KR101539819B1 - Electrode for secondary battery, and secondary battery - Google Patents

Abstract

And an electrode active material layer containing an active material and a binder laminated on the current collector, wherein the segment A having a degree of swelling with respect to the electrolytic solution of 100 to 300% and the segment A having a swelling degree with respect to the electrolyte Of the segment B is 500 to 50,000% or the segment B is dissolved in the electrolytic solution.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode for a secondary battery and a secondary battery,

TECHNICAL FIELD The present invention relates to an electrode for a secondary battery and a binder which is a constituent component thereof, and more particularly to an electrode for use in a lithium ion secondary battery or the like, which can obtain a battery having a high output characteristic and a cycle characteristic. The present invention also relates to a secondary battery having such an electrode.

The lithium ion secondary battery exhibits the highest energy density among the practical use batteries, and is particularly widely used for small-sized electronics. Also, development for automobile applications is expected. Among them, further improvement in reliability such as high output of the lithium ion secondary battery and cycle characteristics is demanded.

Generally, the lithium ion secondary battery is formed by bonding a lithium-containing metal oxide such as LiCoO ₂ , LiMn ₂ O ₄ , LiFePO ₄ or the like, which is used as a positive electrode active material, with a binder such as polyvinylidene fluoride to form a positive electrode . On the other hand, a negative electrode is formed by bonding a carbonaceous material (amorphous), a metal oxide, a metal sulfide, or the like, which is used as a negative electrode active material, with a binder such as a styrene-butadiene copolymer.

In order to solve the problem of the cycle characteristics of the lithium ion secondary battery, for example, Patent Document 1 discloses adding a graft polymer as a dispersing agent to a positive electrode in addition to a binder such as polyvinylidene fluoride. The use of a graft polymer comprising vinylpyrrolidone and styrene as the dispersant improves the dispersibility of the conductive agent. As a result, nonuniformity of the conductive agent in the electrode is suppressed and a battery excellent in cycle characteristics is obtained.

Patent Document 2 discloses the use of a graft polymer composed of olefin and acrylonitrile in a positive electrode. By suppressing the swelling property with respect to an electrolytic solution, it is possible to maintain the binding property with the active material and obtain a battery having excellent cycle characteristics ought.

Japanese Patent Application Laid-Open No. 2003-272634 Japanese Patent Application Laid-Open No. 2004-227974

However, the inventors of the present invention have studied the following. That is, in the method described in Patent Document 1, a binder such as polyvinylidene fluoride is additionally used in addition to the graft polymer in order to maintain both the dispersibility of the conductive agent and the tackiness with the active material, As the resistance component increases, the energy density and output characteristics of the obtained secondary battery are deteriorated. In addition, the method described in Patent Document 2 does not have sufficient dispersibility of the conductive agent, the stability of the slurry over time is inferior, and the electron resistance increases due to nonuniformity of the conductive agent. Particularly, in a high output such as an HEV (hybrid electric vehicle) application, the output characteristic is low. In addition, in Patent Documents 1 and 2, the reaction on the active material active surface can not be suppressed, and swelling during high-temperature operation due to gas generation is seen.

It is therefore an object of the present invention to provide an electrode for a lithium ion secondary battery in which the obtained secondary battery has high output characteristics and gas generation is suppressed.

As a result of intensive studies for solving the above problems, the inventors of the present invention found that, by containing a graphene polymer having a low swelling property and a high component in an electrolyte solution as a binder, the output characteristics are improved , And gas generation is suppressed. That is, the inventors of the present invention have found that the methods described in Patent Documents 1 and 2 can achieve improvement in cycle characteristics due to bondability maintenance and improvement in dispersibility of a conductive agent, but when the graft polymer is composed only of components having a low swelling property of an electrolytic solution Therefore, it was considered that the suppression of the output characteristics and the gas generation could not be achieved. If the graft polymer contains a component having a low swelling property with respect to an electrolytic solution and a high component, a low swelling component is adsorbed to the active material and a conductive agent in the slurry, and the high swelling component spreads in the solvent to exhibit high slurry stability and dispersibility okay. Further, since the smoothness of the obtained electrode and the retentivity of the electrolyte are improved, the output characteristics are enhanced, and the active material surface is reduced and the amount of generated gas is significantly reduced because the graft polymer is adsorbed on the surface of the active material inside the battery The present invention has been completed based on these findings.

The present invention for solving the above problems includes the following matters as gist.

(1) a current collector and an electrode active material layer containing an active material and a binder laminated on the current collector, wherein the binder includes a segment A having a degree of swelling with respect to an electrolyte of 100 to 300% Wherein the graft polymer comprises a graft polymer having a swelling degree of 500 to 50,000% or a segment B dissolved in an electrolytic solution.

(2) The electrode for a secondary battery according to (1), wherein the ratio of the segment A to the segment B in the graft polymer is 20:80 to 80:20 (mass ratio).

(3) The electrode for a secondary battery according to any one of (1) to (2), wherein the graft polymer has a weight average molecular weight of 1,000 to 500,000.

(4) The electrode for a secondary battery according to any one of (1) to (3), wherein the segment B is a segment of a soft polymer having a glass transition temperature of 15 ° C or lower.

(5) A binder for a secondary battery, which comprises a segment A having a swelling degree of 100 to 300% with respect to an electrolytic solution, and a segment B having a swelling degree of 500 to 50,000% with respect to an electrolytic solution or a segment B dissolved in an electrolytic solution.

(6) The binder for a secondary battery according to (5), wherein the ratio of the segment A to the segment B in the graft polymer is 20:80 to 80:20 (mass ratio).

(7) The binder for a secondary battery according to any one of (5) to (6), wherein the segment B is a segment of a soft polymer having a glass transition temperature of 15 ° C or lower.

(8) A slurry comprising a segment A having a degree of swelling with respect to an electrolytic solution of 100 to 300% and a graft polymer consisting of a segment B having a swelling degree of 500 to 50,000% with respect to an electrolytic solution or dissolving in an electrolytic solution, (1) above, wherein the step (c) comprises a step of applying the coating liquid to the electrode and drying the coating liquid.

(9) A lithium ion secondary battery having a positive electrode, an electrolyte, and a negative electrode, wherein at least one of the positive electrode and the negative electrode is the electrode for a secondary battery according to any one of (1) to (4).

According to the present invention, by containing a predetermined graft polymer in relation to the problem of output characteristics and gas generation, the graft polymer suppresses generation of gas on the surface of the electrode active material, and further has high conductive agent dispersibility, An electrode for a secondary battery capable of exhibiting characteristics can be obtained.

Hereinafter, the present invention will be described in detail.

An electrode for a secondary battery (hereinafter sometimes simply referred to as " electrode ") of the present invention is formed by laminating an electrode active material layer containing an active material and a binder on a current collector. That is, the electrode of the present invention includes a current collector, and an electrode active material layer containing the active material and the binder laminated on the current collector. The electrode of the present invention includes a segment A having a degree of swelling with respect to an electrolytic solution of 100 to 300% and a graft polymer comprising a segment B having a swelling degree of 500 to 50,000% with respect to an electrolytic solution or dissolved in an electrolytic solution.

(Electrode active material)

The electrode active material used in the secondary battery electrode of the present invention is generally selected in accordance with the secondary battery in which the electrode is used. Examples of the secondary battery include a lithium ion secondary battery and a nickel hydrogen secondary battery.

When the electrode for a secondary battery of the present invention is used for a positive electrode of a lithium ion secondary battery, the electrode active material (positive electrode active material) for a lithium ion secondary battery is roughly classified into an inorganic compound and an organic compound.

Examples of the positive electrode active material composed of an inorganic compound include transition metal oxides, complex oxides of lithium and transition metals, transition metal sulfides, and the like. As the transition metal, Fe, Co, Ni, Mn or the like is used. Specific examples of the inorganic compound used for the positive electrode active material include lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ and LiFeVO ₄ ; Transition metal sulfides such as TiS ₂ , TiS ₃ and amorphous MoS ₂ ; Transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ and V ₆ O ₁₃ . These compounds may be partially substituted with an element. As the positive electrode active material composed of an organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene may be used. The iron-based oxide lacking electrical conductivity may be used as an electrode active material covered with a carbon material by causing a carbon source material to exist at the time of reduction calcination. These compounds may be partially substituted by an element.

 The positive electrode active material for a lithium ion secondary battery may be a mixture of the inorganic compound and the organic compound. The particle diameter of the positive electrode active material is appropriately selected in terms of balance with other constituent requirements of the battery. From the viewpoint of improvement of battery characteristics such as load characteristics and cycle characteristics, 50% volume cumulative wrinkles, usually 0.1 to 50 μm, To 20 m. When the 50% volume cumulative diameter falls within this range, a secondary battery having a large charging / discharging capacity can be obtained, and handling of the electrode slurry and the electrode is easy. The 50% volume cumulative diameter can be obtained by measuring the particle size distribution by laser diffraction.

When the electrode for a secondary battery of the present invention is used for a lithium ion secondary battery negative electrode, examples of the electrode active material (negative electrode active material) for a lithium ion secondary battery negative electrode include amorphous carbon, graphite, natural graphite, Carbonaceous materials such as pitch-based carbon fibers, and conductive polymers such as polyacene. As the negative electrode active material, metals such as silicon, tin, zinc, manganese, iron and nickel, alloys thereof, oxides and sulfates of the above metals or alloys are used. Lithium alloys such as metal lithium, Li-Al, Li-Bi-Cd and Li-Sn-Cd, lithium transition metal nitride, silicon and the like can be used. The electrode active material may also be one obtained by attaching a conductive material on the surface by a mechanical modification method. The particle size of the negative electrode active material is appropriately selected in terms of balance with other constituent requirements of the battery. From the viewpoint of improving the battery characteristics such as initial efficiency, load characteristics and cycle characteristics, 50% volume cumulative wrinkles, usually 1 to 50 μm, Lt; / RTI >

When the electrode for a secondary battery of the present invention is used for a positive electrode of a nickel-hydrogen secondary battery, nickel hydroxide particles can be mentioned as an electrode active material (positive electrode active material) for a positive electrode of a nickel hydrogen secondary battery. The nickel hydroxide particles may be solid solution of cobalt, zinc, cadmium or the like, or may be coated with a cobalt compound whose surface is subjected to an alkali heat treatment. The nickel hydroxide particles may contain additives such as cobalt compounds such as cobalt oxide, cobalt oxide and cobalt hydroxide, zinc compounds such as zinc metal, zinc oxide and zinc hydroxide, and rare earth compounds such as erbium oxide in addition to yttrium oxide do.

When the electrode for a secondary battery of the present invention is used for a nickel-hydrogen secondary battery negative electrode, as the electrode active material (negative electrode active material) for a nickel hydrogen secondary battery negative electrode, the hydrogen storage alloy particles are preferably electrochemically Any material capable of occluding the generated hydrogen and capable of releasing the occluded hydrogen easily at the time of discharging is not particularly limited but particles made of a hydrogen storage alloy of AB5 type, TiNi type and TiFe type are preferable . Specifically, a part of Ni of LaNi5, MmNi5 (Mm is micro metal), LmNi5 (Lm is at least one selected from rare earth elements including La) and alloys of these metals are changed to Al, Mn, Co, Ti , Cu, Zn, Zr, Cr, B, and the like can be used as the multi-element hydrogen-absorbing alloy particles. In particular, the hydrogen storage alloy particles having the composition represented by the general formula: LmNiwCoxMnyAlz (wherein the sum of the atomic ratios w, x, y and z is 4.80? W + x + y + z? 5.40) Is suppressed and charge / discharge cycle characteristics are improved.

The content of the electrode active material used in the present invention in the electrode active material layer is preferably 90 to 99.9 mass%, more preferably 95 to 99 mass%. When the content of the electrode active material in the electrode is within the above range, flexibility and binding property can be exhibited while exhibiting high capacity.

(Binder)

The electrode for a secondary battery of the present invention includes a segment A having a swelling degree of 100 to 300% with respect to an electrolytic solution and a graft polymer consisting of a segment B having an swelling degree of 500 to 50,000% with respect to an electrolytic solution or dissolved in an electrolytic solution .

(Graft polymer)

The graft polymer used in the present invention has two segments (segment A and segment B), one of the segments constituting the main chain and the other of the segments of the graft polymer constituting the graft portion (side chain). In addition to having the first segment and the second segment, the graft polymer may further comprise at least one arbitrary segment. Each of the first segment and the second segment may be a segment based on only one type of polymerization unit or a segment based on two or more types of polymerization units.

The two segments are composed of a segment A having a degree of swelling with respect to the electrolytic solution of 100 to 300% and a segment A having a degree of swelling with respect to the electrolytic solution so as to enhance the output property by increasing the retentivity of the electrolytic solution, And a segment B having a degree of swelling of 500 to 50,000% or dissolving in an electrolytic solution. The graft polymer forms a branched structure in the segment A and the segment B so that in the electrode including the graft polymer, the sea water structure is formed by the two segments, whereby the graft polymer exhibits adequate swelling property for the electrolytic solution, And maintains the electrolyte solution without causing peeling of the electrode in the electrolyte solution, so that high lithium conductivity can be exhibited. If the graft polymer contains segment A having a swelling degree of 100 to 300% with respect to an electrolytic solution and segment B having a swelling degree of 500 to 50,000% with respect to the electrolytic solution or dissolved in an electrolytic solution, the segment A as a low- It was found that segment B adsorbed to the active material and the conductive agent and a high-swelling component spread in the solvent exhibited high slurry stability and dispersibility. Further, since the smoothness of the obtained electrode and the retentivity of the electrolyte are improved, the output characteristics are enhanced, and the graft polymer is adsorbed on the surface of the active material in the battery, whereby the active material active surface decreases and the gas generation amount is greatly reduced.

In the graft polymer used in the present invention, either of the two segments may constitute the main chain, and the graft portion (side chain) may be constituted. Particularly, since segment B with high swelling in the slurry spreads in the slurry solvent and segment A with low swelling is adsorbed on the active material and the conductive agent, high conductivity agent dispersibility and active material protection effect are exhibited. In particular, Structure is preferable. Therefore, a graft polymer in which segment A constitutes a graft portion (side chain) and segment B constitutes a main chain is preferable.

(Swelling degree)

In the present invention, the degree of swelling of each segment is measured by the following method.

The polymer composed of the constituents of the segment A and the polymer constituted of the constituents of the segment B are each molded into a film having a thickness of about 0.1 mm and cut out to a length of about two centimeters to measure the weight (weight before immersion). Thereafter, it is immersed in an electrolytic solution at a temperature of 60 ° C for 72 hours. The immersed film is lifted and the weight (after immersion) immediately after the electrolytic solution is wiped is measured. The value after (after immersion) / (before immersion) × 100 (%) is defined as the swelling degree.

The electrolytic solution was prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in EC: DEC = 1: 2 (volumetric ratio, EC: volume at 40 DEG C and DEC: volume at 20 DEG C) A solution of LiPF ₆ dissolved at a concentration of 1 mole / liter is used.

The swelling degree of the segment A and the segment B with respect to the electrolytic solution can be controlled by the composition, the molecular weight and the degree of crosslinking. The degree of swelling of the segment A with respect to the electrolytic solution is 100% to 300%, the adsorbability to the active material and the conductive agent increases, and the effect of suppressing gas generation increases. On the other hand, the degree of swelling of the segment B with respect to the electrolytic solution is 500% to 50,000% or dissolution, and it is preferable that the degree of swelling is 500% to 10,000%, more preferably 500% to 5,000% to be.

(Segment A)

In order to control the degree of swelling of the segment A with respect to the electrolyte according to the composition and make the degree of swelling with respect to the electrolytic solution to 100 to 300%, it is preferable to constitute a monomer component having a solubility parameter of less than 8.0 or 11 or more, or a monomer component having a hydrophobic part Do. When the swelling degree is controlled by the weight average molecular weight, the weight average molecular weight of the segment A is preferably 4,000 or more and 10,000 or less. By making the weight average molecular weight fall within this range, it is possible to improve the dispersibility and slurry stability with respect to the conductive agent and the active material. In the present invention, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

Examples of the monomer component having a solubility parameter of less than 8.0 or 11 or more include an?,? - unsaturated nitrile compound such as acrylonitrile and methacrylonitrile; Fluoroacrylic acid esters such as fluoroalkyl acrylate, 2- (fluoroalkyl) methyl acrylate and 2- (fluoroalkyl) ethyl acrylate; Fluorinated acrylic acid esters such as methacrylic acid fluoroalkyl, methacrylic acid 2- (fluoroalkyl) methyl and methacrylic acid 2- (fluoroalkyl) ethyl, and the like.

The solubility parameter of the monomer can be obtained according to " molecular attraction constant method " proposed by Small. (Cal / cm 3) ¹ (cal / cm 3) according to the following formula from the statistics of the molecular attraction constant (G) and the molecular weight (molecular volume) of the functional value of the functional group (atomic group) ^{/ 2. &} Lt; ^{/ RTI} >

? =? G / V = d? G / M

ΣG: Total number of molecular attraction constant G

V: cost (specific volume)

M: Molecular weight

d: specific gravity

Examples of the monomer component having a hydrophobic moiety include styrene monomers such as styrene,? -Styrene, chlorostyrene, vinyltoluene, methyl t-butylstyrene vinylbenzoate, vinylnaphthalene, chloromethylstyrene,? -Methylstyrene and divinylbenzene. .

In the present invention, segment A having a degree of swelling of 100 to 300% does not exhibit any swelling property with respect to an electrolytic solution, and hence an?,? - unsaturated nitrile compound and styrene-based monomer are preferable. And styrene-based monomers are most preferred because of the high dispersibility of the conductive agent.

The content of the monomer component having a hydrophobic portion in the segment A is preferably 10% by mass or more and 100% by mass or less, and more preferably 20% by mass or more and 100% by mass or less, based on 100% by mass of the total amount of the monomers. The content of the monomer component having a hydrophobic portion in the segment A can be controlled by the monomer injection ratio at the time of preparing the graft polymer. By setting the content of the monomer component having a hydrophobic portion in the segment A within the above range, higher electrolyte resistance and high temperature characteristics are exhibited.

In the segment A, these monomers may be used alone or in combination of two or more.

(Segment B)

In order to control the degree of swelling of the segment B with respect to the electrolyte in accordance with the composition and make the degree of swelling with respect to the electrolytic solution to 500 to 50,000%, it is preferable to constitute a monomer component having a solubility parameter of 8.0 or more and less than 11 or a monomer component having a hydrophilic group . When the degree of swelling is controlled by the weight average molecular weight, the weight average molecular weight of the segment B is preferably from 10,000 to 500,000. By making the weight average molecular weight fall within this range, it has a high binding property and does not cause peeling of the electrode active material layer.

Examples of the monomer having a solubility parameter of 8.0 or more and less than 11 include alkenes such as ethylene and propylene; Methacrylic acid alkyl esters such as butyl methacrylate, hexyl methacrylate, lauryl methacrylate and stearyl methacrylate; Alkyl acrylate esters such as butyl acrylate, hexyl acrylate, lauryl acrylate and stearyl acrylate; Diene-based monomers such as butadiene and isoprene; And vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate. Of these, acrylic acid alkyl esters or methacrylic acid alkyl esters are more preferable because of their high swelling property to electrolytic solution and high stability to redox reaction.

Examples of the alkyl acrylate or methacrylate alkyl ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, Ethyl acrylate, 2-ethoxyethyl acrylate, and benzyl acrylate; Propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate Methacrylic acid alkyl esters such as tridecyl methacrylate, stearyl methacrylate, and benzyl methacrylate; .

The content of the monomer component having a solubility parameter (SP) of 8.0 or more and less than 11 in the component B is preferably 30% by mass or more, more preferably 50 to 90% by mass, based on 100% by mass of the total amount of the monomers. The content of the monomer component having the solubility parameter (SP) of 8.0 or more and less than 11 in the second segment can be controlled by the monomer injection ratio at the time of producing the graft polymer. Since the content of the monomer component having a solubility parameter (SP) of 8.0 or more and less than 11 is in an appropriate range, it exhibits swelling property with respect to the electrolytic solution, does not dissolve, does not dissolve in the battery, and exhibits high high temperature characteristics.

Examples of the monomer component having a hydrophilic group include a monomer having -COOH group (carboxylic acid group), a monomer having -OH group (hydroxyl group), a monomer having -SO ₃ H group (sulfonic acid group), a monomer having -PO ₃ H ₂ group , A -PO (OH) (OR) group (R represents a hydrocarbon group), and a monomer having a lower polyoxyalkylene group.

Examples of the monomer having a carboxylic acid group include a monocarboxylic acid and a derivative thereof, a dicarboxylic acid, 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 acrylate, 2-ethyl acrylate, isocrotonate,? -Acetoxyacrylate,? -Trans-allyloxyacrylate,? -Chloro-? Diaminoacrylic acid, and the like. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic acid anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of the dicarboxylic acid derivative include maleic acid methyl allyl such as methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid, maleic acid diphenyl maleate, maleinanyl maleate decyl, Maleic acid esters such as maleic acid dodecyl, maleic acid octadecyl, and maleic acid fluoroalkyl; .

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; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, maleic acid-di-2-hydroxyethyl, Alkanol esters of ethylenically unsaturated carboxylic acids such as 4-hydroxybutyl and di-2-hydroxypropyl itaconate; A polyalkylene glycol represented by the general formula CH ₂ ═CR ¹ -COO- (CnH ₂ nO) mH (m is an integer of 2 to 9, n is an integer of 2 to 4, and R 1 is hydrogen or a methyl group) Esters of acrylic acid; Mono (meth) acrylates of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2 '- (meth) acryloyloxyphthalate and 2-hydroxyethyl- Methacrylic acid esters; Vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; (Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl- Mono (meth) allyl ethers of alkylene glycols such as allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether and (meth) allyl-6-hydroxyhexyl ether; Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; (Poly) alkylene glycols such as glycerin mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, (meth) allyl- And mono (meth) allyl ethers of hydroxy substituents; Mono (meth) allyl ethers and halogen substituents of polyhydric phenols such as eugenol and isoengener; (Meth) allyl-2-hydroxyethyl thioether, and (meth) allyl-2-hydroxypropyl thioether; And the like.

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

Examples of the monomer having -PO ₃ H ₂ group and / or -PO (OH) (OR) group (R represents a hydrocarbon group) include 2- (meth) acryloyloxyethyl phosphate, methyl 2- (Meth) acryloyloxyethyl, and phosphoric acid ethyl- (meth) acryloyloxyethyl.

Examples of the monomer containing a lower polyoxyalkylene group include poly (alkylene oxide) such as poly (ethylene oxide) and the like.

Among the monomers having these hydrophilic groups, in the case where the segment B is composed of a monomer component having a hydrophilic group, a monomer having a carboxylic acid group is preferable from the viewpoint of further improving the dispersibility of the active material.

The content of the monomer component having a hydrophilic group in the segment B is preferably from 0.5 to 40% by mass, more preferably from 3 to 20% by mass, based on 100% by mass of the total monomer amount as a monomer amount having a hydrophilic group at the time of polymerization to be. The content of the monomer having a hydrophilic group in the segment B can be controlled by the monomer injection ratio at the time of producing the graft polymer. When the content of the monomer having a hydrophilic group in the segment B is set to a predetermined range, the swelling property of the electrolyte relative to the electrolyte is exhibited, and elution in the battery does not occur.

In the segment B, these monomers may be used alone or in combination of two or more. In particular, a copolymer of an alkyl acrylate or a methacrylate alkyl ester and a monomer having a carboxylic acid group is preferable because of its high swelling property to an electrolytic solution and high stability to redox oxidation.

Further, it is preferable that the segment A, the segment B, or both of them have a glass transition temperature of 15 占 폚 or less because an electrode having high flexibility can be obtained. Particularly, since the segment A is adsorbed on the surface of the active material inside the electrode and the segment B is present on the outer side (the side of the binder layer adhered to the surface of the particles of the active material on the side farther from the active material) The glass transition temperature of B is preferably 15 占 폚 or lower, more preferably -5 占 폚 or lower, particularly preferably -40 占 폚 or lower. When the Tg of the segment B is within the above range, the segment A site in the graft polymer is adsorbed on the surface of the active material, and the flexibility of the segment B site is improved, thereby improving the Li ion acceptability at low temperatures. The lower limit of the glass transition temperature of the segment A, segment B or both (particularly, the glass transition temperature of the segment when the glass transition temperature of the segment is 15 DEG C or lower) is not particularly limited, can do.

The glass transition temperature of the segment can be adjusted by further combining a combination of the monomers and a copolymerizable monomer described below.

The ratio of the segment A to the segment B in the graft polymer varies depending on the composition and the degree of crosslinking because the polymer has a high rate characteristic while controlling the degree of swelling with respect to the electrolyte within a predetermined range. In the case of not having a copolymerization component other than the segment B, the ratio of segment A: segment B is 20:80 to 80:20, more preferably 30:70 to 70:30 in mass ratio.

The degree of swelling of the segment A and the segment B with respect to the electrolytic solution in the graft polymer can be adjusted by controlling the molecular weight and the degree of crosslinking in addition to the ratio of the segment A and the segment B described above.

The degree of swelling with respect to the electrolytic solution tends to increase as the molecular weight decreases and decreases as the molecular weight increases. Therefore, the range of the weight average molecular weight of the graft polymer for achieving the desired degree of swelling differs depending on the structure, degree of crosslinking and the like. For example, it is measured by gel permeation chromatography using tetrahydrofuran (THF) as a developing solvent Is 1,000 to 500,000, more preferably 2,000 to 100,000 in terms of standard polystyrene. By setting the weight average molecular weight of the graft polymer within the above range, segment A and segment B exhibit predetermined swelling properties and exhibit a high rate characteristic and a gas generation inhibiting effect.

When the swelling degree of the segment A and the segment B in the graft polymer with respect to the electrolytic solution is controlled by the degree of crosslinking of the graft polymer, the preferred range of the degree of crosslinking varies depending on the structure, the molecular weight, and the like. Examples thereof include tetrahydrofuran It is preferable to set the degree of crosslinking to a degree of dissolution or swelling to 400% or more when immersed in a polar solvent for 24 hours. By setting the degree of crosslinking to the above range, segment A and segment B exhibit predetermined swelling properties and exhibit high rate characteristics and cycle characteristics.

As the crosslinking method of the graft polymer, a method of crosslinking by heating or irradiation with energy rays can be mentioned. The degree of crosslinking can be controlled by heating conditions or irradiation conditions (strength, etc.) of irradiation with energy rays by using crosslinked graft polymers by heating or irradiation with energy rays. Further, since the degree of swelling tends to decrease as the degree of crosslinking increases, the degree of swelling can be controlled by changing the degree of crosslinking.

Examples of the method of making a graft polymer that can be crosslinked by heating or energy ray irradiation include a method of introducing a crosslinkable group into the graft polymer and a method of using a crosslinking agent in combination.

Examples of the method of introducing a crosslinkable group into the graft polymer include a method of introducing a photo-crosslinkable crosslinkable group into the graft polymer and a method of introducing a crosslinkable group of a heat crosslinkable. Among these methods, a method of introducing a thermally crosslinkable crosslinkable group into a graft polymer is a method of crosslinking a binder by applying a heat treatment to an electrode plate after application of the electrode plate, dissolving in an electrolyte solution can be suppressed, It is preferable because an electrode plate is obtained. In the case of introducing a heat-crosslinkable crosslinkable group into the graft polymer, the crosslinkable group having heat crosslinkability is preferably at least one selected from the group consisting of an epoxy group, N-methylolamide group, oxetanyl group and oxazoline group , And epoxy groups are more preferable in that crosslinking and crosslinking density can be easily controlled.

Examples of the monomer containing an epoxy group include a monomer containing a carbon-carbon double bond and an epoxy group, and a monomer containing a halogen atom and an epoxy group.

Examples of the monomer containing a carbon-carbon double bond and an epoxy group include unsaturated glycidyls such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether Ether; Dienes such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene and 1,2-epoxy-5,9- Monoepoxides of polyenes; Alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2-epoxy-9-decene; Glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl- Glycidyl esters of unsaturated carboxylic acids such as 3-pentenoate, glycidyl esters of 3-cyclohexenecarboxylic acid, and glycidyl esters of 4-methyl-3-cyclohexenecarboxylic acid; .

Examples of the monomer having a halogen atom and an epoxy group include epihalohydrins such as epichlorohydrin, epibromohydrin, epi-iodohydrin, epifluorohydrin, and? -Methyl epichlorohydrin; p-chlorostyrene oxide; Dibromophenyl glycidyl ether; .

Examples of the monomer containing an N-methylolamide group include (meth) acrylamides having a methylol group such as N-methylol (meth) acrylamide.

Examples of the monomer containing an oxetanyl group include 3 - ((meth) acryloyloxymethyl) oxetane, 3- ((meth) acryloyloxymethyl) -2-trifluoromethyl oxetane, 3- (Meth) acryloyloxymethyl) -2-phenyloxetane, 2 - ((meth) acryloyloxymethyl) oxetane, 2- Oxetane and the like.

Examples of the monomer containing an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2- 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2- .

The content of the thermally crosslinkable crosslinkable group in the graft polymer is preferably from 0.1 to 10% by mass, more preferably from 0.1 to 10% by mass, based on 100% by mass of the total amount of the monomers, 0.1 to 5% by mass. The content ratio of the thermally crosslinkable crosslinkable group in the graft polymer can be controlled by the monomer injection ratio when the graft polymer is produced. When the content ratio of the thermally crosslinkable crosslinking group in the graft polymer is within the above range, the segment A and the segment B exhibit predetermined swelling properties and exhibit a high rate characteristic and a gas generation inhibiting effect.

The thermally crosslinkable crosslinkable group can be introduced into the graft polymer by copolymerizing a monomer containing a thermally crosslinkable crosslinking group and / or another monomer copolymerizable therewith, in addition to the above-mentioned monomer in producing the graft polymer .

In the present invention, the degree of swelling of the graft polymer with respect to the electrolytic solution is preferably in the range of 100% or more and 300% or less, more preferably 100% or more and 200% or less. When the degree of swelling of the graft polymer with respect to the electrolytic solution is in the above range, the swelling property with respect to the electrolytic solution is exhibited while exhibiting binding property in the positive electrode layer at the time of manufacturing the battery, and rate characteristics can be exhibited without causing dropout of the active material. The swelling degree of the graft polymer with respect to the electrolytic solution can be adjusted by controlling the composition, the molecular weight and the degree of crosslinking in the same manner as the degree of swelling of the segment A and the segment B with respect to the electrolytic solution.

The graft polymer used in the present invention may contain monomers copolymerizable therewith, in addition to the above-mentioned monomer components. Examples of the monomer copolymerizable therewith include carboxylic acid esters having at least two carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; Halogen-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; Heterocyclic-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; Amide-based monomers such as acrylamide and N-methylol acrylamide; . By graft copolymerizing these monomers by an appropriate method, a graft polymer having the above-described constitution can be obtained.

In the present invention, the glass transition temperature of the graft polymer is preferably from the viewpoint of imparting flexibility to the electrode plate at room temperature and capable of suppressing cracking during roll winding of the electrode plate, winding at the winding time, Is not more than 20 DEG C, more preferably not more than 0 DEG C. The lower limit of the glass transition temperature of the graft polymer is not particularly limited, but may be -100 deg. C or higher. The glass transition temperature of the graft polymer can be adjusted by changing the use ratio of the constituent monomers and the like.

The graft polymer used in the present invention is synthesized by 1) a method of copolymerizing to form a branched structure and 2) a method of denaturing the obtained polymer to form a branched structure. Among them, the desired structure can be obtained in one step, so that the above method 1) is preferable.

As a method of copolymerizing to form the 1) branched structure, for example, a graft polymer can be obtained by a chain transfer reaction by polymerizing a graft monomer in the presence of a stem polymer by a known polymerization method. A graft polymer can also be obtained by introducing a functional group capable of generating a radical or an ion into the stem polymer and initiating polymerization reaction of the graft monomer from the functional group. In addition, a branched polymer obtained by polymerizing a graft monomer capable of forming a branched structure at the time of polymerization by a known polymerization method may be added to the stem polymer by a radical addition reaction or the like. Specifically, the graft polymer can be produced by the method described in JP-A-6-51767 and the like.

Among them, a method in which a branch polymer obtained by polymerization of a graft monomer capable of forming a branch structure at the time of polymerization by a known polymerization method is added to the stem polymer by a radical addition reaction or the like is the most easily controlled in structure, Is easy to stabilize the slurry for the secondary battery electrode. Specifically, there can be mentioned a method of copolymerizing with a macromonomer as a branched polymer.

As the macromonomer, for example, an end-capped methacryloylated polystyrene oligomer ("AS-6", manufactured by Toa Seikagaku Kogyo Co., Ltd., Mn = 6000) having an acryloyl group or a methacryloyl group at one end of the polymer, (AA-6 manufactured by Toa Seikagaku Kogyo Co., Ltd., Mn = 6000), one end methacryloylated polyacrylic acid butyl oligomer (manufactured by Toa Seikagaku Kogyo Co., Ltd., " AB -6 ", Mn = 6000), and an end-capped methacryloylated polystyrene-acrylonitrile oligomer (" AN-6S "manufactured by Toagosei Chemical Industry Co., Ltd.).

Further, isocyanate ethyl methacrylate, acrylic acid or methacrylic acid (hereinafter sometimes abbreviated as " (meth) acrylic acid ") and (meth) acrylic acid may be added to a polymer having a functional group such as hydroxyl group at one terminal end thereof such as polyoxyethylene monomethyl ether. Methacrylic acid chloride, glycidyl (meth) acrylate and the like can also be obtained by reacting an ethylenically unsaturated monomer having a functional group such as glycidyl (meth) acrylate, glycidyl Graft polymers can be obtained by copolymerizing these macromonomers with other ethylenically unsaturated monomers.

The polymerization method of the graft polymer is not particularly limited, and any of the solution polymerization method, the suspension polymerization method, the bulk polymerization method, and the emulsion polymerization method can be used. As the polymerization method, any of ion polymerization, radical polymerization, and living radical polymerization can be used. Examples of the polymerization initiator to be used in the polymerization include, for example, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexa Organic peroxides such as nonyl peroxide, and azo compounds such as?,? '- azobisisobutyronitrile, and ammonium persulfate and potassium persulfate.

The graft polymer used in the present invention is preferably obtained through a particulate metal removal step for removing particulate metal contained in the polymer solution or the polymer dispersion in the graft polymer production process. When the content of the particulate metal component contained in the graft polymer composition is 0 ppm or more and 10 ppm or less, it is possible to prevent metal ion cross-linking between the polymers in the slurry for secondary battery electrode described later and prevent an increase in viscosity . In addition, there is less concern about an internal short circuit of the secondary battery and an increase in self discharge due to dissolution and precipitation at the time of charging, and the cycle characteristics and safety of the battery are improved.

The method of removing the particulate metal component from the polymer solution or the polymer dispersion in the particulate metal removal step is not particularly limited and includes, for example, a method of removing by filtration using a filter, a method of removing by a vibrator, A method of removing by separation, a method of removing by magnetic force, and the like. Among them, a method of removing by a magnetic force is preferable because the object to be removed is a metal component. The method of removing by a magnetic force is not particularly limited as long as it is a method capable of removing a metal component. However, in consideration of productivity and removal efficiency, preferably, a magnetic filter is disposed in a production line of the graft polymer.

The content of the graft polymer in the binder is preferably 30% by mass or more and 100% by mass or less, more preferably 45% by mass or more and 100% by mass or less, most preferably 60% by mass or less, By mass to 100% by mass or less. When the content ratio of the graft polymer in the binder is within the above range, it is possible to suppress the increase of resistance by inhibiting the movement of lithium while maintaining the binding property between the active material particles and the binding property to the electrode or the separator have.

The binding agent may further contain other binder components in addition to the graft polymer (i.e., the binder of the present invention may include a component capable of functioning as a binder other than the graft polymer The secondary battery electrode of the present invention may contain, in addition to the graft polymer, a component capable of functioning as a binder other than the graft polymer as the binder. As the other binder components, various resin components may be used in combination. For example, it is possible to use polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid, polyacrylonitrile, Polymethacrylate and the like can be used. In addition, a copolymer containing 50% or more of the above-mentioned resin component (that is, a copolymer containing 50% or more and 100% or less of the same unit as the unit constituting the copolymer May also be used. For example, polyacrylonitrile such as acrylic acid-styrene copolymer, acrylic acid-acrylate copolymer and other polyacrylic acid derivatives, acrylonitrile-styrene copolymer, acrylonitrile- Derivatives may also be used.

Further, the soft polymer exemplified below can also be used as a binder.

Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate · styrene copolymer, butyl acrylate · acrylonitrile copolymer, butyl acrylate · Acrylic soft polymer, which is a copolymer of a homopolymer of acrylic acid or methacrylic acid derivative or a monomer copolymerizable therewith, such as acrylonitrile-glycidyl methacrylate copolymer; Isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, and isobutylene-styrene copolymer; Polybutadiene, polyisoprene, butadiene styrene random copolymer, isoprene · styrene random copolymer, acrylonitrile · butadiene copolymer, acrylonitrile · butadiene · styrene copolymer, butadiene · styrene · block copolymer, styrene · butadiene · Styrene block copolymers, isoprene-styrene block copolymers, styrene-isoprene-styrene block copolymers; Silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane and dihydroxypolysiloxane; Olefin series such as liquid polyethylene, polypropylene, poly-1-butene, ethylene /? - olefin copolymer, propylene /? - olefin copolymer, ethylene / propylene / diene copolymer (EPDM) Soft polymers; Vinyl soft polymers such as polyvinyl alcohol, polyvinyl acetate, vinyl polystearate, and vinyl acetate-styrene copolymer; Epoxy soft polymers such as polyethylene oxide, polypropylene oxide, and epichlorohydrin rubber; Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber; And other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer and polyamide thermoplastic elastomer. These soft polymers may have a crosslinked structure, or may be one obtained by introducing a functional group by modification. These may be used alone or in combination of two or more.

Among them, a polyacrylonitrile derivative is preferable because it improves the dispersibility of the active material. The content of the other binder is preferably 5 mass% or more and 80 mass% or less, more preferably 10 mass% or more and 70 mass% or less, and most preferably 20 mass% or less, based on 100 mass% Or more and 60 mass% or less. Other binders fall within the above-mentioned range, so that the resistance of the inside of the battery does not increase and a high life characteristic can be exhibited.

The content of the total binder in the electrode for the secondary battery is 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the active material. When the content of the binder in the secondary battery electrode is in the above range, the resistance to Li is not increased and the resistance is not increased, while the flexibility of the active material and the current collector is excellent.

(Whole house)

The electrode for a secondary battery of the present invention is formed by stacking an electrode active material layer containing an active material and a binder on a current collector.

The current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material. From the viewpoint of heat resistance, the current collector may be made of a metal such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, Are preferable. Among them, aluminum is particularly preferable for the positive electrode of the lithium ion secondary battery, and copper is particularly preferable for the negative electrode of the lithium ion secondary battery. Although the shape of the current collector is not particularly limited, it is preferably a sheet-like shape having a thickness of about 0.001 to 0.5 mm. It is preferable that the current collector is subjected to roughening treatment in advance in order to increase the bonding strength of the electrode. Examples of the roughening method include mechanical roughening, electrolytic roughening, and chemical roughening. In the mechanical polishing, a wire brush having a polishing pad, a grindstone, an emery buff, a steel wire, or the like to which abrasive particles are fixed is used. Further, an intermediate layer may be formed on the surface of the current collector for the purpose of enhancing the bonding strength and conductivity of the electrode.

The secondary battery electrode of the present invention may further contain optional components in addition to the above components. Examples of the optional components include electrolytic solution additives having functions such as a conductivity imparting agent, a reinforcing agent, a dispersant, a leveling agent, an antioxidant, a thickener, and an electrolyte decomposition inhibitor. They are not particularly limited as long as they do not affect the cell reaction.

As the conductive material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, or carbon nanotube can be used. Carbon powder such as graphite, and fibers and foils of various metals. By using the conductivity-imparting material, it is possible to improve the electrical contact between the electrode active materials and, in particular, to improve the discharge load characteristics when used in a lithium ion secondary battery. As the reinforcing material, various inorganic and organic spherical, plate, rod-like or fibrous fillers can be used. By using a reinforcing material, a strong and flexible electrode can be obtained and excellent long-term cycle characteristics can be exhibited. The amount of the conductivity imparting agent and the reinforcing agent is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass based on 100 parts by mass of the electrode active material. By being included in the above range, high capacity and high load characteristics can be exhibited.

Examples of the dispersing agent include anionic compounds, cationic compounds, nonionic compounds, and polymeric compounds. The dispersing agent is selected depending on the electrode active material or conductive agent to be used. The content of the dispersant in the electrode is preferably 0.01 to 10 parts by mass. When the amount of the dispersant is in the above range, the stability of the slurry is excellent, a smooth electrode can be obtained, and a high battery capacity can be obtained.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorochemical surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent cratering occurring at the time of coating (coating) or to improve smoothness of the electrode. The content of the leveling agent in the electrode is preferably 0.01 to 10 parts by mass. Since the leveling agent is in the above range, productivity, smoothness, and battery characteristics at the time of electrode production are excellent.

Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer type phenol compound is preferably a polymer having a phenol structure in the molecule and a polymer type phenol compound having a weight average molecular weight of 200 to 1000, preferably 600 to 700. The content of the antioxidant in the electrode is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass. When the antioxidant is in the above range, the slurry stability, battery capacity and cycle characteristics are excellent.

Examples of the thickener include cellulosic polymers such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (Modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts; (Modified) polyvinyl alcohol, copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, polyvinyl alcohols such as maleic anhydride or maleic acid, or copolymers of fumaric acid and vinyl alcohol; Polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, various modified starches, and acrylonitrile-butadiene copolymer hydride. When the amount of the thickener used is within this range, the coatability and the adhesion with the electrodes and the organic separator are good. In the present invention, "(modified) poly" means "unmodified poly" or "modified poly", and "(meth) acrylic" means "acrylic" or "methacrylic". The content of the thickening agent in the electrode is preferably 0.01 to 10 parts by mass. When the viscosity of the thickener is in the above range, the dispersibility of the active material and the like in the slurry is excellent, a smooth electrode can be obtained, and excellent load characteristics and cycle characteristics are exhibited.

As the electrolyte additive, vinylene carbonate or the like used in an electrode slurry to be described later and in an electrolytic solution may be used. The content of the electrolyte additive in the electrode is preferably 0.01 to 10 parts by mass. When the electrolyte additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include surfactants such as fumed silica and fumed alumina: nano-particles: alkyl surfactants, silicone surfactants, fluorochemical surfactants, and metal surfactants. By mixing the nanoparticles, the tin firing of the slurry for electrode formation can be controlled, and the leveling property of the electrode obtained thereby can be improved. The content of the nano-particles in the electrode is preferably 0.01 to 10 parts by mass. When the nano-particles are in the above-mentioned range, the slurry stability and productivity are excellent and high battery characteristics are exhibited. By mixing the surfactant, the dispersibility of the active material and the like in the electrode-forming slurry can be improved and the smoothness of the electrode obtained thereby can be improved. The content of the surfactant in the electrode is preferably 0.01 to 10 parts by mass. When the surfactant is in the above range, the slurry stability and the electrode smoothness are excellent and the productivity is high.

The method for producing an electrode for a secondary battery of the present invention may be a method of binding electrodes on at least one surface, preferably both surfaces, of the current collector in a layer. For example, a slurry for a secondary battery electrode to be described later is applied to a current collector, followed by drying, followed by heat treatment at 120 DEG C or higher for 1 hour or longer to form an electrode. The upper limit of the heat treatment temperature is not particularly limited, but may be 200 DEG C or lower. The upper limit of the heat treatment time is not particularly limited, but may be 24 hours or less.

(Slurry for secondary battery electrode)

The slurry for a secondary battery electrode used in the present invention includes a binder, an active material, and a solvent including a graft polymer. Examples of the binder and the active material including the graft polymer include those described in the electrode for the secondary battery.

(menstruum)

The solvent is not particularly limited as long as it is capable of uniformly dissolving or dispersing the binder of the present invention.

As the solvent used for the slurry for the secondary battery electrode, either water or an organic solvent can be used. Examples of the organic solvent include cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; Aromatic hydrocarbons such as toluene, xylene and ethylbenzene; Ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane and ethylcyclohexane; Chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; Esters such as ethyl acetate, butyl acetate,? -Butyrolactone and? -Caprolactone; Acylonitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; And amides such as N-methylpyrrolidone and N, N-dimethylformamide.

These solvents may be used alone, or two or more of them may be mixed and used as a mixed solvent. Among these, a solvent having excellent solubility of the polymer of the present invention, excellent dispersibility of an electrode active material and a conductive agent, and a solvent having a low boiling point and a high volatility can be removed in a short time and at a low temperature. Acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, or N-methylpyrrolidone, or a mixed solvent thereof is preferable.

The solid concentration of the slurry for a secondary battery electrode used in the present invention is not particularly limited as long as the slurry can be applied and immersed therein and has a viscosity having fluidity, but generally it is preferably from 10 to 80 mass% to be.

The components other than the solid component are components which are volatilized by the drying step and include a medium which is added to the solvent and dissolved or dispersed in preparing and adding the graft polymer.

Since the slurry for secondary battery electrode of the present invention is for forming the electrode for secondary battery of the present invention, the content ratio of the electrode active material and the graft polymer in the total solid content of the slurry for secondary battery electrode is, of course, The electrode active material layer of the battery electrode is as described above.

The slurry for the secondary battery electrode may contain, in addition to the binder, the active material and the solvent including the graft polymer, an arbitrary component such as a dispersant used for the secondary battery electrode described above or an electrolyte additive having functions such as electrolyte decomposition inhibition May be included. They are not particularly limited as long as they do not affect the cell reaction.

(Manufacturing Method of Slurry for Secondary Battery Electrode)

In the present invention, the method for producing the slurry for a secondary battery electrode is not particularly limited, and can be obtained by mixing a binder, an active material including a graft polymer, and a solvent and other components added as needed.

In the present invention, by using the above-described components, it is possible to obtain an electrode slurry in which the electrode active material and the conductive agent are highly dispersed irrespective of the mixing method and mixing order. The mixing apparatus is not particularly limited as long as it is an apparatus capable of uniformly mixing the above components, and examples thereof include a bead mill, a ball mill, a roll mill, a sand mill, a pigment dispersing apparatus, a brain trajectory, an ultrasonic dispersing apparatus, a homogeniser, a planetary mixer, Among them, it is particularly preferable to use a ball mill, a roll mill, a pigment dispersing machine, a cerebellum, and a planetary mixer in order to disperse at a high concentration.

The viscosity of the slurry for the secondary battery electrode is preferably from 10 mPa · s to 100,000 mPa · s, and more preferably from 100 to 50,000 mPa · s, from the viewpoints of uniform coatability and slurry stability. The viscosity is a value measured at 25 캜 and a rotation speed of 60 rpm using a B-type viscometer.

The method for applying the slurry for the secondary battery electrode to the current collector is not particularly limited. For example, methods such as a doctor blade method, a Jeep method, a reverse roll method, a direct roll method, a gravure method, an extruding method, and a brush coating method can be used. Examples of the drying method include hot air, hot air, low-humidity air drying, vacuum drying, and drying by irradiation with (circle) infrared rays or electron beams.

Next, it is preferable to use a die press or a roll press to lower the porosity of the electrode by pressurization. The preferred range of porosity is 5% to 15%, more preferably 7% to 13%. If the porosity is too high, the charging efficiency and the discharge efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity or the electrode tends to be peeled off, which causes problems such as defects. When a curable polymer is used, curing is preferred.

The thickness of the electrode for a secondary battery of the present invention is usually 5 to 300 占 퐉, preferably 10 to 250 占 퐉. When the electrode thickness is in the above range, both the load characteristic and the energy density exhibit high characteristics.

(Secondary battery)

The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is the electrode for the secondary battery. Among them, in many cases, a conductive agent and an active material are used in combination, and a decrease in rate characteristics due to defective dispersibility of the conductive agent is observed to be large, and a reaction of the electrolytic solution on the surface of the active material due to high dislocation tends to occur Since a large amount of gas is generated, a great effect can be obtained when used for a positive electrode.

Examples of the secondary battery include a lithium ion secondary battery and a nickel hydrogen secondary battery. The lithium ion secondary battery is preferably used because it is most demanded to improve performance such as suppression of gas generation and improvement of output characteristics. Hereinafter, a case where the battery is used in a lithium ion secondary battery will be described.

(Electrolyte for lithium ion secondary battery)

As the electrolyte for a lithium ion secondary battery, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is used. As the supporting electrolyte, a lithium salt is used. A lithium salt, ve is not particularly _{limited, 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, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. In particular, the _{LiPF 6, LiClO 4, CF 3} SO 3 Li indicating a high degree of dissociation easily soluble in solvents. These may be used in combination of two or more. The higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity. Therefore, the lithium ion conductivity can be controlled depending on the type of the supporting electrolyte.

The organic solvent used in the electrolyte solution for the lithium ion secondary battery 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 (PC) , Butylene carbonate (BC), and methyl ethyl carbonate (MEC); esters such as? -butyrolactone and methyl formate; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds such as sulfolane and dimethyl sulfoxide; Is preferably used. A mixed solution of these solvents may also be used. Among them, carbonates are preferable because of high dielectric constant and stable wide potential range. The lower the viscosity of the solvent used, the higher the lithium ion conductivity, so that the lithium ion conductivity can be controlled depending on the type of solvent.

It is also possible to add an additive to the electrolytic solution. Examples of the additive include carbonate-based compounds such as vinylene carbonate (VC) used in the above-described slurry for a secondary battery electrode.

The concentration of the supporting electrolyte in the electrolyte solution for a lithium ion secondary battery is usually 1 to 30 mass%, preferably 5 to 20 mass%. Depending on the type of the supporting electrolyte, the concentration is usually 0.5 to 2.5 mol / l. If the concentration of the supporting electrolyte is excessively low or too high, the ionic conductivity tends to decrease.

Examples of the electrolytic solution other than the above include polymer electrolytes such as polyethylene oxide and polyacrylonitrile, gelated polymer electrolytes in which the polymer electrolytes are impregnated with an electrolytic solution, and inorganic solid electrolytes such as LiI and Li ₃ N.

(Separator for lithium ion secondary battery)

As the separator, a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene or polypropylene; A porous resin coat including an inorganic ceramic powder; May be used. Examples of the separator for a lithium ion secondary battery include a microporous film or nonwoven fabric comprising a polyolefin resin such as polyethylene or polypropylene or an aromatic polyamide resin; A porous resin coat including an inorganic ceramic powder; May be used. For example, a microporous membrane made of a resin such as a polyolefin (polyethylene, polypropylene, polybutene, polyvinyl chloride), and a mixture or copolymer of these, a polyethylene terephthalate, a polycycloolefin, a polyether sulfone, a polyamide, A microporous film or a polyolefin-based fiber composed of a resin such as polyamide, polyamide, amide, polyaramid, polycycloolefin, nylon or polytetrafluoroethylene, or a nonwoven fabric or aggregate of insulating material particles. Among them, a microporous membrane made of a polyolefin-based resin is preferable because it is possible to increase the capacity per volume by increasing the active material ratio in the battery by reducing the thickness of the whole separator.

The thickness of the separator is usually 0.5 to 40 占 퐉, preferably 1 to 30 占 퐉, more preferably 1 to 10 占 퐉. When the content is within this range, resistance due to the separator in the battery is reduced, and the workability in manufacturing the battery is excellent.

As a specific method for producing the lithium ion secondary battery, there is a method in which the positive electrode and the negative electrode are overlapped with each other with a separator interposed therebetween, and the battery is wrapped and folded according to the shape of the battery and the battery container is filled with an electrolytic solution. have. If necessary, an over-current preventing element such as expanded metal, a fuse, a PTC element, or the like, a lead plate, or the like may be inserted to prevent an increase in pressure inside the battery and overcharge discharge. The shape of the battery may be a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, or the like.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto. In the present embodiment, parts and% are on a mass basis unless otherwise specified.

In Examples and Comparative Examples, various physical properties were evaluated as follows.

≪ Polymer properties: swelling degree >

A film of a polymer having a thickness of about 0.1 mm is cut out to a length of about 2 cm and measured for weight (weight before immersion). Thereafter, it is immersed in an electrolytic solution at a temperature of 60 ° C for 72 hours. (Weight after immersion) was measured, and the value of (weight after immersion) / (weight before immersion) × 100 (%) was taken as the degree of swelling, and it was judged according to the following criteria do. As the electrolytic solution, a mixed material obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in EC: DEC = 1: 2 (volume ratio, where EC is the volume at 40 ° C. and DEC is the volume at 20 ° C.) A solution prepared by dissolving LiPF ₆ in a solvent at a concentration of 1 mol / liter is used. The smaller the swelling degree, the higher the electrolyte resistance of the polymer.

A: more than 100% and less than 200%

B: more than 200% and less than 300%

C: more than 300% and less than 500%

D: more than 500% and less than 700%

E: not less than 700% but not more than 1500%

F: more than 1500% and less than 50,000%

G: Greater than or equal to 50,000%

<Slurry characteristics: dispersibility>

Slurry is put into a test tube having a diameter of 1 cm to a height (depth) of 5 cm and used as a test sample. Five test samples are prepared for the measurement of one kind of sample. The test sample is placed vertically on a desk. The state of the installed slurry is observed for 10 days and judged according to the following criteria. Of the five samples, the day the sediment was seen as the fastest settled day. The more the sedimentation is not visible, the better the dispersibility.

A: I can not see sediment after 10 days.

B: Sediment appears after 6 to 10 days.

C: Sediment is visible after 2 to 5 days.

D: Sediment is observed for more than 10 hours and less than 24 hours.

E: Sediment is observed for more than 3 hours and less than 10 hours.

F: Sediment is seen in less than 3 hours.

<Battery characteristics: output characteristics>

The half-cell coin type lithium ion secondary battery is charged to 4.3 V by the constant current method of 0.1 C, and then discharged from 0.1 C to 3.0 V to obtain the 0.1 C discharge capacity. After that, charge from 0.1 C to 4.3 V, then discharge from 20 C to 3.0 V, and calculate the 20 C discharge capacity. These measurements are performed on 10 cells of a half-cell coin type lithium ion secondary battery. The average value of 0.1 C discharge capacity of 10 cells and the average value of 20 C discharge capacity of 10 cells are obtained as a and b, respectively. (B / a) x 100 (unit:%)) of the capacitance of the discharge capacity b at 20 C to the capacitance of the discharge capacity a of 0.1 C, and this is used as the evaluation criterion of the rate characteristic, . The higher the value, the better the output characteristic (rate characteristic).

A: 50% or more

B: 40% or more and less than 50%

C: 20% or more and less than 40%

D: 1% or more and 20% or less

E: less than 1%

&Lt; Battery characteristics: amount of generated gas >

The laminate cell type lithium secondary ion battery is charged to 4.3 V by the constant current method of 0.1 C and then stored at 80 캜 for 50 hours. The thickness of the cell is measured by a micro gauge with a laminate cell type lithium secondary ion battery sandwiched by a glass plate. The ratio (b / a) of the thickness before and after the storage at 80 캜 is determined by the following criteria, assuming that the cell thickness before storage at 80 캜 is a and the cell thickness after storage at 80 캜 for 50 hours is b.

A: 1.00 times or more and 1.05 times or less

B: more than 1.05 times and less than 1.10 times

C: more than 1.10 times and less than 1.15 times

D: More than 1.15 times 1.20 times or less

E: 1.20 times or more

<Lithium Low Temperature Storage Characteristics>

Each of the obtained laminate cell-type batteries was charged at a constant current of 4.2 V at 25 DEG C at a charge / discharge rate of 0.1 DEG C by a constant current constant voltage charging method, and charged at a constant voltage. Discharge to 3 V after charging. The cycle of the constant-current constant-voltage charging and discharging was repeated one more time, and then the constant-current constant-voltage charging was performed at 0.1 C in a thermostatic chamber set at 0 占 폚. The battery capacity obtained at the time of the constant current in the constant current constant voltage charging was determined to be an index of lithium water solubility and it was judged according to the following criteria. The larger the value, the better the lithium water solubility, and the cell performance is not lowered even at a low temperature.

A: 200 mAh / g or more

B: 180 mAh / g or more and less than 200 mAh / g

C: 160 mAh / g or more and less than 180 mAh / g

D: 140 mAh / g or more and less than 160 mAh / g

E: Less than 140 mAh / g

(Example 1)

&Lt; Preparation of graft polymer &

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of styrene macromonomer (one end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as a segment A, 60 parts of butyl acrylate, and 1 part of t-butylperoxy-2-ethylhexanoate as a polymerization initiator, and the mixture was thoroughly stirred and then heated to 90 DEG C for polymerization to obtain a polymer (hereinafter referred to as "graft polymer 1" &Lt; / RTI &gt; The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 1 had a weight average molecular weight of about 50,000. The weight average molecular weight was measured by gel permeation chromatography (GPC), and the weight average molecular weight in terms of standard polystyrene was determined. GPC was carried out using HLC-8220 (manufactured by Tosoh Corporation). The obtained graft polymer was composed of butyl acrylate (component exhibiting swelling property with respect to the electrolytic solution) and styrene (component showing no swelling property with respect to the electrolytic solution) in the side chains. The obtained toluene solution of the graft polymer 1 was dried at 120 캜 for 10 hours under a nitrogen atmosphere to prepare a polymer film, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

&Lt; Production of polymer film composed of segment A &

A toluene solution of a styrene macromonomer (one-end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) was dried at 120 ° C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment A, The glass transition temperature was measured. The results are shown in Table 1.

&Lt; Production of polymer film composed of segment B &

To the autoclave equipped with a stirrer, 230 parts of toluene, 100 parts of butyl acrylate and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added respectively. After sufficiently stirring, the mixture was polymerized by heating at 90 캜, Thereby obtaining a solution of the polymer consisting of segment B. The obtained polymer solution was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment B, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

 &Lt; Preparation of graft polymer solution >

The resulting toluene solution of the graft polymer 1 was phase-inverted with a solution of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) to obtain an NMP solution of graft polymer 1 having a solid concentration of 17.8%.

&Lt; Preparation of electrode slurry for positive electrode &

100 parts of lithium manganese oxide as a positive electrode active material was placed in a planetary mixer with a disper, and 5 parts of acetyl black as a conductive agent was added thereto and mixed. To the resultant mixture was added 3.4 parts of an NMP solution (solid content concentration 17.8%) of the graft polymer 1 (1.2 parts as graft polymer 1), followed by mixing for 60 minutes. The solid content was adjusted to 84% by NMP and mixed for 10 minutes. This was deaerated to obtain an electrode slurry for a positive electrode having good gloss and good fluidity. The sedimentation of the obtained slurry was evaluated. The results are shown in Table 2.

&Lt; Preparation of positive electrode &

The electrode slurry for positive electrode was applied to an aluminum foil having a thickness of 18 占 퐉 and dried at 120 占 폚 for 3 hours, followed by roll pressing to obtain a positive electrode having a positive electrode material mixture layer having a thickness of 50 占 퐉.

&Lt; Preparation of electrode slurry for negative electrode and negative electrode &

98 parts of graphite having a particle size of 20 占 퐉 and a specific surface area of 4.2 m &lt; 2 &gt; / g as a negative electrode active material and 5 parts of PVDF (polyvinylidene) as a binder corresponding to a solid content were mixed and further N-methylpyrrolidone was added, Were mixed with a stirrer to prepare an electrode slurry for a negative electrode. The negative electrode slurry was coated on one side of a copper foil having a thickness of 10 占 퐉 and dried at 110 占 폚 for 3 hours, followed by roll pressing to obtain a negative electrode having a negative active material layer having a thickness of 60 占 퐉.

&Lt; Preparation of laminate cell battery >

A battery container was manufactured using a laminate film coated with a resin made of polypropylene on both sides of an aluminum sheet. Subsequently, the active material layer was removed from each end of the positive and negative electrodes obtained above, and the tab was welded to the exposed foil. For the tab, the positive electrode was a Ni-tapped and the negative electrode was a Cu-tap. The resulting positive electrode and negative electrode with a tab and a separator made of a microporous membrane made of polyethylene were stacked so that the active material layer faces of the positive electrode and the separator were positioned therebetween. The resulting laminate was wound and housed in the battery container. Subsequently, LiPF ₆ was dissolved in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 2 at 25 캜 so as to have a concentration of 1 mol / liter to prepare an electrolytic solution. This electrolytic solution was injected into the battery container. Then, the laminate film was sealed to produce a laminate cell of the present invention as a lithium ion secondary battery. The gas generation amount of the obtained laminate cell was measured. The evaluation results are shown in Table 2.

&Lt; Preparation of half-coin cell &

The positive electrode thus obtained was cut into a circle having a diameter of 13 mm. A metal lithium metal foil was cut into a circular shape having a diameter of 14 mm as a negative electrode. A single-layered polypropylene separator (porosity of 55%) produced by a dry method having a thickness of 25 탆 was cut into a circular shape having a diameter of 18 mm. The circular positive electrode, the metal lithium metal foil and the separator were placed in a coin-shaped outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) made of stainless steel and provided with a packing made of polypropylene. By this arrangement, the surface of the positive electrode mixture layer side of the positive electrode and the metallic lithium metal foil of the negative electrode were opposed to each other with the separator interposed therebetween, and the aluminum foil of the positive electrode was brought into contact with the bottom surface of the external container. The expanded metal was placed on the metal lithium of the negative electrode and stored in an external container. An electrolyte (EC / DEC = 1/2, 1 M LiPF ₆ ) was poured into the outer container in such a manner that no air was left, and a stainless steel cap having a thickness of 0.2 mm was fixed to the outer container via a polypropylene packing, The can was sealed to manufacture a lithium ion secondary battery having a diameter of 20 mm and a thickness of about 3.2 mm (coin cell CR2032). The rate characteristics of the obtained batteries were measured. The results are shown in Table 2.

(Example 2)

To an autoclave equipped with a stirrer, 230 parts of toluene and 40 parts of styrene-acrylonitrile macromonomer (one end methacryloyl polystyrene-acrylonitrile oligomer, manufactured by Toa Seikagaku Kogyo Co., Ltd., &quot; AN-6S & , 60 parts of butyl acrylate as a monomer constituting the segment B and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added to the flask, and the mixture was sufficiently stirred and heated to 90 DEG C to polymerize, Polymer 2 &quot;). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 2 thus obtained had a weight average molecular weight of about 50,000. The obtained graft polymer 2 was composed of butyl acrylate (a component showing swelling property with respect to an electrolytic solution) as a main chain and acrylonitrile and styrene (a component showing no swelling property with respect to an electrolyte) as a side chain.

Polymer films of segment A and segment B were prepared in the same manner as in Example 1 except that styrene-acrylonitrile macromonomer was used instead of styrene macromonomer, and swelling degree and glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for a positive electrode, and a battery were prepared in the same manner as in Example 1 except that graft polymer 2 was used instead of graft polymer 1 as a binder constituting the positive electrode. The swelling degree, the glass transition temperature, the sedimentation property in the slurry for the positive electrode, the rate characteristics of the battery, and the gas generation amount of the polymer film were evaluated. The results are shown in Tables 1 and 2.

(Example 3)

To an autoclave equipped with a stirrer, 230 parts of toluene, 57 parts of ethyl acrylate as a monomer constituting the segment B, 3 parts of glycidyl methacrylate and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator After sufficiently stirring, the mixture was heated to 80 DEG C and polymerized to obtain a polymer solution. Subsequently, 40 parts of polyacrylonitrile whose terminal was modified with a carboxyl group was added as a constituent of the segment A, and the solution was heated to 120 DEG C to denature it, and a solution of a heat-denatured polymer (hereinafter referred to as "graft polymer 3" . The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 3 had a weight average molecular weight of about 70,000. The obtained graft polymer was composed of ethyl acrylate (a component showing swelling property with respect to an electrolytic solution) as a main chain and acrylonitrile (a component showing no swelling property with respect to an electrolytic solution) as a side chain.

230 parts of toluene, 100 parts of acrylonitrile, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed in an autoclave equipped with a stirrer, and the mixture was sufficiently stirred, A solution of the polymer consisting of segment A was obtained. The obtained polymer solution was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment A, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

230 parts of toluene, 95 parts of ethyl acrylate, 5 parts of glycidyl methacrylate and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed in an autoclave equipped with a stirrer, , And the mixture was heated to 90 DEG C and polymerized to obtain a solution of the polymer of segment B. The obtained polymer solution was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment B, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for a positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 3 was used instead of graft polymer 1 as a binder constituting the positive electrode. The swelling degree, the glass transition temperature, the sedimentation property in the slurry for the positive electrode, the rate characteristics of the battery, and the gas generation amount of the polymer film were evaluated. The results are shown in Tables 1 and 2.

(Example 4)

To an autoclave equipped with a stirrer, 230 parts of toluene and 40 parts of styrene-acrylonitrile macromonomer (one end methacryloyl polystyrene-acrylonitrile oligomer, manufactured by Toa Seikagaku Kogyo Co., Ltd., &quot; AN-6S & 60 parts of n-ethyl acrylate as a monomer constituting the segment B, 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator and 0.05 part of n-dodecylmercaptan as a molecular weight regulator were added and sufficiently stirred , And the mixture was heated to 90 DEG C and polymerized to obtain a solution of a polymer (hereinafter referred to as "graft polymer 4"). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 4 had a weight average molecular weight of about 30,000. The obtained graft polymer was composed of n-ethyl acrylate (a component showing swelling property with respect to an electrolytic solution) as the main chain and styrene-acrylonitrile (component showing no swelling property with respect to the electrolytic solution as the side chain).

A polymer film of segment A was prepared in the same manner as in Example 1 except that a styrene-acrylonitrile macromonomer was used in place of the styrene macromonomer, and swelling degree and glass transition temperature were measured. The results are shown in Table 1.

230 parts of toluene, 100 parts of n-ethyl acrylate, 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator, and 0.05 part of n-dodecylmercaptan as a molecular weight regulator were placed in an autoclave equipped with a stirrer, After sufficiently stirring, the solution was heated to 90 DEG C and polymerized to obtain a solution of the polymer consisting of segment B. [ The obtained polymer solution was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment B, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 4 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

(Example 5)

&Lt; Preparation of graft polymer &

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of styrene macromonomer (one end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as a segment A, 58 parts of butyl acrylate, 2 parts of glycidyl methacrylate, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added, and the mixture was sufficiently stirred and heated to 90 DEG C to polymerize, Hereinafter referred to as &quot; graft polymer 5 &quot;). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 5 had a weight average molecular weight of about 50,000. The obtained graft polymer was composed of a copolymer of butyl acrylate and glycidyl methacrylate (the component showing the swelling property with respect to the electrolytic solution) and a side chain of styrene (the component showing no swelling property with respect to the electrolytic solution) as the main chain. The obtained toluene solution of the graft polymer 5 was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film, and the degree of swelling was measured. The results are shown in Table 1.

&Lt; Production of polymer film composed of segment A &

A toluene solution of a styrene macromonomer (one-end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) was dried at 120 ° C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment A, The glass transition temperature was measured. The results are shown in Table 1.

&Lt; Production of polymer film composed of segment B &

230 parts of toluene, 96.3 parts of butyl acrylate, 3.3 parts of glycidyl methacrylate, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed in an autoclave equipped with a stirrer, The solution was heated to 90 DEG C and polymerized to obtain a solution of the polymer consisting of segment B. [ The obtained toluene solution of the segment B polymer was dried at 120 deg. C for 10 hours under a nitrogen atmosphere to prepare a polymer film of segment B, and the degree of swelling and the glass transition temperature were measured. The results are shown in Table 3.

&Lt; Preparation of graft polymer solution >

The obtained toluene solution of graft polymer 5 was transferred to an NMP solution to obtain an NMP solution of graft polymer 5 having a solid concentration of 17.8%.

&Lt; Preparation of electrode slurry for positive electrode &

100 parts of lithium manganese oxide as a positive electrode active material was placed in a planetary mixer with a disper, and 5 parts of acetyl black as a conductive agent was added thereto and mixed. 5 parts of PVDF (polyvinylidene fluoride) corresponding to the solid content was added as a binder and mixed for 60 minutes. The solid content was adjusted to 84% by NMP and mixed for 10 minutes. This was deaerated to obtain a positive electrode slurry.

&Lt; Preparation of positive electrode &

The electrode slurry for positive electrode was applied to an aluminum foil having a thickness of 18 占 퐉 and dried at 120 占 폚 for 3 hours, followed by roll pressing to obtain a positive electrode having a positive electrode material mixture layer having a thickness of 50 占 퐉.

&Lt; Preparation of electrode slurry for negative electrode and negative electrode &

98 parts of graphite having a particle diameter of 20 占 퐉 and a specific surface area of 4.2 m &lt; 2 &gt; / g as a negative electrode active material and 1.6 parts of a graft polymer 5 as a binder corresponding to a solid content were mixed and further N-methylpyrrolidone was added and mixed with a planetary mixer To prepare an electrode slurry for a negative electrode. The negative electrode slurry was coated on one side of a copper foil having a thickness of 10 占 퐉 and dried at 110 占 폚 for 3 hours, followed by roll pressing to obtain a negative electrode having a negative active material layer having a thickness of 60 占 퐉.

&Lt; Preparation of laminate cell battery >

A battery container was manufactured using a laminate film coated with a resin made of polypropylene on both sides of an aluminum sheet. Subsequently, the active material layer was removed from each end of the positive and negative electrodes obtained above, and the tab was welded to the exposed foil. For the tab, the positive electrode was a Ni-tapped and the negative electrode was a Cu-tap. The resulting positive electrode and negative electrode with a tab and a separator made of a microporous membrane made of polyethylene were stacked so that the active material layer faces of the positive electrode and the separator were positioned therebetween. The resulting laminate was wound and housed in the battery container. Subsequently, LiPF ₆ was dissolved in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 2 at 25 캜 so as to have a concentration of 1 mol / liter to prepare an electrolytic solution. This electrolytic solution was injected into the battery container. Then, the laminate film was sealed to produce a laminate cell of the present invention as a lithium ion secondary battery. The lithium cold storage property of the obtained laminate cell was evaluated. The evaluation results are shown in Table 3.

(Example 6)

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of styrene macromonomer (one end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as a segment A, 50 parts of n-ethyl acrylate, 10 parts of acrylonitrile, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed and sufficiently stirred and heated at 90 DEG C to polymerize the polymer (hereinafter, Polymer 6 &quot;). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 6 had a weight average molecular weight of about 50,000. The resulting graft polymer was composed of a main chain of a copolymer of n-ethyl acrylate and acrylonitrile (a component exhibiting swelling property with respect to an electrolytic solution) and a side chain of styrene (a component showing no swelling property with respect to an electrolytic solution).

A polymer film of segment A and segment B was prepared in the same manner as in Example 5 except that 96.7 parts of butyl acrylate and 3.3 parts of glycidyl methacrylate were used instead of 83.3 parts of n-ethyl acrylate and 16.7 parts of acrylonitrile, Swelling degree and glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for negative electrode, and a battery were prepared in the same manner as in Example 5 except that graft polymer 6 was used instead of graft polymer 5 as a binder constituting the positive electrode. Then, the degree of swelling of the polymer film and the low-temperature storage capacity of lithium were evaluated. The results are shown in Tables 1 and 3.

(Comparative Example 1)

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of butyro acrylate macromonomer (one end methacryloylated polystyrene oligomer, "AB-6" manufactured by Toagosei Chemical Industry Co., Ltd.) synthesized as segment A, 40 parts of segment B Butylperoxy-2-ethylhexanate (1 part) as a polymerization initiator, and the mixture was sufficiently stirred and then heated to 90 DEG C to polymerize to obtain a polymer (hereinafter referred to as &quot; graft polymer 7 &quot;) was obtained. The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 7 had a weight average molecular weight of about 50,000.

A polymer film of segment A and segment B was produced in the same manner as in Example 1 except that vinyl pyrrolidone was used instead of butyl acrylate and instead of the styrene macromonomer, The transition temperature was measured. The results are shown in Table 1.

A polymer film, a slurry for a positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 7 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

(Comparative Example 2)

To an autoclave equipped with a stirrer, 230 parts of toluene and 40 parts of styrene-acrylonitrile macromonomer (one end methacryloyl polystyrene-acrylonitrile oligomer, manufactured by Toa Seikagaku Kogyo Co., Ltd., &quot; AN-6S & 30 parts of butyl acrylate as a monomer constituting the segment B, 30 parts of styrene and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed and sufficiently stirred and heated to 90 DEG C to polymerize, (Hereinafter referred to as &quot; graft polymer 8 &quot;). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 8 had a weight average molecular weight of about 50,000.

Except that 500 parts of butyl acrylate and 50 parts of styrene were used instead of 100 parts of butyl acrylate and styrene-acrylonitrile macromonomer was used in place of styrene macromonomer, the polymer film of segment A and segment B And the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 8 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

(Comparative Example 3)

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of butyl acrylate macromonomer (one end methacryloylated polybutyl acrylate oligomer, "AB-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as segment A, 40 parts of segment B 60 parts of butyl acrylate, 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator, and 0.5 part of n-dodecylmercaptan as a molecular weight regulator were added as a monomer constituting the monomer To obtain a solution of a polymer (hereinafter referred to as "graft polymer 9"). The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 9 had a weight average molecular weight of about 10,000.

Except that 100 parts of butylacrylate and 0.5 part of n-dodecylmercaptan were used instead of 100 parts of butyl acrylate and butyl acrylate macromonomer was used in place of the styrene macromonomer, segment A and segment B And the degree of swelling and the glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for a positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 9 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

(Comparative Example 4)

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of styrene macromonomer (one end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as a segment A, 30 parts of butyl acrylate, 30 parts of styrene, and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were placed and sufficiently stirred to be polymerized by heating at 90 DEG C to obtain a polymer (hereinafter referred to as &quot; graft polymer 10 Quot;) was obtained. The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 10 had a weight average molecular weight of about 50,000.

A polymer film of segment A and segment B was prepared in the same manner as in Example 1 except that 50 parts of butyl acrylate and 50 parts of styrene were used instead of 100 parts of butyl acrylate and swelling degree and glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 10 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

(Comparative Example 5)

To the autoclave equipped with a stirrer, 230 parts of toluene, 40 parts of styrene macromonomer (one end methacryloylated polystyrene oligomer, "AS-6" manufactured by Toagosei Chemical Industry Co., Ltd.) as a segment A, 20 parts of ethylene and 40 parts of ethyl acrylate and 1 part of t-butylperoxy-2-ethylhexanate as a polymerization initiator were added to the flask, and the mixture was sufficiently stirred and heated to 90 DEG C to polymerize the polymer (hereinafter referred to as &quot; graft polymer 11 Quot;) was obtained. The polymerization conversion rate determined from the solid content concentration was almost 98%. The graft polymer 11 had a glass transition temperature of 10 占 폚 and a weight average molecular weight of about 50,000.

A polymer film of segment A and segment B was prepared in the same manner as in Example 1 except that 33.3 parts of ethylene and 66.7 parts of ethyl acrylate were used instead of 100 parts of butyl acrylate and swelling degree and glass transition temperature were measured. The results are shown in Table 1.

A polymer film, a slurry for a positive electrode, and a battery were produced in the same manner as in Example 1 except that graft polymer 11 was used instead of graft polymer 1 as a binder constituting the positive electrode. The degree of swelling of the polymer film, the glass transition temperature, the sedimentation property in the positive electrode slurry, the rate characteristics of the cell, and the gas generation were evaluated. The results are shown in Tables 1 and 2.

From the results of Tables 1 and 2, it can be seen that, by using a graft polymer obtained by grafting a swelling component and a non-swelling component with respect to an electrolytic solution as a binder constituting the positive electrode, the degree of swelling with respect to the electrolytic solution can be controlled, , And a battery excellent in rate characteristics can be produced.

It is also evident from Table 3 that by using this graft polymer as a binder constituting the negative electrode, the lithium low temperature storage property is improved.

Claims (11)

And an electrode active material layer containing an active material and a binder laminated on the current collector, wherein the segment A having a swelling degree of 100 to 300% with respect to the electrolytic solution and the segment A having the degree of swelling with respect to the electrolytic solution A graft polymer comprising segment B of 500 to 50,000%
Wherein the segment A is composed of a monomer component having a solubility parameter of less than 8.0 or 11 or more, or a monomer component having a hydrophobic part,
The monomer component having a solubility parameter of less than 8.0 or 11 or more contains at least any of an?,? - unsaturated nitrile compound and a fluorinated acrylic acid ester,
Wherein the monomer component having the hydrophobic portion comprises a styrene-based monomer. The method according to claim 1,
Wherein a ratio of the segment A to the segment B in the graft polymer is 20:80 to 80:20 (mass ratio). The method according to claim 1,
Wherein the graft polymer has a weight average molecular weight in the range of 1,000 to 500,000. The method according to claim 1,
Wherein the segment B is a segment of a soft polymer having a glass transition temperature of 15 DEG C or lower. The method according to claim 1,
Wherein the styrenic monomer is selected from the group consisting of styrene,? -Styrene, chlorostyrene, vinyltoluene, methyl t-butylstyrene vinylbenzoate, vinylnaphthalene, chloromethylstyrene,? -Methylstyrene, divinylbenzene and mixtures thereof The electrode for a secondary battery. A graft polymer consisting of a segment A having a swelling degree of 100 to 300% with respect to an electrolytic solution and a segment B having a swelling degree of 500 to 50,000% with respect to an electrolytic solution
Wherein the segment A is composed of a monomer component having a solubility parameter of less than 8.0 or 11 or more, or a monomer component having a hydrophobic part,
The monomer component having a solubility parameter of less than 8.0 or 11 or more contains at least any of an?,? - unsaturated nitrile compound and a fluorinated acrylic acid ester,
Wherein the monomer component having the hydrophobic portion comprises a styrene-based monomer. The method according to claim 6,
Wherein the ratio of the segment A to the segment B in the graft polymer is 20:80 to 80:20 (mass ratio). 8. The method according to claim 6 or 7,
Wherein the segment B is a segment of a soft polymer having a glass transition temperature of 15 DEG C or lower. The method according to claim 6,
Wherein the styrenic monomer is selected from the group consisting of styrene,? -Styrene, chlorostyrene, vinyltoluene, methyl t-butylstyrene vinylbenzoate, vinylnaphthalene, chloromethylstyrene,? -Methylstyrene, divinylbenzene and mixtures thereof &Lt; / RTI &gt; A step of applying a slurry containing a graft polymer comprising a segment A having a degree of swelling with respect to an electrolytic solution of 100 to 300% and a segment B having a swelling degree of 500 to 50,000% with respect to an electrolytic solution, an active material and a solvent, / RTI &gt;
Wherein the segment A is composed of a monomer component having a solubility parameter of less than 8.0 or 11 or more, or a monomer component having a hydrophobic part,
The monomer component having a solubility parameter of less than 8.0 or 11 or more contains at least any of an?,? - unsaturated nitrile compound and a fluorinated acrylic acid ester,
The method for manufacturing an electrode for a secondary battery according to any one of claims 1 to 5, wherein the monomer component having the hydrophobic portion includes a styrene-based monomer. A lithium ion secondary battery having a positive electrode, an electrolyte, and a negative electrode,
The secondary battery according to any one of claims 1 to 5, wherein at least one of the positive electrode and the negative electrode is an electrode for a secondary battery.