KR20140039226A - Binder composition for secondary cell negative electrode, slurry composition for secondary cell negative electrode, negative electrode for secondary cell, and secondary cell - Google Patents

Abstract

assignment
It is providing the binder composition which has high adhesiveness between the electrical power collector after charge and discharge, and an electrode active material layer, and especially can contribute to the improvement of the cycling characteristics at high temperature of a secondary battery, and low temperature output characteristics.
Solution
The binder composition according to the present invention contains a binder and a propargyl group-containing compound, and the content of the propargyl group-containing compound is 0.1 to 20 parts by mass with respect to 100 parts by mass of the binder.

Description

Binder composition for secondary battery negative electrode, slurry composition for secondary battery negative electrode, negative electrode for secondary battery and secondary battery {BINDER COMPOSITION FOR SECONDARY CELL NEGATIVE ELECTRODE, SLURRY COMPOSITION FOR SECONDARY CELL NEGATIVE ELECTRODE, NEGATIVE ELECTRODE FOR SECONDARY CELL, AND SECONDARY CELL}

The present invention relates to a binder composition for secondary battery negative electrodes, and more particularly to a binder composition for lithium ion secondary battery negative electrodes. Moreover, this invention relates to the slurry composition, the negative electrode, and the secondary battery using such a binder for secondary battery negative electrodes.

2. Description of the Related Art In recent years, portable terminals such as a notebook computer, a mobile phone, and a PDA (Personal Digital Assistant) have become popular. BACKGROUND ART [0002] As secondary batteries used for power supply to these portable terminals, nickel-hydrogen secondary batteries, lithium ion secondary batteries, and the like are widely used. As portable terminals are required for more comfortable portability, miniaturization, thinning, weight reduction, and high performance have rapidly progressed. As a result, portable terminals have been used in various places. In addition, the battery is also required to be smaller, thinner, lighter, and higher in performance as with the portable terminal.

For example, in a lithium ion secondary battery, the conductive carbonaceous material is used as a negative electrode active material from the characteristics of light weight and high energy density, and is used as a binder for bonding to the shape of the electrode active material layer and the current collector. A polymer (hereinafter sometimes referred to as a "polymer binder") is used.

The polymer binder is required to have adhesion with an electrode active material, resistance to a polar solvent used as an electrolyte, and stability under an electrochemical environment. From such demanded characteristics, fluorine-based polymers such as polyvinylidene fluoride are used. However, when the fluorine-based polymer is formed, there is a problem that the conductivity is inhibited or the adhesion strength between the current collector and the electrode active material layer is insufficient. Moreover, when a fluorine-type polymer is used for the negative electrode used as reducing conditions, stability is not enough and there also exists a problem that the cycling characteristics of a secondary battery fall.

For this reason, using a non-fluorine-type polymer as a polymer binder is examined in a negative electrode. For example, Patent Document 1 (Japanese Laid-Open Patent Publication No. Hei 11-25989) and Patent Document 2 (Japanese Laid-Open Patent Publication No. 2010-140684) include conjugated dienes such as ethylenically unsaturated acid monomers such as (meth) acrylic acid and butadiene. And a polymer binder obtained by copolymerizing aromatic vinyl such as styrene. According to such a polymer binder, the adhesiveness between an electrical power collector and an electrode active material layer is high, and a battery with high cycling characteristics can be obtained. Moreover, the improvement of a characteristic by mix | blending various additives with respect to a polymer binder is also examined variously.

In addition, Patent Documents 3 to 5 teach that an alkenyl group-containing compound is added to an electrolyte for the purpose of preventing deterioration of the electrolyte.

Japanese Patent Laid-Open No. 11-25989 Japanese Unexamined Patent Publication No. 2010-140684 Japanese Laid-Open Patent Publication 2001-313072 Japanese Unexamined Patent Publication No. 2009-93839 Japanese Unexamined Patent Publication No. 2009-152133

By using the polymer binders of patent documents 1 and 2 for an electrode active material layer, the adhesiveness between an electrical power collector and an electrode active material layer is high, and a battery high in cycling characteristics can be obtained. However, secondary batteries are constantly being demanded for high functionality and long life. Specifically, improvement in cycle characteristics, low temperature output characteristics, and the like, and improvement in adhesion between the current collector and the electrode active material layer after charge and discharge are also required.

However, in the polymer binders described in Patent Literatures 1 and 2, the adhesiveness between the current collector and the electrode active material layer after charge and discharge is lowered, or the cycle characteristics of the secondary battery obtained, in particular, the cycle characteristics and the low temperature output characteristics at high temperatures are reduced. There was a problem, and further improvement was desired.

Then, this invention is excellent in the adhesiveness between the electrical power collector after an electrical charge and an electrode active material layer, and providing the binder composition for secondary battery negative electrodes which can contribute to the improvement of the cycling characteristics at high temperature of a secondary battery, and low temperature output characteristics. The purpose.

MEANS TO SOLVE THE PROBLEM As a result of continuing earnest examination in order to solve the said subject, as a result of using together the polymer binder used for a negative electrode active material layer, and a specific compound, adhesiveness between an electrical power collector and an electrode active material layer after charge and discharge improves, especially high temperature It was found out that a secondary battery having improved cycle characteristics and low temperature output characteristics was obtained, and thus, the present invention was completed.

That is, the gist of the present invention for solving the above problems is as follows.

(1) The binder composition for secondary battery negative electrodes containing a binder and a propargyl group containing compound, and content of the said propargyl group containing compound is 0.1-20 mass parts with respect to 100 mass parts of said binders.

(2) The binder composition for secondary battery negative electrodes as described in (1) whose said propargyl group containing compound is a monopropargyl group containing compound.

(3) The binder composition for secondary battery negative electrodes as described in (1) or (2) in which the said binder contains an ethylenic unsaturated carboxylic monomer unit.

(4) The binder composition for secondary battery negative electrodes in any one of (1)-(3) whose glass transition temperature of the said binder is -60 degreeC-40 degreeC.

(5) The slurry composition for secondary battery negative electrodes containing the binder composition for secondary battery negative electrodes in any one of said (1)-(4), and a negative electrode active material.

(6) The slurry composition for secondary battery negative electrodes as described in (5) whose BET specific surface area of the said negative electrode active material is 3-20 m <2> / g.

(7) The negative electrode for secondary batteries which has a negative electrode active material layer which consists of a negative electrode binder composition for secondary batteries and a negative electrode active material in any one of said (1)-(4) on an electrical power collector.

(8) The negative electrode for secondary batteries as described in (7) whose BET specific surface area of the said negative electrode active material is 3-20 m <2> / g.

(9) The negative electrode for secondary batteries as described in (7) or (8) whose said negative electrode active material is a carbon material type active material.

(10) A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte solution, and a separator, wherein the negative electrode is a secondary battery according to any one of (7) to (9).

(11) The secondary battery according to (10), in which the electrolyte solution contains vinylene carbonate.

By using together the binder used for a negative electrode active material layer, and a propargyl group containing compound, the adhesiveness between an electrical power collector and an electrode active material layer improves, and the secondary battery which improved especially high temperature cycling characteristics and low temperature output characteristics is obtained. Such a mechanism of action of the present invention is not necessarily clear. Although not limitedly interpreted at all, the present inventors estimate the mechanism by which the said effect appears as follows. That is, it is considered that by blending the propargyl group-containing compound in the negative electrode active material layer, the propargyl group-containing compound is adsorbed on the surface of the negative electrode active material, and the formation of a thin layer called SEI (Solid Electrolyte Interface) film is promoted on the surface of the negative electrode active material. .

When the surface of the negative electrode active material contacts with the electrolyte, in most cases, a part of the electrolyte contacted at the edge of the negative electrode active material is decomposed. The edge portion of such a negative electrode active material is also called an active point. The decomposed product generated at the active point causes the electrode active material layer to swell, thereby decreasing the adhesion between the current collector and the electrode active material layer. As a result, the cycle characteristics and the low temperature output characteristics of the battery are hindered.

However, by forming the SEI film with the propargyl group-containing compound as described above, direct contact between the active point of the negative electrode active material and the electrolyte is reduced, and decomposition of the electrolyte component is prevented. As a result, it is thought that the swelling of the negative electrode active material layer is reduced and the peel strength, that is, the adhesion between the current collector and the negative electrode active material layer is maintained, and the cycle characteristics and the low temperature output characteristics can be improved.

Below, it demonstrates in order of (1) binder composition for secondary battery negative electrodes, (2) slurry composition for secondary battery negative electrodes, (3) negative electrode for secondary batteries, and (4) secondary batteries.

(1) secondary battery For negative electrode  Binder composition

The binder composition for secondary battery negative electrodes of this invention contains a binder and a propargyl group containing compound.

(bookbinder)

The binder used in the present invention is not particularly limited, and various polymer compounds which have conventionally been used as binders for the negative electrode active material layer such as fluorine polymers, diene polymers, and nitrile polymers are used. Among these, the high molecular compound which is easy to synthesize | combine in an aqueous system and is obtained simply in the form of aqueous latex is preferable. As such a high molecular compound, the high molecular compound containing an ethylenic unsaturated acid monomeric unit, Preferably an ethylenic unsaturated carboxylic monomer unit is mentioned.

It is preferable that the high molecular compound containing an ethylenic unsaturated carboxylic monomer unit contains an aliphatic conjugated diene type monomeric unit as a comonomer, and may contain the unit derived from the other monomer copolymerizable with these monomers as needed. . Moreover, it is especially preferable to contain these monomeric units in a specific ratio from a viewpoint of durability, flexibility, adhesiveness, etc. of a binder.

Therefore, the binder particularly preferably used in the present invention is composed of an ethylenically unsaturated carboxylic acid monomer unit, an aliphatic conjugated diene monomer unit, and other monomer units copolymerizable with these, and containing each monomer unit in a specific ratio. desirable. The ethylenically unsaturated carboxylic monomer unit is a polymer repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer, and the aliphatic conjugated diene monomer unit is a polymer repeating unit obtained by polymerizing an aliphatic conjugated diene monomer and copolymerizable with these. The other monomer unit is a polymer repeating unit obtained by polymerizing another copolymerizable monomer.

As an ethylenic unsaturated carboxylic monomer, mono or dicarboxylic acid (anhydride), such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc. are mentioned, 1 type, or 2 or more types can be used. Can be. Among these, acrylic acid, methacrylic acid and itaconic acid are preferable at the point which is excellent in adhesiveness with an electrical power collector, and itaconic acid is especially preferable. When using a polymer binder together with the propargyl group containing compound mentioned later, as the compounding quantity of a propargyl group containing compound increases, the dispersibility in the water of a binder composition (it may abbreviate as water dispersibility suitably after this) may be It may fall. However, water dispersibility is improved by introducing a unit containing a carboxylic acid in the polymer binder. Moreover, especially when itaconic acid which is dicarboxylic acid is introduce | transduced, the affinity of a binder and water becomes high.

Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugated penta Dienes, substituted and side chain conjugated hexadienes; and the like, and one or two or more kinds thereof may be used. Especially 1,3-butadiene is preferable.

As another monomer copolymerizable with these, an aromatic vinyl monomer, a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, an unsaturated monomer containing a hydroxyalkyl group, an unsaturated carboxylic acid amide monomer, etc. are mentioned, and these are 1 Species or two or more kinds may be used. In particular, an aromatic vinyl monomer is preferable at the point which can suppress swelling with respect to electrolyte solution.

Styrene, (alpha) -methylstyrene, vinyltoluene, divinylbenzene, etc. are mentioned as an aromatic vinylic monomer, 1 type or 2 or more types can be used. Among these, styrene is especially preferable at the point which can suppress swelling with respect to electrolyte solution.

As a vinyl cyanide monomer, an acrylonitrile, methacrylonitrile, the (alpha)-chloro acrylonitrile, the (alpha)-ethyl acrylonitrile, etc. are mentioned, 1 type, or 2 or more types can be used. In particular, acrylonitrile and methacrylonitrile are preferable.

As unsaturated carboxylic acid alkyl ester monomer, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl male Eight, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, etc. are mentioned, 1 type, or 2 or more types can be used. In particular, methyl methacrylate is preferable.

Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate and hydroxybutyl Methacrylate, 3-chloro-2-hydroxypropylmethacrylate, di- (ethyleneglycol) maleate, di- (ethyleneglycol) itaconate, 2-hydroxyethylmaleate, bis (2-hydroxy Ethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like, and one kind or two or more kinds can be used. In particular, β-hydroxyethyl acrylate is preferable.

As an unsaturated carboxylic amide monomer, acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N- dimethyl acrylamide, etc. are mentioned, 1 type, or 2 or more types Can be used. In particular, acrylamide and methacrylamide are preferable.

In addition to the monomers described above, any monomers used in conventional emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, and vinylidene chloride can be used.

As for the ratio of each monomer unit of the binder in this invention, an ethylenic unsaturated carboxylic monomer unit becomes like this. Preferably it is 0.1-20 mass%, More preferably, it is 0.5-15 mass%, More preferably, it is 1.0-10 mass %, The aliphatic conjugated diene monomer unit is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, more preferably 30 to 60% by mass, and other monomer units copolymerizable with these are preferable. Is 5-79.9 mass%, More preferably, it is 10-70 mass%, More preferably, it is 20-60 mass%.

When an ethylenic unsaturated carboxylic monomer unit exists in the said range, stability of a binder composition and a slurry composition improves and sufficient adhesiveness of the negative electrode active material and an electrical power collector in a negative electrode for secondary batteries can be obtained. As a result, durability of the secondary battery obtained, especially high temperature cycling characteristics improve and it is preferable.

The aliphatic conjugated diene monomer unit is preferably in the above range because the flexibility of the negative electrode for secondary batteries and the adhesion between the negative electrode active material and the current collector are highly balanced. Moreover, since durability of especially the secondary battery obtained, especially high temperature cycling characteristics is improved, it is preferable.

The other monomeric unit which can be copolymerized exists in the said range, and since the flexibility of the negative electrode for secondary batteries and the adhesiveness of a negative electrode active material and an electrical power collector are highly balanced, it is preferable. Moreover, since durability of especially the secondary battery obtained, especially high temperature cycling characteristics is improved, it is preferable.

Glass transition temperature (Tg) of a binder becomes like this. Preferably it is -60-40 degreeC, More preferably, it is -50-30 degreeC, Especially preferably, it is -40-20 degreeC. Since Tg of a binder exists in the said range, characteristics, such as the softness | flexibility of a negative electrode, binding property and winding property, adhesiveness of a negative electrode active material and an electrical power collector, are highly balanced, and are preferable.

In addition, when aliphatic conjugated diene is used as a copolymerization monomer, you may hydrogenate a diene unit after superposition | polymerization. The method of adding hydrogen is not specifically limited, A conventional method can be used.

(Propargyl group-containing compound)

In the binder composition for secondary battery negative electrodes of the present invention, a specific amount of propargyl group-containing compound is contained with respect to 100 parts by mass of the binder (in terms of solid content). Although not theoretically limited at all, according to the binder composition for secondary battery negative electrodes of the present invention, by containing a specific amount of a propargyl group-containing compound, the propargyl group-containing compound is the active site of the negative electrode active material when it is brought into contact with the negative electrode active material. It is thought to form an SEI film in the vicinity. Since the SEI film prevents the components of the electrolyte from contacting the active point, decomposition of the electrolyte in the battery is suppressed. As a result, since the increase of electrolyte viscosity and the increase of the internal resistance of a secondary battery by decomposition | disassembly of electrolyte solution are suppressed, the high temperature storage characteristic, high temperature cycling characteristic, and low temperature output characteristic of a secondary battery improve. Moreover, swelling of the negative electrode active material layer by the decomposition product of electrolyte solution components is prevented, a peeling strength is maintained, and high temperature cycling characteristics and low temperature output characteristics can be improved further.

Content of the propargyl group containing compound in a binder composition is 0.1-20 mass parts with respect to 100 mass parts (solid content conversion), Preferably it is 0.5-10 mass parts, More preferably, it is 1-5 mass parts. When there is too little content of a propargyl group containing compound, generation | occurrence | production of the said SEI film will become inadequate, electrolyte component will be easy to decompose | disassemble, and there exists a possibility that the cycling characteristics and output characteristics of a battery may fall. On the other hand, when there is too much content of a propargyl group containing compound, stability of the slurry prepared using the binder composition will be inhibited, and the viscosity of a slurry will rise easily. As a result, application | coating of a slurry becomes difficult, there exists a possibility that the uniformity of the negative electrode obtained may fall, and output characteristics may fall.

The propargyl group-containing compound used in the present invention has at least one propargyl group (HC≡C-CH _2- ) in the molecule. Although the number of propargyl groups is not specifically limited, When the number of propargyl groups increases, dispersibility with respect to water falls and there exists a possibility that a uniform aqueous slurry may not be obtained. Therefore, the number of propargyl groups per molecule of propargyl group-containing compound is preferably 2 or less, and particularly preferably 1. Therefore, in the present invention, a monopropargyl group-containing compound is particularly preferably used.

Specific examples of the propargyl group-containing compound include monopropargyl group-containing compounds such as benzenesulfonic acid propargyl, acrylic acid propargyl, methacrylic acid propargyl, and propargyl acetate;

Dipropargyl group containing compounds, such as dipropargyl carbonate, are mentioned.

When such a propargyl group-containing compound is in contact with a negative electrode active material as described later, the propargyl group-containing compound is adsorbed on the surface of the negative electrode active material, and is considered to produce a thin layer called an SEI film. In the negative electrode active material in which an SEI film was formed, since the edge part which is an active point is also covered by a film, the contact of an active point and electrolyte component is reduced. As a result, decomposition of electrolyte component is suppressed, expansion of a negative electrode active material layer, the fall of adhesiveness between the electrical power collector and a negative electrode active material layer resulting from it are prevented, and the high temperature cycling characteristics and low temperature output characteristics of a battery improve. I think.

(Other components)

The binder composition for secondary battery negative electrodes of this invention may contain the dispersion medium for disperse | distributing these components in addition to a binder and a propargyl group containing compound. As the dispersion medium, any of water and an organic solvent may be sufficient as a dispersion medium, and as long as it is a range which does not inhibit the dispersion stability of a binder composition, you may mix a hydrophilic solvent with water as a dispersion medium. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and are preferably 5% by mass or less with respect to water. Moreover, the reaction solvent at the time of binder preparation mentioned later may be used as a dispersion medium, and solvent substitution may be carried out after binder preparation.

When a binder composition contains a dispersion medium, although the total solid content concentration of a binder and a propargyl group containing compound is not specifically limited, About 20-60 mass% is suitable.

Moreover, the binder composition may contain the various dispersing agents etc. which were used at the time of binder preparation. Moreover, the binder composition may further contain anti-aging agent, antiseptic | preservative, etc. in the range which does not impair the dispersibility of a composition.

Examples of the antioxidant include amine antioxidants, phenolic antioxidants, quinone antioxidants, organophosphorus antioxidants, sulfur antioxidants, phenothiazine antioxidants, and the like. Preservatives include isothiazoline compounds and pyrithione compounds. When a binder composition contains these components, solid content concentration of these components in a composition is not specifically limited, About 0.001-1 mass% is suitable.

(Manufacturing method of the binder composition for secondary battery negative electrodes)

As a method of manufacturing the binder composition for secondary battery negative electrodes of this invention, the monomer composition containing the said monomer is superposed | polymerized in an aqueous solvent, and the aqueous dispersion liquid containing a binder (the binder which is a polymer particle having a binding force melt | dissolves in an aqueous solvent, or Dispersed solution or dispersion), and a specific amount of the propargyl group-containing compound and other optional components are added to and mixed with the aqueous dispersion containing the binder. However, the manufacturing method of a binder composition is not limited to this, For example, you may mix | blend a propargyl group containing compound, anti-aging agent, an antiseptic, etc. with a monomer composition previously, and may superpose | polymerize after that. Moreover, you may mix | blend these with a binder composition in the polymerization or at arbitrary stages after superposition | polymerization.

As for the ratio of each monomer in the monomer composition in the process of obtaining the water dispersion liquid containing a binder, an ethylenically unsaturated carboxylic monomer is preferably 0.1-20 mass%, More preferably, it is 0.5-15 mass%, More preferably Preferably it is 1.0-10 mass%, Aliphatic conjugated diene type monomer becomes like this. Preferably it is 20-80 mass%, More preferably, it is 25-70 mass%, More preferably, it is 30-60 mass%, The other copolymerizable with these Preferably monomer is 5-79.9 mass%, More preferably, it is 10-70 mass%, More preferably, it is 20-60 mass%.

As an aqueous solvent, if a binder can be disperse | distributed, it will not specifically limit, Usually, the boiling point in normal pressure is selected from the dispersion medium of 80-350 degreeC, Preferably it is 100-300 degreeC. In addition, the number in () after the dispersion medium name illustrated below is a boiling point (unit degreeC) at normal pressure, and the decimal point is the value rounded off or cut off. For example, as ketones, diacetone alcohol (169) and (gamma) -butyrolactone (204); As alcohol, ethyl alcohol (78), isopropyl alcohol (82), normal propyl alcohol (97); Ethylene glycol (193), propylene glycol (188), diethylene glycol (244) as glycols; Examples of the glycol ethers include propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171), and 3 -Methoxy-3-methyl-1-butanol (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188); Examples of the ethers include 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66). Especially, water is the most preferable from a viewpoint that it is not flammable and the dispersion of a binder is easy to be obtained easily. In addition, water may be used as the main solvent, and an aqueous solvent other than water described above may be mixed and used in a range in which the binder dispersion state can be secured.

The polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization or the like can be used. Ion polymerization, radical polymerization, a living radical polymerization, etc. are mentioned as a polymerization reaction. From the viewpoint of manufacturing efficiency, the high molecular weight is easy to be obtained, the polymer is obtained in the state of being dispersed in water as it is, and the redispersion process is unnecessary, and it can be used as it is for producing the slurry composition for secondary battery negative electrodes. Most preferred is emulsion polymerization.

The emulsion polymerization method is a conventional method, for example, the method described in "Experimental Chemistry Course" Vol. 28, (Published by Maruzen, Nippon Chemical Society), that is, in a sealed container with a stirrer and a heating device. Additives, such as water, a dispersing agent, an emulsifier, and a crosslinking agent, an initiator, and a monomer are added so that it may become a predetermined | prescribed composition, and it will stir to emulsify a monomer etc. in water, and temperature will be raised, stirring, and a polymerization is started. Or after emulsifying the said composition, it puts into a closed container and it is the method of starting reaction similarly.

An emulsifier, a dispersing agent, a polymerization initiator, etc. are generally used by these polymerization methods, The usage-amount may be sufficient as it is generally used. Moreover, at the time of superposition | polymerization, it is also possible to employ | adopt seed particle | grains (seed polymerization).

Although superposition | polymerization temperature and superposition | polymerization time can be arbitrarily selected according to the polymerization method, the kind of polymerization initiator to be used, etc., Usually, polymerization temperature is about 30 degreeC or more, and polymerization time is about 0.5 to 30 hours. Additives, such as amines, can also be used as a polymerization aid. In addition, alkali metal (Li, Na, K, Rb, Cs) hydroxides, ammonia, inorganic ammonium compounds (NH ₄ Cl, etc.), organic amine compounds (ethanolamine, diethylamine) are added to the aqueous dispersion of the polymer particles obtained by these methods. Etc.) can be adjusted so as to be in a range of pH 5 to 10, preferably 5 to 9 by adding a basic aqueous solution in which etc. are dissolved. PH adjustment by alkali metal hydroxide is preferable in order to improve binding property (fill strength) of a binder composition, an electrical power collector, and an active material.

The binder mentioned above may be a composite polymer particle composed of two or more kinds of polymers. The composite polymer particles are also obtained by a method of polymerizing at least one monomer component by a conventional method, then adding another at least one monomer component, and polymerizing by a conventional method (two-stage polymerization method) or the like. Can be.

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.

Moreover, in the said superposition | polymerization, you may add a chain transfer agent. As a chain transfer agent, alkyl mercaptan is preferable, and specifically, n-butyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan and t-dodecyl mercaptan and n-stearyl mercaptan. Among them, n-octyl mercaptan and t-dodecyl mercaptan are preferred from the viewpoint of good polymerization stability.

Moreover, you may use together another chain transfer agent with the said alkyl mercaptan. Examples of the chain transfer agent that may be used in combination include terpinolene, allyl alcohol, allylamine, allyl sulfonic acid sodium (potassium), and metaallyl sulfonic acid sodium (potassium). The amount of the chain transfer agent used is not particularly limited as long as the effect of the present invention is not impaired.

50-500 nm is preferable and, as for the number average particle diameter of the binder in an aqueous dispersion liquid, 70-400 nm is more preferable. Since the number average particle diameter of a binder exists in the said range, the intensity | strength and flexibility of the negative electrode obtained become favorable. Presence of a polymer particle can be easily measured by a transmission electron microscopy method, a Coulter counter method, a laser diffraction scattering method, etc.

The binder may be a binder made of polymer particles having a core shell structure obtained by polymerizing the monomers in stages.

The method of adding and mixing a propargyl group containing compound and other arbitrary components to the aqueous dispersion liquid containing a binder is not specifically limited. As a method of mixing, the method of using mixing apparatuses, such as stirring, shaking, and rotation, is mentioned, for example. Moreover, the method using the dispersion kneading apparatus, such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader, is mentioned.

Moreover, an additive can be added to the obtained binder composition for secondary battery negative electrodes of this invention in order to improve applicability | paintability or to improve charge / discharge characteristics. These additives include cellulose polymers such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, acrylic acid-vinyl alcohol copolymer, Methacrylic acid-vinyl alcohol copolymer, maleic acid-vinyl alcohol copolymer, modified polyvinyl alcohol, polyethylene glycol, ethylene-vinyl alcohol copolymer, polyvinyl acetate partial saponified product, and the like. These additives can be added to the slurry composition for secondary battery negative electrodes of this invention mentioned later other than the method of adding to a binder composition.

(2) secondary battery For negative electrode Slurry  Composition

The slurry composition for secondary battery negative electrodes of this invention contains the said binder composition for secondary battery negative electrodes, and a negative electrode active material. Hereinafter, the aspect which uses the slurry composition for secondary battery negative electrodes of this invention as a slurry composition for lithium ion secondary battery negative electrodes is demonstrated.

(Negative electrode active material)

The negative electrode active material used in the present invention is a substance which transmits and receives electrons in the negative electrode for secondary batteries.

As a negative electrode active material for lithium ion secondary batteries, a carbon material type active material and an alloy type active material are mentioned.

The carbon material-based active material refers to an active material whose main skeleton is carbon into which lithium can be inserted, and specifically, carbonaceous material and graphite material. The carbonaceous material generally refers to a low graphitization (low crystallinity) carbon material obtained by heat treatment (carbonization) of a carbon precursor at 2000 ° C. or lower, and the graphite material is obtained by heat treatment of graphite easy carbon at 2000 ° C. or higher. The graphite material which has high crystallinity close to graphite is shown.

Examples of the carbonaceous material include graphite-easy carbon which easily changes the structure of carbon by heat treatment temperature, and non-graphite carbon having a structure close to the amorphous structure represented by glassy carbon.

Examples of the graphite easy carbon include carbon materials based on tar pitch obtained from petroleum or coal, and examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and thermal decomposition vapor grown carbon fibers. Can be mentioned. MCMB is carbon fine particles obtained by separating and extracting mesophase globules generated by heating pitches at around 400 ° C., and mesophase pitch-based carbon fibers are mesophase pitches obtained by growing and coalescing the mesophase globules as a raw material. It is carbon fiber.

Examples of the non-graphite carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudoisotropic carbon, and furfuryl alcohol resin fired bodies (PFA).

Examples of the graphite material include natural graphite and artificial graphite. As artificial graphite, artificial graphite mainly heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated MCMB at 2000 ° C. or higher, mesophase pitch-based carbon graphitized mesophase pitch-based carbon heat treated at 2000 ° C. or higher Fiber, and the like.

Among these carbon-based active materials, a graphite material is preferable.

The alloy-based active material used in the present invention includes an element capable of inserting lithium in the structure, and refers to an active material having a theoretical electric capacity per mass of 500 mAh / g or more when lithium is inserted, specifically, lithium metal and lithium. Single metals and alloys thereof forming alloys, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like are used.

As a single metal and alloy which form a lithium alloy, the compound containing metals, such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, etc. Can be mentioned. Among them, a single metal such as silicon (Si), tin (Sn) or lead (Pb), an alloy containing these atoms, or a compound of these metals is used.

The alloy-based active material used in the present invention may further contain one or more nonmetallic elements. Specifically, for example, SiC, SiO _x C _y (hereinafter referred to as "Si-OC") (0 <x≤3, 0 <y≤5), Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x (0 <x≤2), SnO _x (0 <x≤2), there may be mentioned LiSiO, LiSnO, etc., among the SiO _x C _y insertion desorption of lithium are possible on the low potential are preferred. For example, SiO _x C _y Can be obtained by baking a polymer material containing silicon. Among SiO _x C _y , from the balance of capacity and cycle characteristics, a range of 0.8? X? 3, 2? Y? 4 is preferably used.

Examples of the oxides, sulfides, nitrides, silicides, carbides, and phosphides include oxides, sulfides, nitrides, silicides, carbides, and phosphides of elements into which lithium can be inserted. Of these, oxides are particularly preferred. Specifically, a lithium-containing metal composite oxide material containing a metal element selected from the group consisting of oxides such as tin oxide, manganese oxide, titanium oxide, niobium oxide, and vanadium oxide, Si, Sn, Pb, and Ti atoms is used. Examples of the oxides of silicon include materials such as silicon carbide (Si-O-C).

As the lithium-containing metal composite oxide, a lithium titanium composite oxide further represented by Li _x Ti _y M _z O ₄ (0.7 ≦ x ≦ 1.5, 1.5 ≦ _y ≦ 2.3, 0 ≦ _z ≦ 1.6, and M is Na, K, Co , Al, Fe, Ti, Mg , Cr, Ga, Cu, Zn , and can be exemplified by Nb), in particular, _{Li 4/3 Ti 5/3} O 4, Li 1 Ti 2 O 4, Li 4/5 Ti 11 _{/ 5} O ₄ is used.

Among these, materials containing silicon (hereinafter, may be described as "silicon-containing material") are preferable, and Si-O-C is more preferable among these. In this compound, it is estimated that insertion detachment of Li to Si (silicon) at high potential and C (carbon) at low potential occur, and expansion and contraction are suppressed more than other alloy-based active materials.

In this invention, a graphite material and a silicon containing material are preferable as a negative electrode active material, and natural graphite and Si-O-C are especially preferable. In such an active material, an SEI film is formed by contact with a propargyl group-containing compound, the active point of the edge portion is easily deactivated, and the decomposition of the electrolyte component can be effectively prevented. In particular, the present invention is effective for an electrode containing a carbon material-based active material.

In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together. When using together, the combination of a graphite material and a silicon containing material is preferable. As for the compounding ratio (graphite material / silicon-containing material), 99/1-40/60 are preferable at a weight ratio, and 95/5-45/55 are more preferable. It is preferable that the shape of a negative electrode active material was grain-sorted. If the particle shape is spherical, an electrode of higher density can be formed at the time of electrode molding.

Although the volume average particle diameter of a negative electrode active material is suitably selected by the balance with the other structural requirements of a battery, it is 0.1-100 micrometers normally, Preferably it is 1-50 micrometers, More preferably, it is 5-20 micrometers. In addition, the 50% volume cumulative diameter of the negative electrode active material is usually 1 to 50 µm, preferably 15 to 30 µm, in view of improvement of battery characteristics such as initial efficiency, load characteristics, and cycle characteristics. The volume average particle diameter is obtained by measuring the particle size distribution by laser diffraction. The 50% volume cumulative diameter is a 50% volume average particle diameter measured by a laser diffraction particle size distribution analyzer (SALD-3100; manufactured by Shimadzu Corporation) and calculated.

The tap density of the negative electrode active material is not particularly limited, but is preferably 0.6 g / cm 3 or more.

The BET specific surface area of the negative electrode active material is preferably 3 to 20 m 2 / g, more preferably 3 to 15 m 2 / g, and particularly preferably 3 to 10 m 2 / g. Since the active point of the surface of a negative electrode active material increases because the BET specific surface area of a negative electrode active material is in the said range, it is excellent in the low temperature output characteristic of a secondary battery.

In the slurry composition for secondary battery negative electrodes of this invention, the sum total content of a negative electrode active material and a binder composition becomes like this. Preferably it is 10-90 mass parts with respect to 100 mass parts of slurry compositions, More preferably, it is 30-80 mass parts. Moreover, content (solid content equivalent) of the binder composition with respect to the total amount of a negative electrode active material becomes like this. Preferably it is 0.1-5 mass parts with respect to 100 mass parts of total amounts of a negative electrode active material, More preferably, it is 0.5-2 mass parts. When the total content of the negative electrode active material and the binder composition in the slurry composition and the content of the binder composition are within the above ranges, the viscosity of the slurry composition for secondary battery negative electrodes obtained is optimized, and the coating can be smoothly applied. The resistance does not increase, and sufficient adhesion strength is obtained. As a result, peeling of the negative electrode active material layer from an electrical power collector in a pole plate press process can be suppressed.

(Dispersion medium)

In this invention, it is preferable to use water as a dispersion medium of a slurry. In this invention, as long as it is a range which does not inhibit the dispersion stability of a binder composition, you may use what mixed the hydrophilic solvent with water as a dispersion medium. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and are preferably 5% by mass or less with respect to water.

(Conductive agent)

In the slurry composition for secondary battery negative electrodes of this invention, it is preferable to contain a electrically conductive agent. As the conductive agent, conductive carbon such as acetylene black, Ketjen black, carbon black, graphite, vapor grown carbon fiber, and carbon nanotube can be used. By containing a electrically conductive agent, the electrical contact of negative electrode active materials can be improved, and when using for a secondary battery, a discharge rate characteristic can be improved. Content of the electrically conductive agent in a slurry composition becomes like this. Preferably it is 1-20 mass parts, More preferably, it is 1-10 mass parts with respect to 100 mass parts of negative electrode active materials.

(Thickener)

In the slurry composition for secondary battery negative electrodes of this invention, it is preferable to contain a thickener. Examples of the thickener include cellulose polymers such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose, ammonium salts and alkali metal salts thereof;

(Modified) poly (meth) acrylic acid and their ammonium salts and alkali metal salts;

(Modified) polyvinyl alcohols, 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 the like.

As for the compounding quantity of a thickener, 0.5-1.5 mass parts is preferable with respect to 100 mass parts of negative electrode active materials. Applicability | paintability and adhesiveness with an electrical power collector are favorable in the compounding quantity of a thickener being the said range. In addition, in this specification, "(modified) poly" means "unmodified poly" or "modified poly", and "(meth) acryl" means "acryl" or "methacryl".

In addition to the above components, the slurry composition for secondary battery negative electrodes may further contain other components such as electrolyte additives having functions such as reinforcing materials, leveling agents, and electrolyte solution decomposition suppression, or may be contained in the negative electrode for secondary batteries described later. They are not particularly limited as long as they do not affect the cell reaction.

As the reinforcing material, various inorganic and organic spherical, plate, rod or fibrous fillers can be used. By using a reinforcing material, a strong and flexible negative electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. Content of the reinforcing material in a slurry composition is 0.01-20 mass parts normally with respect to 100 mass parts of negative electrode active materials, Preferably it is 1-10 mass parts. Being included in the above range shows high capacity and many load characteristics.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorochemical surfactants, and metal surfactants. By mixing the leveling agent, it is possible to prevent the occurrence of cratering at the time of coating or to improve the smoothness of the negative electrode. Content of the leveling agent in a slurry composition becomes like this. Preferably it is 0.01-10 mass parts with respect to 100 mass parts of negative electrode active materials. When the leveling agent is in the above range, the productivity, smoothness and battery characteristics at the time of producing the negative electrode are excellent. By containing surfactant, dispersibility, such as a negative electrode active material, in a slurry composition can be improved, and the smoothness of a negative electrode can be improved.

As the electrolyte solution additive used in the slurry composition and in the electrolyte solution, vinylene carbonate or the like can be used. Content of the electrolyte solution additive in a slurry composition becomes like this. Preferably it is 0.01-10 mass parts with respect to 100 mass parts of negative electrode active materials. When electrolyte solution additive is the said range, it is excellent in cycling characteristics and high temperature characteristics. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, thixotropy of the slurry composition can be controlled, and the leveling property of the negative electrode can be improved. The content of the nano fine particles in the slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When nano fine particle is the said range, it is excellent in slurry stability and productivity, and shows high battery characteristics.

(Water soluble polymer)

The slurry composition for secondary battery negative electrodes of this invention can contain a water-soluble polymer in addition to the said binder composition. As a water-soluble polymer, the water-soluble polymer which consists of 20-60 mass% of ethylenic unsaturated carboxylic monomer units, 20-80 mass% of (meth) acrylic acid ester monomeric units, and 0-20 mass% of other monomeric units copolymerizable with these is preferable. Do. By containing the said water-soluble polymer in the slurry composition for secondary battery negative electrodes, since adhesiveness and durability of the negative electrode for secondary batteries improve, a peeling strength can be improved. The water-soluble polymer in this invention means the polymer whose 1-% aqueous solution viscosity is 0.1-100000 mPa * s in pH12.

As an ethylenic unsaturated carboxylic monomer, mono or dicarboxylic acid (anhydride), such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc. are mentioned, 1 type, or 2 or more types can be used. Can be. The ratio of these ethylenic unsaturated carboxylic monomer units becomes like this. More preferably, it is 25-55 mass%, Especially preferably, it is 30-50 mass%.

As the (meth) acrylic acid ester monomer, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acryl Alkyl acrylates such as acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; And examples thereof include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, Methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-butyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, Esters. The ratio of these (meth) acrylic acid ester monomeric units becomes like this. More preferably, it is 25-75 mass%, Especially preferably, it is 30-70 mass%.

As another monomer which can be copolymerized, Carboxylic acid ester monomer which has 2 or more carbon-carbon double bonds, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylol propane triacrylate; Styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene and divinylbenzene; Amide monomers such as acrylamide, N-methylol acrylamide and acrylamide-2-methylpropanesulfonic acid; Α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Olefins such as ethylene and propylene; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; 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, are mentioned. Among these, α, β-unsaturated nitrile compounds and styrene monomers are preferable, and α, β-unsaturated nitrile compounds are particularly preferable. The ratio of these copolymerizable monomer units becomes like this. More preferably, it is 0-10 mass%, Especially preferably, it is 0-5 mass%.

As a method of manufacturing a water-soluble polymer, the monomer composition containing the said monomer is superposed | polymerized in an aqueous solvent, the water dispersion type polymer is obtained, and the method of alkalizing to pH 7-13 is mentioned. About an aqueous solvent and a polymerization method, it is the same as that of the binder composition for secondary battery negative electrodes mentioned above.

Although it does not specifically limit as a method of alkalizing to pH 7-13, Alkali metal aqueous solutions, such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution, and potassium hydroxide aqueous solution, alkali earth metal aqueous solutions, such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution, alkali, such as aqueous ammonia solution, etc. The method of adding aqueous solution is mentioned.

(Manufacture of the slurry composition for secondary battery negative electrodes)

The slurry composition for secondary battery negative electrodes is obtained by mixing the said binder composition, a negative electrode active material, and the electrically conductive agent used as needed.

Although the mixing method is not specifically limited, For example, the method of using mixing apparatuses, such as stirring, agitation, and rotation, is mentioned. Moreover, the method using the dispersion kneading apparatus, such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader, is mentioned.

(3) for secondary batteries Negative

The negative electrode for secondary batteries of this invention contains the said binder composition and a negative electrode active material, and is obtained by apply | coating and drying the slurry composition for secondary battery negative electrodes of this invention on an electrical power collector specifically ,.

(Method for producing negative electrode for secondary battery)

Although the manufacturing method of the negative electrode for secondary batteries of this invention is not specifically limited, For example, the method of apply | coating and drying the said slurry composition to at least one side, preferably both surfaces of an electrical power collector, and forms a negative electrode active material layer is mentioned.

The method of apply | coating a slurry composition on an electrical power collector is not specifically limited. For example, methods, such as a doctor blade method, a dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, the brush coating method, are mentioned.

As a drying method, the drying method by irradiation with warm air, hot air, low humidity wind, vacuum drying, (far) infrared rays, an electron beam, etc. are mentioned, for example. Drying time is 5-30 minutes normally, and drying temperature is 40-180 degreeC normally.

In manufacturing the negative electrode for secondary batteries of this invention, after apply | coating and drying the said slurry composition on an electrical power collector, it is preferable to have a process of lowering the porosity of a negative electrode active material layer by pressurization process using a metal mold | die press, a roll press, etc. . The range with preferable porosity is 5 to 30%, More preferably, it is 7 to 20%. If the porosity is too high, the charging efficiency and the discharge efficiency are deteriorated. When the porosity is too low, a high volume capacity is hard to be obtained, which causes a problem that the negative electrode active material layer is easily peeled off from the current collector and easily causes defects. In addition, when using a curable polymer for a binder composition, it is preferable to harden | cure.

The thickness of the negative electrode active material layer in the negative electrode for secondary batteries of this invention is 5-300 micrometers normally, Preferably it is 30-250 micrometers. When the thickness of the negative electrode active material layer is in the above range, both the load characteristics and the cycle characteristics exhibit high characteristics.

In this invention, the content rate of the negative electrode active material in a negative electrode active material layer becomes like this. Preferably it is 85-99 mass%, More preferably, it is 88-97 mass%. By setting the content ratio of the negative electrode active material to the above range, flexibility and binding properties can be exhibited while showing a high capacity.

In the present invention, the density of the negative electrode active material layer of the negative electrode for secondary batteries is preferably 1.6 to 1.9 g / cm 3, and more preferably 1.65 to 1.85 g / cm 3. When the density of the negative electrode active material layer is in the above range, a high capacity battery can be obtained.

(Whole house)

The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but since it has heat resistance, a metal material is preferable. For example, iron, copper, aluminum, nickel, stainless steel, Titanium, tantalum, gold, platinum, etc. are mentioned. Especially, copper is especially preferable as an electrical power collector used for the negative electrode for secondary batteries. Although the shape of an electrical power collector is not specifically limited, It is preferable that it is a sheet form with a thickness of about 0.001-0.5 mm. In order that an electrical power collector may raise adhesive strength with a negative electrode active material layer, it is preferable to use it, roughening previously. Examples of the roughening method include mechanical roughening, electrolytic roughening, and chemical roughening. In the mechanical polishing method, a wire brush provided with abrasive cloth, a grindstone, an emery buff, a steel wire or the like to which abrasive particles are fixed are used. Moreover, in order to improve the adhesive strength with a negative electrode active material layer, and electroconductivity, you may form an intermediate | middle layer in the electrical power collector surface.

(4) secondary battery

The secondary battery of this invention is a secondary battery provided with a positive electrode, a negative electrode, a separator, and electrolyte solution, and a negative electrode is the said negative electrode for secondary batteries.

(Positive electrode)

The positive electrode is formed by laminating a positive electrode active material layer containing a positive electrode active material and a binder composition for a secondary battery positive electrode on a current collector.

(Positive electrode active material)

As the positive electrode active material, an active material capable of doping and undoping lithium ions is used, and it is roughly divided into an organic compound and an inorganic compound.

As a positive electrode active material which consists of inorganic compounds, transition metal oxide, transition metal sulfide, lithium containing composite metal oxide of lithium and a transition metal, etc. are mentioned. As the transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo and the like are used.

As the transition metal oxide, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ Etc., and among them, from the cycle stability and the capacity, MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ . Examples of the transition metal sulfides include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like. As a lithium containing composite metal oxide, the lithium containing composite metal oxide which has a layered structure, the lithium containing composite metal oxide which has a spinel structure, the lithium containing composite metal oxide which has an olivine type structure, etc. are mentioned.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co-Ni-Mn, lithium composite oxide of Ni- And a lithium composite oxide of Ni-Co-Al. A lithium-containing composite metal oxide having a spinel structure, lithium manganese oxide (LiMn ₂ O ₄₎ and the substituting a part of Mn with other transition metal _{Li [Mn 3/2 M 1} /2] O 4 ( where, M is Cr, Fe, Co, Ni, Cu, etc.) etc. are mentioned. The lithium-containing composite metal oxide having an olivine-type structure is Li _x MPO ₄ (Wherein M is at least one selected from Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo, 0 ≦ X ≦ 2) The olivine-type lithium phosphate compound represented by is mentioned.

As an organic compound, conductive polymers, such as polyacetylene and poly-p-phenylene, can also be used, for example. 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 with an element. The mixture of the said inorganic compound and an organic compound may be sufficient as the positive electrode active material for secondary batteries.

The volume average particle diameter of a positive electrode active material is 0.01-50 micrometers normally, Preferably it is 0.05-30 micrometers. By the volume average particle diameter being in the said range, the quantity of the binder composition for positive electrodes at the time of preparing the slurry composition for positive electrodes mentioned later can be reduced, the fall of a battery capacity can be suppressed, and the slurry composition for positive electrodes It is easy to prepare with the viscosity suitable for application | coating, and a uniform electrode can be obtained.

Preferably the content rate of the positive electrode active material in a positive electrode active material layer is 90-99.9 mass%, More preferably, it is 95-99 mass%. By making content of the positive electrode active material in a positive electrode into the said range, flexibility and binding property can be exhibited, showing a high capacity | capacitance.

(Binder Composition for Secondary Battery Positive Electrode)

It does not restrict | limit especially as a binder composition for secondary battery positive electrodes, A well-known thing can be used. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, and the like. In addition, soft polymers such as an acrylic soft polymer, a diene soft polymer, an olefin soft polymer, and a vinyl soft polymer can be used. These may be used independently and may use 2 or more types together.

The positive electrode may contain, in addition to the above components, other components such as an electrolyte additive having a function of inhibiting decomposition of the electrolyte solution described above. They are not particularly limited as long as they do not affect the cell reaction.

The current collector can use the current collector used for the above-described negative electrode for secondary batteries, and is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but aluminum is particularly preferable for the secondary battery positive electrode.

The thickness of a positive electrode active material layer is 5-300 micrometers normally, Preferably it is 10-250 micrometers. When the thickness of the positive electrode active material layer is in the above range, both the load characteristics and the energy density exhibit high characteristics.

A positive electrode can be manufactured similarly to the negative electrode for secondary batteries mentioned above.

(Separator)

The separator is a porous substrate having pores, and the usable separators include (a) a porous separator having pores, (b) a porous separator having a polymer coat layer formed on one or both surfaces thereof, or (c) an inorganic ceramic powder. The porous separator in which the porous resin coat layer was formed is mentioned. Non-limiting examples thereof include polypropylene, polyethylene, polyolefin or aramid porous separator, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer, and the like. The separator which coated the porous film layer which consists of a polymer film, the separator which has a coat layer, or an inorganic filler and the dispersing agent for inorganic fillers, etc. are mentioned.

(Electrolytic solution)

Although the electrolyte solution used for this invention is not specifically limited, For example, what melt | dissolved lithium salt in the non-aqueous solvent as a supporting electrolyte can be used. Examples of lithium salts include 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 And lithium salts such as NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are particularly easy to dissolve in a solvent and exhibit a high degree of dissociation, are preferably used. These can be used individually or in mixture of 2 or more types. The amount of the supporting electrolyte is usually 1 mass% or more, preferably 5 mass% or more, and usually 30 mass% or less, preferably 20 mass% or less with respect to the electrolyte solution. Even if the amount of the supporting electrolyte is too large, at least too much, the ionic conductivity is lowered and the charging and discharging characteristics of the battery are lowered.

The solvent used for the electrolyte solution is not particularly limited as long as it dissolves the supporting electrolyte, but is usually dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate ( Alkyl carbonates such as BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are used. Particularly, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate are preferable because they are easy to obtain high ionic conductivity and have a wide temperature range for use. These can be used individually or in mixture of 2 or more types. Moreover, it is also possible to contain an additive and to use electrolyte solution. Moreover, as an additive, carbonate type compounds, such as vinylene carbonate (VC), are preferable, and especially a vinylene carbonate is more preferable. By containing vinylene carbonate in electrolyte solution, a propargyl containing compound and vinylene carbonate can accelerate | decompose decomposition on a negative electrode active material, and the decomposition of electrolyte solution itself can be suppressed. As for the content rate of the vinylene carbonate in electrolyte solution, 0.01-8 volume% is preferable.

Examples of the electrolytic solution other than the above include a gelated polymer electrolyte in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with an electrolytic solution, or an inorganic solid electrolyte such as lithium sulfide, LiI, Li ₃ N and the like.

(Method for Manufacturing Secondary Battery)

The manufacturing method of the secondary battery of this invention is not specifically limited. For example, the above-mentioned negative electrode and the positive electrode are superimposed via a separator, and wound according to the shape of the battery, folded and placed in a battery container, and the electrolyte is injected into the battery container and sealed. If necessary, an overcurrent prevention element such as an expansive metal, a fuse, a PTC element, a lead plate, or the like may be placed to prevent pressure increase and overcharge / discharge inside the battery. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat type.

Example

Although an Example is given to the following and this invention is demonstrated, this invention is not limited to this. In addition, the part and% in a present Example are a mass reference | standard unless there is particular notice. In Examples and Comparative Examples, various physical properties were evaluated as follows.

<Dispersion Stability of Slurry>

About the binder composition for secondary battery negative electrodes manufactured by the Example and the comparative example, the influence on the viscosity at the time of slurry preparation was evaluated as follows.

Slurry viscosity (eta) (mPa * s) before adding a binder composition and slurry viscosity (eta) 1 (mPa * s) after adding a binder composition are B-type viscosity meter (60 rpm, rotor No. 4) in 25 degreeC environment. Was measured, and the slurry viscosity change (eta) 1 / (eta) 0x100 (%) before and after binder addition was computed, and it was set as the evaluation guideline of dispersion stability. The smaller this value, the better the dispersion stability.

<Adhesive Strength: Peel Strength of Negative Electrode Active Material Layer>

The negative electrode for secondary batteries manufactured by the Example and the comparative example was cut out in rectangle of 100 mm in length and 10 mm in width, and it is set as a test piece, and a cellophane tape (as prescribed by JIS Z 1522 2009) on the surface of a negative electrode active material layer facing down. ) Was affixed, and the stress when the one end of the collector was pulled off at a pulling rate of 50 mm / min in the vertical direction was measured (in addition, the cellophane tape is fixed to the test bench). The measurement was performed 3 times, the average value was calculated | required and this was made into peeling strength. The larger the peel strength, the larger the binding force to the current collector of the negative electrode active material layer, that is, the greater the adhesive strength.

Moreover, the adhesion strength was evaluated similarly to the above about the negative electrode after the high temperature cycling characteristics test mentioned later.

<Durability: High Temperature Storage Characteristics>

Using the negative electrode for lithium ion secondary batteries manufactured by the Example and the comparative example, the lithium ion secondary battery of the lamination type cell was produced, and it stopped still for 24 hours in 25 degreeC environment. Then, the charge / discharge operation which charges to 4.2V and discharges to 3.0V by the 0.1C constant-current method under 25 degreeC environment was performed, and initial stage C0 was measured. Furthermore, after charging at 4.2V in a 25 degreeC environment, 60 degreeC, and storing for 7 days, it charges and discharges to 4.2V by the 0.1C constant-current method, and discharges to 3.0V, and operates The capacity C1 after high temperature storage was measured. The high temperature storage characteristic was evaluated by the capacity change rate represented by ΔC = C1 / C0 × 100 (%). The higher this value, the better the high temperature storage characteristics.

<Durability: High Temperature Cycle Characteristics>

Using the negative electrode for lithium ion secondary batteries manufactured by the Example and the comparative example, the lithium ion secondary battery of the lamination type cell was produced, and it stopped still for 24 hours in 25 degreeC environment. Thereafter, charging and discharging to charge up to 4.2 V by a constant current method of 0.1 C and discharge to 3.0 V were performed under an environment of 25 ° C., and the initial capacitance C0 was measured. Furthermore, in 60 degreeC environment, the charging and discharging to charge to 4.2V by the 0.1C constant-current method, to discharge to 3.0V was repeated, and the capacity C2 after 100 cycles was measured. The high temperature cycle characteristic was evaluated by the capacity change rate represented by (DELTA) C = C2 / C0x100 (%). The higher this value, the better the high temperature cycling characteristics.

<Durability: Expansion rate of electrode plate after high temperature cycle characteristic test>

About the negative electrode after the said high temperature cycling characteristics test, the expansion rate of a pole plate was computed from the following formula. Lower value means higher durability.

[Equation 1]

Expansion rate of electrode plate = | Thickness of negative electrode active material layer before test-Thickness of negative electrode active material layer after test | / Thickness of negative electrode active material layer before test x 100

<Low temperature output characteristics>

Using the negative electrode for lithium ion secondary batteries manufactured by the Example and the comparative example, the lithium ion secondary battery of a laminated type cell was produced, and after stopping for 24 hours in 25 degreeC environment, by the 4.2C constant current method 4.2 Charging and discharging to charge to V and discharge to 3.0V was performed. Thereafter, the battery was charged to a 50% state of charge (SOC 50%) by a 0.1 C constant current method, and the voltage V ₀ (V) was measured. Subsequently, under the environment of -25 ℃, the discharge voltage to ₀ V (V) Discharge rate from 0.1 C to measure the voltage V ₁₀ after discharge 10 seconds. Low temperature output characteristics ΔV = V ₀ -V ₁₀ It evaluates by the voltage change represented by (V), and shows that it is excellent in low temperature output characteristics, so that this value is small.

(Example 1)

(Preparation of binder composition)

In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene, 4 parts of itaconic acid, 63 parts of styrene, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and 0.5 parts of potassium persulfate as a polymerization initiator were added. The mixture was stirred sufficiently and then heated to 50 ° C. to initiate polymerization. When the polymerization conversion ratio reached 96%, the mixture was cooled to stop the reaction, thereby obtaining an aqueous dispersion containing a binder. In addition, the glass transition temperature of the binder was 10 degreeC.

After adding 5% sodium hydroxide aqueous solution to the aqueous dispersion containing the said binder and adjusting to pH 8, after removing unreacted monomer by heat-reduced-pressure distillation, it cools to 30 degrees C or less, about 100 parts of binder solids 3 parts of benzene sulfonic acid propargyl was added as a propargyl group containing compound, and the binder composition was obtained.

(Manufacture of the slurry composition for secondary battery negative electrodes)

100 parts of natural graphite (average particle diameter: 24.5 micrometers) of BET specific surface area 5m <2> / g as a negative electrode active material, and 1% aqueous solution of carboxymethylcellulose (made by Nippon Seishi Chemical Co., Ltd. make, MAC350HC) were used as a negative electrode active material to the planer mixer with a disper. 1 part was added in solid content equivalency respectively, after adjusting to 55% of solid content concentration with ion-exchange water, it mixed at 25 degreeC for 60 minutes. Next, the mixture was adjusted to a solid content concentration of 52% with ion-exchanged water, and further mixed at 25 DEG C for 15 minutes to obtain a mixed solution.

1 part (solid content basis) and ion-exchange water were added to the said liquid mixture, it adjusted to become final solid content concentration 42%, and it mixed for 10 more minutes. This was degassed under reduced pressure to obtain a slurry composition for secondary battery negative electrodes having good fluidity. The dispersion stability of the slurry was evaluated as above.

(Production of battery)

The secondary battery negative electrode slurry composition was coated on a copper foil having a thickness of 20 μm with a comma coater so as to have a film thickness of about 150 μm after drying, followed by heat treatment at 60 ° C. for 1 minute, and then heat treatment at 120 ° C. for 1 minute. A disc was obtained. This electrode original disk was rolled by the roll press, and the negative electrode for secondary batteries whose thickness of a negative electrode active material layer is 80 micrometers was obtained.

100 parts of LiFePO ₄ which has a volume average particle diameter of 0.5 micrometer and an olivine crystal structure as a positive electrode active material, and 1% aqueous solution of carboxymethylcellulose (CMC, Daiichi Kogyo Pharmaceutical Co., Ltd. make, "BSH-12") are equivalent to solid content as a dispersing agent. Acrylate polymer (78 mass% of 2-ethylhexyl acrylate, 20 mass% of acrylonitrile, 2 mass% of methacrylic acid) whose glass transition temperature is -40 degreeC, and a number average particle diameter is 0.20 micrometer as a 1 part and binder A 40% aqueous dispersion of a copolymer obtained by emulsion polymerization of a monomer mixture containing 5% by solid phase equivalent, and mixed by a planetary mixer so that the total solid concentration is 40% with ion-exchanged water, and the electrode of the positive electrode The slurry for composition layers was prepared. The secondary battery positive electrode slurry composition was coated on a copper foil having a thickness of 20 μm with a comma coater so that the film thickness after drying was about 200 μm, followed by heat treatment at 60 ° C. for 1 minute, followed by heat treatment at 120 ° C. for 1 minute. A battery positive electrode was obtained.

The single layer polypropylene separator (65 mm in width, 500 mm in length, thickness 25 micrometers, manufactured by the dry method, porosity 55%) was cut out circularly [diameter 18mm].

The obtained positive electrode for lithium ion secondary batteries was arrange | positioned so that an electrical power collector surface may contact an aluminum wrapping material exterior. The separator was arranged on the surface of the positive electrode active material layer side of the positive electrode. Moreover, the obtained negative electrode for lithium ion secondary batteries was arrange | positioned on the separator so that the surface by the side of a negative electrode active material layer may face a separator. In this packing material, electrolyte solution was injected so that air might not remain. Moreover, in order to seal the opening of an aluminum wrapping material, the aluminum exterior was opened by heat-sealing 150 degreeC, and the lithium ion secondary battery was produced. In addition, the electrolyte solution is 1.0 M LiPF ₆ The thing which added 2 volume% of VC (vinylene carbonate) to (EC / DEC = 1/2 volume ratio) was used.

About the obtained negative electrode and secondary battery, adhesive strength, durability, and low temperature output characteristics were evaluated as mentioned above.

(Example 2)

It carried out similarly to Example 1 except having made the addition amount of benzene sulfonic acid propargyl into 7 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Example 3)

It carried out similarly to Example 1 except having made the addition amount of benzene sulfonic acid propargyl into 15 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Example 4)

As a propargyl group containing compound, it carried out similarly to Example 1 except having used propargyl acrylate instead of propargyl benzene sulfonic acid. The results are shown in Table 1.

(Example 5)

As a propargyl group containing compound, it carried out similarly to Example 1 except having used propargyl methacrylate instead of propargyl benzene sulfonic acid. The results are shown in Table 1.

(Example 6)

It carried out similarly to Example 1 except having used methacrylic acid instead of itaconic acid as a comonomer at the time of binder preparation. The results are shown in Table 1.

(Example 7)

Example 1 except for using natural graphite having a BET specific surface area of 8 m 2 / g (average particle diameter: 22 µm) instead of natural graphite having a BET specific surface area of 5 m 2 / g (average particle diameter: 24.5 µm) as the negative electrode active material. Same as The results are shown in Table 1.

(Example 8)

Example 1 except for using natural graphite having a BET specific surface area of 15 m 2 / g (average particle diameter: 15 µm) instead of natural graphite having a BET specific surface area of 5 m 2 / g (average particle diameter: 24.5 µm) as the negative electrode active material. Same as The results are shown in Table 1.

(Example 9)

As the negative electrode active material, instead of the natural graphite having a BET specific surface area of 5 m 2 / g (average particle diameter: 24.5 μm), 80 parts of the natural graphite having a BET specific surface area of 5 m 2 / g (average particle diameter: 24.5 μm) and the BET specific surface area 6.5 It carried out similarly to Example 1 except having used 20 parts of SiO2 (average particle diameter: 10 micrometers) of m <2> / g. In addition, the BET specific surface area of the negative electrode active material was 5.2 m 2 / g. The results are shown in Table 1.

(Example 10)

As the negative electrode active material, 50 parts of natural graphite (average particle diameter: 24.5 μm) having a BET specific surface area of 5.0 m 2 / g instead of BET specific surface area of 5 m 2 / g (average particle diameter: 24.5 μm) and a BET specific surface area of 6.5 It carried out similarly to Example 1 except having used 50 parts of m2 / g SiOC (average particle diameter: 10 micrometers). In addition, the BET specific surface area of the negative electrode active material was 5.8 m 2 / g. The results are shown in Table 1.

(Example 11)

As a propargyl group containing compound, it carried out similarly to Example 1 except having used dipropargyl carbonate instead of benzene sulfonic acid propargyl. The results are shown in Table 1.

(Example 12)

It carried out similarly to Example 1 except not having used itaconic acid as a comonomer at the time of binder preparation. In addition, the glass transition temperature of the binder was 7 degreeC. The results are shown in Table 1.

(Comparative Example 1)

It carried out similarly to Example 1 except not having mix | blended the propargyl group containing compound with a binder composition. The results are shown in Table 1.

(Comparative Example 2)

It carried out similarly to Example 10 except not having mix | blended the propargyl group containing compound with a binder composition. The results are shown in Table 1.

(Comparative Example 3)

It carried out similarly to Example 1 except having made the addition amount of benzene sulfonic acid propargyl into 25 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Comparative Example 4)

It carried out similarly to Example 1 except having used methyl 2-octynate instead of the propargyl benzene sulfonic acid. The results are shown in Table 1.

By using together a propargyl group containing compound for a binder composition, the secondary battery which the adhesiveness between an electrical power collector and an electrode active material layer improved, especially cycling characteristics and low temperature output characteristics was obtained.

On the other hand, when not mix | blending a propargyl group containing compound (Comparative Examples 1 and 2), the said effect did not appear. Moreover, when there are too many compounding quantities of a propargyl group containing compound (comparative example 3), a slurry will become easy to thicken, the uniformity of the negative electrode obtained will fall, and output characteristics will fall. Moreover, even when the methyl ₂ -octynate which has an alkenyl group of the structure similar to a propargyl group (HC≡C-CH2-) was used (comparative example 4), the said effect was not seen.

Claims (11)

The binder composition for secondary battery negative electrodes containing a binder and a propargyl group containing compound and whose content of the said propargyl group containing compound is 0.1-20 mass parts with respect to 100 mass parts of said binders. The method according to claim 1,
The binder composition for secondary battery negative electrodes whose said propargyl group containing compound is a monopropargyl group containing compound. 3. The method according to claim 1 or 2,
The binder composition for secondary battery negative electrodes in which the said binder contains an ethylenic unsaturated carboxylic monomer unit. 4. The method according to any one of claims 1 to 3,
The binder composition for secondary battery negative electrodes whose glass transition temperature of the said binder is -60 degreeC-40 degreeC. The slurry composition for secondary battery negative electrodes containing the binder composition for secondary battery negative electrodes in any one of Claims 1-4, and a negative electrode active material. 6. The method of claim 5,
The slurry composition for secondary battery negative electrodes whose BET specific surface area of the said negative electrode active material is 3-20 m <2> / g. The negative electrode for secondary batteries which has a negative electrode active material layer which consists of the negative electrode binder composition for secondary batteries and a negative electrode active material in any one of Claims 1-4 on an electrical power collector. 8. The method of claim 7,
The negative electrode for secondary batteries whose BET specific surface area of the said negative electrode active material is 3-20 m <2> / g. 9. The method according to claim 7 or 8,
The negative electrode for secondary batteries whose said negative electrode active material is a carbon material type active material. A lithium ion secondary battery provided with a positive electrode, a negative electrode, electrolyte solution, and a separator, The said negative electrode is a secondary battery as described in any one of Claims 7-9. 11. The method of claim 10,
The secondary battery containing the said electrolyte solution vinylene carbonate.