TWI442617B - Non-aqueous electrolyte secondary battery negative electrode and nonaqueous electrolyte secondary battery - Google Patents

Description

Negative electrode mixture for nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

The present invention relates to a negative electrode mixture for a nonaqueous electrolyte secondary battery, a negative 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 machines have been reduced in size and weight. With the miniaturization and weight reduction of the above-mentioned electronic equipment, it is required to reduce the size and weight of the battery that is the power source. As a battery that can obtain a large amount of energy with a small volume and weight, a non-aqueous electrolyte secondary battery using lithium is mainly used as a small electronic device used in a home such as a mobile phone, a personal computer, or a video camera. power supply.

The electrode of the nonaqueous electrolyte secondary battery mainly uses polyvinylidene fluoride (PVDF) as a binder (adhesive resin). PVDF has excellent electrochemical stability, mechanical properties and slurry properties. However, the adhesion of PVDF to the metal foil as a current collector is weak. Therefore, a method of introducing a functional group such as a carboxyl group into PVDF to improve adhesion to a metal foil has been proposed (for example, refer to Patent Documents 1 to 5).

However, PVDF is liable to be unevenly distributed on the surface of the electrode when the active material having a large specific surface area is used, when the amount of the binder is small, and when the electrode is produced by rapid drying. As a result of uneven surface distribution, the amount of bonding near the current collector is reduced, and the adhesion to the current collector is lowered. Further, if the PVDF is unevenly distributed on the surface, the adhesion of the active materials to each other decreases when the amount of PVDF is small. Therefore, in the case where uneven distribution of the binder occurs, even if PVDF having a functional group such as a carboxyl group introduced therein is used, an electrode having a low peel strength is obtained.

Various methods have been proposed for suppressing the uneven distribution of the binder.

A method of suppressing the unevenness of surface distribution by suppressing the movement of the binder to the surface by stabilizing the drying conditions has been proposed (for example, refer to Patent Documents 6 and 7). However, in this method, since the drying conditions must be stabilized, the drying speed of the mixture is lowered, and the productivity of the electrode is lowered.

A method is proposed in which a mixture of different binder contents is prepared, and a multi-layer coating is applied at the same time as the mixture of the binder (the current collector) is applied to the binder (the current collector) to form a binder. An electrode which is uniformly distributed (for example, refer to Patent Document 8). However, this method requires preparation of a plurality of types of the mixture, resulting in an increase in the number of steps in electrode fabrication and a decrease in productivity. Furthermore, multilayer coating requires special equipment.

A method is proposed in which, after the electrode is formed, an organic solvent capable of dissolving the binder is injected into the electrode group and heat-treated in a pressure-bonded state, whereby the binder is dissolved again in the electrode, thereby suppressing the distribution of the binder. Unevenness (for example, refer to Patent Documents 9 and 10). However, this method also increases the steps for manufacturing the battery, so that the productivity of the battery is degraded.

In addition, 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, uneven distribution of the binder on the surface of the electrode cannot be suppressed, and thus adhesion to the current collector is insufficient.

For example, Patent Document 5 discloses that an inorganic particle containing at least one element selected from the group consisting of Si, Ge, Mg, Sn, Pb, Ag, Al, Zn, Cd, Sb, Bi, and In is used as an electrode active material. The modified fluorine-containing polymer is used as a negative electrode material for the binder. This patent document discloses that when an active material having a large volume change accompanying charge and discharge is used, a modified fluorine-containing copolymer such as a vinylidene fluoride copolymer obtained by graft-polymerizing acrylic acid is used. When the molecule is used as a binder, the detachment of the active material or the peeling of the electrode due to the volume change can be prevented, and as a result, the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 6-172245

Patent Document 2: Japanese Patent Laid-Open Publication No. 2005-47275

Patent Document 3: Japanese Patent Laid-Open Publication No. 9-231977

Patent Document 4: Japanese Patent Laid-Open No. 56-133309

Patent Document 5: Japanese Patent Laid-Open Publication No. 2004-200010

Patent Document 6: Japanese Patent Laid-Open No. Hei 5-89871

Patent Document 7: Japanese Patent Laid-Open No. Hei 10-321235

Patent Document 8: Japanese Patent Laid-Open No. Hei 11-339772

Patent Document 9: Japanese Patent Laid-Open Publication No. 2000-268872

Patent Document 10: Japanese Patent Laid-Open Publication No. 2004-95538

Patent Document 11: Japanese Patent Laid-Open No. Hei 11-45720

The present invention has been made in view of the problems of the above-described prior art, and an object of the present invention is to provide a negative electrode mixture for a nonaqueous electrolyte secondary battery containing a carbon-based negative electrode active material, which is capable of producing a negative electrode mixture for a nonaqueous electrolyte secondary battery. When a negative electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery are produced, the uneven distribution of the binder in the mixture layer can be suppressed, and the mixture layer and the mixture can be prevented. The current collector has excellent peel strength. In addition, an object of the present invention is to provide a negative electrode for a nonaqueous electrolyte secondary battery obtained by applying the mixture to a current collector and drying the same, and a nonaqueous electrolyte secondary battery having the electrode.

The inventors of the present invention have conducted intensive studies to achieve the above problems, and have found that a negative electrode mixture for a nonaqueous electrolyte secondary battery containing a carbon-based negative electrode active material using a specific modified vinylidene fluoride-based polymer as a binder can be used. The above problems are solved to complete the present invention.

In other words, the negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention comprises a modified vinylidene fluoride polymer, a carbon negative electrode active material, and an organic solvent, and the modified vinylidene fluoride polymer is intrinsic viscosity. 1.3 A polymer obtained by radiation graft copolymerization of a monomer having a carboxyl group in a dl/g or more of a vinylidene fluoride-based polymer so that the graft amount is 1 to 5% by weight.

When the total amount of the modified vinylidene fluoride-based polymer and the carbon-based negative electrode active material is 100 parts by weight, the modified vinylidene fluoride-based polymer is preferably from 1 to 10 parts by weight.

The specific surface area of the carbon-based negative electrode active material is preferably 2 to 6 m ² /g.

The carboxyl group-containing monomer is preferably at least one unsaturated carboxylic acid selected from the group consisting of acrylic acid and methacrylic acid.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is obtained by applying the negative electrode mixture for a nonaqueous electrolyte secondary battery to a current collector and drying it.

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

The nonaqueous electrolyte secondary battery of the present invention has the above negative electrode for a nonaqueous electrolyte secondary battery.

The negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention contains a carbon-based negative electrode active material, and can produce a non-aqueous electrolyte secondary battery negative electrode and a non-aqueous electrolyte secondary battery with good productivity, and manufacture a non-aqueous electrolyte secondary battery. When the negative electrode is used, uneven distribution of the binder in the mixture layer can be suppressed, and the peel strength of the mixture layer and the current collector is excellent. In addition, the negative electrode for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery of the present invention are produced by using the negative electrode mixture for a nonaqueous electrolyte secondary battery, and thus can be produced with high productivity.

Next, the present invention will be specifically described.

The negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention contains a modified vinylidene fluoride-based polymer, a carbon-based negative electrode active material, and an organic solvent, and the modified vinylidene fluoride-based polymer has an intrinsic viscosity of 1.3 dl. A polymer obtained by subjecting a carboxyl group-containing monomer to a radiation graft copolymerization in such a manner that the graft amount is from 1 to 5% by weight in the vinylidene fluoride polymer of /g or more.

[modified vinylidene fluoride polymer]

The negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention contains a modified vinylidene fluoride polymer.

The modified vinylidene fluoride-based polymer used in the present invention is used in a vinylidene fluoride-based polymer having an intrinsic viscosity of 1.3 dl/g or more, and the carboxyl group-containing monomer is grafted in an amount of 1 to 5% by weight. The polymer obtained by radiation graft copolymerization is carried out in a manner.

The modified vinylidene fluoride-based polymer used in the present invention is obtained from a vinylidene fluoride-based polymer having an intrinsic viscosity of 1.3 dl/g or more and a monomer having a carboxyl group.

The vinylidene fluoride-based polymer is not particularly limited as long as the intrinsic viscosity is within the above range, and a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and another monomer can be used.

The vinylidene fluoride-based polymer contains a polymer of a structural unit derived from vinylidene fluoride of usually 80 parts by weight or more, preferably 85 parts by weight or more per 100 parts by weight of the polymer.

The vinylidene fluoride-based polymer is produced by polymerizing vinylidene fluoride or copolymerizing vinylidene fluoride with other monomers as needed.

Examples of the other monomer include a fluorine-based monomer copolymerizable with vinylidene fluoride, a hydrocarbon-based monomer such as ethylene or propylene, and a monomer having a polar group. Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether represented by perfluoromethyl vinyl ether. .

As the polar group-containing monomer, at least one monomer selected from the group consisting of a carboxyl group-containing monomer and a carboxylic acid anhydride group-containing monomer is usually used.

The monomer having a carboxyl group is preferably an unsaturated monobasic acid, an unsaturated dibasic acid, or a monoester of an unsaturated dibasic acid.

Examples of the unsaturated monobasic acid include acrylic acid, methacrylic acid, and the like. Examples of the unsaturated dibasic acid include maleic acid and methyl maleic acid. Further, the monoester of the unsaturated dibasic acid is preferably a carbon number of 5 to 8, and examples thereof include monomethyl maleate, monoethyl maleate, and methyl cis-butane. Monomethyl methacrylate, methyl maleic acid monoethyl ester, and the like. Among them, as the monomer having a carboxyl group, acrylic acid, methacrylic acid, maleic acid, methyl maleic acid, maleic acid monomethyl ester, methyl maleic acid monomethyl group is preferable. ester. Further, the other monomers may be used alone or in combination of two or more.

The carboxylic acid anhydride group-containing monomer may, for example, be an acid anhydride of the above unsaturated dibasic acid, and specific examples thereof include maleic anhydride and methyl maleic anhydride.

The vinylidene fluoride-based polymer can be produced by a method such as suspension polymerization, emulsion polymerization, or solution polymerization. However, in terms of easiness of subsequent treatment, etc., it is preferably aqueous suspension polymerization or emulsion polymerization, and particularly preferably water system. Suspension polymerization.

In the suspension polymerization using water as a dispersion medium, it is 0.005 to 1.0 part by weight, preferably 100 parts by weight, based on 100 parts by weight of all monomers (vinylidene fluoride and other monomers copolymerized as needed) for copolymerization. 0.01 to 0.4 parts by weight of a suspension of methyl cellulose, methyl methoxide, propoxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, gelatin, etc. Used as a dose.

As the polymerization initiator, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-n-heptafluoropropyl peroxydicarbonate, diisopropyl peroxydicarbonate, and isobutyl hydrazine peroxidation can be used. , bis(chlorofluoroindolyl) peroxide, bis(perfluorodecyl) peroxide, and the like. When all the monomers (vinylidene fluoride and other monomers optionally copolymerized) used for the copolymerization are used in an amount of 100 parts by weight, the amount thereof is 0.1 to 5 parts by weight, preferably 0.3 to 2 parts by weight. .

In addition, a chain transfer agent such as ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propionaldehyde, ethyl propionate or tetra-carbonated carbon may be added to adjust the bias. The degree of polymerization of the difluoroethylene polymer. When all the monomers (vinylidene fluoride and other monomers optionally copolymerized) used for the copolymerization are 100 parts by weight, the chain transfer agent is usually used in an amount of 0.1 to 5 parts by weight, preferably 0.5. ~3 parts by weight.

In addition, in terms of the total weight of the monomers: the weight ratio of water, the total amount of all monomers (vinylidene fluoride and other monomers optionally copolymerized) used for copolymerization is usually 1:1 to 1:10. Preferably, it is 1:2 to 1:5, the polymerization temperature is 10 to 80 ° C, and the polymerization time is 10 to 100 hours. The pressure during polymerization is usually carried out under pressure, preferably 2.0 to 8.0 MPa-G.

By carrying out the aqueous suspension polymerization under the above conditions, the vinylidene fluoride and other monomers which are optionally copolymerized can be easily polymerized to obtain a vinylidene fluoride-based polymer.

The intrinsic viscosity of the vinylidene fluoride polymer (the logarithmic viscosity of a solution obtained by dissolving 4 g of the resin in 1 L of N,N-dimethylformamide at 30 ° C. The same applies hereinafter) is 1.3 dl. Above /g, preferably in the range of 1.7 to 5.0 dl/g, more preferably in the range of 2.0 to 4.0 dl/g. The vinylidene fluoride-based polymer can be suitably used as a negative electrode mixture for a nonaqueous electrolyte secondary battery as long as it has a viscosity within the above range.

Intrinsic viscosity η _i can be calculated by dissolving 80 mg of vinylidene fluoride polymer in 20 ml of N,N-dimethylformamide, using a Ubum viscometer in a 30 ° C thermostat and using To proceed.

η _i =(1/C)‧ln(η/η ₀ )

Here, η is the viscosity of the polymer solution, and η ₀ is the viscosity of the solvent N,N-dimethylformamide alone, and C is 0.4 g/dl.

Further, the vinylidene fluoride-based polymer has a weight average molecular weight in terms of polystyrene measured by GPC (Gel permeation chromatography) of usually 300,000 to 2.5 million, preferably 500,000. ~2 million range.

The modified vinylidene fluoride-based polymer used in the present invention is as described above in a vinylidene fluoride-based polymer having an intrinsic viscosity of 1.3 dl/g or more, and the monomer having a carboxyl group is 1 to 5 in terms of graft amount. A polymer obtained by radiation graft copolymerization in a weight % manner.

The monomer having a carboxyl group is preferably an unsaturated monobasic acid, an unsaturated dibasic acid, or a monoester of an unsaturated dibasic acid.

Examples of the unsaturated monobasic acid include acrylic acid, methacrylic acid, and the like. Examples of the unsaturated dibasic acid include maleic acid and methyl maleic acid. Further, the monoester of the unsaturated dibasic acid is preferably a carbon number of 5 to 8, and examples thereof include monomethyl maleate, monoethyl maleate, and methyl cis-butane. Monomethyl methacrylate, methyl maleic acid monoethyl ester, and the like.

Among them, as the monomer having a carboxyl group, acrylic acid or methacrylic acid is preferred. In addition, one type of the monomer having a carboxyl group may be used alone or two or more types may be used.

Radiation graft copolymerization can be carried out by continuously or intermittently irradiating radiation to a mixture of the above vinylidene fluoride-based polymer, a carboxyl group-containing monomer, and a solvent which is optionally used.

As the solvent, those having a function of dissolving a monomer having a carboxyl group are used, and a solvent having a polarity is preferably used. Specific examples of the solvent include water, alcohols, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl hydrazine. Hexamethylphosphonium triamine, two Alkane, tetrahydrofuran, tetramethylurea, triethylphosphate, trimethylphosphate, etc. are preferably water or alcohol. Further, the solvent may be used alone or in combination of two or more. Further, examples of the radiation include α rays, β rays, γ rays, x rays, neutron rays, proton beams, electron beams, and the like. It is preferable to use γ rays or electron beams, and it is more preferable to use electron beams.

The irradiation of the radiation is preferably carried out in a range in which the absorbed dose of the above mixture is in the range of 0.1 to 200 kGy, more preferably in the range of 1 to 50 kGy.

Further, the amount of the carboxyl group-containing monomer used for the radiation graft copolymerization is usually 1 to 50 parts by weight based on 100 parts by weight of the vinylidene fluoride-based polymer.

The graft amount of the carboxyl group-containing monomer in the modified vinylidene fluoride polymer used in the present invention is 1 to 5% by weight, preferably 2 to 4% by weight. In the above range, the peeling strength of the mixture layer and the current collector is excellent, and the productivity of the negative electrode for a nonaqueous electrolyte secondary battery is also excellent, which is preferable. The graft amount of the monomer having a carboxyl group can be adjusted by adjusting the above absorbed dose or the amount of the carboxyl group-containing monomer used for the radiation graft copolymerization. Further, the graft amount of the monomer having a carboxyl group can be determined by the method described in the examples.

Since the modified vinylidene fluoride-based polymer used in the present invention is modified by radiation graft copolymerization, the graft amount (modification amount) can be increased as compared with the modification using a peroxide. .

Further, the weight average molecular weight of the modified vinylidene fluoride-based polymer measured by GPC in terms of polystyrene is usually in the range of 50,000 to 2,000,000, preferably in the range of 300,000 to 1,500,000.

[Carbon-based anode active material]

The negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention contains a carbon-based negative electrode active material. The carbon-based negative electrode active material is not particularly limited, and a conventionally known carbon-based negative electrode active material can be used.

As the carbon-based negative electrode active material, artificial graphite, natural graphite, non-graphitizable carbon, easily graphitizable carbon, or the like can be used. Further, the above-mentioned carbon materials may be used alone or in combination of two or more.

When the above carbon-based negative electrode active material is used, the energy density of the battery can be improved.

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

The specific surface area of the carbon-based negative electrode active material is preferably from 1 to 10 m ² /g, more preferably from 2 to 6 m ² /g. When the specific surface area is less than 1 m ² /g, even when the prior adhesive is used, uneven distribution of the adhesive is hard to occur, and the effect of the present invention is small. When 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.

Further, the specific surface area of the carbon-based negative electrode active material can be determined by a nitrogen adsorption method.

[Organic solvents]

The negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention contains an organic solvent. As the organic solvent, those having a function of dissolving the above-mentioned modified vinylidene fluoride-based polymer can be 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 hydrazine, and hexamethyl group. Phosphonic triamine, two Alkane, tetrahydrofuran, tetramethylurea, triethylphosphate, trimethylphosphate, etc., preferably N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-di Methyl acetamide, dimethyl hydrazine. Further, the organic solvent may be used alone or in combination of two or more.

The negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention contains the modified vinylidene fluoride-based polymer, a carbon-based negative electrode active material, and an organic solvent.

The negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention is a modified vinylidene fluoride compound in a total of 100 parts by weight of the modified vinylidene fluoride-based polymer (adhesive resin) and the carbon-based negative electrode active material. The polymer is preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight, and the carbon-based negative electrode active material is preferably 85 to 99.5 parts by weight, more preferably 90 to 99 parts by weight. In addition, when the total of the binder resin (modified vinylidene fluoride-based polymer) and the carbon-based negative electrode active material is 100 parts by weight, the organic solvent is preferably 20 to 300 parts by weight, more preferably 50 to 200 parts by weight. Parts by weight.

When the respective components are contained in the above range, the negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention can be used to produce a negative electrode for a nonaqueous electrolyte secondary battery, and the negative electrode for a nonaqueous electrolyte secondary battery can be produced. The distribution unevenness of the binder in the mixture layer can be sufficiently suppressed, and the peel strength of the mixture layer and the current collector is excellent.

In addition, the negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention may contain other components than the above-mentioned modified vinylidene fluoride-based polymer, carbon-based negative electrode active material, and organic solvent. The other component may include a conductive auxiliary agent such as carbon black or a pigment dispersant such as polyvinylpyrrolidone. The other components may include other polymers than the above-mentioned modified vinylidene fluoride polymer. Examples of the other polymer include polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, and a vinylidene fluoride-perfluoromethylvinyl ether copolymer. A vinylidene fluoride-based polymer. In the case where the negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention contains another polymer, the polymerization is usually carried out in an amount of 25 parts by weight or less based on 100 parts by weight or less based on 100 parts by weight of the modified vinylidene fluoride-based polymer. Things.

The viscosity of the negative electrode mixture for a nonaqueous electrolyte secondary battery of the present invention is usually 2,000 to 50,000 mPa s, preferably 5,000 to 30,000 when measured at a shear rate of 2 s ^-1 at 25 ° C using an E-type viscometer. mPa‧s.

In the method for producing a negative electrode mixture for a non-aqueous electrolyte secondary battery of the present invention, the modified vinylidene fluoride-based polymer, the carbon-based negative electrode active material, and the organic solvent may be mixed as a homogeneous slurry. The order of the mixing is not particularly limited, and examples thereof include a method in which the modified vinylidene fluoride-based polymer is dissolved in one part of an organic solvent to obtain a binder solution, and a carbon-based anode active is added to the binder solution. The substance and the remaining organic solvent are stirred and mixed to obtain a negative electrode mixture for a nonaqueous electrolyte secondary battery.

[Negative Electrode for Nonaqueous Electrolyte Secondary Battery]

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is obtained by applying the negative electrode mixture for a nonaqueous electrolyte secondary battery to a current collector and drying it, and includes a current collector and a secondary electrolyte. A layer formed of a negative electrode mixture for a battery.

In the present invention, a layer formed of a negative electrode mixture for a nonaqueous electrolyte secondary battery formed by applying a negative electrode mixture for a nonaqueous electrolyte secondary battery to a current collector and drying is described as Mixture layer.

The current collector used in the present invention is, for example, copper, and examples of the shape thereof include a metal foil or a metal mesh. As the current collector, a copper foil is preferred.

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.

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

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

Further, heat treatment may be performed after drying. In the case of heat treatment, it is usually carried out at a temperature of 100 to 250 ° C for 1 to 300 minutes. Further, the temperature of the heat treatment is the same as the above drying temperature, and the steps may be a separate step or a continuous step.

Further, it is also possible to carry out a pressing treatment. In the case of pressing treatment, it is usually carried out at 1 to 200 MPa-G. If the pressing treatment is carried out, the electrode density can be increased, which is preferable.

According to the above method, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention can be produced. In the case of applying a negative electrode mixture for a nonaqueous electrolyte secondary battery to one of the surfaces of the current collector, the layer of the mixture layer/collector is used as a layer of the negative electrode for a nonaqueous electrolyte secondary battery. When the negative electrode mixture for a nonaqueous electrolyte secondary battery is applied to both surfaces of the current collector, the layer structure is composed of three layers of a mixture layer/current collector/mixture layer.

In the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, since the negative electrode mixture for a non-aqueous electrolyte secondary battery is used, the peel strength of the current collector and the mixture layer is excellent, so that steps such as pressing, cutting, and winding are performed. It is preferable that the electrode is hard to be cracked or peeled, which contributes to an improvement in productivity.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is excellent in peel strength of the current collector and the mixture layer as described above, and specifically, the peel strength of the current collector and the mixture layer is in accordance with JIS K6854 by a 180° peel test. When the measurement is carried out, it is usually 0.5 to 20 gf/mm, preferably 1 to 10 gf/mm.

The negative electrode for a nonaqueous electrolyte secondary battery of the present invention has a mixture layer formed of the negative electrode mixture for a nonaqueous electrolyte secondary battery, and the mixture layer suppresses uneven distribution of the binder. Therefore, the current collector and the mixture layer are excellent in peel strength.

[Non-aqueous electrolyte secondary battery]

The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising the above negative electrode for a nonaqueous electrolyte secondary battery.

The nonaqueous electrolyte secondary battery of the present invention is not particularly limited as long as it has the negative electrode for a nonaqueous electrolyte secondary battery. As the nonaqueous electrolyte secondary battery, a portion other than the negative electrode, for example, a positive electrode, a separator, or the like can be used.

Example

The invention is further illustrated by the following examples, but the invention is not limited thereto.

[Production Example 1] (Production of Polyvinylidene Difluoride (1))

Add 1075 g of ion-exchanged water, 0.4 g of methylcellulose, 2.3 g of di-n-propyl peroxydicarbonate, 5 g of ethyl acetate and 420 g of vinylidene fluoride to the autoclave with a volume of 2 L. The suspension polymerization was carried out for 15 hours at °C. The maximum pressure between them reached 4.0 MPa. After the completion of the polymerization, the polymer slurry was dehydrated and washed with water. Thereafter, drying was carried out at 80 ° C for 20 hours to obtain powdery polyvinylidene fluoride (1) (PVDF (1)). PVDF (1) has a weight average molecular weight of 750,000 and an intrinsic viscosity of 2.1 dl/g.

[Production Example 2] (Production of Polyvinylidene Difluoride (2))

1040 g of ion-exchanged water, 0.4 g of methylcellulose, 2.0 g of di-n-propyl peroxydicarbonate, 8 g of ethyl acetate and 400 g of vinylidene fluoride were added to the autoclave with a volume of 2 L. The suspension polymerization was carried out for 12 hours at °C. The maximum pressure between them reached 4.0 MPa. After the completion of the polymerization, the polymer slurry was dehydrated and washed with water. Thereafter, drying was carried out at 80 ° C for 20 hours to obtain powdery polyvinylidene fluoride (2) (PVDF (2)). PVDF (2) has a weight average molecular weight of 300,000 and an intrinsic viscosity of 1.1 dl/g.

[Production Example 3] (Production of a vinylidene fluoride-based polymer (1) containing a carboxyl group)

1040 g of ion-exchanged water, 0.8 g of methylcellulose, 3.0 g of diisopropyl peroxydicarbonate, 396 g of vinylidene fluoride and monomethyl maleate were added to the autoclave with a volume of 2 L. 4.0 g, suspension polymerization was carried out at 28 ° C for 45 hours. The maximum pressure between them reached 4.1 MPa. After the completion of the polymerization, the polymer slurry was dehydrated and washed with water. Thereafter, the mixture was dried at 80 ° C for 20 hours to obtain a powdery carboxyl group-containing vinylidene fluoride-based polymer (1) (polymer (1)). The polymer (1) had a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Measurement of weight average component]

The polystyrene-equivalent weight average molecular weight of the above PVDF (1), PVDF (2), and polymer (1) is measured by gel permeation chromatography (GPC).

The measurement was performed on a separation column using Shodex KD-806M (manufactured by Showa Denko Co., Ltd.), the detector using RI-930 (refractive index detector) manufactured by JASCO Corporation, and a flow rate of the elution solution of 1 mL/min. The column temperature was 40 ° C.

Further, in the measurement, a LiBr-NMP solution having a concentration of 10 mM was used as a solution, and TSK standard POLY (STYRENE) (manufactured by Tosoh Co., Ltd.) was used as a standard polymer for a calibration curve.

[Measurement of specific surface area of active materials]

The specific surface area of the active material is determined by a nitrogen adsorption method.

Using the approximate formula induced by the BET (Brunauer-Emmett-Tellern) formula: Vm = 1/(v(1-x)) and using the 1 point method (relative pressure) using nitrogen adsorption at liquid nitrogen temperature x = 0.3), and Vm is obtained, and the specific surface area of the sample (active material) is calculated by the following formula.

Specific surface area [m ² /g]=4.35×Vm

Here, Vm is the amount of adsorption (cm ³ /g) necessary for forming a monolayer on the surface of the sample, v is the measured adsorption amount (cm ³ /g), and x is a relative pressure.

Specifically, the amount of adsorption (v) of nitrogen on the active material at a liquid nitrogen temperature was measured by using "Flow Sorb II 2300" manufactured by MICROMETRITICS. The active material was filled in a test tube, and the test tube was cooled to -196 ° C while circulating a helium gas containing nitrogen at a concentration of 20 mol% to adsorb nitrogen on the active material. The tube is then returned to room temperature. At this time, the amount of nitrogen detached from the sample was measured by a thermal conductivity detector and set as the adsorption amount (v).

[Example 1]

(Graft polymerization of acrylic acid to PVDF)

Add PVDF (1) 150 g, acrylic acid 8 g, methanol 232 g to a 500 mL sample vial and mix with stirring. The obtained mixture was transferred to a polyethylene bag (Lamizip (registered trademark), manufactured by Nippon Manufacturing Co., Ltd.), and the inside of the bag was replaced with nitrogen. Thereafter, the opening of the bag is heat sealed and sealed.

Then, the pouch sealed with the above mixture was irradiated with an electron beam in such a manner that the absorbed dose of the mixture became 20 kGy. Thereafter, the reactants were taken out of the bag and transferred to a Butcher funnel (Nutsche) mounted on a suction filter bottle. The reactants were washed and filtered using ion-exchanged water in a Buchner funnel to remove a portion of the unreacted homopolymer of acrylic acid, methanol, and acrylic acid. Thereafter, drying was carried out at 80 ° C for 20 hours to obtain a powdery reaction mixture.

Then, in order to remove the ungrafted polyacrylic acid which cannot be removed from the powdery reaction mixture by water washing, the following purification operation was carried out. First, 10 g of the obtained powdery reaction mixture was added to 90 g of N-methyl-2-pyrrolidone (NMP, N-methyl-2-pyrrolidone), and it was dissolved by stirring at 65 ° C for 5 hours. Then, the obtained solution (A) was dropwise added dropwise to 500 mL of a solution of ion-exchanged water and methanol mixed in a ratio of 1:1 (mass ratio) to reprecipitate.

After 100 g of the solution (A) was added dropwise, the temperature was raised to 60 ° C and stirred for 1 hour. The precipitate was dried at 80 ° C for 20 hours to obtain an acrylic grafted PVDF (1). The acrylic grafted PVDF (1) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g. Further, the weight average molecular weight was determined by the same method as PVDF (1). The weight average molecular weight decreases by electron beam irradiation.

5 g of the obtained acrylic grafted PVDF (1) was added to 45 g of NMP, and stirred at 65 ° C for 5 hours to be dissolved, thereby obtaining a binder containing acrylic acid grafted PVDF (1) having a resin concentration of 10% by weight. Solution (1).

(Measurement of graft amount)

The graft amount of acrylic acid grafted with PVDF (1) was determined by Fourier transform infrared FT-IR.

First, the binder solution (1) was applied to a glass plate. A cast film having a thickness of about 10 μm was obtained by removing the NMP by placing the glass plate in a thermostat at 120 ° C for 60 minutes.

The IR spectrum of the cast film was measured using a Fourier transform infrared spectrophotometer FT-730 manufactured by HORIBA (Hakuto Manufacturing Co., Ltd.).

The graft amount was determined from the obtained spectrum by the absorbance ratio of the peak of the carbonyl group (1710 cm ^-1 ) derived from the graft chain of PAA (polyacrylic acid) and the peak derived from PVDF (3025 cm ^-1 ). The standard sample is a cast film having a thickness of about 10 μm which is produced by changing the ratio of PVDF (1) to a commercially available PAA (JURYMER AC10LP (registered trademark), manufactured by Nippon Pure Chemical Co., Ltd.) by the same method as described above. .

(Solution viscosity measurement)

The adhesive solution (1) was placed in an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.), and then kept at 30 ° C for 1 minute. Thereafter, the solution viscosity was measured at a shear rate of 2 s ^-1 for 5 minutes. The value which is stable and continuously obtained in the measurement is set as the viscosity of the adhesive solution (1).

(swelling test)

First, a cast film having a thickness of about 100 μm was produced by applying a binder solution (1) to a glass plate and placing it in a 150 ° C thermostatic chamber for 5 hours to remove NMP.

The cast film was immersed at 80 ° C for 24 hours in the following electrolyte. Thereafter, the film was taken out from the electrolytic solution, and the surface was gently wiped with a non-woven fabric to measure the weight. The rate of change in weight before and after the impregnation of the electrolyte was calculated as the degree of swelling. The electrolyte was used in a mixture of 23.8 vol% of ethylene (Ethylene carbonate), 42.0 vol% of dimethyl carbonate (DMC), and 34.2 vol% of Ethyl methyl carbonate. The liquid was dissolved in 1 mol/L of LiPF ₆ as an electrolyte.

(electrode production)

Adhesive solution (1) 8 g, 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 mixture viscosity adjustment N-A 5.8 g of pyridine-2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (1) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was 12,500 mPa·s.

The obtained negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was applied as a current collector by using a spacer and a bar coater so that the weight per unit area after drying became 150 g/m ² . The body has a thickness of 10 μm on the copper foil. After drying at 110 ° C in a nitrogen atmosphere, heat treatment was carried out at 130 ° C. Then, the negative electrode for a nonaqueous electrolyte secondary battery (1) having a bulk density of 1.7 g/cm ³ of a mixture layer formed of the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery is obtained by pressing at 40 MPa. . The thickness of the mixture layer was calculated by subtracting the thickness of the current collector from the thickness of the negative electrode.

[Comparative Example 1]

A binder solution (c1) and a negative electrode mixture for a nonaqueous electrolyte secondary battery (c1) were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following electron beam irradiation PVDF (c1). ) A negative electrode (c1) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c1) for a nonaqueous electrolyte secondary battery was 12,300 mPa·s.

(Electrobeam irradiation to PVDF)

Electron beam irradiation of PVDF (c1) was carried out in the same manner as in Example 1 except that 8 g of acrylic acid was not used, instead of grafting PVDF (1) with acrylic acid. The electron beam irradiation PVDF (c1) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Comparative Example 2]

A binder solution (c2) and a negative electrode mixture for a nonaqueous electrolyte secondary battery (c2) were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c2). ) A negative electrode (c2) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c2) for a nonaqueous electrolyte secondary battery was 12,300 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

The acrylic grafted PVDF (c2) was obtained in the same manner as in Example 1 except that it was changed to 4 g of acrylic acid and 236 g of methanol. The acrylic grafted PVDF (c2) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Embodiment 2]

A binder solution (2) and a negative electrode mixture for a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (2). ), a negative electrode for a nonaqueous electrolyte secondary battery (2). The viscosity of the negative electrode mixture (2) for a nonaqueous electrolyte secondary battery was 12,800 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

The acrylic grafted PVDF (2) was obtained in the same manner as in Example 1 except that it was changed to 12 g of acrylic acid and 228 g of methanol. The acrylic grafted PVDF (2) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Example 3]

A binder solution (3) and a negative electrode mixture for a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (3). ) A negative electrode (3) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (3) for a nonaqueous electrolyte secondary battery was 13,500 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

The acrylic grafted PVDF (3) was obtained in the same manner as in Example 1 except that it was changed to 24 g of acrylic acid and 216 g of methanol. The acrylic grafted PVDF (3) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Comparative Example 3]

A binder solution (c3) and a negative electrode mixture for a nonaqueous electrolyte secondary battery (c3) were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c3). ) A negative electrode (c3) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c3) for a nonaqueous electrolyte secondary battery was 16,000 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

In the same manner as in Example 1, except that 40 g of acrylic acid and 200 g of methanol were changed, acrylic acid grafted PVDF (c3) was obtained instead of grafting PVDF (1) with acrylic acid. The acrylic grafted PVDF (c3) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Comparative Example 4]

A binder solution (c4) and a negative electrode mixture for a nonaqueous electrolyte secondary battery (c4) were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c4). ) A negative electrode (c4) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c4) for a nonaqueous electrolyte secondary battery was 18,500 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

An acrylic grafted PVDF (c4) was obtained in the same manner as in Example 1 except that it was changed to 60 g of acrylic acid and 180 g of methanol. The acrylic grafted PVDF (c4) has a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

[Comparative Example 5]

A binder solution (c5) and a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1 except that the acrylic acid grafted PVDF (1) was changed to the above-mentioned carboxyl group-containing vinylidene fluoride polymer (1). A negative electrode mixture (c5) and a negative electrode (c5) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c5) for a nonaqueous electrolyte secondary battery was 12,000 mPa·s.

[Comparative Example 6]

The same procedure as in Example 1 was carried out, except that the acrylic grafted PVDF (1) was changed to the following electron beam irradiation PVDF (c6), and the mixture viscosity adjustment N-methyl-2-pyrrolidone was changed to 3 g. A binder solution (c6), a negative electrode mixture for a nonaqueous electrolyte secondary battery (c6), and a negative electrode for a nonaqueous electrolyte secondary battery (c6). The viscosity of the negative electrode mixture (c6) for a nonaqueous electrolyte secondary battery was 13,000 mPa·s.

(Electrobeam irradiation to PVDF)

In the same manner as in Example 1, except that PVDF (1) was changed to PVDF (2) and 8 g of acrylic acid was not used, electron beam irradiation PVDF (c6) was obtained instead of grafting PVDF (1) with acrylic acid. The electron beam irradiation PVDF (c6) has a weight average molecular weight of 200,000 and an intrinsic viscosity of 0.9 dl/g.

[Comparative Example 7]

The same procedure as in Example 1 was carried out except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c7), and the mixture viscosity adjustment N-methyl-2-pyrrolidone was changed to 3 g. A binder solution (c7), a negative electrode mixture for a nonaqueous electrolyte secondary battery (c7), and a negative electrode for a nonaqueous electrolyte secondary battery (c7). The viscosity of the negative electrode mixture (c7) for a nonaqueous electrolyte secondary battery was 13,500 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

In the same manner as in Example 1, except that PVDF (1) was changed to PVDF (2), acrylic acid grafted PVDF (c7) was obtained instead of grafting PVDF (1) with acrylic acid. The acrylic grafted PVDF (c7) has a weight average molecular weight of 200,000 and an intrinsic viscosity of 0.9 dl/g.

[Comparative Example 8]

The same procedure as in Example 1 was carried out, except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c8), and the mixture viscosity adjustment N-methyl-2-pyrrolidone was changed to 3 g. A binder solution (c8), a negative electrode mixture for a nonaqueous electrolyte secondary battery (c8), and a negative electrode for a nonaqueous electrolyte secondary battery (c8). The viscosity of the negative electrode mixture (c8) for a nonaqueous electrolyte secondary battery was 14,000 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

In the same manner as in Example 1, except that PVDF (1) was changed to PVDF (2) and changed to 24 g of acrylic acid and 216 g of methanol, acrylic acid grafted PVDF (c8) was obtained instead of grafting PVDF (1) with acrylic acid. The acrylic grafted PVDF (c8) has a weight average molecular weight of 200,000 and an intrinsic viscosity of 0.9 dl/g.

[Comparative Example 9]

The same procedure as in Example 1 was carried out, except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c9), and the mixture viscosity adjustment N-methyl-2-pyrrolidone was changed to 3 g. A binder solution (c9), a negative electrode mixture for a nonaqueous electrolyte secondary battery (c9), and a negative electrode for a nonaqueous electrolyte secondary battery (c9). The viscosity of the negative electrode mixture (c9) for a nonaqueous electrolyte secondary battery was 15,000 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

In the same manner as in Example 1, except that PVDF (1) was changed to PVDF (2) and changed to 40 g of acrylic acid and 200 g of methanol, acrylic acid grafted PVDF (c9) was obtained instead of grafting PVDF (1) with acrylic acid. The acrylic grafted PVDF (c9) has a weight average molecular weight of 200,000 and an intrinsic viscosity of 0.9 dl/g.

[Comparative Example 10]

The same procedure as in Example 1 was carried out, except that the acrylic grafted PVDF (1) was changed to the following acrylic grafted PVDF (c10), and the mixture viscosity adjustment N-methyl-2-pyrrolidone was changed to 3 g. A binder solution (c10), a negative electrode mixture for a nonaqueous electrolyte secondary battery (c10), and a negative electrode for a nonaqueous electrolyte secondary battery (c10). The viscosity of the negative electrode mixture (c10) for a nonaqueous electrolyte secondary battery was 18,000 mPa·s.

(Graft polymerization of acrylic acid to PVDF)

In the same manner as in Example 1, except that PVDF (1) was changed to PVDF (2) and changed to 60 g of acrylic acid and 180 g of methanol, acrylic acid grafted PVDF (c10) was obtained instead of grafting PVDF (1) with acrylic acid. The acrylic grafted PVDF (c10) has a weight average molecular weight of 200,000 and an intrinsic viscosity of 0.9 dl/g.

[Comparative Example 11]

A binder solution (c11) and a negative electrode for a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1 except that the acrylic acid grafted PVDF (1) was changed to the following maleic acid grafted PVDF (c11). A mixture (c11) and a negative electrode (c11) for a nonaqueous electrolyte secondary battery. The viscosity of the negative electrode mixture (c11) for a nonaqueous electrolyte secondary battery was 12,500 mPa·s.

(Graft copolymerization of maleic acid to PVDF)

In the same manner as in Example 1, except that 12 g of maleic acid and 228 g of methanol were changed, maleic acid-grafted PVDF (c11) was obtained instead of grafting PVDF (1) with acrylic acid. The maleic acid grafted PVDF (c11) had a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

(Measurement of graft amount)

The graft amount of the maleic acid-grafted PVDF (c11) maleic acid was determined by Fourier transform infrared spectroscopy (FT-IR) using the same method as the graft amount of acrylic acid.

First, the binder solution (c11) was applied to a glass plate. A cast film having a thickness of about 10 μm was produced by removing the NMP by placing the glass plate in a thermostat at 120 ° C for 60 minutes.

The IR spectrum of the cast film was measured by a Fourier transform infrared spectrophotometer FT-730 manufactured by HORIBA (Hakuto Manufacturing Co., Ltd.).

The graft amount was determined from the obtained spectrum by the absorbance ratio of the peak derived from the carbonyl group in the polymaleic acid graft chain (1685 cm ^-1 ) and the peak derived from PVDF (3025 cm ^-1 ). The standard sample is a cast film having a thickness of about 10 μm which is produced by changing the ratio of PVDF (1) to a commercially available PAA (JURYMER AC10LP (registered trademark), manufactured by Nippon Pure Chemical Co., Ltd.) by the same method as described above. .

[Comparative Example 12]

A binder solution (c12) and a negative electrode for a nonaqueous electrolyte secondary battery were obtained in the same manner as in Example 1 except that the acrylic grafted PVDF (1) was changed to the following maleic acid grafted PVDF (c12). Mixture (c12), negative electrode for nonaqueous electrolyte secondary battery (c12). The viscosity of the negative electrode mixture (c12) for a nonaqueous electrolyte secondary battery was 12,500 mPa·s.

(Graft copolymerization of maleic acid to PVDF)

In the same manner as in Example 1, except that 40 g of maleic acid and 200 g of methanol were changed, maleic acid-grafted PVDF (c12) was obtained instead of grafting PVDF (1) with acrylic acid. The maleic acid grafted PVDF (c12) had a weight average molecular weight of 500,000 and an intrinsic viscosity of 1.7 dl/g.

Further, the graft amount of maleic acid grafted with maleic acid to PVDF (c12) is the same as the graft amount of maleic acid grafted with maleic acid to PVDF (c11). It is obtained by the method.

[Example 4]

Adhesive solution (3) 6 g, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG, average particle size 20 μm, specific surface area 4.2 m ² /g) 9.4 g and mixture viscosity adjustment N-A 2.8 g of pyridine-2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (4) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (4) for a nonaqueous electrolyte secondary battery ( 4). The viscosity of the negative electrode mixture (4) for a nonaqueous electrolyte secondary battery was 14,500 mPa·s.

[Comparative Example 13]

Adhesive solution (c5) 6 g, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG, average particle size 20 μm, specific surface area 4.2 m ² /g) 9.4 g and mixture viscosity adjustment N-A 2.8 g of pyridine-2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (c13) for a nonaqueous electrolyte secondary battery.

A non-aqueous electrolyte secondary battery negative electrode was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a non-aqueous electrolyte secondary battery was changed to the negative electrode mixture (c13) for a non-aqueous electrolyte secondary battery. C13). The viscosity of the negative electrode mixture (c13) for a nonaqueous electrolyte secondary battery was 14,000 mPa·s.

[Example 5]

4 g of binder solution (3), 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-methyl group for viscosity adjustment of mixture 7.0 g of 2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (5) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (5) for a nonaqueous electrolyte secondary battery ( 5). The viscosity of the negative electrode mixture (5) for a nonaqueous electrolyte secondary battery was 14,500 mPa·s.

[Comparative Example 14]

4 g of binder solution (c5), 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-methyl group for viscosity adjustment of mixture -2-Pyrrolidone 5.8 g was stirred and mixed to obtain a negative electrode mixture (c14) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (c14) for a nonaqueous electrolyte secondary battery ( C14). The viscosity of the negative electrode mixture (c14) for a nonaqueous electrolyte secondary battery was 14,000 mPa·s.

[Embodiment 6]

Binder solution (3) 4 g, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG, average particle size 38 μm, specific surface area 1.5 m ² /g) 9.6 g and mixture viscosity adjustment N-A The base-2-pyrrolidone 3.9 g was stirred and mixed to obtain a negative electrode mixture (6) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (6) for a nonaqueous electrolyte secondary battery. 6). The viscosity of the negative electrode mixture (6) for a nonaqueous electrolyte secondary battery was 13,500 mPa·s.

[Comparative Example 15]

Binder solution (c5) 4 g, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., MAG, average particle size 38 μm, specific surface area 1.5 m ² /g) 9.6 g and mixture viscosity adjustment N-A The base-2-pyrrolidone 3.9 g was stirred and mixed to obtain a negative electrode mixture (c15) for a nonaqueous electrolyte secondary battery.

A non-aqueous electrolyte secondary battery negative electrode was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a non-aqueous electrolyte secondary battery was changed to the negative electrode mixture (c15) for a non-aqueous electrolyte secondary battery. C15). The viscosity of the negative electrode mixture (c15) for a nonaqueous electrolyte secondary battery was 13,000 mPa·s.

[Embodiment 7]

4 g of binder solution (3), artificial graphite (manufactured by Osaka Gas Co., Ltd., MCMB, average particle size 23 μm, specific surface area 0.9 m ² /g) 9.6 g and N-methyl group for viscosity adjustment of mixture 2.0 g of 2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (7) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (7) for a nonaqueous electrolyte secondary battery ( 7). The viscosity of the negative electrode mixture (7) for a nonaqueous electrolyte secondary battery was 14300 mPa·s.

[Comparative Example 16]

4 g of binder solution (c5), artificial graphite (manufactured by Osaka Gas Co., Ltd., MCMB, average particle size 23 μm, specific surface area 0.9 m ² /g) 9.6 g and N-methyl group for viscosity adjustment of mixture 2.0 g of 2-pyrrolidone was stirred and mixed to obtain a negative electrode mixture (c16) for a nonaqueous electrolyte secondary battery.

A negative electrode for a nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except that the negative electrode mixture (1) for a nonaqueous electrolyte secondary battery was changed to the negative electrode mixture (c16) for a nonaqueous electrolyte secondary battery. C16). The viscosity of the negative electrode mixture (c16) for a nonaqueous electrolyte secondary battery was 13,800 mPa·s.

<Evaluation of the negative electrode>

[peel strength]

The negative electrode obtained in the examples and the comparative examples was used as a sample, and the peel strength of the mixture layer and the current collector was measured in accordance with JIS K6854 by a 180° peel test.

[Fluorine strength]

(Fluority of the surface of the negative electrode)

The electrodes obtained in the examples and the comparative examples were cut into 40 mm squares using a fluorescent X-ray measuring apparatus (manufactured by Shimadzu, fluorescent X-ray apparatus, XRF-1700) at 40 kV, 60 mA, and an irradiation diameter of 30 mm. The fluorine strength of the surface of the negative electrode on the side of the mixture layer was measured under the conditions.

(Fluority of the peeling surface of the mixture layer and the peeling surface of the current collector)

The electrode obtained in the examples and the comparative examples was cut into a 40 mm square, and DANPRON (registered trademark) tape (NO375) (manufactured by Nitto Denko CS System Co., Ltd.) was attached to the surface of the negative electrode on the side of the mixture layer.

The gauge pressure was set to 7 MPa, and the negative electrode to which the DANPRON tape was attached was pressed for 20 seconds, and then the mixture layer was peeled off from the current collector. The fluorine-strength of the surface of the mixture of the current collector and the surface of the mixture of the current collector and the mixture layer of the release mixture layer are measured by the same method as the fluorine strength of the surface of the electrode. strength.

In addition, the peeling surface of the mixture layer of the current collector separated from the current collector is also referred to as "the peeling surface of the mixture layer", and the peeling surface of the mixture layer of the current collector of the peeling mixture layer is referred to as "The peeling surface of the collector".

The composition of the binder solution used in the examples and the comparative examples and the composition of the negative electrode mixture for a nonaqueous electrolyte secondary battery, the thickness of the obtained mixture layer of the negative electrode, and the evaluation results of the negative electrode are shown in Tables 1 and 2.

Claims (8)

A negative electrode mixture for a nonaqueous electrolyte secondary battery comprising a modified vinylidene fluoride-based polymer, a carbon-based negative electrode active material, and an organic solvent, wherein the modified vinylidene fluoride-based polymer has an intrinsic viscosity of 1.3 dl A polymer obtained by radiation graft copolymerization of a carboxyl group-containing monomer in a vinylidene fluoride polymer of /g or more and a graft amount of 1 to 5 wt%. The negative electrode mixture for a non-aqueous electrolyte secondary battery according to claim 1, wherein the modified vinylidene fluoride-based polymer and the carbon-based negative electrode active material are 100 parts by weight in total, and the modified vinylidene fluoride-based system is modified. The polymer is 1 to 10 parts by weight. The negative electrode mixture for a nonaqueous electrolyte secondary battery according to claim 1, wherein the carbon-based negative electrode active material has a specific surface area of 2 to 6 m ² /g. The negative electrode mixture for a nonaqueous electrolyte secondary battery according to claim 2, wherein the carbon-based negative electrode active material has a specific surface area of 2 to 6 m ² /g. The negative electrode mixture for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the carboxyl group-containing monomer is at least one unsaturated carboxylic acid selected from the group consisting of acrylic acid and methacrylic acid. A negative electrode for a nonaqueous electrolyte secondary battery obtained by applying a negative electrode mixture for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 to a current collector and drying it. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 6, which has a mixture layer having a thickness of 20 to 150 μm formed of the negative electrode mixture for a nonaqueous electrolyte secondary battery. A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 6 or 7.