KR20000048387A - Binder composition for lithium ion secondary cell electrode and use of it - Google Patents

Abstract

PURPOSE: A binder composition for a second battery of a lithium ion is provided to improve charge/discharge cycle property of a battery in a high temperature by latex composed of polymer particle, by polymerizing a particular monomer as an electrode binder composition. CONSTITUTION: A binder composition for a second battery of a lithium ion contains a structure unit of an ethylene unsaturated carvone acid ester monomer derive(a) and a structure unit of an ethylene unsaturated carvone acid monomer derive(b). The structure unit(a) divided by the structure unit(b) is equal with 99-60 divided by 1-40(weight rate). The binder composition for the second battery is composed of a polymer particle, which does not contain nitrile corresponded as sum of the both structure units(a,b) is over 80 percents to a whole unit.

Description

Binder composition for lithium ion secondary battery electrodes and its use {BINDER COMPOSITION FOR LITHIUM ION SECONDARY CELL ELECTRODE AND USE OF IT}

The present invention relates to a binder composition for a lithium ion secondary battery electrode and its use.

In recent years, portable terminals such as notebook bypass capacitors, cellular phones, and PDAs have been widely used. As a secondary battery used as such a power source, a lithium ion secondary battery is frequently used.

However, such a portable terminal is rapidly progressing in miniaturization, thinning, weight reduction, and high performance. In connection with this, the same thing is requested | required also about a lithium ion secondary battery (henceforth a battery hereafter), and low cost is calculated | required.

Conventionally, polyvinylidene fluoride (hereinafter referred to as PVD) has been used industrially as a provider for electrodes for lithium ion secondary batteries (hereinafter, simply referred to as batteries). Cannot be responded to. This is considered to be due to the low binding property.

Therefore, in order to obtain a higher performance battery, development of a binder in place of PVDF is being actively performed. For example, a polymer obtained by polymerizing an ethylenically unsaturated carboxylic acid ester containing 40% by weight or more of a unit derived from an ethylenic hydrocarbon, an ethylenic hydrocarbon, and an ethylenically unsaturated dicarboxylic anhydride (see Japanese Patent Application Laid-Open No. 6-223833); Olefinic systems, such as the polymer obtained by superposing | polymerizing the ethylenically unsaturated carboxylic acid ester containing 40 weight% or more of the unit derived from a hydrocarbon, an ethylenic hydrocarbon, and an ethylenically unsaturated dicarboxylic acid (ester) (JP-A-6-325766). It is proposed to use a polymer having a structural unit of as a binder. In addition, it is proposed to use a polymer obtained by copolymerizing at least acrylic acid or methacrylic acid ester, acrylonitrile and a vinyl monomer having an acid component (JP-A-8-287915) as a binder (binder). When the positive electrode and the negative electrode of the battery are manufactured using such a binder composition, since the binding property between the active material and the current collector and the active material are good, it is possible to obtain excellent battery performance, that is, good charge and discharge cycle characteristics and high capacity. have. Moreover, compared with using PVDF as a binder, such a polymer can be reduced in weight in that it may use a small amount of binder at the time of actually using it, and it can be reduced in cost in that a polymer is inexpensive. For this reason, such a polymer is expected as an excellent binder.

On the other hand, as portable terminals become popular and developed, they are used or stored in various conditions, especially high temperature conditions of 50 ° C or higher. However, the lithium ion secondary electrode using the electrode manufactured by PVDF which is already industrially produced as a binder is compared with the charge / discharge cycle characteristic at room temperature conditions of 20-25 degreeC, and this charge / discharge cycle is performed at high temperature conditions of 60 degreeC. The property is extremely deteriorated. Therefore, researches to secure battery characteristics at high temperatures have been conducted by improving battery materials, battery manufacturing methods, battery structures, and the like, but there is not enough, and there is a need for improvement of binders used in electrode production.

According to the inventor's review, a battery using an electrode produced by using a binder instead of the above-mentioned PVDF is surely excellent in charge / discharge cycle characteristics at high temperature, but has many olefinic structural units or many nitrile groups. It has been found that the charge-discharge cycle characteristics at 60 ° C. significantly decrease in the polymer.

From these prior arts, the present inventors earnestly researched to obtain a lithium ion secondary battery having excellent charge and discharge cycle characteristics at high temperature, and as a result, when using a latex made of polymer particles obtained by polymerizing a specific monomer as a binder composition for an electrode, It has been found that the charge and discharge cycle characteristics at high temperatures of the battery are improved, and the present invention has been completed.

According to this invention, as a 1st invention, the structural unit (a) derived from an ethylenic unsaturated carboxylic ester monomer, and the structural unit (b) derived from an ethylenic unsaturated carboxylic acid monomer are contained, and a structural unit (a) / A polymer particle having substantially no nitrile group having a structural unit (b) of 99 to 60/1 to 40 (weight ratio) and having a total of structural unit (a) and structural unit (b) of 80% by weight or more based on the total units; A binder composition for a lithium ion secondary battery electrode made of water is provided, and as a second invention, a slurry for a lithium ion secondary battery electrode (hereinafter referred to as slurry) containing the binder composition and an active material is provided, and a third As an invention of the present invention, there is provided an electrode for a lithium ion secondary battery produced using the slurry, and as a fourth invention, a lithium ion secondary battery produced using the electrode is provided.

The present invention is described in detail below.

1. Binder Composition

The binder composition of the present invention consists of latex in which specific polymer particles are dispersed in water, and the polymer particle content in the composition is 0.2 to 80% by weight, preferably 0.5 to 70% by weight, more preferably 0.5 to 60% by weight. to be.

(Polymer particles)

The polymer particles used in the present invention include a structural unit (a) derived from an ethylenically unsaturated carboxylic acid ester monomer (hereinafter also referred to as structural unit a) and a structural unit (b) derived from an ethylenically unsaturated carboxylic acid monomer (hereinafter, Structural unit b) and substantially free of nitrile groups.

In the present invention, substantially free of nitrile groups means that the structural units containing nitrile groups are 2% by weight or less, preferably 1% by weight or less, more preferably 0.5% by weight or less, based on the total structural units of the polymer, Especially preferably it means that it exists only in the ratio of 0 weight%.

The ratio (a / b) (weight ratio) of the structural unit a and the structural unit b in the polymer particles is 99 to 60/1 to 40, preferably 99 to 65/1 to 35, and more preferably 98 to 70 / 2 to 30. In addition, the sum total of a structural unit (a) and a structural unit (b) is 80 weight% or more with respect to all the units, Preferably it is 90 weight% or more.

When it becomes such a range, the battery which is especially excellent in the charge / discharge cycle characteristic at high temperature is obtained.

Specific examples of the monomer giving the structural unit (a) derived from the ethylenically unsaturated carboxylic acid ester monomer include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, Acrylic esters such as isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxypropyl acrylate, and lauryl acrylate; Methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-methacrylate Methacrylic acid ester, such as ethylhexyl, hydroxypropyl methacrylic acid, and lauryl methacrylic acid;

Methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, n-amyl crotonate, isoamyl crotonate, n-hexyl crotonate, 2-ethylhexyl crotonate, hydroxypropyl crotonate Crotonic acid esters such as these; Methacrylic acid ester containing amino groups such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; Methacrylic acid ester containing an alkoxy group, such as a methoxy polyethyleneglycol monomethacrylate; Ethylenic unsaturated carboxylic ester, such as these, is mentioned. Among these ethylenically unsaturated carboxylic acid esters, those having 1 to 12, preferably 2 to 8 carbon atoms in the alkyl portion of the (meth) acrylic acid ester are particularly preferred examples. Furthermore, the (meth) acrylic acid ester etc. which have a phosphoric acid residue, a sulfonic acid residue, a boric acid residue, etc. are mentioned in these alkyl groups.

As an example of the monomer which gives the structural unit (b) derived from an ethylenic unsaturated carboxylic acid monomer, ethylenic unsaturated monocarboxylic acid monomers, such as acrylic acid, methacrylic acid, and crotonic acid, are mentioned. In addition, unsaturated dicarboxylic acid monomers, such as maleic acid, a fumaric acid, a citraconic acid, a mesaconic acid, a glutamic acid, itaconic acid, a crotonic acid, an isocrotonic acid, an anhydride, etc. are mentioned. Among these, unsaturated monocarboxylic acids, such as acrylic acid and methacrylic acid, are preferable.

In addition to the structural units a and b, those having a structural unit (c) derived from a polyfunctional ethylenically unsaturated monomer (hereinafter referred to as structural unit c) are particularly preferable. As a monomer which gives such a structural unit c, Dimethacrylic acid ester, such as divinyl compounds, such as divinylbenzene, ethylene diglycol dimethacrylate, diethylene glycol dimethacrylate, and ethylene glycol dimethacrylate; Trimethacrylic acid esters such as trimethylolpropane trimethacrylate; Diacrylic acid esters such as polyethylene glycol diacrylate and 1,3-butylene glycol diacrylate; Triacrylic acid ester, such as a trimethylol propane triacrylate, etc. are mentioned. The structural unit c can be present in the polymer particles in a proportion of 20% by weight or less, preferably 15% by weight or less, and more preferably 10% by weight or less based on the total structural units. Among these, when the structural unit c exists in the ratio of 0.1 weight% or more, Preferably it is 0.5 weight% or more, More preferably, it is 1 weight% or more, Since stable charge / discharge cycle characteristics at high temperature are obtained, it is preferable.

As structural units other than these, structural units derived from conjugated diene-based monomers such as butadiene and isopropylene, structural units derived from monofunctional aromatic hydrocarbon-based monomers such as styrene and the like are not more than 15% by weight relative to the total structural units in the polymer particles. Preferably it is 10 weight% or less, More preferably, it may exist in the ratio of about 5 weight% or less.

Usually, in order to superpose | polymerize each monomer and obtain the latex which concerns on this invention, superposition | polymerization subsidiary materials, such as a polymerization initiator and a molecular weight modifier, can be used. These are mixed and used with the monomer mentioned above.

Although the polymerization method of a monomer is not restrict | limited, For example, the method described in the "Experimentation Lecture" Volume 28, (Publisher: Ring Line Co., Japan Chemical Society), ie, in a sealed container with a stirrer and a heating device Add an additive such as water, a dispersant, an emulsifier, a crosslinking agent, an initiator, and a monomer to a predetermined composition, stir to disperse or emulsify the monomer or the like in water, and increase the temperature while stirring to initiate the polymerization. The latex according to the present invention in which the polymer particles are dispersed in water can be obtained by the method of the present invention. The emulsion may also be emulsified by emulsification polymerization or the like which emulsifies the monomer and then puts it in a container to start the reaction.

The emulsifier and the dispersant may be used in an ordinary emulsion polymerization method, suspension polymerization method, dispersion polymerization method or the like, and specific examples thereof include benzene sulfonates such as sodium dodecylbenzene sulfonate and sodium dodecylphenyl ether sulfonate; Alkyl sulfates such as formaldehyde condensate of sodium lauryl sulfate, sodium tetradodecyl sulfate, and sodium alkylnaphthalene sulfonate; Sulfo pumpkin salts such as sodium dioctyl sulfo pumpkin acid and sodium dihexyl sulfo pumpkin acid; Fatty acid salts such as sodium laurate; Ethoxy sulfate salts such as polyoxyethylene lauryl ether sulfate sodium salt and polyoxyethylene nonylphenyl ether sulfate sodium salt; Alkanesulfonates; Alkyl ether phosphate ester sodium salt; Nonionic emulsifiers, such as a polyoxyethylene nonyl phenyl ether, polyoxyethylene sorbitan lauryl ester, and a polyoxyethylene-polyoxypropylene block copolymer, etc. are illustrated, These may be used individually or in combination of 2 or more types. Although the addition amount of an emulsifier and a dispersing agent can be arbitrarily set, it is about 0.01-10 weight part normally with respect to 100 weight part of monomer total amounts, Depending on superposition | polymerization conditions, a dispersing agent may not be used.

In addition, additives, such as a molecular weight modifier, can be used. As a molecular weight modifier, For example, mercaptans, such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan; And halogenated hydrocarbons such as carbon tetrachloride and carbon tetrabromide. These molecular weight modifiers can be added before the start of polymerization or during the polymerization. A molecular weight modifier is 0.01-10 weight part normally with respect to 100 weight part of monomers, Preferably it is used in the ratio of 0.1-5 weight part.

The polymerization initiator is preferably used in ordinary emulsion polymerization, dispersion polymerization and suspension polymerization, and for example, persulfates such as potassium persulfate and ammonium persulfate; Hydrogen peroxide; Organic peroxides such as benzoyl peroxide, cumene hydroperoxide, and the like, and these can be polymerized either alone or by redox-based polymerization initiators used in combination with reducing agents such as acidic sodium sulfite, sodium thiosulfate, and ascorbic acid. '-Azobisisobutyronitrile, 2,2' azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), dimethyl Azo compounds such as 2,2'-azobisisobutyrate and 4,4'-azobis (4-cyanopentanoic acid); 2,2'-azobis (2-aminodipropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamidine), 2,2'-azobis (N, N Amidine compounds, such as "-dimethylene isobutyl amidine) dihydrochloride, etc. can be used, These can be used individually or in combination of 2 or more types. The usage-amount of a polymerization initiator is 0.01-10 weight part with respect to 100 weight part of monomer total weights, Preferably it is 0.1-5 weight part.

Although polymerization temperature and polymerization time can be arbitrarily selected by polymerization method, the kind of polymerization initiator used, etc., it is 30-200 degreeC normally, and polymerization time is about 0.5-30 hours. Additives, such as amines, can also be used as a polymerization aid.

It is preferable that the polymer particle in the obtained latex is difficult to melt | dissolve in electrolyte solution at the temperature of 60 degreeC. For this reason, the gel content measured under the conditions described below is 50% or more and 100% or less, preferably 60% or more and 100% or less, and more preferably 70% or more and 100% or less. When it exists in this range, a polymer particle is hard to melt | dissolve in a dissolution liquid, and the high temperature charge-discharge cycle characteristic in 60 degreeC also becomes favorable.

In the present invention, the gel content is propylene carbonate / ethylene carbonate / diethyl carbonate / dimethyl carbonate / methyl ethyl carbonate = 20/20/20/20/20 (volume ratio at 20 ℃) mixed solvent (electrolyte solvent) ) Is calculated as an insoluble content of polymer particles in an electrolyte solution, a solution in which LiPF ₆ is dissolved at a rate of 1 mol / liter, and the latex is dried in a wind at 120 ° C. for 24 hours, and further vacuum drying at 120 ° C. for 24 hours. The weight (D1) of the obtained polymer membrane and the membrane was immersed in the above-mentioned electrolytic solution at 100 weight ratio for 74 hours at 70 DEG C, and then filtered with 200 mesh, followed by vacuum drying at 120 DEG C for 24 hours. It is the value measured about the weight (D2) of the thing made and computed according to following Formula.

Gel content (%) = (D2 / D1) × 100

In addition, when latex is used by performing pH adjustment mentioned above, gel content is measured by the said method after pH adjustment.

Furthermore, the latex obtained by these methods may include alkali metal (Li, Na, K, Rb, Cs) hydroxides, ammonia, inorganic ammonium compounds (NH ₄ Cl, etc.), organic amine compounds (ethanol amine, diethylamine, etc.). The dissolved aqueous basic solution may be added to prepare a pH in the range of 5 to 10, preferably 5 to 9. Among them, the use of an alkali metal hydroxide is preferred in view of binding property (peel strength) between the current collector and the active material.

In addition, pH here is measured on condition of the following.

Equipment: HM-12P (made by Dong-A Radio Corporation)

Measuring temperature: 25 ℃

Test liquid volume: 100ml

Turn on the pH meter and let stand for 30 minutes. The detection unit is washed three times or more with pure water and wiped with clean cotton wool. Calibration with standard solution is done by 1 point calibration. Dip the electrode in a neutral phosphate standard solution at pH 6.86 and vibrate 2 or 3 degrees to remove bubbles. After leaving for 10 minutes, the measured values are read and corrected. After the calibration is finished, the electrode is washed three times or more with pure water and then wiped with clean cotton wool. Subsequently, the electrode is immersed in the test liquid and vibrated at 2 or 3 degrees to remove bubbles. After 10 minutes, read the pH reading.

Examples of the polymer particles used in the present invention include 2-ethylhexyl acrylate / acrylic acid copolymer, 2-ethylhexyl acrylate / ethyl acrylate / acrylic acid copolymer, butyl acrylate / acrylic acid copolymer, 2-ethylhexyl acrylate / acrylic acid air. Copolymer, 2-ethylhexyl acrylate / acrylic acid / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate / hydroxypropyl acrylate / acrylic acid copolymer, diethylaminoethyl acrylate / acrylic acid copolymer, methoxy polyethyleneglycol monomethacrylate Acrylate / acrylic acid copolymer, crotonic acid 2-ethylhexyl / acrylic acid copolymer, 2-ethylhexyl acrylate / ethyl crotonate / acrylic acid copolymer, 2-ethylhexyl acrylate / ethyl acrylate / acrylic acid / polyethylene glycol diacrylate copolymer Butyl acrylate / acrylic acid / divinylbenzene copolymer, 2-ethylhexyl acrylate Krylic acid / methacrylic acid copolymer, 2-ethylhexyl acrylate / acrylic acid / maleic acid copolymer, 2-ethylhexyl acrylate / itaconic acid acrylic acid, 2-ethylhexyl acrylate / acrylic acid / methacrylic acid copolymer, 2-ethyl methacrylate Hexyl / acrylic acid / maleic acid copolymer, methacrylic acid 2-ethylhexyl / itaconic acid copolymer,

2-ethylhexyl acrylate / methacrylic acid copolymer, 2-ethylhexyl acrylate / ethyl methacrylate / methacrylic acid copolymer, butyl methacrylate / methacrylic acid copolymer, 2-ethylhexyl acrylate / methacrylic acid copolymer, 2-ethylhexyl acrylate / Methacrylic acid / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl methacrylate / hydroxypropyl acrylate / acrylic acid copolymer, diethylaminoethyl methacrylate / methacrylic acid copolymer, methoxy polyethylene glycol monomethacrylate / meta Acrylic acid copolymer, crotonic acid 2-ethylhexyl / methacrylic acid copolymer, acrylic acid 2-ethylhexyl / crotonate ethyl / methacrylic acid copolymer, methacrylic acid 2-ethylhexyl / ethyl acrylate / methacrylic acid / polyethylene glycol diacrylate Copolymer, butyl acrylate / methacrylic acid / divinylbenzene copolymer,

2-ethylhexyl acrylate / crotonic acid acrylate, 2-ethylhexyl acrylate / ethyl acrylate / crotonic acid acrylate, butyl acrylate / crotonic acid acrylate, 2-ethylhexyl acrylate / crotonic acid methacrylate, 2-ethylhexyl acrylate / Crotonic acid / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate / hydroxypropyl acrylate / crotonic acid acrylate, diethylaminoethyl / crotonic acid acrylate, methoxy polyethylene glycol monomethacrylate / croton Acid copolymer, crotonic acid 2-ethylhexyl / crotonic acid copolymer, acrylic acid 2-ethylhexyl / crotonic acid ethyl / crotonic acid copolymer, acrylic acid 2-ethylhexyl / ethyl acrylate / crotonic acid / polyethylene glycol diacrylate copolymer Butyl acrylate / crotonic acid / trimethylol propane triacrylate copolymer,

2-ethylhexyl acrylate / maleic acid copolymer, 2-ethylhexyl acrylate / ethyl methacrylate / maleic acid copolymer, butyl acrylate / maleic acid copolymer, 2-ethylhexyl acrylate / itaconic acid copolymer etc. are mentioned.

The polymer particles having at least the structural units a and b used in the present invention may be composite polymer particles composed of two or more kinds of polymers produced under the above-described monomer conditions. More specifically, the composite polymer polymerizes any one or more monomer components by, for example, a conventional method, and then adds one or more monomer components, followed by polymerization by a conventional method (two-stage polymerization method). Or the like.

Although the composite polymer particles have a release structure, the release structure generally refers to a core cell structure, a composite structure, a local structure, a diploid structure, a culvert shape structure, a raspberry shape structure, and the like in the field of latex. (See "Adhesion", Vol. 34, Nos. 13 to 23, in particular, Fig. 6 on Page 17).

Moreover, in this invention, a viscosity modifier, a fluidizing agent, etc. which improve the coating property of the slurry for battery electrodes mentioned later can be added to a binder composition. These additives include cellulose polymers such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose, polyacrylates such as ammonium salts and alkali metal salts and sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, Copolymer of acrylic acid or acrylate and vinyl alcohol, copolymer of maleic anhydride or maleic acid or fumaric acid and vinyl alcohol, modified polyvinyl alcohol, modified polyacrylic acid, polyethylene glycol, polycarboxylic acid, ethylene vinyl alcohol copolymer, vinyl acetate polymer, etc. And water-soluble polymers. The use ratio of these additives can be selected freely as needed.

Moreover, the binder composition of this invention may contain polymers other than the above-mentioned polymer particle, or polymer particle (henceforth a polymer other than that). The use ratio of such other polymers is 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, particularly preferably 100 parts by weight of the polymer particles according to the present invention described above. Is 10 parts by weight or less.

2. Slurry for Battery Electrode

The slurry of this invention is manufactured by mixing the active material and additive mentioned above with the binder composition of this invention.

(Active material)

Any active material can be used as long as it is used in ordinary lithium ion secondary batteries. For example, as the negative electrode active material, carbonaceous materials such as amorphous carbon, graphite, natural graphite, MCMB, pitch carbon fiber, polyacene, and the like Conductive polymers; AxMyOz (where A is an alkali metal or a transition metal, M is at least one selected from transition metals such as Co, Ni, Al, Sn, Mn, O represents an oxygen atom, and x, y, and z each represent 1.10). ≧ x ≧ 0.05, 4.00 ≧ y ≧ 0.85, and 5.00 ≧ z ≧ 1.5.).

In addition, the cathode active material is not particularly limited as long as it is used in a conventional lithium ion secondary battery, and is not particularly limited. For example, TiS ₂ , TiS ₃ , amorphous MoS ₃ , Cu ₂ V ₂ O ₃ , and amorphous V ₂ OP ₂ O ₅ And lithium-containing composite metal compounds such as MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , LiC ₀ O ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O _4, and the like. Furthermore, organic compounds such as conductive polymers such as polyacetylene and poly-p-phenylene can be used.

The amount of the active material in the slurry for battery electrodes of the present invention is not particularly limited, but is usually 1 to 100 times by weight, preferably 2 to 500 times, more preferably based on the polymer particles (i.e., the solid content of the latex). It is mix | blended so that it is 3-500 times, Especially preferably, it is 5-300 times. If the amount of the active material is too small, there are many inactive portions in the active material layer formed on the current collector, resulting in insufficient function as an electrode. In addition, if the amount of the active material is too large, the active material is not sufficiently fixed to the current collector, and thus easily falls off. In addition, water, which is a dispersion medium, may be added to the slurry for electrodes to adjust the concentration to be easily applied to the current collector.

(additive)

As needed, you may add a viscosity modifier and a fluidizing agent to the slurry of this invention similarly to the binder composition. In addition, a conductive material such as carbon or metal powder such as activated carbon can be added within a range that does not interfere with the object of the present invention.

3. Lithium-ion Secondary Battery Electrode

The electrode of this invention is manufactured by apply | coating the slurry of this invention to electrical power collectors, such as metal foil, and drying and fixing an active material to the electrical power collector surface. The electrode of the present invention may be either an anode or a cathode.

The current collector is not particularly limited as long as it is made of a conductive material, but metals such as iron, copper, aluminum, nickel and stainless steel are usually used. Although the shape in particular is not restrict | limited, either, A sheet-like thing of thickness about 0.001-0.5 mm is used normally.

The method of applying the slurry to the current collector is also not particularly limited. For example, it is apply | coated by the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method, the extrudation method, the immersion, the brushing, etc. The amount to be applied is also not particularly limited, but the thickness of the active material layer formed after removing water is usually about 0.005 to 5 mm, preferably about 0.01 to 2 mm. The drying method is also not particularly limited, and examples thereof include drying by warm air, hot air and low humidity wind, vacuum drying, and drying by irradiation with (far) infrared rays and electron beams. Drying conditions are usually adjusted so that water can be removed as soon as possible within the speed range in which stress concentration occurs and cracks occur in the active material layer or the active material does not peel off from the current collector.

Further, the electrode may be stabilized by pressing the current collector after drying. As a press method, methods, such as a metal mold | die press and a roll press, are mentioned.

4. Lithium-ion Secondary Battery

The lithium ion secondary battery of this invention contains electrolyte solution and the electrode for lithium ion secondary batteries of this invention, and is manufactured according to a conventional method using components, such as a separator, as needed. For example, the following method is mentioned. That is, the positive electrode and the negative electrode are polymerized through the separator, wound in accordance with the shape of the battery, placed in a battery container by bending, or the like, and the electrolyte is injected to seal the inlet. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat type.

Any electrolyte may be used as long as it is normally used for a lithium ion secondary battery, and what is necessary is just to select the thing which functions as a battery according to the kind of negative electrode active material and positive electrode active material.

As the electrolyte, all conventionally known lithium salts can be used, for example, LiClO ₄ , LiBF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lower fatty acid car Lithium carbonate;

The solvent for dissolving this electrolyte (electrolyte solvent) is not particularly limited as long as it is usually used, but may be carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate and diethyl carbonate; lactones such as γ-butyl lactone; Ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; Sulfoxides such as dimethyl sulfoxide; Oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; Jalso-containings, such as acetonitrile and nitromethane; Organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate; Inorganic acid esters such as phosphate triester, diester carbonate such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate; Diglyme; Tricrime; Sulfolane; Oxazolidinones such as 3-methyl-2-oxazolidinone; Single or 2 or more types of mixed solvents, such as sultones, such as 1, 3- propane sultone, 1, 4- butane sultone, and naphtha sultone, can be used.

When the binder composition of the present invention is used for electrode production of a lithium ion secondary battery, it is possible to produce a lithium secondary battery having excellent charge and discharge cycle characteristics at a high temperature of 60 ° C., and also excellent binding property with a current collector.

(Example)

Although an Example is given to the following and this invention is demonstrated, this invention is not limited to these. In addition, the part and% in a present Example are a basis of weight unless there is particular notice.

Evaluation in an Example and a comparative example was performed on condition of the following.

① Bend: Cut the electrode into 3cm width x 9cm length, and support the center of the longitudinal direction (4.5cm place) with a stainless rod of 1mm in diameter to bend the state of the bent portion when bent 180 °. The test was performed on 10 electrode pieces, and the case where no cracking or peeling occurred at all in 10 sheets was determined as o, and the case where one or more cracking or peeling occurred on one or more sheets was evaluated as x.

(2) Peeling strength: Cut the electrode in the same manner as in (1), attach a tape (vertical tape: Nichiban, JIS Z1522) to fix the electrode, and measure the strength (g / cm) when peeling the tape at once. It measured 10 times and calculated | required the average value.

③ High temperature initial discharge capacity: It is the discharge capacity of the 3rd cycle measured at the time of measuring the high temperature charge-discharge cycle characteristic mentioned later.

④ High temperature charge / discharge cycle characteristics: Cathode test (Examples 1 to 4 and Comparative Examples 1 to 2) under a 60 ° C. atmosphere using a coin-type battery manufactured by the following method was conducted at 3 V using the lithium metal as a negative electrode. In V, the discharge capacity at the third cycle (unit = mAh / g (per active material)) and the 50th cycle discharge capacity (unit = mAh / g (per active material)) were measured by a constant current method of 0.1 C. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the cycle is calculated as a percentage, and the larger the value, the smaller the capacity decrease, which is a good result.

In the manufacture of a coin-type battery, the positive electrode slurry was uniformly coated on aluminum foil (20 μm thick) and the negative electrode slurry on copper foil (18 μm thick) by the doctor braid method, respectively, and dried in a dryer at 120 ° C. for 15 minutes. Thereafter, the resultant was further dried under reduced pressure at 5 mmHg and 120 ° C. for 2 hours in a vacuum dryer, and then compressed by biaxial roll press so that the active material density became 3.2 g / cm 3 of the positive electrode and 1.3 g / cm 3 of the negative electrode. The electrode is cut into a circular shape having a diameter of 15 mm, and the active materials face each other through a separator made of a circular polypropylene porous membrane having a diameter of 18 mm and a thickness of 25 µm, and the aluminum foil or metal lithium of the anode contacts the bottom of the outer container. Placed in the copper foil or metal lithium of the cathode, and placed in a stainless steel coin-type outer container (diameter of 20 mm, height 1.8 mm, thickness of stainless steel 0.25 mm) with polypropylene packing. It was. The electrolyte is injected into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery tube is sealed and blocked to obtain a coin-type battery having a diameter of 20 mm and a thickness of about 2 mm. Was prepared. As the electrolyte solution, a solution of 1 mol / liter of LiPF ₆ , propylene carbonate / ethylene carbonate / diethyl carbonate / dimethyl carbonate / methylethyl carbonate = 20/20/20/20/20 (volume ratio at 20 ° C.) was used.

(Example 1) 250 parts of water were added to 92 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, 3 parts of ethylene glycol dimethacrylate, 2 parts of sodium dodecylbenzenesulfonate, and 0.3 parts of potassium persulfate, It superposed | polymerized at 60 degreeC for 8 hours. After cooling to room temperature, 10% aqueous ammonium solution was added to adjust pH to 6 to obtain a pH-adjusted latex (binder composition). About the obtained polymer particle, the gel content was measured on condition mentioned above.

2 parts of this pH adjusted latex was added as solid content, 2 parts of sodium carboxymethylcellulose, and 96 parts of natural graphite, water was stirred, and solid content concentration was adjusted to the slurry of 35%. The negative electrode was obtained by the method mentioned above using the slurry obtained here. The obtained electrode was evaluated. The gel content and measurement results are shown in Table 1.

(Example 2)

The polymerization was carried out in the same manner as in Example 1 except that the monomers and the like used were changed as shown in Table 1. Similarly, after cooling, 5% aqueous lithium hydroxide solution was added to adjust the pH to 7 to obtain a pH adjusted latex.

A negative electrode was produced and evaluated in the same manner as in Example 1 except that the pH-adjusted latex was used. The gel content and measurement results are shown in Table 1.

(Example 3)

The polymerization was carried out in the same manner as in Example 1 except that the monomers and the like used were changed as shown in Table 1. Similarly, after cooling, a 5% aqueous sodium hydroxide solution was added to adjust pH to 7 to obtain a pH adjusted latex.

A negative electrode was produced and evaluated in the same manner as in Example 1 except that the pH-adjusted latex was used. The gel content and measurement results are shown in Table 1.

(Example 4)

The polymerization was carried out in the same manner as in Example 1 except that the monomers and the like used were changed as shown in Table 1. Similarly, after cooling, 5% aqueous potassium hydroxide solution was added to adjust pH to 8 to obtain a pH adjusted latex.

A negative electrode was produced and evaluated in the same manner as in Example 1 except that the pH-adjusted latex was used. The gel content and measurement results are shown in Table 1.

(Comparative Example 1)

The polymerization was carried out in the same manner as in Example 2 except that the monomers and the like used were changed as shown in Table 1. Similarly, after cooling, a 10% aqueous ammonia solution was added to adjust pH to 7 to obtain a pH adjusted latex.

A negative electrode was produced and evaluated in the same manner as in Example 1 except that the pH adjusting reaction solution was used. The gel content and measurement results are shown in Table 1.

(Comparative Example 2)

The polymerization was carried out in the same manner as in Example 2 except that the monomers and the like used were changed as shown in Table 1. Similarly, after cooling, a 10% aqueous ammonia solution was added to adjust pH to 7 to obtain a pH adjusted latex.

A negative electrode was produced and evaluated in the same manner as in Example 1 except that the pH-adjusted latex was used. The gel content and measurement results are shown in Table 1.

(Example 5)

The pH-adjusted latex obtained in Example 1 was mixed with 1.5 parts of solid content, 1.5 parts of sodium carboxymethylcellulose, 92 parts of lithium cobalt acid instead of natural graphite as an active material, and 5 parts of carbon black as a conductive agent, so that the solid content was 58%. Was added to obtain an externally uniform slurry in a stirrer. Using the obtained slurry, a positive electrode was produced by the method described above. Evaluation was performed using the obtained electrode. The gel content and measurement results are shown in Table 2.

(Example 6)

A positive electrode was obtained in the same manner as in Example 5 except that the pH adjusting latex was used in Example 2. Evaluation was performed using the obtained electrode. The gel content and measurement results are shown in Table 2.

(Example 7)

A positive electrode was obtained in the same manner as in Example 5 except that the pH adjusting latex was used in Example 3. Evaluation was performed using the obtained electrode. The gel content and measurement results are shown in Table 2.

(Comparative Example 3)

A positive electrode was obtained in the same manner as in Example 5 except that the pH adjusting latex used in Comparative Example 1 was used. Evaluation was performed using the obtained electrode. The gel content and measurement results are shown in Table 2.

(Comparative Example 4)

A positive electrode was obtained in the same manner as in Example 5 except that the pH-adjusted latex used in Comparative Example 2 was used. Evaluation was performed using the obtained electrode. The gel content and measurement results are shown in Table 2.

Example Comparative example One 2 3 4 One 2 Polymer composition Structural unit a Granted monomer 2-ethylhexyl acrylate Ethyl acrylate 2-butylhexyl acrylate (Part) 92 (Part) 753 (Part) 70 (Part) 88 (Part) 753 (Part) 753 Structural unit b grant monomer acrylic acid methacrylic acid (Part) 5 (Part) 22 (Part) 1515 (Part) 2 (Part) 22 (Part) 4022 Structural unit c grant monomer ethylene glycol dimethacrylate divinylbenzene (Part) 3 (part) (part) (Part) 10 (part) (part) Other monomer acrylonitrile (part) (part) (part) (part) (Part) 7 (part) Emulsifiers and suspending agents (Part) 2 (Part) 2 (Part) 3 (Part) 5 (Part) 2 (Part) 2 Polymerization Initiators Potassium Sulfate Ammonium Persulfate (Part) 0.3 (Part) 0.3 (Part) 0.3 (Part) 0.3 (Part) 0.3 (Part) 0.3 Gel content 95 88 83 92 77 81 Evaluation results Flexural peeling strength (g / cm) High temperature initial discharge capacity High temperature charge / discharge cycle characteristics 1432572 2032171 2531865 2032673 1529344 1329648

Example Comparative example 5 6 7 3 4 Polymer composition Structural unit a Granted monomer 2-ethylhexyl acrylate Ethyl acrylate 2-butylhexyl acrylate (Part) 92 (Part) 753 (Part) 70 (Part) 753 (Part) 753 Structural unit b grant monomer acrylic acid methacrylic acid (Part) 5 (Part) 22 (Part) 1515 (Part) 22 (Part) 4022 Structural unit c grant monomer ethylene glycol dimethacrylate (Part) 3 (part) (part) (part) (part) Other monomer acrylonitrile (part) (part) (part) (Part) 7 (part) Emulsifiers and suspending agents (Part) 2 (Part) 2 (Part) 3 (Part) 2 (Part) 2 Polymerization Initiators Potassium Sulfate Ammonium Persulfate (Part) 0.3 (Part) 0.3 (Part) 0.3 (Part) 0.3 (Part) 0.3 Gel content 95 88 83 77 81 Evaluation results Flexural peeling strength (g / cm) High temperature initial discharge capacity High temperature charge / discharge cycle characteristics 4112272 5512270 5812469 3911042 4210448

From the above results, it was found that a lithium ion secondary battery excellent in battery characteristics at high temperature can be obtained when the structural unit a and the structural unit b have a specific ratio, and when the total ratio of both is constant or higher.

According to the present invention, a binder composition for a lithium ion secondary battery electrode having excellent charge and discharge cycle characteristics at a high temperature and a lithium ion secondary battery are provided.

Claims (6)

Structural unit (a) derived from an ethylenically unsaturated carboxylic acid ester monomer, and structural unit (b) derived from an ethylenically unsaturated carboxylic acid monomer are contained, and a structural unit (a) / structural unit (b) = 99-60 / 1 Binder composition for lithium ion secondary battery electrodes comprising -40 (weight ratio) of polymer particles and water substantially free of nitrile groups having a total of structural units (a) and structural units (b) of 80% by weight or more based on the total units. . The binder composition for lithium ion secondary battery electrodes according to claim 1, wherein the gel content calculated as an insoluble content of the electrolyte solution is 50% or more and 100% or less of the polymer particles. The binder composition for lithium ion secondary battery electrodes of Claim 1 or 2 whose pH is the range of 5-10. The slurry for lithium ion secondary battery electrodes containing the binder composition and active material of any one of Claims 1-3. The electrode for lithium ion secondary batteries manufactured using the slurry of Claim 4. The lithium ion secondary battery manufactured using the electrode of Claim 5.