WO2011122261A1

WO2011122261A1 - Mixture for non-aqueous electrolyte secondary battery, electrode for same, and non-aqueous electrolyte secondary battery

Info

Publication number: WO2011122261A1
Application number: PCT/JP2011/055337
Authority: WO
Inventors: 京平萩原
Original assignee: 株式会社クレハ
Priority date: 2010-03-30
Filing date: 2011-03-08
Publication date: 2011-10-06
Also published as: CN102725889A; CN102725889B; JP5684235B2; KR101464841B1; KR20120104322A; TWI436522B; JPWO2011122261A1; TW201140924A

Abstract

An object of the present invention is to provide a mixture layer and mixture for a non-aqueous electrolyte secondary battery with excellent peeling strength from a power collector, that is highly productive in manufacturing a non-aqueous secondary battery electrode and a non-aqueous secondary battery, and suppresses mal-distribution of a binding agent in the mixture layer when manufacturing the electrode. The non-aqueous secondary battery mixture contains at least one type of unsaturated carboxylic acid polymer (A) selected from a polyacrylic acid and polymethacrylic acid, vinylidene fluoride polymer containing carboxyl (B), an electrode active material, and a weight-average molecular weight of 1,000 - 150,000 of polyethylene oxide conversion measured by GPC of the unsaturated carboxylic acid polymer (A).

Description

Nonaqueous electrolyte secondary battery mixture, nonaqueous electrolyte secondary battery electrode, and nonaqueous electrolyte secondary battery

The present invention relates to a mixture for a nonaqueous electrolyte secondary battery, an electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

In recent years, the development of electronic technology has been remarkable, and various devices have become smaller and lighter. Along with the reduction in size and weight of the electronic device, there is a demand for reduction in size and weight of the battery serving as the power source. Non-aqueous electrolyte secondary batteries using lithium are mainly used as power sources for small electronic devices used in homes such as mobile phones, personal computers, and video camcorders as batteries that can obtain large energy with a small volume and weight. ing.

Polyvinylidene fluoride (PVDF) is mainly used as a binder (binder resin) for electrodes of nonaqueous electrolyte secondary batteries. PVDF has excellent electrochemical stability, mechanical properties, slurry properties, and the like. However, PVDF has poor adhesion to a metal foil that is a current collector. Therefore, a method has been proposed in which a functional group such as a carboxyl group is introduced into PVDF to improve the adhesiveness to the metal foil (see, for example, Patent Documents 1 to 5).

By the way, when an active material having a large specific surface area is used, PVDF tends to be unevenly distributed on the electrode surface when the amount of the binder added is small and when the electrode is manufactured by rapid drying. As a result of the uneven distribution of the surface, the amount of the binder in the vicinity of the current collector is reduced, and the adhesion to the current collector is reduced. Moreover, when PVDF is unevenly distributed on the surface, the binding force between the active materials is reduced at a location where the amount of PVDF is small. Therefore, when the binder is unevenly distributed, an electrode having a low peel strength can be obtained even when PVDF having a functional group such as a carboxyl group is used.

Various methods have been proposed to suppress the uneven distribution of the binder.

A method has been proposed in which the drying condition is moderated to suppress the movement of the binder to the surface and suppress the uneven distribution of the surface (for example, see Patent Documents 6 and 7). However, in this method, since it is necessary to moderate the drying conditions, the drying speed of the mixture is lowered, and the productivity of the electrode is lowered.

By preparing a mixture with a different binder content and applying multiple layers at the same time so that a mixture with a higher binder content is applied closer to the substrate (current collector), A method for producing an electrode with a uniform distribution of an adhesive has been proposed (see, for example, Patent Document 8). However, in this method, it is necessary to prepare several kinds of mixtures, which increases the number of electrode manufacturing steps and decreases productivity. Furthermore, a special apparatus is required for multilayer coating.

After producing the electrode, a method of suppressing the uneven distribution of the binder by injecting an organic solvent capable of dissolving the binder into the electrode group and re-dissolving the binder in the electrode by performing a heat treatment in a pressure contact state. Has been proposed (see, for example, Patent Documents 9 and 10). However, this method also increases the number of steps for manufacturing the battery, which reduces battery productivity.

By the way, it is known that when PVDF and polyacrylic acid are used together as a binder, the adhesion to the current collector is improved (for example, see Patent Document 11). However, even when PVDF and polyacrylic acid are used in combination as a binder, the uneven distribution of the binder on the electrode surface cannot be suppressed, so that the adhesion to the current collector was not sufficient.

On the other hand, an electrode using only polyacrylic acid as a binder is known (see, for example, Patent Documents 12 and 13). When only polyacrylic acid is used as the binder, the higher the molecular weight, the greater the adhesion, and the use of polyacrylic acid with a weight average molecular weight of 300,000 or more improves the cycle durability of the battery. It has been known. However, when only polyacrylic acid is used as the binder, the electrode becomes hard, and in the battery manufacturing process, the electrode may break when the electrode is wound, and the yield of the battery deteriorates.

Also, it is known that when a functional group-containing PVDF and a polar polymer containing a carbonyl group are used in combination as a binder, the safety at the time of internal short circuit of the battery is improved (for example, see Patent Document 14). In Example 2 of Patent Document 14, it is described that carboxyl group-containing PVDF and polyacrylic acid are used in combination as a binder. However, in this example, cross-linked polyacrylic acid having a very large molecular weight was used as polyacrylic acid, and the peel strength of the obtained electrode was not sufficient.

Japanese Patent Application Laid-Open No. 6-172452 JP 2005-47275 A Japanese Patent Laid-Open No. 9-231977 JP 56-133309 A Japanese Patent Laid-Open No. 2004-200010 Japanese Patent Laid-Open No. 5-89871 Japanese Patent Laid-Open No. 10-32235 Japanese Patent Application Laid-Open No. 11-337772 JP 2000-268872 A JP 2004-95538 A Japanese Patent Laid-Open No. 11-45720 Japanese Patent Laying-Open No. 2005-216502 JP 2007-35434 A International Publication No. 2004/049475 Pamphlet

The present invention has been made in view of the above-mentioned problems of the prior art, and can produce a non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery with high productivity. For non-aqueous electrolyte secondary batteries that can suppress the uneven distribution of the binder in the mixture layer and has excellent peel strength between the mixture layer and the current collector when the battery electrode is manufactured The purpose is to provide a mixture. Moreover, it aims at providing the electrode for nonaqueous electrolyte secondary batteries obtained by apply | coating and drying this mixture to a collector, and the nonaqueous electrolyte secondary battery which has this electrode.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have used a specific unsaturated carboxylic acid polymer (A) and a carboxyl group-containing vinylidene fluoride polymer (B) as a binder. The present invention was completed by finding that the mixture for non-aqueous electrolyte secondary batteries used in the above could solve the above problems.

That is, the mixture for non-aqueous electrolyte secondary batteries of the present invention comprises at least one unsaturated carboxylic acid polymer (A) selected from polyacrylic acid and polymethacrylic acid, a carboxyl group-containing vinylidene fluoride polymer ( B), containing an electrode active material and an organic solvent, and having a weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of the unsaturated carboxylic acid polymer (A) is 1,000 to 150,000.

It is preferable that the weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of the unsaturated carboxylic acid polymer (A) is 1,000 to 100,000.

The unsaturated carboxylic acid polymer (A) is 0.5 to 15% by weight per 100% by weight in total of the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B). It is preferably 0.8 to 6% by weight.

The specific surface area of the electrode active material is preferably 1 to 10 m ² / g, and more preferably 2 to 6 m ² / g.

The carboxyl group-containing vinylidene fluoride polymer (B) is at least one carboxyl group-containing monomer selected from unsaturated dibasic acid, unsaturated dibasic acid monoester, acrylic acid and methacrylic acid, and vinylidene fluoride And a copolymer thereof.

The electrode for a non-aqueous electrolyte secondary battery of the present invention can be obtained by applying and drying the mixture for a non-aqueous electrolyte secondary battery on a current collector.

The nonaqueous electrolyte secondary battery electrode preferably has a mixture layer having a thickness of 20 to 150 μm formed from the nonaqueous electrolyte secondary battery mixture.

The non-aqueous electrolyte secondary battery of the present invention has the non-aqueous electrolyte secondary battery electrode.

The mixture for a non-aqueous electrolyte secondary battery of the present invention can produce a non-aqueous electrolyte secondary battery electrode and a non-aqueous electrolyte secondary battery with high productivity. When manufactured, the uneven distribution of the binder in the mixture layer can be suppressed, and the peel strength between the mixture layer and the current collector is excellent. Moreover, since the electrode for nonaqueous electrolyte secondary batteries and the nonaqueous electrolyte secondary battery of this invention are manufactured using this mixture for nonaqueous electrolyte secondary batteries, they are manufactured with high productivity.

Next, the present invention will be specifically described.

The mixture for a non-aqueous electrolyte secondary battery of the present invention comprises at least one unsaturated carboxylic acid polymer (A) selected from polyacrylic acid and polymethacrylic acid, and a carboxyl group-containing vinylidene fluoride polymer (B). A weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of the unsaturated carboxylic acid polymer (A) is 1,000 to 150, 000. The mixture of the present invention is usually used as a negative electrode mixture, that is, a negative electrode mixture.

[Unsaturated carboxylic acid polymer (A)]
The mixture for nonaqueous electrolyte secondary batteries of the present invention contains at least one unsaturated carboxylic acid polymer (A) selected from polyacrylic acid and polymethacrylic acid. As the unsaturated carboxylic acid polymer (A), a polymer having a polyethylene oxide equivalent weight average molecular weight of 1,000 to 150,000 measured by gel permeation chromatography (GPC) is used.

The unsaturated carboxylic acid polymer (A) contained in the nonaqueous electrolyte secondary battery of the present invention may be polyacrylic acid, polymethacrylic acid, or polyacrylic acid and polymethacrylic acid. It may be a mixture. The unsaturated carboxylic acid polymer (A) used in the present invention may be used alone or in combination of two or more. As the unsaturated carboxylic acid polymer (A), polyacrylic acid is preferable from the viewpoint of availability.

Examples of the polyacrylic acid include a homopolymer of acrylic acid and a copolymer of acrylic acid and other monomers. As polyacrylic acid, a polymer having, in 100% by weight of the polymer, a structural unit derived from acrylic acid is usually 60% by weight or more, preferably 75% by weight or more, more preferably 90% by weight or more. As the polyacrylic acid, a homopolymer of acrylic acid is preferable.

As the monomer other than acrylic acid, a monomer that can be copolymerized with acrylic acid can be used. Specifically, other monomers include: methacrylic acid; α-olefins such as ethylene, propylene, and 1-butene; acrylic acid alkyl esters such as methyl acrylate and ethyl acrylate; methyl methacrylate, ethyl methacrylate, and the like Examples thereof include alkyl methacrylates; vinyl acetate; aromatic vinyl compounds such as styrene.

Examples of polymethacrylic acid include a homopolymer of methacrylic acid and a copolymer of methacrylic acid and other monomers. As polymethacrylic acid, a polymer having a structural unit derived from methacrylic acid in an amount of usually 60% by weight or more, preferably 75% by weight or more, more preferably 90% by weight or more in 100% by weight of the polymer is used. As the polymethacrylic acid, a homopolymer of methacrylic acid is preferable.

As other monomers other than methacrylic acid, monomers capable of copolymerizing with methacrylic acid can be used. Specifically, the other monomers include acrylic acid; α-olefins such as ethylene, propylene, and 1-butene; acrylic acid alkyl esters such as methyl acrylate and ethyl acrylate; methyl methacrylate, ethyl methacrylate, and the like. Examples thereof include alkyl methacrylates; vinyl acetate; aromatic vinyl compounds such as styrene.

The unsaturated carboxylic acid polymer (A) used in the present invention preferably contains 8 × 10 ⁻³ to 1.4 × 10 ⁻² mol / g of carboxyl groups.

As described above, the unsaturated carboxylic acid polymer (A) used in the present invention has a weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of 1,000 to 150,000. A polymer is used. The weight average molecular weight of the unsaturated carboxylic acid polymer (A) is preferably 1,000 to 100,000. When the weight average molecular weight is less than 1,000, the electrolyte solution resistance of the unsaturated carboxylic acid polymer (A) is insufficient. On the other hand, when the molecular weight exceeds 150,000, the compatibility between the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B) is inferior, and thus the peel strength is not improved. .

As the unsaturated carboxylic acid polymer (A) used in the present invention, a part of the carboxyl group may be neutralized.

Commercially available products may be used as the unsaturated carboxylic acid polymer (A) used in the present invention.

[Carboxyl group-containing vinylidene fluoride polymer (B)]
The mixture for nonaqueous electrolyte secondary batteries of the present invention contains a carboxyl group-containing vinylidene fluoride polymer (B) and the aforementioned unsaturated carboxylic acid polymer (A) as a binder resin (binder).

In the present invention, the carboxyl group-containing vinylidene fluoride polymer (B) is a polymer containing a carboxyl group in a polymer and obtained using at least vinylidene fluoride as a monomer. The carboxyl group-containing vinylidene fluoride polymer (B) is a polymer that is usually obtained using vinylidene fluoride and a carboxyl group-containing monomer, and other monomers may be used.

Moreover, the carboxyl group-containing vinylidene fluoride polymer (B) used in the present invention may be used alone or in combination of two or more.

The carboxyl group-containing vinylidene fluoride polymer (B) is a polymer having usually 80 parts by weight or more, preferably 85 parts by weight or more of structural units derived from vinylidene fluoride per 100 parts by weight of the polymer.

The carboxyl group-containing vinylidene fluoride polymer (B) used in the present invention is usually (1) a method of copolymerizing vinylidene fluoride and a carboxyl group-containing monomer and, if necessary, another monomer (hereinafter referred to as (1) And (2) polymerizing vinylidene fluoride or copolymerizing vinylidene fluoride and other monomers, polymerizing vinylidene fluoride polymer and carboxyl group-containing monomer, or carboxyl A method of grafting a carboxyl group-containing polymer onto a vinylidene fluoride polymer using a carboxyl group-containing polymer obtained by copolymerizing a group-containing monomer and another monomer (hereinafter referred to as (2) (3) Polymerization of vinylidene fluoride or copolymerization of vinylidene fluoride and other monomers to produce a vinylidene fluoride polymer After the, the vinylidene fluoride-based polymer, a method of graft-polymerization using a carboxyl group-containing monomers such as acrylic acid is produced by any method (hereinafter, (3) referred to as method).

Since the carboxyl group-containing vinylidene fluoride polymer (B) used in the present invention has a carboxyl group, the adhesion to the current collector is improved as compared with polyvinylidene fluoride not having a carboxyl group. The carboxyl group-containing vinylidene fluoride polymer (B) has an electrolytic solution resistance equivalent to that of polyvinylidene fluoride having no carboxyl group.

As the method for producing the carboxyl group-containing vinylidene fluoride polymer (B), among the methods (1) to (3), the method (1) is used from the viewpoint of the number of steps and production cost. Is preferred. That is, the carboxyl group-containing vinylidene fluoride polymer (B) is preferably a copolymer of vinylidene fluoride and a carboxyl group-containing monomer.

The carboxyl group-containing vinylidene fluoride polymer (B) used in the present invention is usually 80 to 99.9 parts by weight of vinylidene fluoride, preferably 95 to 99.7 parts by weight, and a carboxyl group-containing monomer. Usually 0.1 to 20 parts by weight, preferably 0.3 to 5 parts by weight (provided that the total of vinylidene fluoride and carboxyl group-containing monomers is 100 parts by weight) copolymerized vinylidene fluoride based weight It is a coalescence. The carboxyl group-containing vinylidene fluoride polymer (B) may be a polymer obtained by copolymerizing another monomer in addition to the vinylidene fluoride and the carboxyl group-containing monomer. When other monomers are used, the other monomers are usually used in an amount of 0.1 to 20 parts by weight, assuming that the total of the vinylidene fluoride and carboxyl group-containing monomers is 100 parts by weight.

As the carboxyl group-containing monomer, unsaturated monobasic acid, unsaturated dibasic acid, monoester of unsaturated dibasic acid and the like are preferable.

Examples of the unsaturated monobasic acid include acrylic acid and methacrylic acid. Examples of the unsaturated dibasic acid include maleic acid and citraconic acid. The unsaturated dibasic acid monoester preferably has 5 to 8 carbon atoms, and examples thereof include maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester. Can do.

Among them, the carboxyl group-containing monomer is preferably at least one monomer selected from unsaturated dibasic acid, unsaturated dibasic acid monoester, acrylic acid and methacrylic acid, maleic acid, citraconic acid, maleic acid monomethyl ester, Citraconic acid monomethyl ester, acrylic acid and methacrylic acid are more preferred.

The other monomer that can be copolymerized with the vinylidene fluoride and the carboxyl group-containing monomer means a monomer other than the vinylidene fluoride and the carboxyl group-containing monomer, and examples of the other monomer include a copolymer with vinylidene fluoride. Examples thereof include polymerizable fluorine monomers and hydrocarbon monomers such as ethylene and propylene. Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include perfluoroalkyl vinyl ethers typified by vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and perfluoromethyl vinyl ether. . In addition, the said other monomer may be used individually by 1 type, and may use 2 or more types.

As the method (1), methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be employed. From the viewpoint of ease of post-treatment, aqueous suspension polymerization and emulsion polymerization are preferred, and aqueous suspension is preferred. Turbid polymerization is particularly preferred.

In suspension polymerization using water as a dispersion medium, all monomers used for copolymerization with suspension agents such as methylcellulose, methoxymethylcellulose, propoxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl alcohol, polyethylene oxide, and gelatin (Vinylidene fluoride and a carboxyl group-containing monomer, and other monomers copolymerized as necessary) 0.005 to 1.0 part by weight, preferably 0.01 to 0.4 part by weight based on 100 parts by weight Add in the range of.

As the polymerization initiator, diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, diisopropyl peroxydicarbonate, isobutyryl peroxide, di (chlorofluoroacyl) peroxide, Di (perfluoroacyl) peroxide and the like can be used. The amount used is 0.1 to 5 parts by weight, assuming that 100 parts by weight of all monomers used for copolymerization (vinylidene fluoride and carboxyl group-containing monomers, and other monomers copolymerized as necessary) The amount is preferably 0.3 to 2 parts by weight.

Also, a carboxyl group-containing vinylidene fluoride system obtained by adding a chain transfer agent such as ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propyl aldehyde, ethyl propionate, carbon tetrachloride, etc. It is also possible to adjust the degree of polymerization of the polymer (B). The amount used is usually 0.1 to 5 when 100 parts by weight of all monomers used for copolymerization (vinylidene fluoride, carboxyl group-containing monomers, and other monomers copolymerized as necessary) are used. Part by weight, preferably 0.5 to 3 parts by weight.

The total amount of monomers used for copolymerization (vinylidene fluoride and carboxyl group-containing monomers, and other monomers copolymerized as necessary) is usually in the weight ratio of the total monomer: water. The ratio is 1: 1 to 1:10, preferably 1: 2 to 1: 5, the polymerization is at a temperature of 10 to 80 ° C., the polymerization time is 10 to 100 hours, and the polymerization pressure is usually carried out under pressure. Preferably, it is 2.0 to 8.0 MPa-G.

By performing aqueous suspension polymerization under the above conditions, it is possible to easily copolymerize vinylidene fluoride, a carboxyl group-containing monomer, and other monomers copolymerized as necessary. A group-containing vinylidene fluoride polymer (B) can be obtained.

Further, when the carboxyl group-containing vinylidene fluoride polymer (B) is produced by the method (2), for example, the following method can be used.

When the carboxyl group-containing vinylidene fluoride polymer (B) is produced by the method (2), first, vinylidene fluoride is polymerized or vinylidene fluoride is copolymerized with another monomer to obtain vinylidene fluoride. A polymer is obtained. The polymerization or copolymerization is usually performed by suspension polymerization or emulsion polymerization. In addition to the vinylidene fluoride polymer, a carboxyl group-containing polymer is obtained by polymerizing a carboxyl group-containing monomer or copolymerizing a carboxyl group-containing monomer and another monomer. The carboxyl group-containing polymer is usually obtained by emulsion polymerization or suspension polymerization. Further, the carboxyl group-containing vinylidene fluoride polymer (B) is obtained by grafting the carboxyl group-containing polymer onto the vinylidene fluoride polymer using the vinylidene fluoride polymer and the carboxyl group-containing polymer. be able to. The grafting may be performed using a peroxide or may be performed using radiation. Preferably, a mixture of a vinylidene fluoride polymer and a carboxyl group-containing polymer is heated in the presence of a peroxide. It is done by processing.

The carboxyl group-containing vinylidene fluoride polymer (B) used in the present invention has an inherent viscosity (logarithmic viscosity at 30 ° C. of a solution obtained by dissolving 4 g of resin in 1 liter of N, N-dimethylformamide. The same applies hereinafter). A value in the range of 0.5 to 5.0 dl / g is preferable, and a value in the range of 1.1 to 4.0 dl / g is more preferable. If it is a viscosity within the said range, it can use suitably for the mixture for nonaqueous electrolyte secondary batteries.

The inherent viscosity η _i is calculated by dissolving 80 mg of the carboxyl group-containing vinylidene fluoride polymer (B) in 20 ml of N, N-dimethylformamide and using an Ubbelote viscometer in a constant temperature bath at 30 ° C. Can be performed.

η _i = (1 / C) · ln (η / η ₀ )
Where η is the viscosity of the polymer solution, η ₀ is the viscosity of the solvent N, N-dimethylformamide alone, and C is 0.4 g / dl.

In addition, the carboxyl group-containing vinylidene fluoride polymer (B) has a polystyrene-equivalent weight average molecular weight measured by GPC usually in the range of 50,000 to 2,000,000, preferably in the range of 200,000 to 1,500,000. It is.

The carboxyl group-containing vinylidene fluoride polymer (B) has an absorbance ratio (I _R ) represented by the following formula (1) when an infrared absorption spectrum is measured, in the range of 0.1 to 5.0. Preferably, it is 0.3 to 2.5. If I _R is less than 0.1, there is a case where adhesion between the current collector becomes insufficient. On the other hand, if I _R exceeds 5.0, electrolyte resistance of the resulting polymer tends to decrease. In addition, the measurement of the infrared absorption spectrum of this polymer is performed by measuring an infrared absorption spectrum about the film manufactured by hot-pressing this polymer.

I _R = I _1650-1800 / I _3000-3100 (1)
In the above formula (1), I _1650-1800 is the absorbance from the carbonyl group which is detected in the range of 1650 ~ 1800cm ^-1, I _3000-3100 are derived from CH structures detected in the range of 3000 ~ 3100 cm ^-1 Absorbance. I _R becomes a measure of the abundance of the carbonyl group in the carboxyl group-containing vinylidene fluoride-based polymer (B), a measure of the abundance of the resulting carboxyl group.

[Electrode active material]
The mixture for nonaqueous electrolyte secondary batteries of the present invention contains an electrode active material. The electrode active material is not particularly limited, and conventionally known electrode active materials for negative electrodes can be used, and specific examples include carbon materials, metal / alloy materials, metal oxides, etc. Material is preferred.

As the carbon material, artificial graphite, natural graphite, non-graphitizable carbon, graphitizable carbon, or the like is used. Moreover, the said carbon material may be used individually by 1 type, or may use 2 or more types.

When such a carbon material is used, the energy density of the battery can be increased.

The artificial graphite can be obtained, for example, by carbonizing an organic material, heat-treating it at a high temperature, pulverizing and classifying it. As the artificial graphite, MAG series (manufactured by Hitachi Chemical Co., Ltd.), MCMB (manufactured by Osaka Gas) and the like are used.

The specific surface area of the electrode active material is preferably 1 to 10 m ² / g, and more preferably 2 to 6 m ² / g. When the specific surface area is less than 1 m ² / g, even when a conventional binder is used, the uneven distribution of the binder is unlikely to occur, so the effect of the present invention is small. If the specific surface area exceeds 10 m ² / g, the amount of decomposition of the electrolytic solution increases and the initial irreversible capacity increases, which is not preferable.

The specific surface area of the electrode active material can be determined by a nitrogen adsorption method.

〔Organic solvent〕
The mixture for nonaqueous electrolyte secondary batteries of the present invention contains an organic solvent. As the organic solvent, those having an action of dissolving the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B) are used, and a solvent having polarity is preferably used. Specific examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate. And N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethyl sulfoxide are preferable. Moreover, the organic solvent may be used alone or in combination of two or more.

The non-aqueous electrolyte secondary battery mixture of the present invention contains the unsaturated carboxylic acid polymer (A), a carboxyl group-containing vinylidene fluoride polymer (B), an electrode active material, and an organic solvent.

The mixture for a non-aqueous electrolyte secondary battery of the present invention includes an unsaturated carboxylic acid polymer (A) and a carboxyl group-containing vinylidene fluoride polymer (B), but the unsaturated carboxylic acid polymer (A) and The unsaturated carboxylic acid polymer (A) is preferably 0.5 to 15% by weight, preferably 0.8 to 6% by weight, per 100% by weight of the total of the carboxyl group-containing vinylidene fluoride polymer (B). More preferably. In addition, the binder resin is 0.5 to 15 weights per 100 parts by weight in total of the binder resin (unsaturated carboxylic acid polymer (A) and carboxyl group-containing vinylidene fluoride polymer (B)) and the electrode active material. Parts, preferably 1 to 10 parts by weight, and the active material is preferably 85 to 99.5 parts by weight, and more preferably 90 to 99 parts by weight. Further, when the total of the binder resin (unsaturated carboxylic acid polymer (A) and carboxyl group-containing vinylidene fluoride polymer (B)) and the electrode active material is 100 parts by weight, the organic solvent is 20 to 300 weights. Parts, preferably 50 to 200 parts by weight.

When each component is contained within the above range, it is possible to produce a nonaqueous electrolyte secondary battery electrode with high productivity using the nonaqueous electrolyte secondary battery mixture of the present invention. When the secondary battery electrode is produced, the uneven distribution of the binder in the mixture layer can be sufficiently suppressed, and the peel strength between the mixture layer and the current collector is excellent.

The mixture for a non-aqueous electrolyte secondary battery of the present invention is other than the unsaturated carboxylic acid polymer (A), the carboxyl group-containing vinylidene fluoride polymer (B), the electrode active material, and the organic solvent. The component may be contained. As other components, a conductive aid such as carbon black, a pigment dispersant such as polyvinylpyrrolidone, and the like may be included. As said other component, polymers other than the said unsaturated carboxylic acid polymer (A) and a carboxyl group-containing vinylidene fluoride polymer (B) may be included. Examples of the other polymer include fluorides such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, and vinylidene fluoride-perfluoromethyl vinyl ether copolymer. Examples include vinylidene polymers. When the non-aqueous electrolyte secondary battery mixture of the present invention contains other polymers, the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B) are usually used. It is contained in an amount of 25 parts by weight or less with respect to a total of 100 parts by weight.

The viscosity of the mixture for a non-aqueous electrolyte secondary battery of the present invention when measured with an E-type viscometer at 25 ° C. and a shear rate of 2 s ⁻¹ is usually 2000 to 50000 mPa · s, preferably Is 5000 to 30000 mPa · s.

The method for producing the mixture for a non-aqueous electrolyte secondary battery of the present invention includes the unsaturated carboxylic acid polymer (A), the carboxyl group-containing vinylidene fluoride polymer (B), the electrode active material, and the organic solvent. What is necessary is just to mix so that it may become a uniform slurry, and the order at the time of mixing is not specifically limited, For example, the said unsaturated carboxylic acid polymer (A) and a carboxyl group-containing vinylidene fluoride polymer (B), Dissolving in a part of the organic solvent to obtain a binder solution, adding the electrode active material and the remaining organic solvent to the binder solution, mixing by stirring, and obtaining a mixture for a non-aqueous electrolyte secondary battery, The saturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B) are each dissolved in a part of an organic solvent to obtain two binder solutions. Ndoshi, was added blended binder solution in the electrode active material and the remaining organic solvent, stirring and mixing, a method may be mentioned of obtaining a nonaqueous electrolyte secondary battery mixture.

[Electrode for non-aqueous electrolyte secondary battery]
The electrode for a non-aqueous electrolyte secondary battery of the present invention is obtained by applying and drying the mixture for a non-aqueous electrolyte secondary battery on a current collector, and the current collector and for the non-aqueous electrolyte secondary battery And a layer formed from a mixture. The electrode for a nonaqueous electrolyte secondary battery of the present invention is usually used as a negative electrode.

In the present invention, a layer formed from a mixture for a nonaqueous electrolyte secondary battery, which is formed by applying and drying a mixture for a nonaqueous electrolyte secondary battery on a current collector, a mixture layer I write.

The current collector used in the present invention includes, for example, copper, and the shape thereof includes, for example, a metal foil, a metal net, and the like. As the current collector, a copper foil is preferable.

The thickness of the current collector is usually 5 to 100 μm, preferably 5 to 20 μm.

Further, the thickness of the mixture layer is usually 20 to 250 μm, preferably 20 to 150 μm.

When producing the electrode for nonaqueous electrolyte secondary battery of the present invention, the mixture for nonaqueous electrolyte secondary battery is applied to at least one surface, preferably both surfaces of the current collector. The method for coating is not particularly limited, and examples thereof include a method using a bar coater, a die coater, or a comma coater.

Further, the drying performed after the coating is usually performed at a temperature of 50 to 150 ° C. for 1 to 300 minutes. Moreover, the pressure at the time of drying is not particularly limited, but it is usually carried out under atmospheric pressure or reduced pressure.

Furthermore, heat treatment may be performed after drying. When heat treatment is performed, it is usually performed at a temperature of 100 to 250 ° C. for 1 to 300 minutes. In addition, although the temperature of heat processing overlaps with the said drying, these processes may be a separate process and the process performed continuously.

Further, press processing may be performed. When the pressing process is performed, it is normally performed at 1 to 200 MP-G. It is preferable to perform the press treatment because the electrode density can be improved.

By the above method, the electrode for nonaqueous electrolyte secondary batteries of the present invention can be produced. In addition, as a layer structure of the electrode for nonaqueous electrolyte secondary batteries, when the mixture for nonaqueous electrolyte secondary batteries is applied to one surface of the current collector, the layer structure of the mixture layer / current collector is Yes, when the mixture for a non-aqueous electrolyte secondary battery is applied on both sides of the current collector, it has a three-layer structure of a mixture layer / current collector / mixture layer.

The electrode for a non-aqueous electrolyte secondary battery of the present invention is excellent in peel strength between the current collector and the mixture layer by using the mixture for a non-aqueous electrolyte secondary battery, so that press, slit, winding, etc. In this process, cracks and peeling are unlikely to occur in the electrode, which is preferable because it leads to an improvement in productivity.

The electrode for a non-aqueous electrolyte secondary battery of the present invention is excellent in the peel strength between the current collector and the mixture layer as described above. Specifically, the peel strength between the current collector and the mixture layer is According to JIS K6854, it is usually 0.5 to 20 gf / mm, preferably 1 to 10 gf / mm when measured by a 180 ° peel test.

The electrode for a non-aqueous electrolyte secondary battery of the present invention has a mixture layer formed from the mixture for the non-aqueous electrolyte secondary battery, and the mixture layer suppresses uneven distribution of the binder. ing. Therefore, the peel strength between the current collector and the mixture layer is excellent.

[Nonaqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention is characterized by having the non-aqueous electrolyte secondary battery electrode.

The nonaqueous electrolyte secondary battery of the present invention is not particularly limited except that it has the electrode for nonaqueous electrolyte secondary battery. As the nonaqueous electrolyte secondary battery, the electrode for a nonaqueous electrolyte secondary battery is usually used as a negative electrode, and conventionally known ones other than the negative electrode, such as a positive electrode and a separator, can be used.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[Production Example 1] (Production of carboxyl group-containing vinylidene fluoride polymer (1))
An autoclave having an internal volume of 2 liters was charged with 1040 g of ion-exchanged water, 0.8 g of methylcellulose, 3.0 g of diisopropyl peroxydicarbonate, 396 g of vinylidene fluoride and 4.0 g of maleic acid monomethyl ester, and suspension polymerization at 28 ° C. for 45 hours. I did it. The maximum pressure during this period reached 4.1 MPa. After completion of the polymerization, the polymer slurry was dehydrated and washed with water. Then, it dried at 80 degreeC for 20 hours, and obtained the powdery carboxyl group containing vinylidene fluoride polymer (1) (polymer (1)). The weight average molecular weight of the polymer (1) is 500,000, the inherent viscosity is 1.7 dl / g, and I _R (= I _1650-1800 / I _3000-3100 ) ( _{note that} the absorbance derived from the carbonyl group is ₁₇₅₀ cm). ^-1 and the absorbance derived from the CH structure was observed at 3025 cm ^-1 ).

[Production Example 2] (Production of polyvinylidene fluoride)
An autoclave with an internal volume of 2 liters was charged with 1075 g of ion-exchanged water, 0.4 g of methylcellulose, 2.5 g of dinormalpropyl peroxydicarbonate, 5 g of ethyl acetate, and 420 g of vinylidene fluoride, and subjected to suspension polymerization at 25 ° C. for 14 hours. It was. The maximum pressure during this period reached 4.0 MPa. After completion of the polymerization, the polymer slurry was dehydrated and washed with water. Then, it dried at 80 degreeC for 20 hours, and obtained the powdery polyvinylidene fluoride (PVDF). PVDF had a weight average molecular weight of 500,000 and an inherent viscosity of 1.7 dl / g.

[Measurement of weight average molecular weight of carboxyl group-containing vinylidene fluoride polymer (1) and polyvinylidene fluoride]
The weight average molecular weight in terms of polystyrene of the carboxyl group-containing vinylidene fluoride polymer (1) and polyvinylidene fluoride was measured by gel permeation chromatography (GPC).

For the measurement, Shodex KD-806M (made by Showa Denko KK) is used for the separation column, RI-930 (differential refractive index detector) made by JASCO Corporation is used for the detector, and the flow rate of the eluent is 1 mL. / Min and column temperature of 40 ° C.

In the measurement, a LiBr-NMP solution having a concentration of 10 mM was used as the eluent, and TSK standard POLY (STYRENE) (standard polystyrene) (manufactured by Tosoh Corporation) was used as the standard polymer for the calibration curve.

[Measurement of weight average molecular weight of polyacrylic acid]
The weight average molecular weight in terms of polyethylene oxide of the polyacrylic acid used in Examples and Comparative Examples was measured by gel permeation chromatography (GPC).

For the measurement, Shodex Asahipak GF-7M HQ (made by Showa Denko KK) was used for the separation column, and RID-6A (differential refractive index detector) made by Shimadzu Corporation was used for the detector. The measurement was performed under conditions of a flow rate of 0.6 mL / min and a column temperature of 40 ° C.

In the measurement, Na ₂ HPO ₄ / CH ₃ CN = 90/10 (weight ratio) was used as the eluent, and TSK standard POLY (ETHYLENE OXIDE) (standard polyethylene oxide) (Tosoh Corporation) was used as the standard polymer for the calibration curve. Used).

[Specific surface area measurement of active material]
The specific surface area of the active material was measured by a nitrogen adsorption method.

Using an approximate expression derived from the BET equation: Vm = 1 / (v (1-x)), Vm is determined by a one-point method by nitrogen adsorption (relative pressure x = 0.3) at liquid nitrogen temperature. The specific surface area of the sample (active material) was calculated by the following formula.

Specific surface area [m ² /g]=4.35×Vm
Here, Vm is an adsorption amount (cm ³ / g) necessary for forming a monomolecular layer on the sample surface, v is an actually measured adsorption amount (cm ³ / g), and x is a relative pressure.

Specifically, using a “Flow Sorb II2300” manufactured by MICROMETRITICS, the adsorption amount (v) of nitrogen on the active material at the liquid nitrogen temperature was measured as follows. The sample tube is filled with the active material, and while flowing a helium gas containing nitrogen gas at a concentration of 20 mol%, the sample tube is cooled to −196 ° C. to adsorb nitrogen to the active material. The test tube is then returned to room temperature. At this time, the amount of nitrogen desorbed from the sample was measured with a thermal conductivity detector, and was defined as the adsorption amount (v).

[Example 1]
(Preparation of non-aqueous electrolyte secondary battery mixture)
9.9 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.1 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (1). 8 g of the obtained binder solution (1), artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG, average particle size 20 μm, specific surface area 4.2 m ² / g) 9.2 g, and N-methyl-2 for adjusting the viscosity of the mixture -5.8 g of pyrrolidone was stirred and mixed to obtain a nonaqueous electrolyte secondary battery mixture (1). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (1) was 12000 mPa · s.

(Production of electrodes)
A non-aqueous electrolyte secondary battery mixture (1) obtained by using a spacer and a bar coater so as to have a basis weight after drying of 150 g / m ² was used as a current collector of copper having a thickness of 10 μm. It was applied on the foil. After drying at 110 ° C. in a nitrogen atmosphere, heat treatment was performed at 130 ° C. Subsequently, pressing is performed at 40 MPa, and the electrode layer for nonaqueous electrolyte secondary battery (1) having a bulk density of 1.6 g / cm ³ of the mixture layer formed from the mixture for nonaqueous electrolyte secondary battery (1). Got. The thickness of the mixture layer was calculated by subtracting the thickness of the current collector from the thickness of the electrode.

[Comparative Example 1]
10.0 g of the carboxyl group-containing vinylidene fluoride polymer (1) was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c1). Except having used this binder solution (c1), it carried out similarly to Example 1 and obtained the mixture for nonaqueous electrolyte secondary batteries (c1) and the electrode for nonaqueous electrolyte secondary batteries (c1). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c1) was 12000 mPa · s.

[Example 2]
9.75 g of a carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.25 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (2). Except having used this binder solution (2), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (2) and the electrode for nonaqueous electrolyte secondary batteries (2) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (2) was 11800 mPa · s.

Example 3
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (3). Except having used this binder solution (3), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (3) and the electrode for nonaqueous electrolyte secondary batteries (3) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (3) was 11500 mPa · s.

Example 4
9.0 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 1.0 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (4). Except having used this binder solution (4), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (4) and the electrode for nonaqueous electrolyte secondary batteries (4) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (4) was 11500 mPa · s.

Example 5
8.7 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 1.3 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (5). Except having used this binder solution (5), it carried out similarly to Example 1 and obtained the mixture (5) for nonaqueous electrolyte secondary batteries, and the electrode (5) for nonaqueous electrolyte secondary batteries. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (5) was 11000 mPa · s.

[Comparative Example 2]
10.0 g of PVDF was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c2). Except having used this binder solution (c2), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c2) and the electrode for nonaqueous electrolyte secondary batteries (c2) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c2) was 12500 mPa · s.

[Comparative Example 3]
9.9 g of PVDF and 0.1 g of polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) were added to N-methyl-2-pyrrolidone. Dissolved in 90 g, a 10% by weight binder solution (c3) was obtained. Except having used this binder solution (c3), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c3) and the electrode for nonaqueous electrolyte secondary batteries (c3) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c3) was 12500 mPa · s.

[Comparative Example 4]
9.75 g of PVDF, 0.25 g of polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g), N-methyl-2-pyrrolidone Dissolved in 90 g, a 10 wt% binder solution (c4) was obtained. Except having used this binder solution (c4), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c4) and the electrode for nonaqueous electrolyte secondary batteries (c4) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c4) was 12000 mPa · s.

[Comparative Example 5]
9.5 g of PVDF and 0.5 g of polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) are mixed with N-methyl-2-pyrrolidone. Dissolved in 90 g, a 10 wt% binder solution (c5) was obtained. Except having used this binder solution (c5), it carried out similarly to Example 1 and obtained the mixture for nonaqueous electrolyte secondary batteries (c5) and the electrode for nonaqueous electrolyte secondary batteries (c5). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c5) was 11800 mPa · s.

[Comparative Example 6]
9.0 g of PVDF and 1.0 g of polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) were added to N-methyl-2-pyrrolidone. Dissolved in 90 g, a 10% by weight binder solution (c6) was obtained. Except having used this binder solution (c6), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c6) and the electrode for nonaqueous electrolyte secondary batteries (c6) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c6) was 11500 mPa · s.

[Comparative Example 7]
9.75 g of carboxyl group-containing vinylidene fluoride polymer (1) and cross-linked polyacrylic acid (trade name “AQUPEC HV-501”, manufactured by Sumitomo Seika Co., Ltd., carboxyl group content: 1.3 × 10 ⁻² mol) / G) 0.25 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c7). Except having used this binder solution (c7), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c7) and the electrode for nonaqueous electrolyte secondary batteries (c7) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c7) was 13000 mPa · s.

[Comparative Example 8]
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and cross-linked polyacrylic acid (trade name “AQUPEC HV-501”, manufactured by Sumitomo Seika Co., Ltd., carboxyl group content: 1.3 × 10 ⁻² mol) / G) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c8). Except having used this binder solution (c8), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c8) and the electrode for nonaqueous electrolyte secondary batteries (c8) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c8) was 13500 mPa · s.

[Comparative Example 9]
9.2 g of carboxyl group-containing vinylidene fluoride polymer (1) and cross-linked polyacrylic acid (trade name “AQUPEC HV-501”, manufactured by Sumitomo Seika Co., Ltd., carboxyl group content: 1.3 × 10 ⁻² mol) / G) 0.8 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c9). Except having used this binder solution (c9), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c9) and the electrode for nonaqueous electrolyte secondary batteries (c9) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c9) was 14000 mPa · s.

Example 6
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 15,000 (trade name “Julimer AC-10P”, manufactured by Nippon Pure Chemical Co., Ltd., carboxyl group amount: 1. (4 × 10 ⁻² mol / g) (0.5 g) was dissolved in N-methyl-2-pyrrolidone (90 g) to obtain a 10 wt% binder solution (6). Except having used this binder solution (6), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (6) and the electrode for nonaqueous electrolyte secondary batteries (6) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (6) was 12000 mPa · s.

Example 7
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 25,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (7). Except having used this binder solution (7), it carried out similarly to Example 1 and obtained the mixture (7) for nonaqueous electrolyte secondary batteries, and the electrode (7) for nonaqueous electrolyte secondary batteries. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (7) was 12300 mPa · s.

Example 8
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 73,000 (trade name “Julimer AC-10LP”, manufactured by Nippon Pure Chemical Co., Ltd., carboxyl group amount: 1. (4 × 10 ⁻² mol / g) (0.5 g) was dissolved in N-methyl-2-pyrrolidone (90 g) to obtain a 10 wt% binder solution (8). Except having used this binder solution (8), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (8) and the electrode for nonaqueous electrolyte secondary batteries (8) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (8) was 12500 mPa · s.

[Comparative Example 10]
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 250,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c10). Except having used this binder solution (c10), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c10) and the electrode for nonaqueous electrolyte secondary batteries (c10) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c10) was 13000 mPa · s.

[Comparative Example 11]
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 800,000 (trade name “AQUALIC”, manufactured by Nippon Shokubai Co., Ltd., carboxyl group amount: 1.4 × 10 ^-2 mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c11). Except having used this binder solution (c11), it carried out like Example 1 and the mixture for nonaqueous electrolyte secondary batteries (c11) and the electrode for nonaqueous electrolyte secondary batteries (c11) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c11) was 13000 mPa · s.

[Comparative Example 12]
10.0 g of polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) was dissolved in 90 g of N-methyl-2-pyrrolidone, A 10% by weight binder solution (c12) was obtained. The same procedure as in Example 1 was conducted except that the binder solution (c12) was used and that N-methyl-2-pyrrolidone for adjusting the viscosity of the mixture was changed to 3 g, and a mixture for a nonaqueous electrolyte secondary battery ( c12) and a non-aqueous electrolyte secondary battery electrode (c12) were obtained. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c12) was 8500 mPa · s.

[Comparative Example 13]
10.0 g of the carboxyl group-containing vinylidene fluoride polymer (1) was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c13). 4 g of the obtained binder solution (c13), artificial graphite (manufactured by Osaka Gas, MCMB, average particle size 6.5 μm, specific surface area 2.9 m ² / g), 9.6 g, and N-methyl for adjusting the mixture viscosity 7.0 g of 2-pyrrolidone was stirred and mixed to obtain a nonaqueous electrolyte secondary battery mixture (c13).

The same procedure as in Example 1 was performed except that the nonaqueous electrolyte secondary battery mixture (c13) was used to obtain a nonaqueous electrolyte secondary battery electrode (c13). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c13) was 13500 mPa · s.

Example 9
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (9). 4 g of the obtained binder solution (9), artificial graphite (manufactured by Osaka Gas Co., Ltd., MCMB, average particle size 6.5 μm, specific surface area 2.9 m ² / g) 9.6 g, and N— 7.0 g of methyl-2-pyrrolidone was mixed with stirring to obtain a mixture (9) for a nonaqueous electrolyte secondary battery. The viscosity of the mixture for nonaqueous electrolyte secondary batteries (9) was 13000 mPa · s.

The same procedure as in Example 1 was performed except that the non-aqueous electrolyte secondary battery mixture (9) was used to obtain a non-aqueous electrolyte secondary battery electrode (9).

[Comparative Example 14]
10.0 g of the carboxyl group-containing vinylidene fluoride polymer (1) was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (c14). 8 g of the obtained binder solution (c14), 9.2 g of spherical natural graphite (produced in China, average particle size 24 μm, specific surface area 5.4 m ^{2 /} g), and N-methyl-2-pyrrolidone 5 for adjusting the mixture viscosity .8 g was mixed with stirring to obtain a nonaqueous electrolyte secondary battery mixture (c14). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (c14) was 13000 mPa · s.

The same procedure as in Example 1 was performed except that the nonaqueous electrolyte secondary battery mixture (c14) was used to obtain a nonaqueous electrolyte secondary battery electrode (c14).

Example 10
9.5 g of carboxyl group-containing vinylidene fluoride polymer (1) and polyacrylic acid having a weight average molecular weight of 5,000 (manufactured by Wako Pure Chemical Industries, Ltd., carboxyl group amount: 1.4 × 10 ⁻² mol / g) 0.5 g was dissolved in 90 g of N-methyl-2-pyrrolidone to obtain a 10 wt% binder solution (10). 8 g of the obtained binder solution (10), 9.2 g of spherical natural graphite (produced in China, average particle size 24 μm, specific surface area 5.4 m ^{2 /} g), and N-methyl-2-pyrrolidone 5 for adjusting the mixture viscosity .8 g was mixed by stirring to obtain a nonaqueous electrolyte secondary battery mixture (10). The viscosity of the mixture for nonaqueous electrolyte secondary batteries (10) was 13000 mPa · s.

The same procedure as in Example 1 was performed except that the non-aqueous electrolyte secondary battery mixture (10) was used to obtain a non-aqueous electrolyte secondary battery electrode (10).

<Evaluation of electrode>
[Peel strength]
Using the electrodes obtained in Examples and Comparative Examples as samples, the peel strength between the mixture layer and the current collector was measured by a 180 ° peel test in accordance with JISK6854.

[Fluorine strength]
(Fluorine strength on electrode surface)
The electrodes obtained in Examples and Comparative Examples were cut into 40 mm square, and using a fluorescent X-ray measuring device (manufactured by Shimadzu, fluorescent X-ray device, XRF-1700), conditions of 40 kV, 60 mA, irradiation diameter 30 mm Then, the fluorine intensity of the electrode surface on the mixture layer side was measured.

(Fluorine strength of the release surface of the mixture layer and the release surface of the current collector)
The electrodes obtained in Examples and Comparative Examples were cut into 40 mm squares, and Damplon (registered trademark) tape (NO375) (manufactured by Nitto Denko CS System Co., Ltd.) was attached to the electrode surface on the mixture layer side.

The gauge pressure was set to 7 MPa, the electrode on which the damplon tape was attached was pressed for 20 seconds, and then the mixture layer was peeled from the current collector. Similar to the fluorine strength of the electrode surface, the release surface of the mixture layer from which the current collector has been peeled off and the release surface of the current collector from which the mixture layer has been peeled off from the mixture layer. The fluorine intensity was measured by this method.

In addition, the release surface of the mixture layer from which the current collector has been peeled off is also referred to as the “release surface of the mixture layer”, and the current collector layer from which the mixture layer has been peeled off This peeling surface is also referred to as a “current collector peeling surface”.

Tables 1 and 2 show the compositions of the binder solution and the non-aqueous electrolyte secondary battery mixture used in Examples and Comparative Examples, the thickness of the obtained electrode mixture layer, and the electrode evaluation results.

Claims

Containing at least one unsaturated carboxylic acid polymer (A) selected from polyacrylic acid and polymethacrylic acid, a carboxyl group-containing vinylidene fluoride polymer (B), an electrode active material, and an organic solvent,
Nonaqueous electrolyte secondary battery mixture having a weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of the unsaturated carboxylic acid polymer (A) of 1,000 to 150,000. .
The non-aqueous electrolyte according to claim 1, wherein the unsaturated carboxylic acid polymer (A) has a weight average molecular weight in terms of polyethylene oxide measured by gel permeation chromatography (GPC) of 1,000 to 100,000. Secondary battery mix.
The unsaturated carboxylic acid polymer (A) is 0.5 to 15% by weight per 100% by weight in total of the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B). Item 3. A mixture for a non-aqueous electrolyte secondary battery according to Item 1 or 2.
The unsaturated carboxylic acid polymer (A) is 0.8 to 6% by weight per 100% by weight in total of the unsaturated carboxylic acid polymer (A) and the carboxyl group-containing vinylidene fluoride polymer (B). Item 3. A mixture for a non-aqueous electrolyte secondary battery according to Item 1 or 2.
The mixture for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the specific surface area of the electrode active material is 1 to 10 m 2 / g.
The mixture for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the specific surface area of the electrode active material is 2 to 6 m 2 / g.
The carboxyl group-containing vinylidene fluoride polymer (B) is at least one carboxyl group-containing monomer selected from unsaturated dibasic acid, unsaturated dibasic acid monoester, acrylic acid and methacrylic acid, and vinylidene fluoride The mixture for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, which is a copolymer of
An electrode for a non-aqueous electrolyte secondary battery obtained by applying the mixture for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 to a current collector and drying.
The electrode for a non-aqueous electrolyte secondary battery according to claim 8, comprising a mixture layer having a thickness of 20 to 150 µm formed from the mixture for non-aqueous electrolyte secondary batteries.
A nonaqueous electrolyte secondary battery comprising the electrode for a nonaqueous electrolyte secondary battery according to claim 8 or 9.