JP5955496B2 - Secondary battery negative electrode binder composition, secondary battery negative electrode slurry composition, secondary battery negative electrode, secondary battery, and method for producing secondary battery negative electrode binder composition - Google Patents

Description

  The present invention relates to a binder composition for a secondary battery negative electrode used to form a negative electrode used in a secondary battery such as a lithium ion secondary battery, and a slurry composition for a secondary battery negative electrode using the binder composition. The present invention relates to a negative electrode for a secondary battery, a secondary battery, and a method for producing a binder composition for a secondary battery negative electrode.

  In recent years, portable terminals such as notebook 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.

  In order to improve the performance of a battery, improvement of an electrode, an electrolytic solution, and other battery members has been studied. As for the electrode, an electrode active material (hereinafter, sometimes simply referred to as “active material”) or a current collector. In addition to studying the body itself, studies have been made on polymers that serve as binders for binding active materials to current collectors. The electrode is usually obtained by mixing a binder composition in which a polymer serving as a binder is dispersed or dissolved in a liquid medium such as water or an organic liquid with an active material and, if necessary, a conductive agent such as conductive carbon to obtain a slurry. The slurry is applied to a current collector and dried.

  As the binder composition, Patent Document 1 describes a binder composition for a secondary battery negative electrode containing α-methylstyrene dimer as a molecular weight regulator. Patent Document 2 describes a binder composition for secondary battery electrodes containing an alkyl mercaptan as a molecular weight regulator.

JP 2002-319402 A Japanese Patent Laid-Open No. 10-302797

However, according to the study by the inventors, the α-methylstyrene dimer used when producing the binder composition described in Patent Document 1 is used when producing the binder composition by an emulsion polymerization method or the like. It has been found that there is a problem of lowering the productivity of the binder composition in order to reduce the polymerization rate. Furthermore, when α-methylstyrene dimer is used in a large amount, the polymerization stability is lowered, which is a great adverse effect in producing a binder composition. Moreover, since the reactive point remained in the polymer terminal in the binder composition containing (alpha) -methylstyrene dimer, it turned out that the cycling characteristics of a battery deteriorate with a time-dependent change.
Patent Document 2 discloses a negative electrode obtained by coating an electrode composition containing the binder composition on a copper current collector. However, since the alkyl mercaptan is liberated (residual) in the binder composition, it has been found that the liberated alkyl mercaptan reacts with the copper current collector to deteriorate the cycle characteristics of the battery.

  Accordingly, the present invention has been made in view of the above-described problems, and has a high productivity and good battery cycle characteristics, and a secondary battery negative electrode binder composition, and a secondary battery negative electrode using the binder composition It aims at providing the manufacturing method of the slurry composition, the negative electrode for secondary batteries, a secondary battery, and the binder composition for secondary battery negative electrodes.

  Therefore, as a result of investigations by the present inventors, by making the content of free alkyl mercaptan in the binder composition into a specific range, the reaction with the copper current collector is suppressed, and the cycle characteristics of the battery are improved. I found out that I can.

The gist of the present invention aimed at solving such problems is as follows.
(1) Aliphatic conjugated diene monomer units 20 to 60% by weight, ethylenically unsaturated carboxylic acid monomer units 1 to 10% by weight, and other monomer units 30 to 79 copolymerizable therewith The binder composition for secondary battery negative electrodes containing the binder which consists of weight%, and 0.5-50 ppm of free alkyl mercaptans with respect to 100 weight part of this binder.

(2) The other monomer unit is an aromatic vinyl monomer unit, and includes 50 ppm or less of the aliphatic conjugated diene monomer and 1000 ppm or less of the aromatic vinyl monomer (1 ) Secondary battery negative electrode binder composition.

(3) A secondary battery negative electrode slurry composition comprising the secondary battery negative electrode binder composition described in (1) or (2) above and a negative electrode active material.

(4) A secondary battery negative electrode obtained by applying the slurry composition for secondary battery negative electrode described in (3) above onto a current collector and drying.

(5) A secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolytic solution, wherein the negative electrode is the secondary battery negative electrode described in (4).

(6) From 20 to 60% by weight of aliphatic conjugated diene monomer, 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and 30 to 79% by weight of other monomers copolymerizable therewith A monomer composition obtained by polymerizing the monomer composition in an aqueous solvent in the presence of 0.1 to 5.0 parts by weight of an alkyl mercaptan with respect to 100 parts by weight of the monomer composition. And a stripping step of stripping the aqueous dispersion to make the content of the released alkyl mercaptan 0.5 to 50 ppm with respect to 100 parts by weight of the binder. The manufacturing method of the binder composition for battery negative electrodes.

(7) The other monomer is an aromatic vinyl monomer, and the stripping step makes the aliphatic conjugated diene monomer 50 ppm or less and the aromatic vinyl monomer 1000 ppm or less. The manufacturing method of the binder composition for secondary battery negative electrodes as described in (6) which is a process.

  According to the present invention, an aliphatic conjugated diene monomer unit (hereinafter sometimes referred to as “component A”), an ethylenically unsaturated carboxylic acid monomer unit (hereinafter sometimes referred to as “component B”). ), And other monomer units copolymerizable therewith (hereinafter sometimes referred to as “component C”), a binder containing each monomer unit in a specific ratio, and 100 parts by weight of the binder When a secondary battery is manufactured using copper as a current collector by using a binder composition for a secondary battery negative electrode containing a specific amount of free alkyl mercaptan, the cycle characteristics of the battery are improved. be able to. Moreover, since the secondary battery negative electrode using this binder composition has high electrolyte solution resistance, even if it repeats charging / discharging, it is hard to deteriorate and can extend the lifetime of a secondary battery.

1 represents a conceptual diagram of an apparatus for carrying out the method of the invention.

  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 sequentially described.

(1) Binder composition for secondary battery negative electrode The binder composition for secondary battery negative electrode of the present invention contains a binder and a specific amount of free alkyl mercaptan. The binder is composed of an aliphatic conjugated diene monomer unit, an ethylenically unsaturated carboxylic acid monomer unit, and other monomer units copolymerizable therewith, and includes each monomer unit in a specific ratio. . The aliphatic conjugated diene monomer unit is a polymer repeating unit obtained by polymerizing an aliphatic conjugated diene monomer, and the ethylenically unsaturated carboxylic acid monomer unit is ethylenically unsaturated. Polymer repeating units obtained by polymerizing carboxylic acid monomers, and other monomer units copolymerizable therewith are polymer repeating units obtained by polymerizing other copolymerizable monomers. Unit.

  Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, Examples thereof include chain conjugated pentadienes, substituted and side chain conjugated hexadienes and the like, and one kind or two or more kinds can be used. 1,3-butadiene is particularly preferable.

  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.

  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.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, and the like, and one or more kinds can be used. Styrene is particularly preferable.

  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, Monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like can be mentioned, 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, and 3-chloro-2-hydroxypropyl. 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 preferable.

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

  Further, 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 such that the aliphatic conjugated diene monomer unit is 20 to 60% by weight, preferably 30 to 55% by weight, and the ethylenically unsaturated carboxylic acid monomer unit. Is 1 to 10% by weight, preferably 2 to 8% by weight, more preferably 3 to 7% by weight, and other monomer units copolymerizable therewith are 30 to 79% by weight, preferably 40 to 69%. % By weight.

  When the aliphatic conjugated diene monomer unit is less than 20% by weight, it is contained in the slurry composition when the slurry composition containing the secondary battery negative electrode binder composition of the present invention is applied to the current collector. Sufficient adhesion between the electrode active material and the current collector cannot be obtained. On the other hand, when the content exceeds 60% by weight, the resistance to the electrolytic solution decreases when the slurry composition is applied to a current collector to produce a negative electrode.

  When the ethylenically unsaturated carboxylic acid monomer unit is less than 1% by weight, the stability of the binder composition and the slurry composition is lowered. On the other hand, if it exceeds 10% by weight, the viscosity of the binder composition becomes high and handling becomes difficult.

  If the other copolymerizable monomer unit is less than 30% by weight, the electrolytic solution resistance is lowered when a slurry composition containing the binder composition of the present invention is applied to a current collector to produce a negative electrode. On the other hand, if it exceeds 79% by weight, sufficient adhesion between the electrode active material and the current collector contained in the slurry composition cannot be obtained when the slurry composition is applied to the current collector.

  The content of the free alkyl mercaptan contained in the binder composition for a negative electrode of the secondary battery of the present invention is 0.5 to 50 ppm, preferably 1.0 to 30 ppm with respect to 100 parts by weight of the binder described above. In the present invention, the liberated alkyl mercaptan means a state in which the alkyl mercaptan is dissolved in the aqueous solvent as ions by mixing the alkyl mercaptan and the aqueous solvent described later. When the content of the liberated alkyl mercaptan is less than 0.5 ppm, the electrolytic solution resistance of the negative electrode active material layer containing the binder composition is reduced, and the life of the secondary battery is reduced. When it exceeds 50 ppm, the cycle characteristics of the secondary battery using the binder composition are deteriorated, and the battery life is reduced.

  The alkyl mercaptan in the present invention is mixed in the binder composition as a chain transfer agent, 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 are mentioned. Among these, n-octyl mercaptan and t-dodecyl mercaptan are preferable from the viewpoint of good polymerization stability.

  In the present invention, α-methylstyrene dimer, terpinolene, allyl alcohol, allylamine, sodium allyl sulfonate (potassium), sodium methallyl sulfonate (potassium) and the like are listed as chain transfer agents that can be used in combination with the above-described alkyl mercaptan. It is done. The amount of the serial transfer agent used is not particularly limited as long as the effect of the present invention is not hindered.

  In addition, when an aromatic vinyl monomer is used as the other monomer described above, an unreacted aliphatic conjugated diene monomer is preferably used in the binder composition for a secondary battery negative electrode of the present invention. 50 ppm or less, more preferably 10 ppm or less, and an unreacted aromatic vinyl monomer is preferably 1000 ppm or less, more preferably 200 ppm or less. If the content of the aliphatic conjugated diene monomer contained in the binder composition exceeds 50 ppm, the surface of the electrode plate may be roughened by foaming or due to odor when the electrode plate is prepared by coating and drying of the negative electrode slurry. It may be an environmental burden. In addition, when the content of the aromatic vinyl monomer exceeds 1000 ppm, depending on the drying conditions, there is a concern that the environmental load and the surface of the electrode plate may be roughened, and the electrolytic solution resistance of the binder composition is reduced. There is.

  The binder composition for secondary battery negative electrode of the present invention is a compound particle capable of binding to each other an electrode active material to be described later and a conductive agent added as necessary, and is a polymer particle having a binding force. A solution or dispersion in which a binder is dissolved or dispersed in an aqueous solvent (hereinafter, these may be collectively referred to as “an aqueous dispersion containing a binder”) is filtered.

(Production of aqueous dispersion containing binder)
An aqueous dispersion containing a polymer binder is produced, for example, by polymerizing a monomer composition containing the monomer in an aqueous solvent in the presence of an alkyl mercaptan. In the present invention, a residual monomer of the monomer and a component free of the alkyl mercaptan are present in the aqueous dispersion after the polymerization reaction.

  The ratio of each monomer in the monomer composition in the step of obtaining an aqueous dispersion containing a polymer binder is 20 to 60% by weight of an aliphatic conjugated diene monomer, preferably 30 to 55% by weight. 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, preferably 1.5 to 8% by weight, more preferably 2 to 7% by weight, and other monomers copolymerizable therewith. The monomer is 30 to 79% by weight, preferably 40 to 69% by weight.

  The content of the alkyl mercaptan in the step of obtaining the aqueous dispersion containing the binder is 0.1 to 5.0 parts by weight, preferably 0.2 to 3 parts by weight with respect to 100 parts by weight of the monomer composition. . When the content of the alkyl mercaptan is less than 0.1 parts by weight, a large amount of aggregates and scales are generated during the polymerization, and sufficient adhesion to the electrode active material described later cannot be obtained. On the other hand, when the amount exceeds 5.0 parts by weight, a large amount of aggregates and scales are generated during the polymerization, and the secondary battery negative electrode slurry composition, which will be described later, is applied to a current collector and dried. The electrolytic solution resistance of the battery negative electrode is reduced.

  The aqueous solvent is not particularly limited as long as the binder can be dispersed, and is usually selected from a dispersion medium having a boiling point of 80 to 350 ° C., preferably 100 to 300 ° C. at normal pressure. The number in parentheses after the name of the dispersion medium is the boiling point (unit: ° C) at normal pressure, and the value after the decimal point is rounded off or rounded down. For example, diacetone alcohol (169), γ-butyrolactone (204) as ketones, ethyl alcohol (78), isopropyl alcohol (82), normal propyl alcohol (97), glycol ethers as alcohols , 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 pyrether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188) As the ethers, 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66). 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. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. From the viewpoint of production efficiency, it is easy to obtain a high molecular weight product, it can be obtained in a state where the polymer is dispersed in water as it is, no redispersion treatment is required, and it can be used as it is for slurry preparation for secondary battery negative electrode. Among them, 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 equipped 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.

  An emulsifier, a dispersant, a polymerization initiator, and the like are generally used in these polymerization methods, and the amount used may be a generally used amount. 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. Furthermore, an aqueous dispersion of polymer particles obtained by these methods is added to 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. Among these, pH adjustment with an alkali metal hydroxide is preferable because it improves the binding property (peel strength) between the current collector and the active material.

  The binder described above 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 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.

  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.

  The glass transition temperature of the binder is preferably 40 ° C. or lower, more preferably −75 to + 30 ° C., still more preferably −55 to + 20 ° C., and most preferably −35 to 15 ° C. When the glass transition temperature of the binder is in 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.

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

(Manufacture of binder composition for secondary battery negative electrode)
The binder composition for a secondary battery negative electrode strips the aqueous dispersion, and the content of the released alkyl mercaptan is 0.5 to 50 ppm, preferably 1.0 to 30 ppm with respect to 100 parts by weight of the binder. It is manufactured by doing.

  The aqueous dispersion containing the above binder is a secondary battery negative electrode binder composition in which the residual monomer and alkyl mercaptan free components in the aqueous dispersion are removed by a stripping method or the like, and the content is within a specific range. Things are manufactured.

  The stripping method refers to, for example, maintaining the temperature of the aqueous dispersion at a temperature of about 60 to 140 ° C., performing steam distillation while blowing steam at 100 to 160 ° C., and volatile residual monomers in the aqueous dispersion ( This is a method for removing free components of unreacted monomer) and alkyl mercaptan.

  An aqueous dispersion containing a binder after polymerization (hereinafter sometimes referred to as “polymer aqueous dispersion”) is usually subjected to a stripping step in order to remove volatile substances such as unreacted monomers. The Also, the polymer aqueous dispersion is prepared to have a predetermined solid content concentration by evaporating and removing water by a concentration step after the stripping step due to problems in handling and transportation.

  As a method for removing unreacted monomers remaining in the polymer aqueous dispersion after completion of the polymerization, a method of allowing steam to flow through the polymer aqueous dispersion in the tank (steam aeration method), or a multi-stage There is a so-called steam stripping method in which a polymer aqueous dispersion and steam are counter-contacted in a tower. In particular, the multi-stage stripper system in which the aqueous dispersion is allowed to flow down from the top of the multi-stage tower and steam is blown from the bottom of the tower can efficiently remove volatile substances.

  On the other hand, as a method for concentrating the polymer aqueous dispersion, an evaporation method, an ultrafiltration membrane method, and the like are known, but usually an evaporation method is often used. The evaporation method is a method in which a polymer aqueous dispersion is heated to evaporate water in a reduced-pressure atmosphere, and a thin film evaporator or a tank evaporator is used as an apparatus.

  In the tank type evaporator, the polymer aqueous dispersion is heated while forcibly circulating between the tank and an external heat exchanger for heating, and the tank is kept at a reduced pressure so that the water content in the tank is reduced. Evaporate. In the concentration by these evaporation methods, residual monomers as well as moisture are removed by the principle of steam distillation. However, since the amount of water vapor required for stripping and the amount of water vapor generated by evaporation do not match, only the evaporation method is used. However, there are cases where residual monomers and the like cannot be removed sufficiently. Therefore, generally, a stripping process by a steam stripping method and a concentration process by an external heating forced circulation type evaporator are used in combination in series.

  As a method for performing steam stripping and concentration at the same time, there is a flash evaporation method in which steam for stripping is blown into a tank type evaporator using an external heat exchanger [Ind. Eng. Chem. , Vol. 43, no. 1, p, 215 (1951)]. However, since this method returns the aqueous dispersion heated by an external heat exchanger from the upper part of the tank and flash-evaporates there, the water vapor generated by flash evaporation is not in contact with the polymer aqueous dispersion, It hardly contributes to stripping of volatile substances such as unreacted monomers. Further, in this method, the solid content concentration in the aqueous dispersion increases during steam stripping, and the aggregates may increase rapidly.

  In general, when producing a small amount of a variety of polymer aqueous dispersions, the polymerization method is a batch method, and the subsequent post-treatment steps such as stripping and concentration of residual monomers are also a batch method. If only these post-treatment steps are made continuous, it is difficult to match the polymerization cycle and the post-treatment cycle, and the size of the apparatus in the post-treatment step is relative to that required for the batch method. The equipment efficiency becomes worse. Furthermore, the product type switching operation in the post-processing process may be complicated.

  A method of stripping and concentrating a polymer aqueous dispersion simultaneously in a batch system, which has high thermal efficiency and high equipment efficiency, and that can suppress the generation of coagulum, is a cylinder provided with a stirrer. Using a vertical evaporation tank, dispose the multiple steam nozzle tip openings at a position below the surface of the liquid to be treated, and reduce the pressure in the tank while blowing steam at about 100 to 140 ° C. from each steam nozzle. There is a method of holding and concentrating. Also, the polymer aqueous dispersion heated by an external heat exchanger is forced to circulate, and the heated polymer aqueous dispersion is forced to return from the position of the stirring blade of the stirrer to the lower position in the evaporation tank. If the volatile substance is stripped from the polymer aqueous dispersion using the water vapor evaporated in the tank while stirring under reduced pressure, the efficiency is further improved. According to the above method, it is more preferable that stripping and concentration of the polymer aqueous dispersion can be carried out simultaneously in a batch manner while greatly suppressing the generation of coagulum. In particular, the water-based dispersion liquid is stirred with the stirring blade attached to the container tank while steam 110-140 ° C. (saturation temperature) is blown into the container tank at 1000-1500 kg / hr in a batch system, and the temperature of the water-based dispersion liquid Is carried out while maintaining the temperature at 80 to 100 ° C., and is less likely to generate agglomerates, and can be carried out simultaneously with the concentration step after the stripping step. preferable. The pressure in the evaporation tank is preferably 760 to 10 torr, and more preferably 600 to 100 torr. The temperature in the can and the filling volume in the container may be selected in a timely manner within a range in which bumping or the like does not occur and processing can be performed stably. In the above method, when the amount of steam necessary for stripping is not sufficient, steam may be replenished to the forced circulation line between the evaporation tank and the external heat exchanger.

  In addition, when an aromatic vinyl-based monomer is used as the other monomer described above, in the method for producing a secondary battery negative electrode binder composition of the present invention, a fat is contained in the secondary battery negative electrode binder composition. The group conjugated diene monomer is preferably contained at 50 ppm or less, more preferably 10 ppm or less, and the aromatic vinyl monomer is preferably contained at 1000 ppm or less, more preferably 200 ppm or less. If the content of the aliphatic conjugated diene monomer contained in the binder composition exceeds 50 ppm, the surface of the electrode plate may be roughened by foaming or due to odor when the electrode plate is prepared by coating and drying of the negative electrode slurry. It may be an environmental burden. In addition, when the content of the aromatic vinyl monomer exceeds 1000 ppm, depending on the drying conditions, there is a concern that the environmental load and the surface of the electrode plate may be roughened, and the electrolytic solution resistance of the binder composition is reduced. There is.

  Moreover, an additive can be added to the binder composition 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 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. The use ratio of these additives is preferably less than 300% by weight, more preferably 30% by weight or more and 250% by weight or less, particularly preferably 40% by weight or more and 200% by weight, based on the total solid weight of the binder composition. It is as follows. If it is this range, the secondary battery negative electrode excellent in smoothness can be obtained. In addition to the method of adding these additives to the binder composition, these additives can also be added to the slurry composition for secondary battery electrodes 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 contains the secondary battery negative electrode binder composition and the 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 within the secondary battery negative electrode.

  Specific examples of negative electrode active materials for lithium ion secondary batteries include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon fibers; high conductivity such as polyacene Examples include molecules. Crystalline carbonaceous materials such as graphite, natural graphite, and mesocarbon microbeads (MCMB) are preferable. Moreover, as a negative electrode active material, metals, such as silicon, tin, zinc, manganese, iron, nickel, these alloys, the oxide or sulfate of the said metal or alloy can be used. In addition, lithium alloys such as metallic lithium, Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitride, silicon, and the like can also be used. The said negative electrode active material can be used individually or in combination of 2 or more types.

  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 size of the negative electrode active material is appropriately selected in consideration of other constituent requirements 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 tap density of the negative electrode active material is not particularly limited, but 0.6 g / cm ³ or more is preferably used.

  In the slurry composition for secondary battery negative electrode of the present invention, the total content of the negative electrode active material and the binder composition is preferably 10 to 90 parts by mass, more preferably 30 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 in the above range, the viscosity of the slurry composition for a secondary battery negative electrode obtained 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 binder composition from the negative electrode active material in the electrode plate pressing step can be suppressed.

(Dispersion medium)
In the present invention, water is used as the dispersion medium. 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 the amount 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 total amount 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 cellulosic 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; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches.

  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. 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 invention, “(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 secondary battery negative electrode 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. Content of the reinforcing material in a slurry composition is 0.01-20 mass parts normally with respect to 100 mass parts of total amounts of a negative electrode active material, Preferably it is 1-10 mass parts. By being included in the said range, a high capacity | capacitance and a high load characteristic can be shown.

  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 total amount 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 obtained thereby can be improved.

  As the electrolytic solution additive, vinylene carbonate used in the slurry composition and the electrolytic solution 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 total amount 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 obtained thereby 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 total amount 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.

(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) Secondary battery negative electrode The secondary battery negative electrode of the present invention is obtained by applying and drying the slurry composition for a secondary battery negative electrode of the present invention on a current collector.

(Method for producing secondary battery negative electrode)
The method for producing the secondary battery negative electrode of the present invention is not particularly limited, and examples thereof include 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. It is done.

  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 by 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.

  When the secondary battery negative electrode of the present invention is produced, 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 a process. The 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 secondary battery negative electrode 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 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 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 secondary battery negative electrode is preferably 1.6 to 1.9 g / cm ³ , 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.

(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 secondary battery negative electrode. 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 of the mixture.

(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 secondary battery negative electrode.

(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.

Examples of 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.

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 ), Co—Ni—Mn lithium composite oxide, and 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 average particle diameter of the positive electrode active material is usually 1 to 50 μm, preferably 2 to 30 μm. When the particle diameter is in the above range, the amount of the positive electrode binder composition when preparing the positive electrode slurry composition described later can be reduced, the decrease in battery capacity can be suppressed, and the positive electrode slurry composition. It becomes easy to prepare a product with a proper viscosity 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 components, the positive electrode may further contain other components such as an electrolyte additive having a function of suppressing the decomposition of the electrolyte described above. These are not particularly limited as long as they do not affect the battery reaction.

  As the current collector, the current collector used for the negative electrode of the secondary battery described above can be used, and is not particularly limited as long as the material has electrical conductivity and is electrochemically durable. Aluminum is particularly preferred for the 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 secondary battery negative electrode.

(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 solids such as polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers. There are polymer films for polymer electrolytes or gel polymer electrolytes, separators coated with gelled polymer coating layers, or separators coated with porous membrane layers made of inorganic fillers and dispersants for inorganic fillers. .

(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 charging characteristics and discharging characteristics of the battery are degraded.

  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 and 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. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.

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.

(Measurement of free alkyl mercaptan in binder composition)
After adding 200 mL of MEK / IPA mixed solution (volume ratio = 75/25) to a sample container with a lid (volume ratio = 75/25) and stirring with a stirrer, the binder sample was added while being accurately weighed with an electronic balance, and further dispersed. 2 mL of% ammonia solution was added and stirred for 30 minutes. This preparation solution was subjected to potentiometric titration (COM-1750, manufactured by Hiranuma Sangyo Co., Ltd.) with a 1/1000 N-silver nitrate specified solution, and the amount of residual alkyl mercaptan was determined by titration.

(Measurement of residual monomer in binder composition)
(A) Quantification of residual butadiene Using capillary FID gas chromatography, the peak areas of butadiene and toluene were determined by an internal standard method using toluene as an internal standard, and the content was calculated.
(1) Preparation of internal standard solution and measurement of correction coefficient 30 mL of a 3% polyoxyethylene alkyl ether aqueous solution (using Emulgen 1150S-60 manufactured by Kao Co., Ltd.) prepared in advance in a pressure-proof ampoule container, and toluene ( Wako Pure Chemical Industries, Ltd. (special grade) is precisely weighed with a 25 μL microsyringe and a precision electronic balance with a sensitivity of 0.1 mg.
Put a rubber stopper on the pressure-proof ampule container and stopper with a crown. Add about 20 μL of butadiene with a well-cooled syringe. The peak integrated value is obtained under the conditions of sample measurement gas chromatography.
Correction factor = (butadiene weight / toluene weight) / (butadiene integrated value / toluene integrated value)
(2) Preparation of sample for measurement 30 mL of 3% polyoxyethylene alkyl ether aqueous solution (for example, prepared from Emulgen 1135S-70 manufactured by Kao Corporation) was collected in an Erlenmeyer flask with a stopper (50 mL), and an internal standard ( Toluene) solution is weighed by 20 μL with a 25 μL microsyringe and precisely weighed with a precision electronic balance with a sensitivity of 0.1 mg and added. About 5 g of the aqueous dispersion for measurement is added thereto with a precision electronic balance. Furthermore, after putting a stirring bar in the conical stoppered Erlenmeyer flask and stoppering, it stirred with the magnetic stirrer for 20 minutes, and was set as the sample for a measurement.
(3) Quantitative Measurement of Gas Chromatograph After confirming the stability of the apparatus, 2 μL of a sample for measurement was taken with a microsyringe and measured by injecting from a GC injection port. The apparatus and conditions used for the measurement were as follows.
Gas chromatography device: GC353 manufactured by GL Sciences
Column (Inevt Cap 1 inner diameter: 0.25 mm, film thickness: 1.5 μm, length: 30 m)
Oven temperature: 40 ° C
Column temperature: Initial Temp: 40 ° C., Initial Time: 1 min. , Rate: 10 ° C./min. Final Temp: 220 ° C., Final Time: 2 min.
Carrier gas: He 1 mL / min.
Split ratio: 25/100
Make-up gas: N ₂ 35 mL / min. Air 270 mL / min. He 36 mL / min.
Residual butadiene content (ppm) = 10 ⁶ · (A · D · E) / (C · B)
A: butadiene integrated value, B: internal standard (toluene) integrated value, C: sample weight (g), D: internal standard (toluene) weight (g), E: correction coefficient

(B) Quantification of residual styrene Using capillary FID gas chromatography, the peak areas of styrene and toluene were determined by an internal standard method using toluene as an internal standard, and the content was calculated.
(1) Preparation of internal standard solution and measurement of correction coefficient 30 mL of a 3% polyoxyethylene alkyl ether aqueous solution (Emulgen 1150S-60 manufactured by Kao Co., Ltd.) prepared in advance was collected in an Erlenmeyer flask with a stopper (50 mL). Then, toluene (Wako Pure Chemical Industries, Ltd. reagent special grade) is precisely weighed with a 25 μL microsyringe with a precision electronic balance of 20 μL and sensitivity of 0.1 mg. The peak integrated value is obtained under the conditions of sample measurement gas chromatography.
Correction coefficient = (styrene weight / toluene weight) / (integrated value of styrene / integrated value of toluene)
(2) Preparation of sample for measurement In an Erlenmeyer flask with a stopper, 30 mL of a 3% polyoxyethylene alkyl ether aqueous solution (for example, prepared from Emulgen 1135S-70 manufactured by Kao Corporation) was collected, and an internal standard / toluene solution was further added. Using a 25 μL microsyringe, weigh 20 μL, add it with a precision electronic balance with a sensitivity of 0.1 mg, and add. To this, about 3 g of the aqueous dispersion is added while precisely weighing with a precision electronic balance. Furthermore, after putting a stirring bar in the conical stoppered Erlenmeyer flask and stoppering, it stirs with a magnetic stirrer for 20 minutes to extract residual styrene. The extract obtained here was used as a sample for measurement.
(3) Quantitative measurement Gas chromatograph measurement After confirming the stability of the apparatus, 2 μL of a sample for measurement was taken with a microsyringe and measured by injecting it from a GC inlet. The apparatus and conditions used for the measurement were as follows.
Gas chromatography device: GC353 manufactured by GL Sciences
Column (Inevt Cap 1 inner diameter: 0.25 mm, film thickness: 1.5 μm, length: 30 m)
In addition, non-volatile content collection column connection 0.53mm x 1m
Oven temperature: 70 ° C., 2 min, then heated up at 10 ° C./min Column temperature: Initial Temp: 40 ° C., Initial Time: 1 min. , Rate: 10 ° C./min. Final Temp: 220 ° C., Final Time: 2 min. Injection Temp: 220 ° C, Detect Temp: 200 ° C
Carrier gas: He 1 mL / min.
Split ratio: 1/100
Make-up gas: N ₂ 35 mL / min. Air 270 mL / min. He 36 mL / min.
Residual styrene content (ppm) = 10 ⁶ · (A · D · E) / (C · B)
A: Styrene integrated value, B: Internal standard (toluene) integrated value, C: Sample weight (g), D: Internal standard (toluene) weight (g), E: Correction coefficient

(Peel strength)
Each of the negative electrodes is cut into a rectangle having a width of 1 cm and a length of 10 cm to form a test piece, and fixed with the negative electrode active material layer surface facing upward. After the cellophane tape is attached to the surface of the negative electrode active material layer of the test piece, the stress when the cellophane tape is peeled off from the end of the test piece at a rate of 50 mm / min in the 180 ° direction is measured. The measurement is performed 10 times, the average value is obtained, and this is used as the peel strength, and the determination is made according to the following criteria. It shows that the adhesion strength of a negative electrode is so large that this value is large.
A: 6 N / m or more B: 5 N / m or more to less than 6 N / m C: 4 N / m or more to less than 5 N / m D: 3 N / m or more to less than 4 N / m E: Less than 3 N / m

(Electrolytic solution resistance)
Each of the negative electrodes was cut into a rectangle having a width of 2 cm and a length of 2 cm to obtain a test piece, and LiPF ₆ was mixed in a mixed solvent (ethylene carbonate (EC): diethyl carbonate (DEC) = 1: 2 (volume ratio at 20 ° C.)). Each test piece is immersed in an electrolytic solution dissolved at a concentration of 1 mol / L (60 ° C., 72 hours), and the state of peeling of the negative electrode active material layer from the current collector is visually observed. Judgment was made. The measurement was performed by preparing three test specimens and averaging the results of two favorable test specimens. It shows that it is excellent in electrolyte solution resistance, so that the area without peeling is large.
A: Area without peeling 100%
B: Area without peeling 95% or more and less than 100% C: Area without peeling 90% or more and less than 95% D: Area without peeling 80% or more and less than 90% E: Area without peeling 80% or less

(Charge / discharge cycle characteristics)
Using the obtained secondary battery, the battery was charged at a constant current until it became 4.2 V by a constant current constant voltage charging method of 0.1 C at 25 ° C., and then charged at a constant voltage. A charge / discharge cycle for discharging to 3.0 V at a constant current was performed. The charge / discharge cycle was performed up to 100 cycles, and the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity was taken as the capacity maintenance rate, and the determination was made based on the number of batteries generated with this capacity maintenance rate of 80% or less. The discharge capacity at the 50th cycle was defined as the battery capacity, and the test was performed by producing 20 batteries each. It shows that it is excellent in charging / discharging cycling characteristics, so that this number is small.

Example 1
(Manufacture of binder composition)
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion exchange water, 0.2 parts of sodium dodecylbenzenesulfonate, 0.2 parts of sodium carbonate, 1.5 parts of t-dodecyl mercaptan, 1,3-butadiene 45 Part, 30 parts of styrene, 15 parts of methyl methacrylate, 6 parts of acrylonitrile, 1.5 parts of acrylamide, and 2.5 parts of itaconic acid, and sufficiently stirring and preparing the emulsion aqueous solution obtained in the container (A) over 4 hours It was dripped continuously across. When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 96.5%.

(Steam stripping A method)
Next, a 5% aqueous sodium hydroxide solution was added to the aqueous dispersion to adjust the pH to 8, and then an appropriate amount of antifoaming agent was added. Next, the aqueous dispersion is charged so as to be half the internal volume of the evaporation tank (can), mixed with stirring, and the aqueous dispersion in the evaporation tank is heated to 80 ° C. by an external heat exchanger according to the flow shown in FIG. Until heated. Then, while reducing the pressure in the evaporation tank to 150 torr, steam at 110 ° C. (saturation temperature) was blown at 1200 kg / Hr and concentrated while performing steam stripping, and unreacted monomer and free in the aqueous dispersion The t-dodecyl mercaptan was removed. Thereafter, the aqueous dispersion was filtered through a 200-mesh (mesh size of about 77 μm) stainless steel wire mesh while adjusting the solid content concentration with ion-exchanged water to obtain a binder composition having a solid content concentration of 40%. The content of free t-dodecyl mercaptan in the binder composition was 10 ppm with respect to 100 parts by weight of the binder. The butadiene content in the binder composition was 0 ppm, and the styrene content was 150 ppm. The processing time for stripping was 10 hours.

(Production of slurry composition for secondary battery negative electrode)
As a thickener, carboxymethylcellulose (CMC, “BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used. The polymerization degree of the thickener was 1700, and the etherification degree was 0.65.

  Artificial graphite (average particle size: 24.5 μm, graphite interlayer distance (surface distance of (002) plane (d value) by X-ray diffraction method): 0.354 nm) as a negative electrode active material in a planetary mixer with a disper 100 parts and 1 part of a 1% aqueous solution of the above thickener were added, adjusted to a solids concentration of 55% with ion-exchanged water, and 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.

  1 part (based on solid content) of the binder composition and ion-exchanged water were added to the mixed solution, 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.

(Manufacture of batteries)
The slurry composition for secondary battery negative electrode 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 200 μm, and dried for 2 minutes (0.5 m / min). Speed, 60 ° C.) and heat treatment (120 ° C.) for 2 minutes to obtain an electrode raw material. This raw electrode was rolled with a roll press to obtain a secondary battery negative electrode having a negative electrode active material layer thickness of 80 μm. Table 1 shows the evaluation results of the peel strength of the negative electrode.

  The negative electrode is cut into a disk shape having a diameter of 15 mm, and a separator made of a disk-shaped porous polypropylene film having a diameter of 18 mm and a thickness of 25 μm, a metallic lithium used as the positive electrode, and an expanded metal are sequentially laminated on the surface of the negative electrode active material layer. This was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A half cell (secondary battery) having a thickness of 20 mm and a thickness of about 2 mm was produced.

In addition, as an electrolytic solution, LiPF ₆ was added at 1 mol / liter in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 1: 2 (volume ratio at 20 ° C.). A solution dissolved at a concentration was used. The evaluation results of the performance of this half cell are shown in Table 1.

(Example 2)
In a 5 MPa pressure vessel with a stirrer, 47 parts of styrene, 50 parts of 1,3-butadiene, 1.5 parts of methacrylic acid, 1.5 parts of acrylic acid, 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water, a chain transfer agent As a polymerization initiator, 0.4 part of t-dodecyl mercaptan and 0.5 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred, 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.

  Except having used the aqueous dispersion containing the said binder, operation similar to Example 1 was performed, the binder composition was obtained, and the slurry composition, the negative electrode, and the half cell were produced, and evaluation was performed. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 8 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 1 ppm, and the content of styrene was 210 ppm. The processing time for stripping was 10 hours.

Example 3
About the steam stripping of the aqueous dispersion containing the binder, the same operation as in Example 2 was performed except that steam stripping (Steam stripping B method) was performed by the following method to obtain a binder composition. A slurry composition, a negative electrode, and a half cell were prepared and evaluated. The results are shown in Table 1.

(Steam stripping method B)
A 5% sodium hydroxide aqueous solution was added to the aqueous dispersion to adjust the pH to 8, and then an appropriate amount of antifoaming agent was added. Next, the aqueous dispersion is charged so as to be half the internal volume of the evaporation tank (can), mixed by stirring, and the aqueous dispersion in the evaporation tank is 90 ° C. by an external heat exchanger according to the flow shown in FIG. Until heated. Then, while reducing the pressure in the evaporation tank to 150 torr, steam at 130 ° C. (saturation temperature) was blown at 1500 kg / Hr and concentrated while performing steam stripping, and unreacted monomer and free in the aqueous dispersion The t-dodecyl mercaptan was removed. Thereafter, the aqueous dispersion was filtered through a 200-mesh (mesh size approximately 77 μm) stainless steel wire mesh while adjusting the solid content concentration with ion-exchanged water to obtain a binder composition having a solid content concentration of 40%. The content of free t-dodecyl mercaptan in the binder composition was 3 ppm with respect to 100 parts by weight of the binder. The butadiene content in the binder composition was 0 ppm, and the styrene content was 50 ppm. The processing time for stripping was 8 hours.

Example 4
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion-exchanged water, 0.2 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, 0.5 part of t-dodecyl mercaptan, α-methylstyrene dimer 1 .5 parts, 1,3-butadiene 55 parts, styrene 20 parts, methyl methacrylate 6 parts, methacrylonitrile 15 parts, acrylamide 2 parts, itaconic acid 1.0 part, β-hydroxyethyl acrylate 1.0 part, The emulsion aqueous solution obtained by sufficiently stirring was continuously dropped into the container (A) over 4 hours. When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 97.4%.

  Except that the aqueous dispersion containing the binder was used, steam stripping (Method B) was performed in the same manner as in Example 3 to obtain a binder composition, and a slurry composition, a negative electrode, and a half cell were produced and evaluated. went. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 8 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 3 ppm, and the content of styrene was 30 ppm. The stripping processing time was 8 hours.

(Example 5)
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, 0.5 part of t-dodecyl mercaptan, α-methylstyrene dimer 0 .5 parts, 1,3-butadiene 45 parts, styrene 18 parts, methyl methacrylate 8 parts, acrylonitrile 25 parts, acrylamide 1.0 part, itaconic acid 1.5 parts, acrylic acid 1.5 parts The prepared emulsion aqueous solution was continuously dropped into the container (A) over 4 hours. When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 96.8%.

  Except having used the aqueous dispersion containing the said binder, operation similar to Example 1 was performed, the binder composition was obtained, and the slurry composition, the negative electrode, and the half cell were produced, and evaluation was performed. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 3 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 2 ppm, and the content of styrene was 120 ppm. The processing time for stripping was 6 hours.

(Example 6)
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, 0.5 part of t-dodecyl mercaptan, 1,3-butadiene 30 Parts, styrene 60 parts, methyl methacrylate 4 parts, methacrylonitrile 1.0 part, methacrylamide 1.0 part, fumaric acid 1.0 part, methacrylic acid 1.0 part, acrylic acid 1.0 part, β-hydroxy An emulsion aqueous solution obtained by adding 1.0 part of ethyl methacrylate and sufficiently stirring it was continuously dropped into the container (A) over 4 hours. When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 96.2%.

  Except having used the aqueous dispersion containing the said binder, operation similar to Example 1 was performed, the binder composition, the slurry composition, the negative electrode, and the half cell were produced and evaluated. The results are shown in Table 1. The content of liberated t-dodecyl mercaptan in the binder composition was 5 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 0 ppm, and the content of styrene was 330 ppm. The processing time for stripping was 10 hours.

(Example 7)
In the steam stripping A method, except that the processing time was 6 hours, the same operation as in Example 1 was performed to obtain a binder composition, and a slurry composition, a negative electrode, and a half cell were produced and evaluated. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 32 ppm with respect to 100 parts by weight of the binder. The butadiene content in the binder composition was 4 ppm, and the styrene content was 280 ppm.

(Example 8)
In the steam stripping A method, except that the processing time was changed to 5 hours, the same operation as in Example 2 was performed to obtain a binder composition, and a slurry composition, a negative electrode, and a half cell were prepared and evaluated. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 8 ppm with respect to 100 parts by weight of the binder. The butadiene content in the binder composition was 3 ppm, and the styrene content was 800 ppm.

Example 9
For steam stripping of the aqueous dispersion containing the binder, the same operation as in Example 1 was performed except that steam stripping (steam stripping C method) was performed by the following method to obtain a binder composition. A slurry composition, a negative electrode, and a half cell were prepared and evaluated. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 40 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 3 ppm, and the content of styrene was 950 ppm.

(Steam stripping C method)
A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion obtained in Example 1, adjusted to pH 8, and then an appropriate amount of antifoaming agent was added. Next, the aqueous dispersion is charged so that the inner volume of the evaporation tank (can) becomes half, and stirred and mixed. According to the flow shown in FIG. 1, the aqueous dispersion in the evaporation tank is 95 ° C. by an external heat exchanger. Until heated. Then, without reducing the pressure of the evaporation tank (can), steam stripping was performed while blowing steam at 110 ° C. (saturation temperature) at 1000 kg / Hr and venting the tank, and unreacted single amount in the aqueous dispersion Body and free t-dodecyl mercaptan were removed. Thereafter, the aqueous dispersion was filtered through a 200-mesh (mesh size of about 77 μm) stainless steel wire mesh to obtain a binder composition having a solid content concentration of 25%. The processing time for stripping was 10 hours.

(Comparative Example 1)
The binder was prepared in the same manner as in Example 1 except that the content of t-dodecyl mercaptan in the production of the binder composition was 1.2 parts and the binder composition was obtained without performing the steam stripping treatment. A composition was obtained, and a slurry composition, a negative electrode and a half cell were prepared and evaluated. The results are shown in Table 1. The content of free t-dodecyl mercaptan in the binder composition was 60 ppm with respect to 100 parts by weight of the binder. The butadiene content in the binder composition was 70 ppm, and the styrene content was 7800 ppm.

(Comparative Example 2)
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion-exchanged water, 0.2 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, 0.5 part of t-dodecyl mercaptan, α-methylstyrene dimer 1 .5 parts, 1,3-butadiene 65 parts, styrene 20 parts, methyl methacrylate 6 parts, methacrylonitrile 5.0 parts, acrylamide 1.0 part, β-hydroxyethyl acrylate 1.0 part, itaconic acid 1.0 Part and acrylic acid 1.0 part were prepared, and the emulsion aqueous solution obtained by sufficiently stirring was continuously dropped into the container (A) over 4 hours. When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 97.5%.

  Except having used the aqueous dispersion containing the said binder, operation similar to Example 1 was performed, the binder composition was obtained, and the slurry composition, the negative electrode, and the half cell were produced and evaluated. The results are shown in Table 1. The content of liberated t-dodecyl mercaptan in the binder composition was 15 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 8 ppm, and the content of styrene was 250 ppm. The processing time for stripping was 10 hours.

(Comparative Example 3)
A 5 MPa pressure vessel (A) equipped with a stirrer was charged with 50 parts of ion-exchanged water and 0.2 part of sodium dodecylbenzenesulfonate as an emulsifier and stirred sufficiently. Added with aqueous potassium. In another 5 MPa pressure vessel (B) with a stirrer, 55 parts of ion-exchanged water, 0.2 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, 2.0 parts of α-methylstyrene dimer, 1,3-butadiene An emulsion aqueous solution prepared by adding 55 parts, 42 parts of styrene, 1.5 parts of methacrylic acid and 1.5 parts of acrylic acid and stirring sufficiently was continuously dropped into the container (A) over 4 hours. . When the polymerization conversion rate reached 90%, the reaction temperature was set to 80 ° C., and the reaction was further carried out for 3 hours. Then, the reaction was stopped by cooling to obtain an aqueous dispersion containing a binder. The polymerization conversion rate was 92.1%, and adhesion of aggregates (scale) was observed on the inner wall of the reaction vessel and the stirring blade.

  Except having used the aqueous dispersion containing the said binder, operation similar to Example 1 was performed, the binder composition, the slurry composition, the negative electrode, and the half cell were produced and evaluated. The results are shown in Table 1. In the binder composition, free t-dodecyl mercaptan was not detected and was 0 ppm with respect to 100 parts by weight of the binder. Further, the content of butadiene in the binder composition was 2 ppm, and the content of styrene was 40 ppm. The processing time for stripping was 10 hours.

From the results in Table 1, the following can be said.
From 20 to 60% by weight of aliphatic conjugated diene monomer units, 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer units, and 30 to 79% by weight of other monomer units copolymerizable therewith A negative electrode with good electrolyte resistance is obtained by using a binder composition for a secondary battery negative electrode containing a binder and a binder composition for a secondary battery negative electrode containing 0.5 to 50 ppm of free alkyl mercaptan with respect to 100 parts by weight of the binder. And a secondary battery with good charge / discharge cycle characteristics can be obtained.

1 Cylindrical tank-type evaporation tank (aqueous dispersion treatment container)
2 Steam nozzle 3 Aqueous dispersion circulation pump 4 Aqueous dispersion External heat exchanger for heating 5 Aqueous dispersion circulation line (circuit)
6 Condenser 7 Condensate receiver 8 Vacuum pipe 9 Stirrer 10 Stirring blade 11 Polymer aqueous dispersion

Claims (7)

From 20 to 60% by weight of aliphatic conjugated diene monomer units, 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer units, and 30 to 79% by weight of other monomer units copolymerizable therewith And a binder composition for a negative electrode of a secondary battery containing 1.0 to 50 ppm of free alkyl mercaptan with respect to 100 parts by weight of the binder.   The said other monomer unit is an aromatic vinyl type monomer unit, The said aliphatic conjugated diene type monomer is 50 ppm or less, and the said aromatic vinyl type monomer is 1000 ppm or less. A secondary battery negative electrode binder composition.   The slurry composition for secondary battery negative electrodes formed by containing the binder composition for secondary battery negative electrodes and negative electrode active material of Claim 1 or 2.   The secondary battery negative electrode formed by apply | coating and drying the slurry composition for secondary battery negative electrodes of Claim 3 on a collector.   A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the negative electrode is a secondary battery negative electrode according to claim 4. A monomer comprising 20 to 60% by weight of an aliphatic conjugated diene monomer, 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, and 30 to 79% by weight of another monomer copolymerizable therewith. An aqueous system comprising a binder composed of a polymer obtained by polymerizing a body composition in an aqueous solvent in the presence of 0.1 to 5.0 parts by weight of an alkyl mercaptan with respect to 100 parts by weight of the monomer composition A secondary battery negative electrode comprising a step of obtaining a dispersion, and a stripping step of stripping the aqueous dispersion to bring the content of the released alkyl mercaptan to 1.0 to 50 ppm with respect to 100 parts by weight of the binder A method for producing a binder composition. The other monomer is an aromatic vinyl monomer, and the stripping step is a step of bringing the aliphatic conjugated diene monomer to 50 ppm or less and the aromatic vinyl monomer to 1000 ppm or less. The manufacturing method of the binder composition for secondary battery negative electrodes of Claim 6.

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