WO2013002322A1 - 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

[Problem] To provide a binder composition with which the adhesiveness between a collector and an electrode active substance layer after charging and discharging is high, and it is possible to improve cycle properties under a high temperature and low-temperature output properties of a secondary cell in particular. [Solution] The binder composition of the invention is characterized by comprising a binder and a propargyl group-containing compound, and the content of the propargyl group-containing compound is between 0.1 and 20 parts by mass per 100 parts by mass of binder.

Description

Secondary battery negative electrode binder composition, secondary battery negative electrode slurry composition, secondary battery negative electrode and secondary battery

The present invention relates to a binder composition for a negative electrode of a secondary battery, and particularly relates to a binder composition for a negative electrode of a lithium ion secondary battery. The present invention also relates to a slurry composition, a negative electrode and a secondary battery using such a secondary battery negative electrode binder.

In recent years, portable terminals such as notebook personal computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. As a secondary battery used for the power source of these portable terminals, a nickel hydrogen secondary battery, a lithium ion secondary battery, and the like are frequently used. Mobile terminals are required to have more comfortable portability, and are rapidly becoming smaller, thinner, lighter, and higher in performance. As a result, mobile terminals are used in various places. In addition, the battery is required to be smaller, thinner, lighter, and higher in performance as in the case of the portable terminal.

For example, in a lithium ion secondary battery, a conductive carbonaceous material is used as a negative electrode active material because of its light weight and high energy density, and the binder is used for shape retention of the electrode active material layer and adhesion to the current collector. As such, a polymer (hereinafter sometimes referred to as “polymer binder”) is used.

This polymer binder is required to have adhesion with an electrode active material, resistance to a polar solvent used as an electrolyte, and stability in an electrochemical environment. From such required characteristics, fluorine-based polymers such as polyvinylidene fluoride are used. However, the fluorine-based polymer has problems such as impeding conductivity when the electrode active material layer is formed and insufficient adhesive strength between the current collector and the electrode active material layer. Furthermore, when a fluorine-based polymer is used for the negative electrode which is a reduction condition, there are problems such as insufficient stability and deterioration of the cycle characteristics of the secondary battery.

For this reason, in the negative electrode, the use of a non-fluorine polymer as a polymer binder has been studied. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 11-25899) and Patent Document 2 (Japanese Patent Laid-Open No. 2010-140684), an ethylenically unsaturated acid monomer such as (meth) acrylic acid and a conjugated material such as butadiene are disclosed. A polymer binder obtained by copolymerizing a diene and an aromatic vinyl such as styrene is disclosed. According to such a polymer binder, a battery having high adhesion between the current collector and the electrode active material layer and high cycle characteristics can be obtained. In addition, various studies have been made to improve the characteristics by blending various additives with the polymer binder.

Note that Patent Documents 3 to 5 teach that an alkenyl group-containing compound is added to the electrolytic solution for the purpose of preventing deterioration of the electrolytic solution.

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

By using the polymer binder described in Patent Documents 1 and 2 for the electrode active material layer, a battery with high adhesion between the current collector and the electrode active material layer and high cycle characteristics can be obtained. However, secondary batteries are constantly required to have higher functionality and longer life. Specifically, improvement in cycle characteristics, low-temperature output characteristics, and the like, and improvement in adhesion between the current collector after charging and discharging and the electrode active material layer are also required.
However, in the polymer binders described in Patent Documents 1 and 2, the adhesion between the current collector after charging and discharging and the electrode active material layer is reduced, or the cycle characteristics of the resulting secondary battery, particularly at high temperatures, are reduced. There has been a problem that cycle characteristics and low-temperature output characteristics deteriorate, and further improvement has been desired.
Therefore, the present invention is excellent in adhesion between a current collector after charging and discharging and an electrode active material layer, and can be used for secondary battery negative electrodes that can contribute to improvement of cycle characteristics and low-temperature output characteristics of secondary batteries at high temperatures. An object is to provide a binder composition.

The inventors of the present invention have continually studied to solve the above-mentioned problems. As a result, the polymer binder used for the negative electrode active material layer and the specific compound are used in combination, whereby the current collector and the electrode active material layer after charging and discharging are used. As a result, the present inventors have found that a secondary battery having improved cycle characteristics at low temperatures and improved low-temperature output characteristics can be obtained.

That is, the gist of the present invention aimed at solving the above problems is as follows.
(1) A binder composition for a secondary battery negative electrode, comprising a binder and a propargyl group-containing compound, wherein 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.

(2) The binder composition for a secondary battery negative electrode according to (1), wherein the 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 binder contains an ethylenically unsaturated carboxylic acid monomer unit.

(4) The binder composition for a secondary battery negative electrode according to any one of (1) to (3), wherein the binder has a glass transition temperature of −60 ° C. to 40 ° C.

(5) A secondary battery negative electrode slurry composition comprising the secondary battery negative electrode binder composition according to any one of (1) to (4) above and a negative electrode active material.

(6) The slurry composition for secondary battery negative electrode according to (5), wherein the negative electrode active material has a BET specific surface area of 3 to 20 m ² / g.

(7) A negative electrode for a secondary battery, comprising a negative electrode active material layer comprising the negative electrode binder composition for a secondary battery and the negative electrode active material according to any one of (1) to (4) above on a current collector.

(8) The negative electrode for a secondary battery as described in (7), wherein the negative electrode active material has a BET specific surface area of 3 to 20 m ² / g.

(9) The negative electrode for a secondary battery according to (7) or (8), wherein the negative electrode active material is a carbon material-based active material.

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

(11) The secondary battery according to (10), wherein the electrolytic solution contains vinylene carbonate.

By using the binder used in the negative electrode active material layer and the propargyl group-containing compound in combination, the adhesion between the current collector and the electrode active material layer is improved, and in particular, the high temperature cycle characteristics and the low temperature output characteristics are improved. A secondary battery is obtained. Such an action mechanism of the present invention is not necessarily clear. Although not construed as limiting in any way, the present inventors presume the mechanism by which the above effect is achieved as follows. That is, by adding a propargyl group-containing compound to the negative electrode active material layer, the propargyl group-containing compound is adsorbed on the negative electrode active material surface, and a thin layer called SEI (Solid Electrolyte Interface) coating is formed on the negative electrode active material surface. Will be promoted.

When the surface of the negative electrode active material and the electrolytic solution are in contact, in many cases, a part of the electrolytic solution in contact with the edge portion of the negative electrode active material is decomposed. Such an edge portion of the negative electrode active material is also called an active point. The decomposition product generated at the active point swells the electrode active material layer, and the adhesion between the current collector and the electrode active material layer decreases. As a result, the cycle characteristics and low-temperature output characteristics of the battery are impaired.

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

Hereinafter, (1) secondary battery negative electrode binder composition, (2) secondary battery negative electrode slurry composition, (3) secondary battery negative electrode, and (4) secondary battery will be described in this order.

(1) Secondary battery negative electrode binder composition The secondary battery negative electrode binder composition of the present invention contains a binder and a propargyl group-containing compound.

(binder)
The binder used in the present invention is not particularly limited, and various polymer compounds that have been conventionally used as binders for negative electrode active material layers such as fluoropolymers, diene polymers, and nitrile polymers can be used. Used. Among these, a polymer compound that can be easily synthesized in an aqueous system and easily obtained in the form of an aqueous latex is preferable. Examples of such a polymer compound include a polymer compound containing an ethylenically unsaturated acid monomer unit, preferably an ethylenically unsaturated carboxylic acid monomer unit.

The polymer compound containing an ethylenically unsaturated carboxylic acid monomer unit preferably contains an aliphatic conjugated diene monomer unit as a comonomer, and, if necessary, other monomers that can be copolymerized with these monomers. Units derived from the mer may be included. Furthermore, it is particularly preferable to contain these monomer units in a specific ratio from the viewpoint of the durability, flexibility, adhesiveness, and the like of the binder.

Accordingly, the binder particularly preferably used in the present invention comprises an ethylenically unsaturated carboxylic acid monomer unit, an aliphatic conjugated diene monomer unit, and other monomer units copolymerizable therewith, Those containing monomer units in a specific ratio are preferred. The ethylenically unsaturated carboxylic acid monomer unit is a polymer repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer, and the aliphatic conjugated diene monomer unit is an aliphatic conjugated diene type. It is a polymer repeating unit obtained by polymerizing monomers, and other monomer units copolymerizable with these are polymer repeating units obtained by polymerizing other copolymerizable monomers. is there.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Can be used. Among these, acrylic acid, methacrylic acid, and itaconic acid are preferable, and itaconic acid is particularly preferable in terms of excellent adhesion to the current collector. When a polymer binder is used in combination with a propargyl group-containing compound described later, the dispersibility of the binder composition in water increases as the amount of the propargyl group-containing compound increases (hereinafter, sometimes abbreviated as water dispersibility). May decrease. However, water dispersibility is improved by introducing a unit containing a carboxylic acid into the polymer binder. In particular, when itaconic acid, which is a dicarboxylic acid, is introduced, the affinity between the binder and water increases.

Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted Examples thereof include linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and one or more kinds can be used. In particular, 1,3-butadiene is preferred.

Other monomers copolymerizable with these include aromatic vinyl monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, and unsaturated monomers containing hydroxyalkyl groups. Body, unsaturated carboxylic acid amide monomer, etc., and these can be used alone or in combination. In particular, an aromatic vinyl monomer is preferable from the viewpoint that swelling with respect to the electrolytic solution can be suppressed.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, divinylbenzene and the like, and one or more kinds can be used. Among these, styrene is particularly preferable in that swelling with respect to the electrolytic solution can be suppressed.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like, and one or more can be used. In particular, acrylonitrile and methacrylonitrile are preferable.

Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, Examples thereof include monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like, and one or more can be used. Particularly preferred is methyl methacrylate.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl Examples include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, etc. More than one species can be used. In particular, β-hydroxyethyl acrylate is preferred.

Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N, N-dimethylacrylamide, and the like, and one or more can be used. Particularly preferred are acrylamide and methacrylamide.

Furthermore, in addition to the above monomers, any of the monomers used in ordinary emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, can be used.

The ratio of each monomer unit of the binder in the present invention is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and more preferably 1 to ethylenically unsaturated carboxylic acid monomer units. The aliphatic conjugated diene monomer unit is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, and even more preferably 30 to 60% by mass. The other polymerizable monomer units are preferably 5 to 79.9% by mass, more preferably 10 to 70% by mass, and more preferably 20 to 60% by mass.

When the ethylenically unsaturated carboxylic acid monomer unit is in the above range, the stability of the binder composition and the slurry composition is improved, and sufficient adhesion between the negative electrode active material and the current collector in the negative electrode for a secondary battery is obtained. Sex can be obtained. As a result, durability of the obtained secondary battery, in particular, high temperature cycle characteristics is improved, which is preferable.

When the aliphatic conjugated diene monomer unit is in the above range, the flexibility of the negative electrode for secondary battery and the adhesion between the negative electrode active material and the current collector are highly balanced, which is preferable. In addition, the durability of the obtained secondary battery, in particular, the high temperature cycle characteristics is improved, which is preferable.

When the other monomer units that can be copolymerized are in the above range, the flexibility of the negative electrode for a secondary battery and the adhesion between the negative electrode active material and the current collector are highly balanced, which is preferable. In addition, the durability of the obtained secondary battery, in particular, the high temperature cycle characteristics is improved, which is preferable.

The glass transition temperature (Tg) of the binder is preferably −60 to 40 ° C., more preferably −50 to 30 ° C., and particularly preferably −40 to 20 ° C. When the Tg of the binder is within the above range, characteristics such as flexibility, binding and winding properties of the negative electrode, and adhesion between the negative electrode active material and the current collector are highly balanced, which is preferable.

In addition, when an aliphatic conjugated diene is used as a copolymerization monomer, hydrogenation may be performed on the diene unit after polymerization. The method for hydrogenation is not particularly limited, and a normal method can be used.

(Propargyl group-containing compound)
The binder composition for a secondary battery negative electrode of the present invention contains a specific amount of a propargyl group-containing compound with respect to 100 parts by mass (in terms of solid content) of the binder. Although not theoretically limited at all, according to the binder composition for a negative electrode of a secondary battery of the present invention, when containing a specific amount of a propargyl group-containing compound, propargyl is brought into contact with the negative electrode active material. It is considered that the group-containing compound forms an SEI film in the vicinity of the active point of the negative electrode active material. The SEI coating prevents the components of the electrolytic solution from coming into contact with the active points, so that the decomposition of the electrolytic solution in the battery is suppressed. As a result, the increase in the electrolyte viscosity due to the decomposition of the electrolyte and the increase in the internal resistance of the secondary battery are suppressed, so that the high-temperature storage characteristics, the high-temperature cycle characteristics, and the low-temperature output characteristics of the secondary battery are improved. Further, swelling of the negative electrode active material layer due to the decomposition product of the electrolyte component is prevented, the peel strength is maintained, and the high temperature cycle characteristics and the low temperature output characteristics can be further improved.

The content of the propargyl group-containing compound in the binder composition is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight with respect to 100 parts by weight of the binder (in terms of solid content). Part. When the content of the propargyl group-containing compound is too small, the formation of the SEI coating becomes insufficient, the electrolytic solution component is easily decomposed, and the battery cycle characteristics and output characteristics may be deteriorated. On the other hand, when the content of the propargyl group-containing compound is too large, the stability of the slurry prepared using the binder composition is impaired, and the viscosity of the slurry tends to increase. As a result, it becomes difficult to apply the slurry, the uniformity of the obtained negative electrode is lowered, and the output characteristics may be lowered.

The propargyl group-containing compound used in the present invention has one or more propargyl groups (HC—C—CH ₂ —) in the molecule. The number of propargyl groups is not particularly limited. However, when the number of propargyl groups is increased, the dispersibility in water may be reduced, and a uniform aqueous slurry may not be obtained. Therefore, the number of propargyl groups per molecule of the propargyl group-containing compound is preferably 2 or less, particularly preferably 1. Accordingly, monopropargyl group-containing compounds are particularly preferably used in the present invention.

Specific examples of the propargyl group-containing compound include monopropargyl group-containing compounds such as propargyl benzenesulfonate, propargyl acrylate, propargyl methacrylate, and propargyl acetate;
Examples include dipropargyl group-containing compounds such as dipropargyl carbonate.

It is considered that when such a propargyl group-containing compound is brought into 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 to form a thin layer called an SEI coating. In the negative electrode active material on which the SEI film is formed, the edge portion, which is the active point, is also covered with the film, so that contact between the active point and the electrolyte component is reduced. As a result, the decomposition of the electrolyte component is suppressed, and the negative electrode active material layer is prevented from expanding and the adhesion between the current collector and the negative electrode active material layer is prevented from being lowered. The output characteristics are considered to be improved.

(Other ingredients)
The binder composition for secondary battery negative electrode of the present invention may contain a dispersion medium for dispersing these components in addition to the binder and the propargyl group-containing compound. The dispersion medium may be either water or an organic solvent. As long as the dispersion stability of the binder composition is not impaired, a hydrophilic solvent may be mixed with water as the dispersion medium. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and it is preferably 5% by mass or less based on water. In addition, a reaction solvent at the time of preparing the binder described later may be used as a dispersion medium as it is, or the solvent may be replaced after preparing the binder.

When the binder composition contains a dispersion medium, the total solid concentration of the binder and the propargyl group-containing compound is not particularly limited, but about 20 to 60% by mass is appropriate.

Furthermore, the binder composition may contain various dispersants used at the time of preparing the binder. The binder composition may further contain an antiaging agent, an antiseptic, and the like as long as the dispersibility of the composition is not impaired.

Examples of the antioxidant include amine-based antioxidants, phenol-based antioxidants, quinone-based antioxidants, organic phosphorus-based antioxidants, sulfur-based antioxidants, and phenothiazine-based antioxidants. Examples of the preservative include isothiazoline compounds and pyrithione compounds. When the binder composition contains these components, the solid content concentration of these components in the composition is not particularly limited, but about 0.001 to 1% by mass is appropriate.

(Method for producing binder composition for secondary battery negative electrode)
As a method for producing a binder composition for a secondary battery negative electrode of the present invention, a monomer composition containing the above monomer is polymerized in an aqueous solvent to prepare an aqueous dispersion containing a binder (a binder having a binding force). A solution or dispersion in which a binder as a coalesced particle is dissolved or dispersed in an aqueous solvent), and a specific amount of a propargyl group-containing compound and other optional components are added to and mixed with an aqueous dispersion containing the binder. . However, the method for producing the binder composition is not limited to this. For example, a propargyl group-containing compound, an anti-aging agent, or an antiseptic may be blended in advance in the monomer composition, and then polymerization may be performed. Good. Moreover, you may mix | blend these with a binder composition in the arbitrary steps during superposition | polymerization or after superposition | polymerization.

The ratio of each monomer in the monomer composition in the step of obtaining an aqueous dispersion containing a binder is preferably 0.1 to 20% by mass, more preferably 0. 5 to 15% by mass, more preferably 1.0 to 10% by mass, and aliphatic conjugated diene monomer is preferably 20 to 80% by mass, more preferably 25 to 70% by mass, and more preferably 30 to 30% by mass. The amount of the other monomer copolymerizable with these is preferably 5 to 79.9% by mass, more preferably 10 to 70% by mass, and still more preferably 20 to 60% by mass.

The aqueous solvent is not particularly limited as long as it can disperse the binder, and is usually selected from dispersion media having a boiling point of 80 to 350 ° C., preferably 100 to 300 ° C. at normal pressure. In addition, the number in parentheses after the name of the following exemplified dispersion medium is a boiling point (unit: ° C) at normal pressure, and a value after the decimal point is rounded off or rounded down. For example, as ketones, diacetone alcohol (169), γ-butyrolactone (204); as alcohols, ethyl alcohol (78), isopropyl alcohol (82), normal propyl alcohol (97); as glycols, ethylene Glycol (193), propylene glycol (188), diethylene glycol (244); glycol ethers include propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152) Butyl cellosolve (171), 3-methoxy-3-methyl-1-butanol (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl pyrute (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188); ethers include 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66) Can be mentioned. Among these, water is most preferable from the viewpoint that it is not flammable and a binder dispersion is easily obtained. In addition, water may be used as the main solvent, and an aqueous solvent other than the above-described water may be mixed and used within a range in which the dispersion state of the binder can be ensured.

The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. Examples of the polymerization reaction include ionic polymerization, radical polymerization, and living radical polymerization. Manufacturing efficiency, such as easy to obtain high molecular weight, obtained in a state where the polymer is dispersed in water as it is, no redispersion treatment is required, and can be used as it is for slurry composition preparation for secondary battery negative electrode From the viewpoint of the above, the emulsion polymerization method is most preferable.

The emulsion polymerization method is a conventional method, for example, the method described in “Experimental Chemistry Course” Vol. 28, (Publisher: Maruzen Co., Ltd., edited by The Chemical Society of Japan), that is, water in a sealed container with a stirrer and a heating device. Add additives such as dispersants, emulsifiers and crosslinkers, initiators and monomers to the prescribed composition, stir to emulsify the monomers in water, start the polymerization by increasing the temperature while stirring Is the method. Or after emulsifying the said composition, it is the method of starting reaction similarly in an airtight container.

Emulsifiers, dispersants, polymerization initiators and the like are those generally used in these polymerization methods, and the amount used thereof may be generally used. In the polymerization, seed particles can be employed (seed polymerization).

The polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator used, but the polymerization temperature is usually about 30 ° C. or higher and the polymerization time is about 0.5 to 30 hours. Additives such as amines can also be used as polymerization aids. Further, an aqueous dispersion of polymer particles obtained by these methods is mixed with an alkali metal (Li, Na, K, Rb, Cs) hydroxide, ammonia, an inorganic ammonium compound (NH ₄ Cl, etc.), an organic amine compound (ethanol). A basic aqueous solution in which amine, diethylamine, etc.) are dissolved can be added to adjust the pH to 5 to 10, preferably 5 to 9. The pH adjustment with the alkali metal hydroxide is preferable because the binding property (peel strength) between the binder composition, the current collector and the active material is improved.

The above-mentioned binder may be composite polymer particles composed of two or more kinds of polymers. The composite polymer particles can also be obtained by a method (two-stage polymerization method) in which at least one monomer component is polymerized by a conventional method, and then at least one other monomer component is added and polymerized by a conventional method. Can do.

Examples of the polymerization initiator used for the polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

In the polymerization, a chain transfer agent may be added. The chain transfer agent is preferably an alkyl mercaptan, specifically, n-butyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan. N-stearyl mercaptan. Among these, n-octyl mercaptan and t-dodecyl mercaptan are preferable from the viewpoint of good polymerization stability.

In addition, other chain transfer agents may be used in combination with the alkyl mercaptan. Examples of chain transfer agents that may be used in combination include terpinolene, allyl alcohol, allylamine, sodium allyl sulfonate (potassium), and sodium methallyl sulfonate (potassium). The amount of the serial transfer agent used is not particularly limited as long as the effect of the present invention is not hindered.

The number average particle size of the binder in the aqueous dispersion is preferably 50 to 500 nm, and more preferably 70 to 400 nm. When the number average particle diameter of the binder is in the above range, the strength and flexibility of the obtained negative electrode are improved. The presence of the polymer particles can be easily measured by a transmission electron microscope method, a Coulter counter, a laser diffraction scattering method, or the like.

Further, the binder may be a binder composed of polymer particles having a core-shell structure obtained by polymerizing the above monomers stepwise.

The method of adding and mixing the propargyl group-containing compound and other optional components to the aqueous dispersion containing the binder is not particularly limited. Examples of the mixing method include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

In addition, an additive may be added to the obtained binder composition for a negative electrode of the secondary battery of the present invention in order to improve applicability and charge / discharge characteristics. These additives include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, acrylic acid-vinyl alcohol copolymer, Examples thereof include methacrylic acid-vinyl alcohol copolymer, maleic acid-vinyl alcohol copolymer, modified polyvinyl alcohol, polyethylene glycol, ethylene-vinyl alcohol copolymer, and partially saponified polyvinyl acetate. In addition to the method of adding these additives to the binder composition, these additives can also be added to the slurry composition for a secondary battery negative electrode of the present invention described later.

(2) Slurry composition for secondary battery negative electrode The secondary battery negative electrode slurry composition of the present invention comprises the above secondary battery negative electrode binder composition and a negative electrode active material. Below, 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 material that transfers electrons in the negative electrode for a secondary battery.

Examples of the negative electrode active material for a lithium ion secondary battery include a carbon material-based active material and an alloy-based active material.

The carbon material-based active material refers to an active material having carbon as a main skeleton into which lithium can be inserted, and specifically includes a carbonaceous material and a graphite material. The carbonaceous material generally indicates a carbon material having a low graphitization (low crystallinity) obtained by heat-treating (carbonizing) a carbon precursor at 2000 ° C. or less, and the graphitic material is a graphitizable carbon at 2000 ° C. A graphitic material having high crystallinity close to that of the graphite obtained by heat treatment as described above will be shown.

Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon.

Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum and coal, such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Is mentioned. MCMB is a carbon fine particle obtained by separating and extracting mesophase spherules produced in the process of heating pitches at around 400 ° C., and mesophase pitch-based carbon fiber is a mesophase pitch obtained by growing and coalescing the mesophase spherules. Is a carbon fiber made from a raw material.

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

Examples of the graphite material include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite heat-treated at 2800 ° C or higher, graphitized MCMB heat-treated MCMB at 2000 ° C or higher, and graphitized mesophase pitch carbon fiber heat-treated at 2000 ° C or higher. It is done.
Among these carbon-based active materials, a graphite material is preferable.

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

Examples of single metals and alloys forming lithium alloys include compounds containing metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. Is mentioned. Among these, silicon (Si), tin (Sn) or lead (Pb) simple metals, alloys containing these atoms, or compounds of these metals are 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—O—C”) (0 <x ≦ 3, 0 <y ≦ 5), Si ₃ N ₄ , Si ₂ N ₂ O, Examples thereof include SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO, etc. Among them, SiO _x C _y capable of inserting and releasing lithium at a low potential is preferable. For example, SiO _x C _y can be obtained by firing a polymer material containing silicon. Among SiO _x C _y , the range of 0.8 ≦ x ≦ 3 and 2 ≦ y ≦ 4 is preferably used in view of the balance between capacity and cycle characteristics.

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

As the lithium-containing metal composite oxide, a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ (0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, 0 ≦ z ≦ 1.6, M includes Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb), among which Li _4/3 Ti _5/3 O ₄ , Li1Ti ₂ O ₄ and Li _4/5 Ti _11/5 O ₄ are used.

Of these, materials containing silicon (hereinafter sometimes referred to as “silicon-containing materials”) are preferable, and Si—O—C is more preferable. In this compound, it is presumed that insertion / extraction of Li to / from Si (silicon) occurs at a high potential and C (carbon) at a low potential, and expansion / contraction is suppressed as compared with other alloy-based active materials.

In the present invention, as the negative electrode active material, a graphite material and a silicon-containing material are preferable, and natural graphite and Si—O—C are particularly preferable. In such an active material, an SEI film is formed by contact with a propargyl group-containing compound, the active sites at the edge portion are easily deactivated, and 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 used in combination, a combination of a graphite material and a silicon-containing material is preferred. The blending ratio (graphitic material / silicon-containing material) is preferably 99/1 to 40/60, more preferably 95/5 to 45/55, by weight. The shape of the negative electrode active material is preferably a granulated particle. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.

The volume average particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent elements of the battery, but is usually 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 20 μm. Further, the 50% volume cumulative diameter of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics. The volume average particle diameter is determined by measuring the particle size distribution by laser diffraction. The 50% volume cumulative diameter is a 50% volume average particle diameter calculated by measuring with a laser diffraction particle size distribution analyzer (SALD-3100; manufactured by Shimadzu Corporation).

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

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. When the BET specific surface area of the negative electrode active material is in the above range, the active points on the surface of the negative electrode active material are increased, so that the low-temperature output characteristics of the secondary battery are excellent.

The total content of the negative electrode active material and the binder composition in the secondary battery negative electrode slurry composition of the present invention is preferably 10 to 90 parts by mass, more preferably 30 parts, relative to 100 parts by mass of the slurry composition. ~ 80 parts by mass. The content of the binder composition relative to the total amount of the negative electrode active material (solid content equivalent amount) is preferably 0.1 to 5 parts by mass, more preferably 0.005 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material. 5 to 2 parts by mass. 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 obtained slurry composition for secondary battery negative electrode is optimized, and the coating is smoothly performed. In addition, sufficient adhesion strength can be obtained without increasing the resistance of the obtained negative electrode. As a result, peeling of the negative electrode active material layer from the current collector in the electrode plate pressing step can be suppressed.

(Dispersion medium)
In the present invention, water is preferably used as a dispersion medium for the slurry. In the present invention, as long as the dispersion stability of the binder composition is not impaired, a mixture of water and a hydrophilic solvent may be used as a dispersion medium. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and it is preferably 5% by mass or less based on 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 conductive agent, the electrical contact between the negative electrode active materials can be improved, and the discharge rate characteristics can be improved when used in a secondary battery. The content of the conductive agent in the slurry composition is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

(Thickener)
In the slurry composition for secondary battery negative electrodes of this invention, it is preferable to contain a thickener. Examples of thickeners include cellulose polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof;
(Modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof;
(Modified) Polyvinyl alcohols such as polyvinyl alcohol, a copolymer of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or a copolymer of maleic acid or fumaric acid and vinyl alcohol;
Examples include polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches.

The blending amount of the thickener is preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the blending amount of the thickener is within the above range, the coating property and the adhesion with the current collector are good. In the present 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 electrode may further contain other components such as a reinforcing material, a leveling agent, and an electrolyte additive having a function of inhibiting electrolyte decomposition, It may be contained in a negative electrode for a secondary battery described later. These are not particularly limited as long as they do not affect the battery reaction.

As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible negative electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The content of the reinforcing material in the slurry composition is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. By being included in the above range, high capacity and high load characteristics are exhibited.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the leveling agent, the repelling that occurs during coating can be prevented and the smoothness of the negative electrode can be improved. The content of the leveling agent 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 the leveling agent is in the above range, the productivity, smoothness, and battery characteristics during the production of the negative electrode are excellent. By containing the surfactant, the dispersibility of the negative electrode active material and the like in the slurry composition can be improved, and the smoothness of the negative electrode can be improved.

As the electrolytic solution additive used in the slurry composition and the electrolytic solution, vinylene carbonate or the like can be used. The content of the electrolytic solution additive 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 the electrolytic solution additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the slurry composition can be controlled, and the leveling property of the negative electrode can be improved. The content of the nanoparticles 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 the nanoparticles are in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

(Water-soluble polymer)
The slurry composition for a secondary battery negative electrode of the present invention can contain a water-soluble polymer in addition to the binder composition. Examples of the water-soluble polymer include ethylenically unsaturated carboxylic acid monomer units of 20 to 60% by mass, (meth) acrylic acid ester monomer units of 20 to 80% by mass and other monomer units copolymerizable therewith. A water-soluble polymer consisting of 0 to 20% by mass is preferred. By including the water-soluble polymer in the slurry composition for a secondary battery negative electrode, the adhesion and durability of the secondary battery negative electrode are improved, so that the peel strength can be improved. The water-soluble polymer in the present invention refers to a polymer having a 1% aqueous solution viscosity of 0.1 to 100,000 mPa · s at pH 12.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Can be used. The ratio of these ethylenically unsaturated carboxylic acid monomer units is more preferably 25 to 55% by mass, particularly preferably 30 to 50% by mass.

(Meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2- Acrylic acid alkyl esters such as ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate , Pentyl methacrylate, hexyl methacrylate, heptyl methacrylate Rate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. The proportion of these (meth) acrylic acid ester monomer units is more preferably 25 to 75% by mass, particularly preferably 30 to 70% by mass.

Other monomers that can be copolymerized include carboxylic acid ester monomers having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylolpropane triacrylate; styrene, chlorostyrene, Styrene monomers such as vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene; acrylamide, N-methylol aqua amide, Amide monomers such as 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; methyl vinyl ketone and ethyl Examples include vinyl ketones such as vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole. 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 is more preferably 0 to 10% by mass, particularly preferably 0 to 5% by mass.

Examples of the method for producing a water-soluble polymer include a method in which a monomer composition containing the above monomer is polymerized in an aqueous solvent to obtain a water-dispersible polymer and alkalized to pH 7-13. About an aqueous solvent and the polymerization method, it is the same as that of the above-mentioned binder composition for secondary battery negative electrodes.

The method for alkalinizing to pH 7 to 13 is not particularly limited, but alkaline earth solutions such as an aqueous alkali metal solution such as an aqueous lithium hydroxide solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, and an aqueous magnesium hydroxide solution. Examples include a method of adding an aqueous metal solution or an aqueous alkali solution such as an aqueous ammonia solution.

(Production of slurry composition for secondary battery negative electrode)
The slurry composition for a secondary battery negative electrode is obtained by mixing the binder composition, the negative electrode active material, and a conductive agent used as necessary.

The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

(3) Negative electrode for secondary battery The negative electrode for secondary battery of the present invention comprises the binder composition and the negative electrode active material, and specifically, the slurry composition for secondary battery negative electrode of the present invention is collected. It is obtained by applying and drying on an electric body.

(Method for producing secondary battery negative electrode)
The method for producing the negative electrode for secondary battery of the present invention is not particularly limited. For example, a method of forming the negative electrode active material layer by applying and drying the slurry composition on at least one surface, preferably both surfaces of the current collector. Can be mentioned.

The method for applying the slurry composition onto the current collector is not particularly limited. Examples of the method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.

In producing the negative electrode for secondary battery of the present invention, the porosity of the negative electrode active material layer is lowered by pressure treatment using a die press or a roll press after applying and drying the slurry composition on the current collector. It is preferable to have the process to do. A preferable range of the porosity is 5 to 30%, more preferably 7 to 20%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity, and the negative electrode active material layer is liable to be peeled off from the current collector, resulting in a defect. Furthermore, when using a curable polymer for a binder composition, it is preferable to make it harden | cure.

The thickness of the negative electrode active material layer in the negative electrode for secondary battery of the present invention is usually 5 to 300 μm, preferably 30 to 250 μm. When the thickness of the negative electrode active material layer is in the above range, both load characteristics and cycle characteristics are high.

In the present invention, the content ratio of the negative electrode active material in the negative electrode active material layer is preferably 85 to 99% by mass, more preferably 88 to 97% by mass. By making the content rate of a negative electrode active material into the said range, a softness | flexibility and a binding property can be shown, showing a high capacity | capacitance.

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

(Current collector)
The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, a metal material is preferable because it has heat resistance. For example, iron, copper, aluminum Nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among these, copper is particularly preferable as the current collector used for the negative electrode for the secondary battery. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength with the negative electrode active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity with the negative electrode active material layer.

(4) Secondary battery The secondary battery of the present invention is a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolytic solution, and the negative electrode is the negative electrode for a secondary battery.

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

(Positive electrode active material)
As the positive electrode active material, an active material that can be doped and dedoped with lithium ions is used, and the positive electrode active material is roughly classified into an inorganic compound and an organic compound.

Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides of lithium and transition metals, and the like. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O. ₅ , V ₆ O _{13 and the} like. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle stability and capacity. The transition metal _sulfide, TiS _2, TiS _3, amorphous _MoS 2, FeS, and the like. Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

As the lithium-containing composite metal oxide having a layered structure, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium Examples thereof include composite oxides and lithium composite oxides of Ni—Co—Al. Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and Li [Mn _3/2 M _1/2 ] O _{4 in} which a part of Mn is substituted with another transition metal (wherein M may be Cr, Fe, Co, Ni, Cu or the like. Li _X MPO ₄ (wherein, M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Li _X MPO ₄ as the lithium-containing composite metal oxide having an olivine structure) An olivine type lithium phosphate compound represented by at least one selected from Si, B, and Mo, 0 ≦ X ≦ 2) may be mentioned.

As the organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene can be used. An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted. The positive electrode active material for the secondary battery may be a mixture of the above inorganic compound and organic compound.

The volume average particle diameter of the positive electrode active material is usually 0.01 to 50 μm, preferably 0.05 to 30 μm. When the volume average particle diameter is in the above range, the amount of the binder composition for the positive electrode when preparing the slurry composition for the positive electrode described later can be reduced, the decrease in the capacity of the battery can be suppressed, and for the positive electrode It becomes easy to prepare the slurry composition to have a viscosity suitable for application, and a uniform electrode can be obtained.

The content ratio of the positive electrode active material in the positive electrode active material layer is preferably 90 to 99.9% by mass, more preferably 95 to 99% by mass. By setting the content of the positive electrode active material in the positive electrode within the above range, flexibility and binding properties can be exhibited while exhibiting high capacity.

(Binder composition for secondary battery positive electrode)
The binder composition for the secondary battery positive electrode is not particularly limited and a known one can be used. For example, resins such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, acrylic soft heavy A soft polymer such as a polymer, a diene soft polymer, an olefin soft polymer, or a vinyl soft polymer can be used. These may be used alone or in combination of two or more.

In addition to the above-described components, the positive electrode may further contain other components such as an electrolyte additive having a function of suppressing the above-described electrolyte decomposition. These are not particularly limited as long as they do not affect the battery reaction.

As the current collector, the current collector used in the above-described negative electrode for a secondary battery can be used, and there is no particular limitation as long as the material has electrical conductivity and is electrochemically durable. Aluminum is particularly preferred for the secondary battery positive electrode.

The thickness of the positive electrode active material layer is usually 5 to 300 μm, preferably 10 to 250 μm. When the thickness of the positive electrode active material layer is in the above range, both load characteristics and energy density are high.
The positive electrode can be produced in the same manner as the above-described negative electrode for secondary battery.

(separator)
The separator is a porous substrate having pores, and usable separators include (a) a porous separator having pores, and (b) a porous separator in which a polymer coat layer is formed on one or both sides. Or (c) a porous separator in which a porous resin coat layer containing an inorganic ceramic powder is formed. Non-limiting examples of these include high-grade polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers. Examples include a separator having a molecular film and a coat layer, or a separator coated with a porous film layer made of an inorganic filler or a dispersant for inorganic filler.

(Electrolyte)
The electrolytic solution used in the present invention is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt 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 NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used alone or in admixture of two or more. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered and the battery charging and discharging characteristics are lowered.

The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane; tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used alone or in admixture of two or more. Moreover, it is also possible to use an electrolyte containing an additive. Moreover, as an additive, carbonate type compounds, such as vinylene carbonate (VC), are preferable, and vinylene carbonate is more preferable especially. By including vinylene carbonate in the electrolytic solution, the propargyl-containing compound and vinylene carbonate can promote decomposition on the negative electrode active material and suppress decomposition of the electrolytic solution itself. The content of vinylene carbonate in the electrolytic solution is preferably 0.01 to 8% by volume.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N.

(Method for manufacturing secondary battery)
The manufacturing method of the secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard. In the 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 an Example and a comparative example, the influence on the viscosity at the time of slurry preparation was evaluated as follows.
The slurry viscosity η0 (mPa · s) before adding the binder composition and the slurry viscosity η1 (mPa · s) after adding the binder composition were measured in a B-type viscometer (60 rpm, rotor) in an environment of 25 ° C. No. 4) was measured and the change in slurry viscosity η1 / η0 × 100 (%) before and after addition of the binder was calculated and used as an evaluation guideline for dispersion stability. The smaller this value, the better the dispersion stability.

<Adhesion strength: peel strength of negative electrode active material layer>
The negative electrode for a secondary battery manufactured in Examples and Comparative Examples was cut into a rectangle having a length of 100 mm and a width of 10 mm to obtain a test piece, and a cellophane tape (in JIS Z1522 2009) was formed on the surface of the negative electrode active material layer with the negative electrode active material layer side down. Then, stress was measured when one end of the current collector was pulled in a vertical direction at a pulling speed of 50 mm / min and peeled off (the cellophane tape was fixed to a test stand). The measurement was performed three times, and the average value was obtained and used as the peel strength. The higher the peel strength, the greater the binding force of the negative electrode active material layer to the current collector, that is, the higher the adhesion strength.

Also, the adhesion strength of the negative electrode after the high-temperature cycle characteristic test described later was evaluated in the same manner as described above.

<Durability: High temperature storage characteristics>
Using a negative electrode for a lithium ion secondary battery produced in the examples and comparative examples, a lithium ion secondary battery of a laminate type cell was prepared and left to stand in an environment of 25 ° C. for 24 hours. After that, under an environment of 25 ° C., charge / discharge operation of charging to 4.2 V and discharging to 3.0 V was performed by a constant current method of 0.1 C, and an initial capacity C0 was measured. Furthermore, after charging to 4.2 V in an environment of 25 ° C., storing at 60 ° C. for 7 days, charging to 4.2 V and discharging to 3.0 V by a constant current method of 0.1 C The operation was performed, and the capacity C1 after high temperature storage was measured. The high-temperature storage characteristics were evaluated by the capacity change rate represented by ΔC = C1 / C0 × 100 (%). Higher values indicate better high temperature storage characteristics.

<Durability: High-temperature cycle characteristics>
Using a negative electrode for a lithium ion secondary battery produced in the examples and comparative examples, a lithium ion secondary battery of a laminate type cell was prepared and left to stand in an environment of 25 ° C. for 24 hours. After that, under an environment of 25 ° C., charge / discharge operation of charging to 4.2 V and discharging to 3.0 V was performed by a constant current method of 0.1 C, and an initial capacity C0 was measured. Furthermore, in a 60 ° C. environment, charging / discharging of charging to 4.2 V and discharging to 3.0 V was repeated by a constant current method of 0.1 C, and the capacity C2 after 100 cycles was measured. The high-temperature cycle characteristics were evaluated by a capacity change rate represented by ΔC = C2 / C0 × 100 (%). Higher values indicate better high temperature cycle characteristics.

<Durability: Swelling rate of electrode plate after high-temperature cycle characteristics test>
About the negative electrode after said high temperature cycling characteristic test, the swelling rate of the electrode plate was computed from the following formula. The lower the value, the higher the durability.
Number 1
Swelling 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 × 100

<Low temperature output characteristics>
Using a negative electrode for a lithium ion secondary battery produced in Examples and Comparative Examples, a lithium ion secondary battery of a laminate type cell was prepared and left at 25 ° C. for 24 hours. The charging / discharging operation of charging to 4.2V and discharging to 3.0V was performed by the constant current method. Thereafter, the battery was charged to a 50% charged state (SOC 50%) by a constant current method of 0.1 C under an environment of 25 ° C., and a voltage V ₀ (V) was measured. Next, the battery was discharged from the voltage V ₀ (V) at a discharge rate of 0.1 C in an environment of −25 ° C., and the voltage V ₁₀ after 10 seconds of discharge was measured. The low temperature output characteristic is evaluated by a voltage change represented by ΔV = V ₀ −V ₁₀ (V), and the smaller this value is, the better the low temperature output characteristic is.

Example 1
(Manufacture 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 potassium persulfate 0.5 as a polymerization initiator A portion was added and stirred sufficiently, and then heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The glass transition temperature of the binder was 10 ° C.

After adding 5% aqueous sodium hydroxide solution to the aqueous dispersion containing the binder and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C. or lower to obtain a binder solid. As a propargyl group-containing compound, 3 parts of propargyl benzenesulfonate was added to 100 parts per minute to obtain a binder composition.

(Production of slurry composition for secondary battery negative electrode)
In a planetary mixer with a disper, 100 parts of natural graphite (average particle size: 24.5 μm) having a BET specific surface area of 5 m ² / g as a negative electrode active material and a 1% aqueous solution of carboxymethyl cellulose (manufactured by Nippon Paper Chemical Co., Ltd., MAC350HC) 1 part was added in an amount corresponding to the solid content, adjusted to a solid content concentration of 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting the solid content concentration to 52% with ion-exchanged water, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.

The above mixture was mixed with 1 part of the binder (based on solid content) and ion-exchanged water, adjusted to a final solid content concentration of 42%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode having good fluidity. The dispersion stability of the slurry was evaluated as described above.

(Manufacture of batteries)
The secondary battery negative electrode slurry composition was applied on a copper foil having a thickness of 20 μm with a comma coater so that the film thickness after drying was about 150 μm, heat-treated at 60 ° C. for 1 minute, and then 120 An electrode raw material was obtained by heat treatment at 0 ° C. for 1 minute. The raw electrode was rolled with a roll press to obtain a negative electrode for a secondary battery having a negative electrode active material layer thickness of 80 μm.

As a positive electrode active material, 100 parts of LiFePO ₄ having a volume average particle diameter of 0.5 μm and an olivine crystal structure is used, and a 1% aqueous solution of carboxymethyl cellulose (CMC, “BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is used as a dispersant. An acrylate polymer having a solid content equivalent of 1 part, a glass transition temperature of −40 ° C. as a binder and a number average particle size of 0.20 μm (2-ethylhexyl acrylate 78% by mass, acrylonitrile 20% by mass, methacrylic acid 2 A planetar such that a 40% aqueous dispersion of a copolymer obtained by emulsion polymerization of a monomer mixture containing% by mass is 5 parts in terms of solids and the total solids concentration is 40% with ion-exchanged water. A slurry for a positive electrode composition layer was prepared by mixing with a Lee mixer. The secondary battery positive electrode slurry composition was applied onto a 20 μm thick copper foil with a comma coater so that the film thickness after drying was about 200 μm, and heat-treated at 60 ° C. for 1 minute, and then 120 A positive electrode for a secondary battery was obtained by heat treatment at 0 ° C. for 1 minute.

A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by a dry method, porosity 55%) was cut into a circle having a diameter of 18 mm.

The obtained positive electrode for a lithium ion secondary battery was disposed such that the current collector surface was in contact with the aluminum packaging exterior. A separator was disposed on the surface of the positive electrode on the positive electrode active material layer side. Furthermore, the negative electrode for a lithium ion secondary battery obtained above was placed on the separator so that the surface on the negative electrode active material layer side faces the separator. The electrolyte was poured into the packaging material so that no air remained. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. The electrolyte used was 1.0M LiPF ₆ (EC / DEC = 1/2 volume ratio) with 2% by volume of VC (vinylene carbonate) added.

The obtained negative electrode and secondary battery were evaluated for adhesion strength, durability, and low-temperature output characteristics as described above.

(Example 2)
The same procedure as in Example 1 was performed except that the amount of propargyl benzenesulfonate was 7 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Example 3)
The amount of propargyl benzenesulfonate added was the same as in Example 1 except that the amount was 15 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Example 4)
The same procedure as in Example 1 was conducted except that propargyl acrylate was used instead of propargyl benzenesulfonate as the propargyl group-containing compound. The results are shown in Table 1.

(Example 5)
The same procedure as in Example 1 was conducted except that propargyl methacrylate was used instead of propargyl benzenesulfonate as the propargyl group-containing compound. The results are shown in Table 1.

(Example 6)
The same procedure as in Example 1 was performed except that methacrylic acid was used in place of itaconic acid as a comonomer at the time of preparing the binder. The results are shown in Table 1.

(Example 7)
As the negative electrode active material, natural graphite having a BET specific surface area of 8 m ² / g (average particle diameter: 22 μm) was used instead of natural graphite having a BET specific surface area of 5 m ² / g (average particle diameter: 24.5 μm). Same as Example 1. The results are shown in Table 1.

(Example 8)
As the negative electrode active material, natural graphite having a BET specific surface area of 15 m ² / g (average particle diameter: 15 μm) was used instead of natural graphite having a BET specific surface area of 5 m ² / g (average particle diameter: 24.5 μm). Same as Example 1. The results are shown in Table 1.

Example 9
As the negative electrode active material, natural graphite (average particle size: 24.5μm) of a BET specific surface area of ^{5 m} 2 / g natural graphite (average particle size: 24.5μm) of a BET specific surface area of ^{5 m} 2 / g instead of 80 parts and The procedure was the same as Example 1 except that 20 parts of SiOC (average particle size: 10 μm) having a BET specific surface area of 6.5 m ² / g was used. 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, natural graphite (average particle size: 24.5μm) of a BET specific surface area of ^{5 m} 2 / g BET specific instead of surface area 5.0 m ² / g natural graphite (average particle size: 24.5μm) 50 Parts and a BET specific surface area of 6.5 m ² / g of SiOC (average particle size: 10 μm) were used in the same manner as in Example 1 except that 50 parts were used. 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)
The same procedure as in Example 1 was performed except that dipropargyl carbonate was used as the propargyl group-containing compound instead of propargyl benzenesulfonate. The results are shown in Table 1.

Example 12
The same procedure as in Example 1 was conducted except that itaconic acid was not used as a comonomer for preparing the binder. The glass transition temperature of the binder was 7 ° C. The results are shown in Table 1.

(Comparative Example 1)
The procedure was the same as Example 1 except that the propargyl group-containing compound was not blended in the binder composition. The results are shown in Table 1.

(Comparative Example 2)
The procedure was the same as Example 10 except that the propargyl group-containing compound was not blended in the binder composition. The results are shown in Table 1.

(Comparative Example 3)
The amount of propargyl benzenesulfonate added was the same as in Example 1 except that the amount was 25 parts with respect to 100 parts of binder solid content. The results are shown in Table 1.

(Comparative Example 4)
Example 1 was repeated except that methyl 2-octanoate was used in place of propargyl benzenesulfonate. The results are shown in Table 1.

By blending the propargyl group-containing compound with the binder composition, the adhesion between the current collector and the electrode active material layer was improved, and in particular, a secondary battery with improved cycle characteristics and low-temperature output characteristics was obtained. .

On the other hand, when the propargyl group-containing compound was not blended (Comparative Examples 1 and 2), the above effect was not achieved. Moreover, when there are too many compounding quantities of a propargyl group containing compound (comparative example 3), a slurry tends to thicken, the uniformity of the negative electrode obtained will fall, and output characteristics will fall. Further, even when methyl 2-octanoate having an alkenyl group having a structure similar to that of the propargyl group (HC—C≡C—CH ₂ —) was used (Comparative Example 4), the above effect was not exhibited.

Claims (11)

1. A binder composition for a secondary battery negative electrode containing a binder and a propargyl group-containing compound, wherein 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.
2. The binder composition for a secondary battery negative electrode according to claim 1, wherein the propargyl group-containing compound is a monopropargyl group-containing compound.
3. The binder composition for a secondary battery negative electrode according to claim 1 or 2, wherein the binder contains an ethylenically unsaturated carboxylic acid monomer unit.
4. 4. The binder composition for a secondary battery negative electrode according to claim 1, wherein the binder has a glass transition temperature of −60 ° C. to 40 ° C.
5. A secondary battery negative electrode slurry composition comprising the secondary battery negative electrode binder composition according to any one of claims 1 to 4 and a negative electrode active material.
6. The slurry composition for secondary battery negative electrode according to claim 5, wherein the negative electrode active material has a BET specific surface area of 3 to 20 m ² / g.
7. A negative electrode for a secondary battery comprising a negative electrode active material layer comprising the negative electrode binder composition for a secondary battery according to any one of claims 1 to 4 and a negative electrode active material on a current collector.
8. The negative electrode for a secondary battery according to claim 7, wherein the negative electrode active material has a BET specific surface area of 3 to 20 m ² / g.
9. The negative electrode for a secondary battery according to claim 7 or 8, wherein the negative electrode active material is a carbon material-based active material.
10. A secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the negative electrode is a negative electrode for a secondary battery according to any one of claims 7 to 9.
11. The secondary battery according to claim 10, wherein the electrolytic solution contains vinylene carbonate.