer layer covering the positive electrode active material layer.

The volume average particle diameter D50 of the polymer particles is determined by adjusting the preparation conditions of the polymer particles (polymerization concentration, polymerization temperature and stirring speed, kind and amount of dispersant, polymerization initiator and chain transfer agent, spraying rate of spray drying, Can be changed by adjusting.

The ratio of the volume average particle diameter D50 of the polymer particles to the volume average particle diameter D50 of the positive electrode active material is required to be 0.1 or more, preferably 1 or more, more preferably 5 or more, further preferably 10 or more, And is preferably 200 or less, more preferably 100 or less, and even more preferably 50 or less. If the particle size ratio of the polymer particles to the positive electrode active material is less than 0.1, the layer of the copolymer that covers the positive electrode active material in the positive electrode composite material layer becomes excessively thin, so that the high potential durability of the positive electrode can not be ensured, . On the other hand, if the particle diameter ratio of the polymer particles to the positive electrode active material is 200 or less, the internal resistance of the secondary battery can be reduced without increasing the thickness of the copolymer layer covering the positive electrode active material layer.

≪ Positive electrode active material &

The positive electrode active material is a substance exchanging electrons at the positive electrode of the secondary battery. For example, as a positive electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium is generally used.

Concretely, the positive electrode active material for a lithium ion secondary battery is not particularly limited, and lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ) (Li (CoMnNi) O ₂ ) of Mn, a lithium-containing complex oxide of Ni-Mn-Al, a lithium-containing complex oxide of Ni-Co-Al, an olivine-type lithium iron phosphate (LiFePO ₄ ) Lithium manganese lithium (LiMnPO ₄ ), lithium excess spinel compound represented by Li _{1 + x} Mn _{2 -x} O ₄ (0 <X <2), Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ , LiNi _0.5 Mn _1.5 O _4, and the like.

Among the above, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium-containing complex oxide of Co-Ni-Mn, and the like are preferable as the positive electrode active material from the viewpoint of improving the battery capacity and the like of the secondary battery. _{Li [Ni 0.17 Li 0.2 Co 0.07} Mn 0.56] O 2 , or LiNi _0.5 is preferred to use the Mn _1.5 O ₄ and lithium-containing cobalt oxide _{(LiCoO 2), Li [Ni} 0.17 Li 0.2 Co 0.07 Mn 0.56] O 2 , or LiNi _0.5 Mn _1.5 O ₄ is more preferably used.

These may be used alone or in combination of two or more.

The volume average particle diameter D50 of the positive electrode active material is not particularly limited as long as the particle diameter ratio of the polymer particles to the positive electrode active material falls within a predetermined range, but is preferably 0.1 占 퐉 or more and 100 占 퐉 or less.

&Lt; Conductive material &

The conductive material is for securing electrical contact between the positive electrode active materials. Examples of the conductive material include carbon black (for example, acetylene black, Ketjenblack (registered trademark), furnace black, etc.), graphite, carbon fiber, carbon flake, carbon short- Grown carbon fiber, etc.), fiber of various metals, foil and the like can be used. Among them, carbon black is preferable as the conductive material, and acetylene black is more preferable.

These may be used alone or in combination of two or more.

<Dispersion>

The dispersion medium to be added to the dry mixture obtained by dry mixing the polymer particles, the positive electrode active material, and the conductive material is not particularly limited and an organic solvent may be used. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, Alcohols such as methanol and ethanol, alcohols such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether, dioxane and tetrahydrofuran, N, N-dimethylform Amide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. These may be used singly or in combination of two or more kinds.

Among them, NMP is preferable as the dispersion medium.

&Lt; Other components &gt;

In the method for producing the slurry composition of the present invention, other components than those described above may be used. Examples of such other components include polymer powder comprising a binder other than the above-mentioned copolymer, and known additives such as a reinforcing material, a leveling agent, a viscosity adjusting agent, and an electrolyte additive described in International Publication No. 2012/115096 . These components may be used singly or in combination of two or more in an arbitrary ratio. The timing of addition of these other components is not particularly limited, and may be suitably added in any one step according to the properties. The properties of the binder (polymer) constituting the above-mentioned polymer powder are optional, and for example, a polymer having a glass transition temperature of 40 캜 or lower may be used.

<Preparation order>

In the slurry composition for a secondary battery positive electrode of the present invention, the above-mentioned components are used to prepare a slurry composition. Concretely, a process (dry mixing process) of dry-mixing the polymer particles for a positive electrode of a secondary battery, a positive electrode active material and a conductive material to obtain a dry mixture and a dry mixture obtained in a dry mixing process are mixed with a dispersion medium, The slurry composition is prepared through a step of obtaining a slurry composition for use (a dispersion medium mixing step).

[Dry mixing process]

First, the polymer particles, the positive electrode active material, and the conductive material are mixed (dry mixed) in a state where the solid concentration of the mixture at the time of mixing exceeds 90% by mass to obtain a dry mixture. The solid content concentration of the mixture at the time of dry mixing is preferably 95% by mass or more, and more preferably 97% by mass or more. In the dry mixing, it is preferable to intentionally mix water or an organic solvent in the powder state without adding them. In the present invention, in the present invention, the solid content concentration (%) of the mixture at the time of dry mixing can be obtained by transferring the mixture before mixing, for example, about 3 g of a product having a temperature of 25 캜 to an aluminum dish and precisely weighing After drying, it was dried in a dryer at 105 ° C for 24 hours to volatilize the water. Thereafter, the mass of the dried material (after drying) obtained by cooling to 25 ° C in a desiccator was precisely weighed, And multiplying by 100.

The mixing method of dry mixing is not particularly limited, but it is preferable to mix using a mixer. Examples of the mixer used for dry mixing include a dry tumbler, a super mixer, a Henschel mixer, a flash mixer, an air blender, a flow jet mixer, a drum mixer, a Ribocon mixer, a Pug mixer, a Nauta mixer, a ribbon mixer, , A planetary mixer, and further kneading apparatuses such as a screw type kneader, a defoaming kneader, a paint shaker, a pressurized kneader, and a two-roll kneader. Mixers such as a planetary mixer capable of dispersing by stirring are preferable, and planetary mixers and Henschel mixers are particularly preferable among the above-mentioned devices, which can be relatively easily used.

The mixing time of dry mixing is not particularly limited as long as each component is homogeneously mixed, but is preferably 1 minute or more, more preferably 2 minutes or more, still more preferably 10 minutes or more, and preferably 60 Min, more preferably not more than 30 minutes, further preferably not more than 20 minutes.

In the dry mixing, the addition amount ratio of the polymer particles, the positive electrode active material and the conductive material is not particularly limited.

For example, the amount of the polymer particles added is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and most preferably 5 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the positive electrode active material. If the addition amount of the polymer particles per 100 parts by mass of the positive electrode active material is 0.5 parts by mass or more, the copolymer satisfactorily covers the positive electrode active material in the positive electrode composite material layer formed using the obtained slurry composition and the high- It can be ensured sufficiently. On the other hand, if the blending amount of the polymer particles per 100 parts by mass of the positive electrode active material is 5 parts by mass or less, the internal resistance of the secondary battery is not excessively increased.

The amount of the conductive material to be added is preferably at least 1 part by mass, more preferably at least 1.5 parts by mass, and most preferably at most 7 parts by mass, and most preferably at most 5 parts by mass per 100 parts by mass of the positive electrode active material. When the amount of the conductive material to be added is within the above-mentioned range, the conductive path is well formed in the positive electrode composite material layer formed by using the obtained slurry composition, so that the internal resistance of the secondary battery can be reduced and the high potential durability of the positive electrode can be sufficiently secured .

[Dispersion Mixing Process]

Then, the above-mentioned dispersion medium is added to the dry mixture obtained through the dry mixing process and mixed to prepare a slurry composition.

The method of adding the dispersion medium to the dry mixture is not particularly limited and may be added in a batch or in a sequential manner. In view of obtaining a slurry composition in which each component is uniformly dispersed, the sequential addition is preferable.

The amount of the dispersion medium to be added in the dispersion medium mixing step is not particularly limited. For example, the solid content concentration of the obtained slurry composition is preferably 50% by mass or more, more preferably 60% by mass or more, and preferably 80% By mass or less, more preferably 75% by mass or less.

The method of mixing the dry mixture and the dispersion medium is not particularly limited, and examples thereof include a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a brain ball, an ultrasonic disperser, a homogenizer, a planetary mixer, Can be used to prepare a slurry composition by mixing the dry mixture and the dispersion medium.

The mixing time in the dispersion medium mixing step is not particularly limited as long as the dry mixture and the dispersion medium are homogeneously mixed, but is preferably 1 minute or more, more preferably 2 minutes or more, still more preferably 10 minutes or more, Preferably 120 minutes or less, more preferably 90 minutes or less, further preferably 60 minutes or less.

(Positive electrode for secondary battery)

The positive electrode for a secondary battery of the present invention comprises a current collector and a positive electrode composite material layer formed on the current collector, wherein the positive electrode material layer is a slurry composition for a secondary battery positive electrode obtained by the method for manufacturing the secondary battery positive electrode slurry composition As shown in Fig.

The positive electrode for a secondary battery of the present invention is manufactured by using the slurry composition for a secondary battery positive electrode obtained by the method for producing a slurry composition for a secondary battery positive electrode of the present invention and therefore has excellent durability at high potential and high peel strength . Further, the positive electrode for a secondary battery of the present invention can reduce the internal resistance of the secondary battery, and even when the secondary battery is exposed to a long time for a long time, the secondary battery can exhibit excellent life characteristics.

&Lt; Preparation method of positive electrode &gt;

The positive electrode for a secondary battery according to the present invention can be obtained by, for example, a step of applying the above-described slurry composition onto a current collector (coating step), a step of drying the slurry composition applied on the current collector, (Drying step).

The positive electrode for a secondary battery of the present invention can also be produced by a method in which the above-mentioned slurry composition is dry-assembled to prepare composite particles, and the positive electrode composite material layer is formed on the current collector using the composite particles.

[Application step]

The method of applying the slurry composition onto the current collector is not particularly limited and a known method can be used. Specifically, as a coating method, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method and the like can be used. At this time, the slurry composition may be applied to only one surface of the current collector, or may be applied to both surfaces. The thickness of the slurry film on the collector on the current collector after application and drying can be appropriately set in accordance with the thickness of the positive electrode composite material layer obtained by drying.

Here, as the current collector to which the slurry composition is applied, a material having electric conductivity and electrochemically durable is used. Specifically, as the current collector, a current collector made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum can be used. Among them, an aluminum foil is particularly preferable as a collector used as a positive electrode. The above materials may be used singly or in combination of two or more in an arbitrary ratio.

[Drying process]

The method for drying the slurry composition on the current collector is not particularly limited and a known method can be used. For example, a drying method by hot air, hot air, low-humidity air, vacuum drying, . By drying the slurry composition on the current collector in this way, a positive electrode composite material layer is formed on the current collector to obtain a positive electrode for a secondary battery having a current collector and a positive electrode material layer.

After the drying step, the positive electrode composite material layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the positive electrode composite material layer and the current collector can be improved.

Furthermore, when the positive electrode composite material layer contains a curable polymer, it is preferable to cure the polymer after formation of the positive electrode composite material layer.

(Secondary battery)

The secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode for a secondary battery of the present invention is used as the positive electrode. Further, since the secondary battery of the present invention is provided with the positive electrode for secondary battery of the present invention, the rise of the internal resistance is suppressed. Even when the secondary battery is exposed to a high potential for a long time (for example, 4.4V or more) Excellent lifetime characteristics.

<Negative electrode>

As the negative electrode, a known negative electrode can be used. Specifically, as the negative electrode, for example, a negative electrode comprising a thin metal plate of lithium, or a negative electrode comprising a negative electrode mixture layer formed on a current collector may be used.

The current collector may be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold or platinum. As the negative electrode composite material layer, a layer containing a negative electrode active material and a binder may be used. Further, the binder is not particularly limited, and any known material can be used.

<Electrolyte>

As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte of the lithium ion secondary battery, for example, a lithium salt is used. As the lithium salt, _{e.g., LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) 2 NLi, and the like _{(CF 3 SO 2) 2 NLi} , (C 2 F 5 SO 2) NLi. Of these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easy to dissolve in a solvent and exhibits a high degree of dissociation. The electrolytes may be used singly or in combination of two or more in an arbitrary ratio. Generally, the lithium ion conductivity tends to increase with the use of a supporting electrolyte having a high degree of dissociation, so that the lithium ion conductivity can be controlled depending on the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of the organic solvent include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate Examples of the organic solvent include carbonates such as butylene carbonate (BC) and ethyl methyl carbonate (EMC), esters such as? -Butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran, Sulfoxide compounds such as dimethyl sulfoxide and the like are preferably used. A mixed solution of these solvents may also be used. Among them, carbonates are preferably used because they have a high dielectric constant and a wide stable potential range, and it is more preferable to use a mixture of ethylene carbonate and ethylmethyl carbonate.

The concentration of the electrolyte in the electrolytic solution can be adjusted arbitrarily, and is preferably 0.5 to 15 mass%, more preferably 2 to 13 mass%, and more preferably 5 to 10 mass% . To the electrolytic solution, known additives such as fluoroethylene carbonate, ethylmethylsulfone and the like may be added.

<Separator>

The separator is not particularly limited, and for example, those described in Japanese Laid-Open Patent Publication No. 2012-204303 can be used. Among them, polyolefins such as polyethylene, polypropylene, polybutene, poly (ethylene terephthalate), polybutylene terephthalate, polybutylene terephthalate, polybutylene terephthalate, Polyvinyl chloride) resin is preferable.

<Manufacturing Method of Secondary Battery>

In the secondary battery of the present invention, for example, the positive electrode and the negative electrode are overlapped with each other with a separator interposed therebetween. The battery is wound into a battery container by winding or folding according to the necessity, It can be manufactured by punching. An overcurrent prevention element such as a fuse, a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary in order to prevent internal pressure rise and overcharge discharge of the secondary battery from occurring. The shape of the secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.

Example

Hereinafter, the present invention will be described concretely based on examples, but the present invention is not limited to these examples. In the following description, &quot;% &quot; and &quot; part &quot; representing amounts are on a mass basis unless otherwise specified.

In the polymer produced by copolymerizing a plurality of kinds of monomers, the proportion of the structural units formed by polymerizing certain monomers in the polymer is generally, unless otherwise specified, (Input ratio) of the monomer to the total amount of the monomer.

In the Examples and Comparative Examples, the volume average particle diameter D50 of each particle, the molecular weight (weight average molecular weight, number average molecular weight, molecular weight distribution) and glass transition temperature of the copolymer, the peel strength and high- The internal resistance of the secondary battery was measured and evaluated by the following method.

&Lt; Volume average particle diameter D50 &

Was determined as a particle diameter at which the cumulative volume calculated from the small diameter side was 50% in a dry particle size distribution using a laser diffraction scattering particle size distribution measuring apparatus ("Microtruck MT3200II" manufactured by Nikkiso Co., Ltd.).

<Molecular Weight>

The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the copolymer contained in the polymer particles were measured by gel permeation chromatography (GPC) using a 10 mM LiBr-DMF solution under the following measurement conditions , And the molecular weight distribution (Mw / Mn) was calculated.

· Separation column: Shodex KD-806M (manufactured by Showa Denko KK)

· Detector: differential refractometer detector RID-10A (manufactured by Shimadzu Corporation)

· Flow rate of eluent: 0.3 mL / min

· Column temperature: 40 DEG C

· Standard Polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

<Glass transition temperature>

Polymer particles were molded to obtain a film having a thickness of 1 占 0.3 mm. The film was dried in a hot air oven at 120 캜 for 1 hour. Thereafter, using a dried film as a sample and using a DSC6220SII (differential scanning calorimeter, manufactured by Nanotechnology) under the conditions of a measurement temperature of -100 DEG C to 180 DEG C and a temperature rise rate of 5 DEG C / min according to JIS K7121, The glass transition temperature (占 폚) of the copolymer contained in the polymer particles was measured.

<Peel Strength>

The positive electrodes prepared in Examples and Comparative Examples were cut into squares having a width of 1.0 cm and a length of 10 cm to prepare test pieces. Then, a cellophane tape was attached to the surface of the positive electrode mixture layer side of the test piece. At this time, the cellophane tape specified in JIS Z1522 was used. Thereafter, the stress was measured when the test piece was peeled from the one end side toward the other end side at a speed of 50 mm / min while the cellophane tape was fixed to the test stand. The measurement was carried out 10 times, and an average value of the stress was obtained. The stress was evaluated on the basis of the following criteria. The larger the fill strength, the better the adhesion of the positive electrode composite layer to the current collector.

A: Peel strength of 50 N / m or more

B: Peel strength of 10 N / m or more and less than 50 N / m

C: Peel strength less than 10 N / m

<High potential durability>

The slurry composition for a secondary battery positive electrode prepared in Examples and Comparative Examples was coated on an aluminum foil (20 μm thick) as a current collector with a comma coater so that the weight per unit area after drying was 20 mg / cm ² , Minute at 120 캜 for 20 minutes, and further heat-treated at 60 캜 for 10 hours under vacuum to obtain a positive electrode having a positive electrode composite layer on the current collector.

This positive electrode was cut into a circular shape having a diameter of 12 mm and a circular polypropylene porous film (diameter 18 mm, thickness 25 占 퐉), metal lithium (diameter 14 mm), and expanded metal were formed in this order on the positive electrode composite material layer side of the cut- To obtain a laminate. This laminate was housed in a stainless steel coin-shaped outer container (20 mm in diameter, 1.8 mm in height, and 0.25 mm in thickness of stainless steel) provided with a polypropylene packing. An electrolytic solution (LiPF ₆ solution having a concentration of 1.0 M (solvent: a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3/7 (weight ratio))) was injected into the vessel so that no air remained. After injecting the electrolyte solution, a stainless steel cap having a thickness of 0.2 mm was put on the outer container through a packing made of polypropylene and fixed, and the battery can was sealed to prepare a coin cell having a diameter of 20 mm and a thickness of about 2 mm.

A voltage of 4.4 V was applied to the obtained coin cell in an atmosphere of 25 캜 for 10 hours. The current density per unit mass (mA / g) of the positive electrode composite material layer flowing after 10 hours was obtained as the oxidation current density. The smaller the oxidation current density is, the more excellent the high-durability copolymer is coated with the positive electrode active material, and the oxidation reaction of the surface of the positive electrode active material when the high voltage is applied and the oxidation reaction of the electrolyte near the surface of the positive electrode active material are suppressed , That is, the positive electrode shows excellent high-potential durability.

A: The oxidation current density is less than 0.2 mA / g

B: oxidation current density of 0.2 mA / g or more and less than 0.3 mA / g

C: Oxidation current density of 0.3 mA / g or more and less than 0.4 mA / g

D: oxidation current density of 0.4 mA / g or more and less than 0.5 mA / g

E: oxidation current density of 0.5 mA / g or more

<Internal resistance>

In order to evaluate the internal resistance of the secondary battery, the IV resistance was measured as follows. After charging to 50% of SOC (State of Charge) at a temperature of 25 ° C at 1C (C is a value expressed by rated capacity (mA) / 1h (hour)), 0.5C, 1.0C, 1.5C, and 2.0C for 20 seconds and discharge for 20 seconds, respectively. The battery voltage after 20 seconds in each case (charging side and discharging side) was plotted against the current value, and the slope thereof was obtained as IV resistance (?) (IV resistance at charging and IV resistance at discharging). The value (Ω) of the obtained IV resistance was evaluated according to the following criteria. The smaller the value of the IV resistance is, the smaller the internal resistance is.

A: IV resistance is 2.0Ω or less

B: IV resistance is more than 2.0Ω and less than 2.3Ω

C: IV resistance is more than 2.3Ω and less than 2.5Ω

D: IV resistance is more than 2.5Ω and less than 3.0Ω

E: IV resistance exceeds 3.0Ω

(Example 1)

&Lt; Preparation of Polymer Particle for Secondary Battery Positive Electrode &gt;

400 parts of ion-exchanged water was charged into a pressure-resistant container equipped with a stirrer, a thermometer, a cooling tube and a nitrogen gas introducing tube, and the pressure was reduced three times with reduced pressure (-600 mmHg) and nitrogen gas while gently rotating the stirrer, The oxygen concentration in the gas phase portion of the reaction vessel was 1% or less and the dissolved oxygen in the water was 1 ppm or less was confirmed by using a dissolved oxygen meter. Thereafter, 0.2 part of partially saponified polyvinyl alcohol (GOSENOL GH-20, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) (degree of saponification 86.5 mol% to 89.0 mol%) as a dispersant was slowly added thereto and dispersed well. The stirring was continued, and the partial saponification polyvinyl alcohol was dissolved for 30 minutes.

Subsequently, 85 parts of acrylonitrile as a nitrile group-containing monomer, 5 parts of methacrylic acid as a monomer containing a hydrophilic group and 0.2 part of t-dodecylmercaptan as a chain transfer agent were introduced under the conditions of a nitrogen gas aeration rate of 0.5 ml / And the mixture was stirred and maintained at 60 ± 2 ° C. 0.4 part of 1,1-azobis (1-acetoxy-1-phenylethane) ("OTAZO-15" manufactured by OTSUKA CHEMICAL INDUSTRIES, LTD .; abbreviated as OT Azo-15), which is an oil- The solution dissolved in 10 parts of acrylonitrile as a monomer was added to initiate the reaction. The reaction was allowed to proceed at 60 ± 2 ° C for 3 hours, followed by further reaction at 70 ± 2 ° C for 2 hours and then at 80 ± 2 ° C for 2 hours. Thereafter, the mixture was cooled to 40 DEG C or lower to obtain polymer particles containing a copolymer. The obtained polymer particles were recovered in a filter cloth of 200 mesh, washed three times with 100 parts of ion-exchanged water, and then dried under reduced pressure at 70 캜 for 12 hours to recover and recover (70% recovery). The volume average particle diameter D50 of the polymer particles after the isolation and purification and the molecular weight (weight average molecular weight, number average molecular weight, molecular weight distribution) and the glass transition temperature of the copolymer constituting the polymer particles were measured. The results are shown in Table 1.

&Lt; Preparation of slurry composition for secondary battery positive electrode &

Ternary active material having a layered structure as positive electrode active material _{(LiNi 0.5 Co 0.2 Mn 0.3 O} 2) ( volume average particle diameter D50: 10μm) 100 part and the conductive acetylene black (Denka Black powder as a material: Denki Chemical Co., a specific surface area of 68m ² / g, number average particle diameter 35 nm) and 2.0 parts of the polymer particles described above were put in a planetary mixer and dry mixed at a rotation speed of 5 rpm and a solid content concentration of more than 90% for 20 minutes to obtain a dry mixture Dry mixing process). The resulting dry mixture was mixed for 20 minutes while a proper amount of NMP was added as a dispersion medium in succession to obtain a secondary battery positive electrode slurry composition (dispersion medium mixing step). The solid content concentration of the obtained slurry composition was 70% by mass, and the viscosity at 60 rpm as measured by a B-type viscometer according to JIS Z8803: 1991 was 4400 mPa 占 퐏 (25 占 폚, spindle shape: 4). The slurry composition was used to evaluate the high-potential durability of the positive electrode. The results are shown in Table 1.

&Lt; Preparation of positive electrode for secondary battery &

An aluminum foil having a thickness of 20 mu m was prepared as a current collector. The slurry composition for a secondary battery positive electrode was applied to one surface of an aluminum foil so that the coating amount after drying was 20 mg / cm ² , and dried at 90 캜 for 20 minutes and then at 120 캜 for 20 minutes. Thereafter, it was further heat-treated at 60 DEG C for 10 hours to obtain a positive electrode cloth. The positive electrode was rolled by a roll press to produce a positive electrode having a thickness of 70 탆 and composed of a positive electrode mixture layer having a density of 3.2 g / cm ³ and an aluminum foil. The obtained positive electrode was used to evaluate the peel strength of the positive electrode. The results are shown in Table 1.

<Fabrication of negative electrode for secondary battery>

100 parts of artificial graphite (volume average particle diameter D50: 24.5 mu m, specific surface area 4 m &lt; ² &gt; / g) as a negative electrode active material and 1% aqueous solution of carboxymethylcellulose (available from Daiichi Kogyo Pharmaceutical Co., , &Quot; BSH-12 &quot;) was added in an amount of 1 part in terms of solid content, adjusted to a solid content concentration of 55% by ion exchange water, and then mixed at 25 DEG C for 60 minutes. Then, the mixture was adjusted to a solid content concentration of 52% with ion-exchanged water and mixed again at 25 캜 for 15 minutes to obtain a mixed solution. To this mixed solution, a 40% aqueous dispersion of a styrene-butadiene copolymer (glass transition temperature: -15 占 폚) as a binder was added in an amount of 1.0 part in terms of solid content and ion-exchanged water so as to have a final solid concentration of 50% Mix for a few minutes. This was degassed under a reduced pressure to obtain a slurry composition for secondary battery negative electrode having good flowability.

The slurry composition for a secondary battery negative electrode was coated on a copper foil having a thickness of 20 mu m as a current collector with a comma coater so as to have a thickness of about 150 mu m after drying and dried. This drying was carried out by conveying the copper foil in an oven at 60 캜 for 2 minutes at a speed of 0.5 m / min. Thereafter, the resultant was heat-treated at 120 DEG C for 2 minutes to obtain a negative electrode cloth. The fabricated negative electrode was rolled by a roll press to produce a negative electrode having a thickness of 80 m as the negative electrode composite material layer.

<Preparation of Separator>

A single-layer polypropylene separator (65 mm wide, 500 mm long, 25 탆 thick, manufactured by the dry method, porosity of 55%) was cut into a square of 5 cm x 5 cm.

&Lt; Preparation of Secondary Battery &gt;

As an exterior of the battery, an aluminum-coated exterior was prepared. The positive electrode thus obtained was cut out into a square of 4 cm x 4 cm, and the surface of the collector side was placed so as to be in contact with the aluminum-covered sheath. Subsequently, a 5 cm x 5 cm square separator obtained above was placed on the surface of the positive electrode composite material layer of the positive electrode. Further, the negative electrode thus obtained was cut into a square of 4.2 cm x 4.2 cm, placed on the separator, and the surface on the negative electrode composite material layer side was disposed so as to face the separator. Then, an electrolytic solution (a mixed solvent of a 1.0 M LiPF ₆ solution (solvent: ethylene carbonate / ethyl methyl carbonate = 3/7 (weight ratio) and 1.5 vol.% (Solvent ratio) of vinylene carbonate as an additive) Charged. Further, in order to seal the openings of the aluminum-covered sheath, the aluminum-covered sheath was subjected to heat sealing at 150 ° C to obtain a lithium ion secondary battery. Using the obtained lithium ion secondary battery, the internal resistance was evaluated. The results are shown in Table 1.

(Examples 2 and 3)

Except that the amount of the partially saponified polyvinyl alcohol as the dispersing agent was changed to 0.1 part and 2.0 parts, respectively, at the time of preparation of the polymer particles, the polymer particles for the secondary battery positive electrode, the slurry for the positive electrode of the secondary battery A positive electrode for a secondary battery, a negative electrode for a secondary battery, and a secondary battery were prepared, and evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Examples 4 to 6)

Polymer particles for a secondary battery positive electrode, slurry composition for a positive electrode of a secondary battery, and secondary particles for a secondary battery were prepared in the same manner as in Example 1, except that the monomers described in Table 1 were used in the respective ratios in preparing the polymer particles. A positive electrode for a battery, a negative electrode for a secondary battery, and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

Further, in Example 6, 2-ethylhexyl acrylate was used as the (meth) acrylic acid ester monomer.

(Example 7)

Except that the amount of t-dodecyl mercaptan as a chain transfer agent was changed to 0.1 part at the time of preparation of the polymer particles, the polymer particles for the secondary battery positive electrode, the slurry composition for the secondary battery positive electrode, A positive electrode for a secondary battery, a negative electrode for a secondary battery, and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)

A polymer particle for a secondary battery positive electrode, a slurry composition for a positive electrode of a secondary battery, and a secondary particle for a secondary battery were prepared in the same manner as in Example 1 except that polyvinylidene fluoride particles (volume average particle diameter D50: A positive electrode for a battery, a negative electrode for a secondary battery, and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)

<Preparation of Varnish for Secondary Battery Positive Electrode>

100 parts of the polymer particles obtained in Example 1 and 1800 parts of NMP were charged into a pressure-resistant container equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas introducing tube. Under nitrogen gas ventilation in a trace amount (200 ml / The temperature was raised to ± 2 ° C and maintained for 3 hours. In order to remove the contained water, the solution was stirred and melted at a temperature of 85 ± 2 ° C. and under reduced pressure (25 torr or less) until the water content became 1000 ppm or less. Thereafter, the mixture was cooled to 40 캜 or lower, and filtered through a 100 탆 filtration filter to obtain a secondary battery positive electrode varnish (solid content: 6%).

&Lt; Preparation of slurry composition for secondary battery positive electrode &

Ternary active material having a layered structure as positive electrode active material _{(LiNi 0.5 Co 0.2 Mn 0.3 O} 2) ( volume average particle diameter D50: 10μm) 100 part and the conductive acetylene black (Denka Black powder as a material: Denki Chemical Co., a specific surface area of 68m ² / g, number average particle diameter 35 nm) was added to a planetary mixer, and the mixture was stirred at a rotation speed of 5 rpm at a stirring speed of 5 rpm to obtain a mixture. The slurry composition for a secondary battery positive electrode was obtained by mixing the obtained mixture with the above-mentioned varnish (2.0 parts by solid content) and an appropriate amount of NMP as a dispersion medium in that order for 20 minutes. The solid content concentration of the obtained slurry composition was 70% by mass, and the viscosity at 60 rpm as measured by a B-type viscometer according to JIS Z8803: 1991 was 4400 mPa 占 퐏 (25 占 폚, spindle shape: 4). The slurry composition was used to evaluate the high-potential durability of the positive electrode. The results are shown in Table 1.

A positive electrode for a secondary battery, a negative electrode for a secondary battery, and a secondary battery were produced in the same manner as in Example 1 except that the thus obtained slurry composition for a secondary battery positive electrode was used, . The results are shown in Table 1.

(Comparative Example 3)

Except that the amount of the partially saponified polyvinyl alcohol as the dispersing agent was changed to 3.0 parts at the time of preparing the polymer particles, the polymer particles for the secondary battery positive electrode, the slurry composition for the secondary battery positive electrode, A positive electrode for a battery, a negative electrode for a secondary battery, and a secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 4)

Polymer particles for a secondary battery positive electrode, slurry composition for a positive electrode of a secondary battery, and secondary battery positive electrode particles were prepared in the same manner as in Example 1, except that the monomers described in Table 1 were used at the time of preparation of the polymer particles A positive electrode, a negative electrode for a secondary battery, and a secondary battery were prepared and evaluated in the same manner as in Example 1. [ The results are shown in Table 1.

In Comparative Example 4, 2-ethylhexyl acrylate was used as the (meth) acrylic acid ester monomer.

In Table 1 shown below,

&Quot; AN &quot; represents acrylonitrile,

&Quot; MAA &quot; represents methacrylic acid,

&Quot; 2EHA &quot; represents 2-ethylhexyl acrylate,

"PVDF" represents polyvinylidene fluoride.

From Examples 1 to 7 and Comparative Examples 1 to 4 in Table 1, it can be seen that in Examples 1 to 7, a positive electrode excellent in high-potential durability is obtained. In Examples 1 to 7, it can be seen that the positive electrode has excellent peel strength and the internal resistance of the secondary battery can be sufficiently reduced.

From Examples 1 to 3 in Table 1, it is possible to further improve the peel strength and high-potential durability of the positive electrode by adjusting the volume average particle diameter D50 of the polymer particles, and further reduce the internal resistance of the secondary battery Can be done.

From Examples 1 and 4 to 6 of Table 1, it is possible to further improve the peel strength and high-potential durability of the positive electrode by changing the composition of the copolymer contained in the polymer particles, It can be understood that it can be further reduced.

From Examples 1 and 7 in Table 1, it is possible to further improve the high-potential durability of the positive electrode by controlling the molecular weight distribution of the copolymer contained in the polymer particles, and further reduce the internal resistance of the secondary battery Can be done.

According to the present invention, it is possible to provide a method for producing a slurry composition for a secondary battery positive electrode that exhibits excellent high-potential durability on a positive electrode.

According to the present invention, it is possible to provide a secondary battery having a positive electrode for a secondary battery excellent in high-potential durability and a positive electrode for the secondary battery and having excellent battery characteristics.

Claims (7)

A step of dry-mixing the polymer particles for the positive electrode of the secondary battery, the positive electrode active material and the conductive material to obtain a dry mixture,
And mixing the dry mixture and the dispersion medium to obtain a slurry composition for a secondary battery positive electrode,
Wherein the secondary battery positive electrode polymer particles contain a copolymer including both of a nitrile group-containing monomer unit and a hydrophilic group-containing monomer unit, wherein the volume average particle diameter D50 is 1 占 퐉 or more,
The ratio of the volume average particle diameter D50 of the secondary battery positive electrode polymer particles to the volume average particle diameter D50 of the positive electrode active material is 0.1 or more. The method according to claim 1,
Wherein the volume average particle diameter D50 of the secondary battery positive electrode polymer particles is 2000 占 퐉 or less and the ratio of the volume average particle diameter D50 of the secondary battery positive electrode polymer particles to the volume average particle diameter D50 of the positive electrode active material is 200 or less, / RTI &gt; 3. The method according to claim 1 or 2,
Wherein the copolymer contains 80% by mass or more and 99.9% by mass or less of the nitrile group-containing monomer units, and 0.1% by mass or more and 20% by mass or less of the hydrophilic group-containing monomer units. 4. The method according to any one of claims 1 to 3,
Wherein the copolymer has a molecular weight distribution (Mw / Mn) of 10 or less. 5. The method according to any one of claims 1 to 4,
Wherein the copolymer has a glass transition temperature of 60 占 폚 or more and 170 占 폚 or less. And a positive electrode composite material layer formed on at least one surface of the current collector,
Wherein the positive electrode composite material layer is formed from the slurry composition for a secondary battery positive electrode obtained by the method for producing a slurry composition for a secondary battery positive electrode according to any one of claims 1 to 5. A secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution and a separator, wherein the positive electrode is the positive electrode for a secondary battery according to claim 6.