JP6237306B2 - Slurry composition for positive electrode of lithium ion secondary battery, positive electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a slurry composition for a positive electrode of a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  Lithium ion secondary batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion secondary batteries.

  Here, a positive electrode for a lithium ion secondary battery usually includes a current collector and a positive electrode mixture layer (also referred to as a “positive electrode active material layer”) formed on the current collector. The positive electrode mixture layer is formed, for example, by applying a slurry composition obtained by dissolving or dispersing a positive electrode active material, a conductive material, a binder, or the like in an organic solvent on a current collector and drying it. Therefore, in recent years, attempts have been made to improve the slurry composition used for forming the positive electrode mixture layer in order to achieve further performance improvement of the lithium ion secondary battery.

  Specifically, for example, in Patent Document 1, (meth) acrylic acid alkyl ester, sulfonic acid group-containing unsaturated monomer, amide group-containing unsaturated monomer, and sulfonic acid group / amide group-containing unsaturated monomer By blending into the slurry composition, as a binder, a composite polymer obtained by seed polymerization of at least one selected from the group consisting of bodies in the presence of a seed made of a fluorine-based polymer, the slurry composition It has been proposed to improve the cycle characteristics of a lithium ion secondary battery including a positive electrode manufactured using the above.

International Publication No. 2007/088979

  However, here, there is still room for improvement in terms of further improving the electrical characteristics, particularly the output characteristics and the cycle characteristics, in the lithium ion secondary battery prepared using the slurry composition containing the conventional binder. there were. In addition, when a binder containing a fluorine-containing polymer is used, a dehydrofluorination reaction or thermal decomposition of the fluorine-containing polymer occurs in the lithium ion secondary battery, and the current collector is generated by the generated hydrogen fluoride. From the point that it is thought that there is a possibility that electrical characteristics such as cycle characteristics may be reduced due to corrosion of the active material and deterioration of the active material, the lithium ion secondary battery prepared using the conventional slurry composition However, there was still room for improvement in electrical characteristics.

Then, an object of this invention is to provide the slurry composition for lithium ion secondary battery positive electrodes which can fully improve the output characteristic and cycling characteristic of a lithium ion secondary battery.
The present invention also provides a positive electrode for a lithium ion secondary battery capable of sufficiently improving the output characteristics and cycle characteristics of the lithium ion secondary battery, and a lithium ion secondary battery excellent in output characteristics and cycle characteristics. For the purpose.

  The inventor has intensively studied to achieve the above object. The present inventor includes, as a binder, an amide group-containing monomer unit and a (meth) acrylic acid alkyl ester monomer unit, and the content ratio of the amide group-containing monomer unit is within a specific range. It has been found that the output characteristics and cycle characteristics of a lithium ion secondary battery can be improved by using a slurry composition containing a certain copolymer and a fluorine-containing polymer for forming a positive electrode, and the present invention has been completed. It was.

That is, this invention aims to solve the above-mentioned problem advantageously, and the slurry composition for a lithium ion secondary battery positive electrode of the present invention comprises a binder, a positive electrode active material, a conductive material, and an organic solvent. A slurry composition for a positive electrode of a lithium ion secondary battery, wherein the binder contains an amide group-containing monomer unit and a (meth) acrylic acid alkyl ester monomer unit, and the amide group-containing monomer It contains a copolymer (P1) having a body unit content of 10 to 60% by mass and a fluorine-containing polymer (P2).
Thus, the fluorine-containing copolymer containing the (meth) acrylic acid alkyl ester monomer unit and the amide group-containing monomer unit, and the content ratio of the amide group-containing monomer unit is within the above specific range. If the positive electrode produced using the slurry composition containing the binder used together with the polymer is used, the output characteristics and cycle characteristics of the lithium ion secondary battery can be sufficiently improved.

  Here, the slurry composition for a lithium ion secondary battery positive electrode of the present invention has a content ratio (P1: P2) of the copolymer (P1) and the fluorine-containing polymer (P2) of 5 on a mass basis. : It is preferable that it is 95-50: 50. If the mass ratio of the copolymer (P1) and the fluorine-containing polymer (P2) is within the specific range, the output characteristics and cycle of a lithium ion secondary battery comprising a positive electrode prepared using the slurry composition The characteristics can be further improved.

  Moreover, it is preferable that the electrolyte solution swelling degree of the said copolymer (P1) is 5 times or less as for the slurry composition for lithium ion secondary battery positive electrodes of this invention. If the degree of swelling of the electrolyte solution of the copolymer (P1) is 5 times or less, it is possible to further improve the output characteristics and cycle characteristics of a lithium ion secondary battery including a positive electrode produced using the slurry composition.

  Furthermore, in the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the amide group-containing monomer unit preferably includes at least one of an N-vinylacetamide monomer unit and an acrylamide monomer unit. When the amide group-containing monomer unit includes a monomer unit derived from at least one of N-vinylacetamide and acrylamide, the copolymer (P1) is sufficiently dissolved in the organic solvent in the slurry composition, and the slurry The output characteristics and cycle characteristics of a lithium ion secondary battery including a positive electrode produced using the composition can be further improved.

  In the slurry composition for a positive electrode of a lithium ion secondary battery of the present invention, the (meth) acrylic acid alkyl ester monomer unit is a linear chain in which an alkyl group bonded to a non-carbonyl oxygen atom is 4 or more carbon atoms. Or it is preferable that it is a branched alkyl group. If the alkyl group bonded to the non-carbonyl oxygen atom in the (meth) acrylic acid alkyl ester monomer unit is a linear or branched alkyl group having 4 or more carbon atoms, the copolymer (P1) is in the electrolyte. The output characteristics and cycle characteristics of a lithium ion secondary battery comprising a positive electrode that is suitably swollen and provided with the slurry composition can be further improved.

  And as for the slurry composition for lithium ion secondary battery positive electrodes of this invention, it is preferable that the said fluorine-containing polymer (P2) contains 75 mass% or more of vinylidene fluoride monomer units. If the fluorine-containing polymer (P2) contains 75% by mass or more of a monomer unit derived from vinylidene fluoride, the output characteristics and cycle characteristics of a lithium ion secondary battery including a positive electrode prepared using the slurry composition Further improvement can be achieved.

  In addition, in the slurry composition for a lithium ion secondary battery positive electrode of the present invention, the positive electrode active material is an oxide of at least one element selected from the group consisting of Mg, Ca, Ti, Zr, B, and Al. It is preferable to include lithium cobaltate particles on the surface. If lithium cobalt oxide particles having the oxide as described above on at least a part of the surface are used as a positive electrode active material, decomposition of the electrolyte solution on the surface of the positive electrode active material is suppressed, and a positive electrode manufactured using the slurry composition The cycle characteristics of a lithium ion secondary battery provided with can be further improved.

  Moreover, this invention aims at solving the said subject advantageously, The positive electrode for lithium ion secondary batteries of this invention is the slurry composition for lithium ion secondary battery positive electrodes in any one of the above-mentioned. It has the positive mix layer obtained by using, It is characterized by the above-mentioned. Thus, if a positive electrode mixture layer is formed using the slurry composition described above, a positive electrode for a lithium ion secondary battery capable of sufficiently improving the output characteristics and cycle characteristics of a lithium ion secondary battery is obtained. It is done.

  Furthermore, this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is the above-mentioned positive electrode for lithium ion secondary batteries, a negative electrode, electrolyte solution, And a separator. Thus, if the positive electrode for lithium ion secondary batteries described above is used, a lithium ion secondary battery having excellent output characteristics and cycle characteristics can be obtained.

ADVANTAGE OF THE INVENTION According to this invention, the slurry composition for lithium ion secondary battery positive electrodes which can fully improve the output characteristic and cycling characteristics of a lithium ion secondary battery can be provided.
According to the present invention, there are provided a positive electrode for a lithium ion secondary battery capable of sufficiently improving the output characteristics and cycle characteristics of the lithium ion secondary battery, and a lithium ion secondary battery excellent in output characteristics and cycle characteristics. be able to.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the slurry composition for a lithium ion secondary battery positive electrode of the present invention is used when forming a positive electrode of a lithium ion secondary battery. And the positive electrode for lithium ion secondary batteries of this invention can be produced using the slurry composition for lithium ion secondary battery positive electrodes of this invention. The lithium ion secondary battery of the present invention is characterized by using the positive electrode for a lithium ion secondary battery of the present invention.

(Slurry composition for positive electrode of lithium ion secondary battery)
The slurry composition for a lithium ion secondary battery positive electrode of the present invention is a composition using an organic solvent as a dispersion medium, and includes a binder, a positive electrode active material, and a conductive material in the organic solvent. And as a binder, at least the following polymers (1) and (2):
(1) Copolymer (P1) containing 10 to 60% by mass of an amide group-containing monomer unit and further containing a (meth) acrylic acid alkyl ester monomer unit
(2) Fluorine-containing polymer (P2)
It is characterized by including.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit is contained in a polymer obtained using the monomer”.
In the present invention, “(meth) acryl” means acryl and / or methacryl.

And according to the slurry composition for lithium ion secondary battery positive electrodes of this invention, since the above-mentioned copolymer (P1) and fluorine-containing polymer (P2) are used together as a binder, lithium ion two The electrical characteristics such as output characteristics and cycle characteristics of the secondary battery can be further improved.
Here, the improvement of the electrical characteristics of the lithium ion secondary battery by using the copolymer (P1) and the fluorine-containing polymer (P2) together is the various characteristics (binding properties) of the fluorine-containing polymer (P2). , Mechanical strength, slurry properties, etc.) and the following two properties of the copolymer (P1).

First, since the copolymer (P1) has an amide group-containing monomer unit in a predetermined ratio or more, halogen ions or the like are generated by the amide group in the copolymer (P1) when the positive electrode is formed. It is presumed that the cycle characteristics can be improved by trapping the corrosive substances and suppressing deterioration of the positive electrode active material and corrosion of the current collector. The halogen ion trapped by the amide group of the copolymer (P1) in the lithium ion secondary battery is, for example, hydrogen fluoride generated by dehydrofluorination reaction or thermal decomposition of the fluorine-containing polymer (P2). Fluorine ions derived from them, and halogen ions contained in materials used when manufacturing each battery member (for example, chloride ions mixed in carboxymethyl cellulose used for manufacturing negative electrodes, etc.) .
Secondly, the copolymer (P1) contains a (meth) acrylic acid alkyl ester monomer unit and contains an amide group-containing monomer unit at a predetermined ratio or less, so that it swells appropriately in the electrolyte solution. To do. Since the shape of the copolymer (P1) is maintained in the positive electrode without being excessively swollen (that is, not dissolved) in the electrolyte, the copolymer (P1) is not bonded. It is presumed that the adhesion, the positive electrode active material deterioration suppressing effect, and the current collector corrosion suppressing effect are secured, and the cycle characteristics of the lithium ion secondary battery can be improved. On the other hand, since the copolymer (P1) is swollen to some extent in the electrolytic solution, the diffusibility of the electrolytic solution and the ease of trapping halogen ions by the amide group are preferably ensured. It is presumed that output characteristics and cycle characteristics can be improved.
Hereafter, each component contained in the said slurry composition for lithium ion secondary battery positive electrodes is demonstrated.

<Binder>
In the positive electrode manufactured by forming the positive electrode mixture layer on the current collector using the slurry composition of the present invention, the binder is not desorbed from the positive electrode mixture layer. It is a component that can be held as such. Generally, when the binder in the positive electrode mixture layer is immersed in the electrolytic solution, the positive electrode active material, the positive electrode active material and the conductive material, or between the conductive materials absorb the electrolytic solution and swell. To prevent the positive electrode active material and the like from falling off the current collector.

  And the binder used for the slurry composition of the present invention contains an amide group-containing monomer unit and a (meth) acrylic acid alkyl ester monomer unit, and the content ratio of the amide group-containing monomer unit is 10 to 10. It contains at least the copolymer (P1) and the fluorine-containing polymer (P2) that are 60% by mass. The binder may further contain a known polymer that is conventionally used as a binder, but from the viewpoint of obtaining the above-mentioned effects satisfactorily, the proportion of other polymers in the binder is The content is preferably 10% by mass or less, and the binder is preferably composed only of the copolymer (P1) and the fluorine-containing polymer (P2).

[Copolymer (P1)]
The amide group-containing monomer that can form the amide group-containing monomer unit of the copolymer (P1) is an amide group and a group copolymerizable with another monomer (for example, a carbon group such as a vinyl group). Compound having a carbon unsaturated bond), a compound having an amide group and a carbon-carbon double bond (an amide group-containing vinyl compound) is preferable. Examples of the amide group-containing vinyl compound include N-vinylacetamide, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), N-methylol (meth) acrylamide, and the like. Among these, N-vinylacetamide and acrylamide are preferable from the viewpoint of ensuring the solubility of the copolymer (P1) in the organic solvent in the slurry composition and improving the output characteristics and cycle characteristics. From the viewpoint of improving the output characteristics of the lithium ion secondary battery, N-vinylacetamide is more preferable. That is, the copolymer (P1) preferably contains at least one of an N-vinylacetamide monomer unit and an acrylamide monomer unit as the amide group-containing monomer unit. It is more preferable to contain.
These amide group-containing monomers may be used alone or in combination of two or more.

  Further, the copolymer (P1) used as the binder must have a content ratio of the amide group-containing monomer unit of 10% by mass or more and 60% by mass or less, and 15% by mass or more. Preferably, it is 20 mass% or more, more preferably 50 mass% or less, and even more preferably 40 mass% or less. When the content ratio of the monomer unit derived from the amide group-containing monomer is less than 10% by mass, the cycle characteristics of the lithium ion secondary battery are deteriorated, and the copolymer (P1) of the copolymer (P1) is contained in the slurry composition. Solubility in organic solvents decreases. On the other hand, when the content ratio of the monomer unit derived from the amide group-containing monomer is more than 60% by mass, the copolymer (P1) is excessively swollen in the electrolytic solution, and the output characteristics of the lithium ion secondary battery. In addition, the cycle characteristics deteriorate.

  Examples of the (meth) acrylic acid alkyl ester monomer that can form the (meth) acrylic acid alkyl ester monomer unit of the copolymer (P1) include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n -Alkyl acrylates such as butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl Methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, and methacrylic acid alkyl esters such as stearyl methacrylate. These may be used alone or in combination of two or more.

In the (meth) acrylic acid alkyl ester monomer unit, the number of carbon atoms of the alkyl group bonded to the non-carbonyl oxygen atom is preferably 4 or more, more preferably 6 or more, preferably 14 or less, more preferably Is 10 or less. In the (meth) acrylic acid alkyl ester monomer unit constituting the copolymer (P1), the number of carbon atoms of the alkyl group bonded to the non-carbonyl oxygen atom is 4 or more, whereby the copolymer (P1) It swells moderately in the electrolyte and can further improve the output characteristics and cycle characteristics of the lithium ion secondary battery. Moreover, manufacture of a copolymer (P1) becomes easy because carbon number of the alkyl group couple | bonded with a non-carbonyl oxygen atom is 14 or less. The alkyl group bonded to the non-carbonyl oxygen atom may be a linear alkyl group or a branched alkyl group.
Specifically, as the (meth) acrylic acid alkyl ester monomer, 2-ethylhexyl acrylate (the number of carbon atoms of the alkyl group bonded to the non-carbonyl oxygen atom) is particularly preferable.

  In the copolymer (P1) used as the binder, the content ratio of the (meth) acrylic acid alkyl ester monomer unit is preferably 20% by mass or more, more preferably 30% by mass or more, and particularly preferably. It is 40% by mass or more, preferably 90% by mass or less, more preferably 85% by mass or less, and particularly preferably 80% by mass or less. By making the content rate of the monomer unit derived from the (meth) acrylic acid alkyl ester monomer 20% by mass or more, the flexibility of the copolymer (P1) is increased, and the slurry composition of the present invention is used. The positive electrode obtained in this way can be made difficult to break. Moreover, the solubility to the organic solvent of the copolymer (P1) in a slurry composition can be improved by setting it as 90 mass% or less.

Further, the copolymer (P1) may contain monomer units derived from other monomers copolymerizable with the above-mentioned amide group-containing monomer and (meth) acrylic acid alkyl ester monomer. Good. Examples of such other monomers include (meth) acrylonitrile, unsaturated carboxylic acids such as (meth) acrylic acid, unsaturated sulfonic acids, unsaturated carboxylic acid ester ethylene oxide adducts, and aromatic vinyl compounds such as styrene. And other vinyl compounds excluding amide group-containing monomers and (meth) acrylic acid alkyl ester monomers. These may be used alone or in combination of two or more.
In addition, the adhesiveness of copolymer (P1) improves because copolymer (P1) contains a monomer unit derived from a highly polar monomer such as (meth) acrylic acid or (meth) acrylotolyl. The contact resistance is reduced, and the output characteristics of the lithium ion secondary battery can be improved.

  In the copolymer (P1), the content ratio of the monomer unit derived from the other vinyl compound is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less. Preferably it is 25 mass% or less. By setting the content ratio of monomer units derived from other vinyl compounds to 50% by mass or less, the content ratio of the amide group-containing monomer can be sufficiently ensured, and the cycle characteristics of the lithium ion secondary battery are ensured. can do.

Here, the copolymer (P1) preferably has an electrolyte swelling degree of 5 times or less, more preferably 4 times or less, and still more preferably 3 times or less. If the degree of swelling of the electrolytic solution is 5 times or less, the lithium ion two produced using the slurry composition containing the copolymer (P1) with an appropriate degree of swelling of the copolymer (P1) with respect to the electrolytic solution. The cycle characteristics and output characteristics of the secondary battery can be ensured.
Further, the copolymer (P1) preferably has a degree of electrolyte swelling of 1 or more, more preferably 2 or more. If the degree of swelling of the electrolytic solution is 1 or more, the diffusibility of the electrolytic solution is ensured, and the output characteristics of the lithium ion secondary battery manufactured using the slurry composition containing the copolymer (P1) can be secured. it can. Here, the degree of swelling of the electrolytic solution can be appropriately adjusted by changing the preparation conditions of the copolymer (P1) (for example, monomers used, polymerization conditions, etc.).
In the present invention, the “electrolyte swelling degree” can be measured by using the measuring method described in the examples of the present specification.

  Moreover, the weight average molecular weight of the polystyrene conversion value by the gel permeation chromatography of a copolymer (P1) becomes like this. Preferably it is 10,000-2,000,000, More preferably, it is 50,000-1,000,000, Particularly preferred is 100,000 to 500,000. The viscosity adjustment of a slurry composition becomes easy by making the weight average molecular weight of a copolymer (P1) into the said range.

[Fluorine-containing polymer (P2)]
The fluorine-containing polymer (P2) is a polymer containing a fluorine-containing monomer unit. Specifically, as the fluorine-containing polymer (P2), a homopolymer or copolymer of one or more types of fluorine-containing monomers, one or more types of fluorine-containing monomers and a single amount not containing fluorine. And a copolymer (hereinafter referred to as “a fluorine-free monomer”).
In addition, the content rate of the fluorine-containing monomer unit in a fluorine-containing polymer (P2) is 70 mass% or more normally, Preferably it is 80 mass% or more. Moreover, the content rate of the fluorine-free monomer unit in the fluorine-containing polymer (P2) is usually 30% by mass or less, preferably 20% by mass or less. And the content rate of the amide group containing monomer unit of a fluorine-containing polymer (P2) is less than 10 mass%.

  Here, examples of the fluorine-containing monomer that can form a fluorine-containing monomer unit include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride chloride, vinyl fluoride, and perfluoroalkyl vinyl ether. It is done. Among these, as the fluorine-containing monomer, vinylidene fluoride is preferable.

  Examples of the fluorine-free monomer that can form a fluorine-free monomer unit include a fluorine-free monomer copolymerizable with the fluorine-containing monomer, such as ethylene, propylene, and 1-butene. 1-olefin; aromatic vinyl compounds such as styrene, α-methylstyrene, pt-butylstyrene, vinyltoluene, chlorostyrene; unsaturated nitrile compounds such as (meth) acrylonitrile; methyl (meth) acrylate, ( (Meth) acrylic acid ester compounds such as (meth) butyl acrylate and (meth) acrylic acid 2-ethylhexyl; (meth) such as (meth) acrylamide, N-methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide Acrylamide compound (amide group-containing monomer); (meth) acrylic acid, itaconic acid, Vinyl compounds containing carboxyl groups such as malic acid, crotonic acid and maleic acid; epoxy group-containing unsaturated compounds such as allyl glycidyl ether and glycidyl (meth) acrylate; dimethylaminoethyl (meth) acrylate and (meth) acrylic Amino group-containing unsaturated compounds such as diethylaminoethyl acid; Sulphonic acid group-containing unsaturated compounds such as styrene sulfonic acid, vinyl sulfonic acid, (meth) allyl sulfonic acid; and sulfate groups such as 3-allyloxy-2-hydroxypropanesulfuric acid Unsaturated compounds; phosphate group-containing unsaturated compounds such as (meth) acrylic acid-3-chloro-2-phosphate, 3-allyloxy-2-hydroxypropane phosphate, and the like.

The fluorine-containing polymer (P2) is preferably a polymer using vinylidene fluoride as the fluorine-containing monomer and a polymer using hexafluoropropylene as the fluorine-containing monomer. A polymer using vinylidene fluoride is more preferable.
Specifically, the fluorine-containing polymer (P2) is preferably a homopolymer of vinylidene fluoride (polyvinylidene fluoride), a copolymer of vinylidene fluoride and hexafluoropropylene, or polyvinyl fluoride, and polyvinylidene fluoride. Is more preferable.
In addition, the fluorine-containing polymer (P2) described above may be used alone or in combination of two or more.

  In the fluorine-containing polymer (P2), the content ratio of the vinylidene fluoride monomer unit is preferably 75% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 98%. % By mass or more, most preferably 100% by mass. When the content ratio of the monomer unit derived from the vinylidene fluoride monomer is 75% by mass or more, excessive swelling of the fluorine-containing polymer (P2) in the electrolytic solution is suppressed, and the slurry composition is The output characteristic of a lithium ion secondary battery provided with the positive electrode produced by using can be further improved.

  The weight average molecular weight in terms of polystyrene by gel permeation chromatography of the fluorine-containing polymer (P2) is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, particularly Preferably it is 400,000-1,000,000. By setting the weight average molecular weight of the fluorine-containing polymer (P2) within the above range, detachment (powder falling) from the positive electrode mixture layer such as the positive electrode active material or the conductive material is suppressed, and the viscosity of the slurry composition is adjusted. Becomes easier.

[Method for Preparing Copolymer (P1) and Fluorine-Containing Polymer (P2)]
The copolymer (P1) and the fluorine-containing polymer (P2) are produced, for example, by polymerizing a monomer composition containing the above-described monomers in an aqueous solvent. In the present invention, the content ratio of each monomer in the monomer composition is determined according to the content ratio of the monomer units (repeating units) in the copolymer (P1) and the fluorine-containing polymer (P2). Can do.
Here, the production method of the copolymer (P1) and the fluorine-containing polymer (P2) described above is not particularly limited. For example, any of a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsion polymerization method and the like can be used. This method can also be used.
As the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization and the like can be used. Moreover, as a polymerization initiator, a known polymerization initiator can be used.

  The copolymer (P1) and the fluorine-containing polymer (P2) are in the state of a polymer in which at least a part is complexed, for example, by producing either one by using one as a seed and seed polymerizing the other. In the slurry composition of the present invention, it is preferable to prepare and use the copolymer (P1) and the fluorine-containing polymer (P2) separately. When the copolymer (P1) and the fluorine-containing polymer (P2) are combined, there is a risk that the coating properties of the slurry composition will decrease, and the copolymer (P1) and the fluorine-containing polymer This is because there is a possibility that the effect of using the combination (P2) together cannot be obtained sufficiently.

  The copolymer (P1) and the fluorine-containing polymer (P2) are used in the state of a dispersion liquid or a dissolved solution dispersed in a dispersion medium. The dispersion medium for the copolymer (P1) and the fluorine-containing polymer (P2) is not particularly limited as long as it can uniformly disperse or dissolve the copolymer (P1) and the fluorine-containing polymer (P2). First, water or an organic solvent can be used, and an organic solvent is preferably used. In addition, it does not specifically limit as an organic solvent, The organic solvent used for the slurry composition of this invention can be used.

[Contents of copolymer (P1) and fluorine-containing polymer (P2) in slurry composition]
Here, in the slurry composition of the present invention, the content ratio (P1: P2) of the copolymer (P1) and the fluorine-containing polymer (P2) is 5:95 to 50:50 on a mass basis. It is preferably 5:95 to 30:70, more preferably 115: 85 to 30:70, and particularly preferably 20:80 to 30:70. When the copolymer (P1) is larger than P1: P2 = 5: 95, the cycle characteristics of the lithium ion secondary battery can be sufficiently improved. Further, P1: P2 = the amount of fluorine-containing polymer (P2) is larger than 50:50, whereby aggregation of the conductive material and the positive electrode active material in the slurry composition is suppressed, and a positive electrode produced using the slurry composition is provided. The output characteristics of the lithium ion secondary battery can be further improved.

  The content of the binder (including the copolymer P1 and the fluorine-containing polymer P2) in the slurry composition of the present invention is preferably 0.1 per 100 parts by mass of the positive electrode active material in terms of solid content. It is at least part by mass, more preferably at least 0.5 part by mass, preferably at most 10 parts by mass, more preferably at most 5 parts by mass. By setting the content of the binder to 0.1 parts by mass or more per 100 parts by mass of the positive electrode active material, the positive electrode active materials, the positive electrode active material and the conductive material, and the binding property between the positive electrode active material and the current collector are increased. Therefore, when a lithium ion secondary battery is used, good output characteristics can be obtained and the battery life can be extended. Moreover, when the positive electrode obtained by using the slurry composition containing the binder is applied to the lithium ion secondary battery by setting it to 10 parts by mass or less, the diffusibility of the electrolytic solution is ensured and good output characteristics are obtained. Can be obtained.

<Positive electrode active material>
As a positive electrode active material mix | blended with a slurry composition, it does not specifically limit, For example, known positive electrode active materials, such as the positive electrode active material described in Unexamined-Japanese-Patent No. 2013-152955, can be used. Among these, as the positive electrode active material, lithium cobalt oxide (LiCoO ₂ ) particles having an oxide of at least one element selected from the group consisting of Mg, Ca, Ti, Zr, B, and Al on the surface are preferable. By using lithium cobaltate particles in which at least a part of the particle surface contains an oxide of at least one element selected from the group consisting of Mg, Ca, Ti, Zr, B, and Al, the surface of the positive electrode active material The decomposition of the electrolytic solution in the battery can be suppressed, and the cycle characteristics of the lithium ion secondary battery can be improved. This effect is particularly prominent when the lithium ion secondary battery is used at a high voltage.

And from the viewpoint of improving the cycle characteristics of the lithium ion secondary battery, the positive electrode active material is a lithium cobalt oxide particle having an oxide of at least one element selected from the group consisting of Mg, Ti, Zr, and Al on the surface Are more preferable, and lithium cobaltate particles having a Zr oxide on the surface are particularly preferable. Examples of the Zr oxide that may be present on at least a part of the surface of the lithium cobalt oxide particles include ZrO ₂ and the Zr compounds described in JP-A-2008-311132. Among these, ZrO ₂ is particularly preferable.

  Here, the compounding amount and particle size of the positive electrode active material, and the amount of oxide present on the surface of the lithium cobalt oxide particles are not particularly limited, and may be the same as those of conventionally used positive electrode active materials. it can.

<Conductive material>
The conductive material is for ensuring electrical contact between the positive electrode active materials. The conductive material is not particularly limited, and a known conductive material can be used. Specifically, as the conductive material, acetylene black, ketjen black (registered trademark), furnace black, graphite, carbon fiber, carbon flake, carbon ultrashort fiber (for example, carbon nanotube, vapor grown carbon fiber, etc.), etc. Conductive carbon materials: various metal fibers, foils and the like can be used. Among these, acetylene black is used as the conductive material from the viewpoint of improving the electrical contact between the positive electrode active materials and improving the electrical characteristics of the lithium ion secondary battery using the positive electrode formed using the slurry composition. Ketjen Black (registered trademark) and furnace black are preferably used, and acetylene black is particularly preferably used.
In addition, these electrically conductive materials may be used individually by 1 type, and may be used in combination of 2 or more types.

  The blending amount of the conductive material is preferably 1 part by mass or more, more preferably 1.2 parts by mass or more, and preferably 3 parts by mass or less, per 100 parts by mass of the positive electrode active material. It is more preferable that it is 2.8 parts by mass or less. If the blending amount of the conductive material is too small, sufficient electrical contact between the positive electrode active materials cannot be secured, and the electrical characteristics of the lithium ion secondary battery may not be secured sufficiently. On the other hand, when the blending amount of the conductive material is too large, the stability of the slurry composition is lowered and the density of the positive electrode mixture layer in the positive electrode is lowered, so that the capacity of the lithium ion secondary battery cannot be sufficiently increased. There is a fear.

<Organic solvent>
As the organic solvent contained in the slurry composition of the present invention, an organic solvent capable of dissolving the binder can be used. Specifically, as the organic solvent, acetonitrile, N-methyl-2-pyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethylsulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, and the like can be used. Among these, N-methyl-2-pyrrolidone is particularly preferable as the organic solvent from the viewpoints of ease of handling, safety, and ease of synthesis.

<Other ingredients>
In addition to the above components, the slurry composition of the present invention may contain components such as a viscosity modifier, a reinforcing material, an antioxidant, and an electrolytic solution additive having a function of suppressing decomposition of the electrolytic solution. Good. As these other components, known ones can be used.

<Method for producing slurry composition for positive electrode of lithium ion secondary battery>
The slurry composition of the present invention can be prepared by dissolving and / or dispersing each component in an organic solvent. Specifically, the slurry composition is prepared in advance, for example, by containing a copolymer (P1) -containing composition containing a copolymer (P1) as a binder and an organic solvent (containing the copolymer (P1)). Composition preparation step), then copolymer (P1) -containing composition, fluorine-containing polymer (P2) as a binder, positive electrode active material, conductive material, and optionally other components and additions It can be prepared by mixing with an organic solvent (mixing step).

  Here, the copolymer (P1) -containing composition described above can be prepared, for example, by replacing water in the aqueous dispersion of the copolymer (P1) with an organic solvent. The replacement of water with an organic solvent can be performed, for example, by adding an organic solvent having a boiling point higher than that of water and then evaporating the entire amount of water and a part of the organic solvent under reduced pressure.

  For mixing in the mixing step, known mixers such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crushed grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, and a fill mix can be used. Moreover, as an additional organic solvent, the same thing as the organic solvent used for preparation of a copolymer (P1) containing composition can be used.

(Positive electrode for lithium ion secondary battery)
The positive electrode for a lithium ion secondary battery of the present invention has a positive electrode mixture layer obtained using the slurry composition of the present invention. More specifically, the positive electrode for a lithium ion secondary battery of the present invention includes a current collector and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer includes at least a positive electrode active layer. A substance, a conductive material, and a binder are included. The positive electrode active material, the conductive material and the binder contained in the positive electrode are those contained in the slurry composition of the present invention, and the preferred abundance ratio of each of these components is the present invention. It is the same as the suitable abundance ratio of each component in the slurry composition.

  In the positive electrode for a lithium ion secondary battery of the present invention, since the positive electrode mixture layer is formed using the slurry composition of the present invention described above, the output characteristics and cycle characteristics of the lithium ion secondary battery are sufficient. Can be improved.

  The positive electrode for a lithium ion secondary battery of the present invention is applied to, for example, a step of applying the above-described slurry composition for a lithium ion secondary battery positive electrode on a current collector (application step), and a current collector. The lithium ion secondary battery positive electrode slurry composition is dried to form a positive electrode mixture layer on the current collector (drying step).

<Application process>
A method for applying the slurry composition for a lithium ion secondary battery positive electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied to only one side of the current collector or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the positive electrode mixture layer obtained by drying.

  Here, as the current collector to which the slurry composition is applied, an electrically conductive and electrochemically durable material is used. Specifically, a current collector made of aluminum or an aluminum alloy can be used as the current collector. At this time, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they have heat resistance and are electrochemically stable.

<Drying process>
A method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying with warm air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. A drying method is mentioned. In this way, by drying the slurry composition on the current collector, a positive electrode mixture layer is formed on the current collector to obtain a positive electrode for a lithium ion secondary battery including the current collector and the positive electrode mixture layer. be able to.

Note that after the drying step, the positive electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the positive electrode mixture layer and the current collector can be improved.
Furthermore, when the positive electrode mixture layer contains a curable polymer, the polymer is preferably cured after the positive electrode mixture layer is formed.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the positive electrode for a lithium ion secondary battery of the present invention is used as the positive electrode. And since the lithium ion secondary battery of this invention uses the positive electrode for lithium ion secondary batteries of this invention, it is excellent in an output characteristic and cycling characteristics.

<Negative electrode>
As a negative electrode of a lithium ion secondary battery, a known negative electrode used as a negative electrode for a lithium ion secondary battery can be used. Specifically, as the negative electrode, for example, a negative electrode made of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode mixture layer on a current collector can be used.
In addition, as a collector, what consists of metal materials, such as iron, copper, aluminum, nickel, stainless steel, titanium, a tantalum, gold | metal | money, platinum, can be used. As the negative electrode mixture layer, a layer containing a negative electrode active material and a binder can be used.

  Here, when a negative electrode formed by forming a negative electrode mixture layer on a current collector as a negative electrode and a viscosity modifier such as carboxymethyl cellulose is contained in the negative electrode mixture layer, as described above, When a lithium ion secondary battery is formed, there is a possibility that halogen ions such as chloride ions mixed during the production of carboxymethylcellulose may elute into the electrolyte. However, when the positive electrode of the present invention is used, halogen ions such as chloride ions can be trapped by the amide group of the copolymer (P1), so that chloride ions eluted from the negative electrode side into the electrolyte solution can be used. Halogen ions can suppress deterioration of the positive electrode active material and corrosion of the current collector.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, a lithium salt is used as the supporting electrolyte. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easily dissolved in a solvent and exhibits a high degree of dissociation. In addition, electrolyte may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Usually, the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, so that the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide Etc. are preferably used. Moreover, you may use the liquid mixture of these solvents. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential region, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted depending on the type of solvent.
In addition, the density | concentration of the electrolyte in electrolyte solution can be adjusted suitably, for example, it is preferable to set it as 0.5-15 mass%, it is more preferable to set it as 2-13 mass%, and it shall be 5-10 mass%. Is more preferable. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolytic solution.

<Separator>
As a separator, it is not specifically limited, For example, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used. Among these, the film thickness of the entire separator can be reduced, thereby increasing the ratio of the electrode active material in the secondary battery and increasing the capacity per volume. A microporous film made of a resin such as polyethylene, polypropylene, polybutene, or polyvinyl chloride is preferable.

<Method for producing lithium ion secondary battery>
In the lithium ion secondary battery of the present invention, for example, a positive electrode and a negative electrode are overlapped via a separator, and this is wound into a battery container according to the battery shape as necessary, and placed in the battery container. It can manufacture by inject | pouring electrolyte solution into and sealing. In order to prevent an increase in pressure inside the lithium ion secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, and a flat shape.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
The electrolyte solution swelling degree of the copolymer (P1), the output characteristics and the cycle characteristics of the lithium ion secondary battery were evaluated using the following methods, respectively.

<Electrolytic solution swelling>
An N-methyl-2-pyrrolidone solution (copolymer (P1) -containing composition) having a concentration of 8% of the prepared copolymer (P1) is dried to a Teflon (registered trademark) petri dish so that the thickness after drying becomes 100 μm. The polymer film was prepared by pouring into and drying. A circular sample having a diameter of 16 mm was punched out of the obtained polymer film, and the weight was measured (weight is assumed to be “A”). Next, a nonaqueous electrolytic solution (composition: a LiPF ₆ solution having a concentration of 1.0 M (a solvent is a mixed solvent of ethylene carbonate / diethyl carbonate = 1/2 (weight ratio)) was prepared. Then, the circular sample was immersed for 72 hours at 60 ° C. After that, the swollen circular sample was taken out and the surface non-aqueous electrolyte was lightly wiped, and the weight was measured (weight is set to “B”). The degree of swelling of the electrolyte solution (= B / A) was determined from the value, and the larger the value, the easier the swelling in the electrolyte solution and the greater the deformation amount.
<Output characteristics>
The prepared pouch-type lithium ion secondary battery was charged with constant current at a current of 140 mA until the voltage reached 4.4 V in a 25 ° C. environment, and was charged with a constant voltage until the charging current reached 14 mA at a voltage of 4.4 V. . Subsequently, constant current discharge was performed until the battery voltage became 3 V at a current of 140 mA to obtain an initial capacity.
A pouch-type lithium-ion secondary battery whose initial capacity was measured was charged at a constant current in an environment of 25 ° C. at 140 mA until the battery voltage reached 4.4 V, and then charged at a voltage of 4.4 V until the charging current reached 14 mA. Went. Subsequently, constant current discharge was performed until the battery voltage reached 3.0 V at a current of 1400 mA to obtain a 2C capacity. The value of (2C capacity) / (initial capacity) × 100 (%) was used as an output characteristic, and evaluation was performed according to the following criteria. The higher this value, the better the initial output characteristics, that is, the smaller the internal resistance.
A: The output characteristic is 90% or more.
B: Output characteristics are 87% or more and less than 90%.
C: The output characteristic is 84% or more and less than 87%.
D: The output characteristic is less than 84%.
<Cycle characteristics>
For a pouch-type lithium ion secondary battery whose output characteristics were evaluated, an operation was performed 100 times in an environment of 60 ° C., charging at 700 mA until the battery voltage reached 4.4 V, and discharging at 700 mA until the battery voltage reached 3.0 V. The discharge capacity was measured repeatedly (100 cycles). The ratio of the discharge capacity at the end of one cycle to the discharge capacity at the end of 100 cycles is calculated as a percentage (= (discharge capacity at the end of 100 cycles) / (discharge capacity at the end of one cycle) × 100%). The cycle characteristics were evaluated based on the following criteria using the discharge capacity retention rate. The higher the charge / discharge capacity retention value, the better the high-temperature cycle characteristics.
A: The charge / discharge capacity retention is 80% or more.
B: The charge / discharge capacity retention is 77% or more and less than 80%.
C: The charge / discharge capacity retention is 74% or more and less than 77%.
D: The charge / discharge capacity retention is 70% or more and less than 74%.
D: The charge / discharge capacity retention is less than 70%.

Example 1
<Preparation of copolymer (P1)>
In a flask equipped with a stirrer, 90 parts by mass of ion-exchanged water and 0.7 parts by mass of sodium dodecyl diphenyl ether sulfonate as an emulsifier were added. Then, 25 parts by mass of N-vinylacetamide as an amide group-containing monomer, (meth) acrylic acid As an alkyl ester monomer, 75 parts by mass of 2-ethylhexyl acrylate was added and sufficiently stirred. Thereafter, the temperature was raised to 70 ° C. and kept at the temperature. After adding 0.3 part of potassium persulfate as a polymerization initiator, polymerization was carried out by heating at 70 ° C. for 3 hours and at 80 ° C. for 2 hours to obtain an aqueous dispersion of copolymer P1.
Subsequently, N-methyl-2-pyrrolidone (NMP) was added to the aqueous dispersion of the obtained copolymer P1 so that the solid content of the copolymer was 7%. Then, distillation under reduced pressure was carried out at 90 ° C. to remove water and excess NMP, and an NMP solution (copolymer (P1) -containing composition) of a copolymer (P1) having a solid content concentration of 8% was obtained. .
And the electrolyte solution swelling degree of the copolymer (P1) was measured using the obtained copolymer (P1) containing composition. The results are shown in Table 1.

<Preparation of slurry composition for positive electrode of lithium ion secondary battery>
100 parts of lithium cobaltate particles (volume average particle diameter: 20 μm) having Zr oxide (ZrO ₂ ) on the particle surface as a positive electrode active material, and acetylene black (AcB, manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black as a conductive material) (Registered Trademark) Powdery Product: 2.0 parts of number average particle diameter 35 nm, specific surface area 68 m ^{2 /} g) and the copolymer (P1) -containing composition prepared as described above is 0.4 in terms of solid content. And 1.6 parts of PVDF (100% content of monomer units derived from vinylidene fluoride) as the fluorine-containing polymer (P2) in solid content, and NMP in the planetary mixer Was added to 78% and kneaded for 60 minutes. The share during the kneading was 680 W / kg. Thereafter, NMP was further added and kneaded using a planetary mixer to prepare a positive electrode slurry composition. This positive electrode slurry composition had a viscosity of about 4000 mPa · s measured using a double-cylinder rotational viscometer under conditions of a temperature of 25 ° C. and a shear rate of 20 s ⁻¹ .

<Preparation of positive electrode for lithium ion secondary battery>
An aluminum foil having a thickness of 15 μm was prepared as a current collector. And the said slurry composition for positive electrodes was apply | coated so that the application quantity after drying might be 20 mg / cm < ² > on both surfaces of aluminum foil, and it dried for 20 minutes at 60 degreeC and 20 minutes, and obtained the positive electrode original fabric It was. This positive electrode original fabric was rolled by a roll press to produce a sheet-like positive electrode comprising a positive electrode mixture layer having a density of 3.7 g / cm ³ and an aluminum foil. And the sheet-like positive electrode was cut | disconnected to width 4.8mm and length 50cm, and it was set as the positive electrode for secondary batteries.

<Preparation of negative electrode for lithium ion secondary battery>
Spherical artificial graphite (volume average particle diameter: 12 μm) 100 parts as negative electrode active material, styrene butadiene polymer (number average particle diameter: 180 nm, glass transition temperature: −40 ° C.) 1 part as binder, carboxy as viscosity modifier 1 part of methylcellulose and an appropriate amount of water were stirred with a planetary mixer to prepare a slurry composition for a negative electrode.
Next, a copper foil having a thickness of 15 μm was prepared as a current collector. And the said slurry composition for negative electrodes was apply | coated so that the application quantity after drying might be set to 12 mg / cm < ² > on both surfaces of copper foil, after drying for 20 minutes at 50 degreeC and 120 degreeC, for 2 hours at 150 degreeC The negative electrode raw material was obtained by heat treatment. This negative electrode raw material was rolled with a roll press to prepare a sheet-like negative electrode comprising a negative electrode mixture layer having a density of 1.8 g / cm ³ and a copper foil. And the sheet-like negative electrode was cut | disconnected to width 5.0mm and length 52cm, and it was set as the negative electrode for secondary batteries.

<Production of lithium ion secondary battery>
The produced positive electrode for a lithium ion secondary battery and the negative electrode for a lithium ion secondary battery were wound using a core having a diameter of 20 mm with a separator (a polypropylene microporous film having a thickness of 20 μm) interposed therebetween to obtain a wound body. Obtained. The obtained wound body was compressed from one direction until the thickness became 4.5 mm at a speed of 10 mm / second. The wound body after compression had an elliptical shape in plan view, and the ratio of the major axis to the minor axis (major axis / minor axis) was 7.7.
Further, a nonaqueous electrolytic solution (composition: LiPF ₆ solution having a concentration of 1.0 M (a solvent is a mixed solvent of ethylene carbonate / diethyl carbonate = 1/2 (weight ratio)) was prepared.
And the compressed winding body was accommodated in the predetermined aluminum laminate case with 3.2 g of non-aqueous electrolyte. And after connecting the nickel lead wire connected to the negative electrode and the aluminum lead wire connected to the positive electrode to a predetermined location, the opening of the case was sealed with heat to obtain a lithium ion secondary battery. This lithium ion secondary battery is a pouch having a width of 35 mm, a height of 48 mm, and a thickness of 5 mm, and the nominal capacity of the battery is 700 mAh. The output characteristics and cycle characteristics of the obtained lithium ion secondary battery were evaluated. The results are shown in Table 1.

(Examples 2, 4 to 7)
The slurry composition for the copolymer P1 and the positive electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amounts of N-vinylacetamide and 2-ethylhexyl acrylate were changed as shown in Table 1 when preparing the copolymer P1. Products, positive electrodes for lithium ion secondary batteries, negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries were manufactured and evaluated. The results are shown in Table 1.

(Example 3)
Copolymer P1, slurry composition for positive electrode of lithium ion secondary battery, lithium, except that N-vinylacetamide as an amide group-containing monomer was changed to acrylamide at the time of preparing copolymer P1, lithium ion secondary battery positive electrode slurry composition, lithium A positive electrode for an ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were manufactured and evaluated. The results are shown in Table 1.

(Example 8)
Copolymer P1 and lithium ion secondary battery were the same as in Example 1 except that 2-ethylhexyl acrylate as a (meth) acrylic acid alkyl ester monomer was changed to n-butyl acrylate at the time of preparing copolymer P1. A slurry composition for positive electrode, a positive electrode for lithium ion secondary battery, a negative electrode for lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Examples 9 and 10)
The amount of 2-ethylhexyl acrylate was changed to 45 parts by mass at the time of preparing the copolymer P1, and as other monomers, 30 parts by mass of methacrylic acid and 30 parts by mass of acrylonitrile were added, respectively. Similarly, copolymer P1, lithium ion secondary battery positive electrode slurry composition, lithium ion secondary battery positive electrode, lithium ion secondary battery negative electrode and lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

(Examples 11 to 13)
The slurry composition for the copolymer P1 and the positive electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amounts of the copolymer P1 and the fluorine-containing polymer P2 were changed as shown in Table 1 when the slurry composition was prepared. Products, positive electrodes for lithium ion secondary batteries, negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries were manufactured and evaluated. The results are shown in Table 1.

(Examples 14 and 15)
Except for using lithium cobaltate particles having an oxide of Al (Al ₂ O ₃ ) on the particle surface and lithium cobaltate particles having an oxide of Mg (MgO) on the particle surface as the positive electrode active material, A copolymer P1, a slurry composition for a lithium ion secondary battery positive electrode, a positive electrode for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were manufactured and evaluated in the same manner as in Example 1. I did it. The results are shown in Table 1.

(Comparative Example 1)
The slurry composition for the copolymer P1 and the positive electrode of the lithium ion secondary battery in the same manner as in Example 1 except that the blending amounts of N-vinylacetamide and 2-ethylhexyl acrylate were changed as shown in Table 1 when preparing the copolymer P1. Products, positive electrodes for lithium ion secondary batteries, negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries were manufactured and evaluated. The results are shown in Table 1.

(Comparative Example 2)
An aqueous dispersion of the copolymer P1 was prepared in the same manner as in Example 1 except that the blending amounts of N-vinylacetamide and 2-ethylhexyl acrylate were changed as shown in Table 1 when the copolymer P1 was prepared. The polymer P1 was not dissolved in NMP, and a slurry composition for a lithium ion secondary battery positive electrode could not be prepared.

(Comparative Example 3)
A lithium ion secondary battery was carried out in the same manner as in Example 1 except that the copolymer P1 was not used and 2.0 parts of PVDF as the fluorine-containing polymer (P2) was used as the binder, corresponding to the solid content. A slurry composition for positive electrode, a positive electrode for lithium ion secondary battery, a negative electrode for lithium ion secondary battery, and a lithium ion secondary battery were produced and evaluated. The results are shown in Table 1.

  In Table 1 below, N-vinylacetamide is "NVA", acrylamide is "AA", 2-ethylhexyl acrylate is "2-EHA", n-butyl acrylate is "n-BA", methacryl The number of carbon atoms of the alkyl group bonded to the non-carbonyl oxygen atom in the (meth) acrylic acid alkyl ester monomer unit is “MAA” for the acid, “AN” for the acrylonitrile, “VDF” for the vinylidene fluoride. Abbreviated as “carbon number”.

From Table 1, it contains a copolymer (P1) containing an amide group-containing monomer unit at a predetermined ratio and containing a (meth) acrylic acid alkyl ester monomer unit, and a fluorine-containing polymer (P2). In Examples 1 to 15 using the binder, it can be seen that the cycle characteristics and the output characteristics are excellent.
On the other hand, in Comparative Example 1 using the copolymer (P1) in which the content ratio of the amide group-containing monomer unit exceeds the predetermined range, the cycle characteristics can be secured to some extent, but the output characteristics are extremely bad, It can be seen that the cycle characteristics and the output characteristics cannot be improved in a balanced manner. Further, in Comparative Example 2 using the copolymer (P1) in which the content ratio of the amide group-containing monomer unit is less than the predetermined range, the copolymer P1 is not dissolved in NMP as described above. A slurry composition for an ion secondary battery positive electrode could not be prepared.

Furthermore, it can be seen from Examples 1 and 3 in Table 1 that the output characteristics of the lithium ion secondary battery can be further improved by changing the type of the amide group-containing monomer in the copolymer (P1).
Further, from Examples 1, 2, and 4 to 7 in Table 1, the output characteristics and cycle characteristics of the lithium ion secondary battery are further improved by changing the ratio of the amide group-containing monomer in the copolymer (P1). It can be seen that it can be improved.
Furthermore, from Examples 1 and 8 in Table 1, the output characteristics and cycle characteristics of the lithium ion secondary battery are further improved by changing the type of the (meth) acrylic acid alkyl ester monomer in the copolymer (P1). It can be seen that it can be improved.
In addition, by changing the content ratio of the copolymer (P1) and the fluorine-containing polymer (P2) from Examples 1 and 11 to 13 in Table 1, the output characteristics and cycle of the lithium ion secondary battery It can be seen that the characteristics can be further improved.
Further, from Examples 1, 14 and 15 of Table 1, the cycle characteristics of the lithium ion secondary battery can be further improved by changing the type of oxide present on the surface of the lithium cobalt oxide particles as the positive electrode active material. I know you get.

ADVANTAGE OF THE INVENTION According to this invention, the slurry composition for lithium ion secondary battery positive electrodes which can fully improve the output characteristic and cycling characteristics of a lithium ion secondary battery can be provided.
According to the present invention, there are provided a positive electrode for a lithium ion secondary battery capable of sufficiently improving the output characteristics and cycle characteristics of the lithium ion secondary battery, and a lithium ion secondary battery excellent in output characteristics and cycle characteristics. be able to.

Claims (9)

A slurry composition for a lithium ion secondary battery positive electrode containing a binder, a positive electrode active material, a conductive material, and an organic solvent, wherein the binder comprises:
A copolymer (P1) containing an amide group-containing monomer unit and a (meth) acrylic acid alkyl ester monomer unit, wherein the content of the amide group-containing monomer unit is 10 to 60% by mass;
Fluorine-containing polymer and (P2) only contains,
The slurry composition for a lithium ion secondary battery positive electrode , wherein the content ratio (P1: P2) of the copolymer (P1) and the fluorine-containing polymer (P2) is 5:95 to 30:70 on a mass basis. object. The slurry composition for lithium ion secondary battery positive electrodes of Claim 1 whose electrolyte solution swelling degree of the said copolymer (P1) is 5 times or less. The slurry composition for a lithium ion secondary battery positive electrode according to claim 1 or 2 , wherein the amide group-containing monomer unit includes at least one of an N-vinylacetamide monomer unit and an acrylamide monomer unit. The slurry composition for lithium ion secondary battery positive electrodes as described in any one of Claims 1-3 in which the said fluorine-containing polymer (P2) contains 75 mass% or more of vinylidene fluoride monomer units. The positive electrode active material, Mg, including Ca, Ti, Zr, B, lithium cobalt oxide particles having an oxide of at least one element selected from the group consisting of Al on the surface, any one of claims 1 to 4 The slurry composition for a lithium ion secondary battery positive electrode according to one item. The lithium ion secondary according to any one of claims 1 to 5, wherein the (meth) acrylic acid alkyl ester monomer unit has 6 or more carbon atoms of an alkyl group bonded to a non-carbonyl oxygen atom. A slurry composition for a battery positive electrode. The lithium ion as described in any one of Claims 1-6 whose content rate of the said (meth) acrylic-acid alkylester monomer unit of the said copolymer (P1) is 20 mass% or more and 85 mass% or less. A slurry composition for a secondary battery positive electrode.   The positive electrode for lithium ion secondary batteries which has a positive mix layer obtained using the slurry composition for lithium ion secondary battery positive electrodes as described in any one of Claims 1-7.   A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 8, a negative electrode, an electrolytic solution, and a separator.