JP2017069108A - Slurry composition for lithium ion secondary battery electrode, lithium ion secondary battery electrode and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry composition for a lithium ion secondary battery electrode, which has good coatability, and enables the formation of a lithium ion secondary battery electrode superior in peel strength.SOLUTION: A slurry composition for a lithium ion secondary battery electrode comprises: a water-soluble chitosan compound; a particulate polymer; and an electrode active material.SELECTED DRAWING: None

Description

  The present invention relates to a slurry composition for a lithium ion secondary battery electrode, an 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, the electrode for lithium ion secondary batteries is normally equipped with the electrical power collector and the electrode compound-material layer (positive electrode compound material layer or negative electrode compound material layer) formed on the electrical power collector. And this electrode compound-material layer is formed by apply | coating the slurry composition containing an electrode active material and a binder on a collector, and drying the apply | coated slurry composition, for example.

  In recent years, therefore, attempts have been made to improve the slurry composition used for forming the electrode mixture layer in order to achieve further improvement in the performance of the lithium ion secondary battery. (For example, refer to Patent Documents 1 and 2).

In Patent Document 1, by using a slurry composition containing a chitosan derivative having a predetermined structure as a binder, the contact resistance is reduced while improving the adhesion between the positive electrode mixture layer and the current collector, Techniques for improving battery characteristics of lithium ion secondary batteries have been reported.
In Patent Document 2, by using carboxyalkyl chitosan having an average substitution degree of 0.1 or more or a salt thereof as a binder, the coating property of the slurry composition and the adhesion between the electrode mixture layer and the current collector are improved. Technology to improve has been reported. According to Patent Document 2, a binder composed of a carboxyalkyl chitosan having an average degree of substitution of 0.1 or more and a salt thereof having excellent binding properties does not need to be used in combination with other binders. The handleability can be improved.

JP 2009-277660 A Japanese Patent Laying-Open No. 2015-5474

  However, in the conventional electrode slurry composition, if the amount of the predetermined chitosan derivative used as the binder is increased in order to more firmly adhere the electrode mixture layer and the current collector, the electrode slurry composition is excessively increased. As a result, the coating property is impaired and the battery characteristics such as cycle characteristics are deteriorated. That is, the above conventional technique still has a good balance between improving the coating property of the electrode slurry composition and the peel strength of the electrode (adhesiveness between the electrode mixture layer and the current collector). There was room for improvement.

Then, an object of this invention is to provide the slurry composition for lithium ion secondary battery electrodes which can form the electrode for lithium ion secondary batteries which has favorable coating property and is excellent in peel strength.
Another object of the present invention is to provide a lithium ion secondary battery electrode having excellent peel strength and a lithium ion secondary battery having excellent cycle characteristics.

  The present inventor has intensively studied for the purpose of solving the above problems. Then, the present inventor found that a slurry composition containing a water-soluble chitosan compound, a particulate polymer, and an electrode active material is excellent in coating properties on a current collector, and peel strength can be obtained by using the slurry composition. The present invention was completed by finding that an electrode excellent in resistance was obtained.

  That is, the object of the present invention is to advantageously solve the above problems, and the slurry composition for lithium ion secondary battery electrodes of the present invention comprises a water-soluble chitosan compound, a particulate polymer, and an electrode active material. It is characterized by containing a substance. Thus, the slurry composition using both the water-soluble chitosan compound and the particulate polymer has good coatability, and an electrode having excellent peel strength can be obtained by using the slurry composition.

Here, in the slurry composition for a lithium ion secondary battery electrode of the present invention, it is preferable that the particulate polymer contains an acid group-containing monomer unit in an amount of 0.1% by mass to 10% by mass. If the particulate polymer contains the acidic group-containing monomer unit in the above-described proportion, the peel strength of the electrode can be further improved while further improving the coating property of the slurry composition. In addition, the production stability and storage stability of the particulate polymer can be ensured.
In the present invention, “comprising a monomer unit” means “a monomer-derived structural unit (repeating unit) is contained in a polymer obtained using the monomer”. To do.

In the slurry composition for a lithium ion secondary battery electrode of the present invention, the particulate polymer preferably contains 20% by mass or more and 90% by mass or less of a (meth) acrylic acid ester monomer unit. If the particulate polymer contains (meth) acrylic acid ester monomer units in the above-described proportion, the mechanical strength and flexibility can be sufficiently imparted to the electrode while further increasing the peel strength of the electrode.
In the present invention, “(meth) acryl” means acryl and / or methacryl.

And in the slurry composition for lithium ion secondary battery electrodes of the present invention, it is preferable that the particulate polymer contains 3% by mass or more and 40% by mass or less of (meth) acrylonitrile monomer units. If the particulate polymer contains (meth) acrylonitrile monomer units in the above-mentioned proportion, the mechanical strength and flexibility can be sufficiently imparted to the electrode while ensuring the peel strength of the electrode.
In the present invention, “(meth) acrylo” means acrylo and / or methacrylo.

  In addition, in the slurry composition for a lithium ion secondary battery electrode of the present invention, the particulate polymer contains 0.1% by mass or more and 10% by mass or less of a fluorine-containing (meth) acrylic acid ester monomer unit. Is preferred. If the particulate polymer contains the fluorine-containing (meth) acrylic acid ester monomer unit in the above-described ratio, the polymerization stability and storage stability of the particulate polymer are improved. In addition, while further improving the peel strength of the electrode, deterioration of the particulate polymer due to charge / discharge is suppressed, and excellent cycle characteristics can be exhibited in the secondary battery.

  Here, the slurry composition for a lithium ion secondary battery electrode of the present invention preferably further contains a preservative. If the slurry composition contains a preservative, the decay of the water-soluble chitosan compound can be suppressed, and an excessive decrease in viscosity and cloudiness of the slurry composition can be suppressed.

  And it is preferable that the slurry composition for lithium ion secondary battery electrodes of this invention contains a electrically conductive material further. If the slurry composition contains a conductive material, a good conductive path is formed in the electrode mixture layer prepared using the slurry composition, and in particular, when the slurry composition is used for a positive electrode, lithium ion Battery characteristics such as the rate characteristic of the secondary battery can be improved.

  Moreover, this invention aims at solving the said subject advantageously, The electrode for lithium ion secondary batteries of this invention is either of the slurry composition for lithium ion secondary battery electrodes mentioned above. It has the electrode compound-material layer formed using, It is characterized by the above-mentioned. Thus, if the slurry composition for lithium ion secondary battery electrodes mentioned above is used, the electrode for lithium ion secondary batteries excellent in peel strength can be obtained.

  Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and at least one of the positive electrode and the negative electrode Is the electrode for a lithium ion secondary battery described above. As described above, when the above-described electrode for a lithium ion secondary battery is used, battery characteristics such as cycle characteristics can be sufficiently improved.

ADVANTAGE OF THE INVENTION According to this invention, it can provide the slurry composition for lithium ion secondary battery electrodes which can form the electrode for lithium ion secondary batteries which has favorable coating property and is excellent in peel strength.
Moreover, according to this invention, the lithium ion secondary battery which is excellent in the electrode for lithium ion secondary batteries excellent in peel strength, and cycling characteristics can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the slurry composition for a lithium ion secondary battery electrode of the present invention can be used when forming the electrode of the lithium ion secondary battery of the present invention. And the lithium ion secondary battery of this invention used the electrode for lithium ion secondary batteries of this invention, It is characterized by the above-mentioned.

(Slurry composition for lithium ion secondary battery electrode)
The slurry composition for a lithium ion secondary battery electrode of the present invention comprises a water-soluble chitosan compound, a particulate polymer, an electrode active material, and a dispersion medium such as water, and optionally, a preservative, a conductive material, It further contains other components that can be blended in the electrode of the lithium ion secondary battery.

And since the slurry composition of this invention contains a water-soluble chitosan compound and a particulate polymer, it has favorable coating property. That is, the slurry composition of the present invention is less prone to excessive thickening even when the solid content concentration is increased, and the surface of the electrode mixture layer and the electrode mixture layer by air entrainment at the time of slurry composition preparation Generation of holes at the interface with the current collector and defects such as uneven coating can be suppressed. In addition, since the slurry composition of the present invention can sufficiently increase the solid content concentration, it can be efficiently dried after coating on the current collector. Moreover, the electrode obtained by drying the slurry composition of this invention is excellent in peel strength.
The reason why the coating property of the slurry composition and the peel strength of the electrode can be improved in a well-balanced manner by using the water-soluble chitosan compound and the particulate polymer is not clear, but is presumed to be due to the following reason. That is, when the water-soluble chitosan compound and the particulate polymer interact in the slurry composition, the interaction between the water-soluble chitosan compounds is suppressed, and an excessive increase in viscosity due to the water-soluble chitosan compound is suppressed. . Therefore, since the slurry composition can maintain an appropriate viscosity even when the solid content concentration is high, it is considered that the coating property can be secured. Moreover, according to the slurry composition of the present invention, in addition to the point that a homogeneous electrode mixture layer can be formed due to its good coatability, by using a water-soluble chitosan compound and a particulate polymer in combination, It is considered that these properties as a binder are expressed well, and the electrode mixture layer and the current collector can be firmly adhered to each other.

<Water-soluble chitosan compound>
In the slurry composition of the present invention, the water-soluble chitosan compound functions as a viscosity modifier by dissolving in a dispersion medium such as water, while using the slurry composition to form an electrode mixture layer on the current collector. In the electrode manufactured by forming, it is a component that can also function as a binder for holding the component contained in the electrode mixture layer so as not to be detached from the electrode mixture layer.

Here, chitosan compounds include chitosan obtained by deacetylating chitin and its derivatives (chitosan derivatives). The chitosan compound may be in the form of a salt such as a sodium salt. Here, examples of the chitosan derivative include those in which at least a part of the hydroxyl groups and / or amino group hydrogen atoms present in chitosan are substituted with other structures. Examples of such chitosan derivatives include those described in JP2009-277660A, JP2015-5474A, and JP2013-229110A.
Among these chitosan compounds, it is necessary to use a water-soluble chitosan compound in the present application. The chitosan compound being “water-soluble” means that the evaluation sample containing the chitosan compound and water does not pass through the screen with respect to the mass (corresponding to the solid content) of the added chitosan compound when passing through the 250-mesh screen. The ratio (hereinafter referred to as “residue ratio in the water solubility test”) of the residue remaining on the screen (corresponding to the solid content) is 50% by mass or less. Here, in the sample for evaluation described above, a mixture obtained by adding 1 part by mass (corresponding to a solid content) of a chitosan compound per 100 parts by mass of ion-exchanged water and stirring the mixture is within a temperature range of 20 ° C. or more and 70 ° C. or less. And it is adjusted to at least one of the conditions within the range of pH 5 to 7 (using HCl aqueous solution for pH adjustment). Even if the sample for evaluation is in an emulsion state that separates into two phases when left standing, the chitosan compound is defined as water-soluble if the above definition is satisfied.
When the chitosan compound is water-insoluble, the coating property of the slurry composition is impaired, and the peel strength of the electrode and the cycle characteristics of the lithium ion secondary battery are deteriorated. And it is preferable that the residue ratio in the water solubility test mentioned above is 40 mass% or less from a viewpoint of further improving the applicability | paintability of a slurry composition.

  Here, chitin, the raw material of chitosan, has α-type (orthorhombic), β-type (monorhombic), and γ-type (mixture of α-type and β-type) due to the difference in crystal structure. However, in the present invention, it is preferable to use a water-soluble chitosan compound derived from α-type chitin. Use of water-soluble chitosan compound derived from α-type chitin will further improve the coating properties of the slurry composition, reduce defects and voids in the resulting electrode, and exhibit more excellent cycle characteristics for the secondary battery. Can do.

The degree of deacetylation of the water-soluble chitosan compound is preferably 80% or more and 100% or less, and more preferably 85% or more and 100% or less. If the degree of deacetylation of the water-soluble chitosan compound is 80% or more and 100% or less, the interaction between the water-soluble chitosan compound and the particulate polymer is enhanced, thereby further improving the coating property of the slurry composition and the electrode peel. The strength and cycle characteristics of the lithium ion secondary battery can be further improved.
The degree of deacetylation of the water-soluble chitosan compound can be determined from the proton intensity ratio in solid nuclear magnetic resonance.

  And the compounding quantity of the water-soluble chitosan compound in a slurry composition is although it does not specifically limit, It is preferable that it is 0.01 mass part or more per 100 mass parts of electrode active materials mentioned later, 0.05 mass part or more More preferably, it is 0.07 parts by mass or more, more preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and 0.5 parts by mass or less. More preferably, it is particularly preferably 0.2 parts by mass or less. If the slurry composition contains 0.01 part by mass or more of a water-soluble chitosan compound per 100 parts by mass of the electrode active material, the peel strength of the electrode is further increased, and the cycle characteristics of the lithium ion secondary battery are further improved. On the other hand, when the slurry composition contains 10 parts by mass or less of a water-soluble chitosan compound per 100 parts by mass of the electrode active material, the peel strength and lithium ion of the resulting electrode are not difficult due to excessive increase in viscosity and the like. Sufficient cycle characteristics of the secondary battery can be secured.

<Particulate polymer>
In the slurry composition of the present invention, the particulate polymer is a component capable of functioning as a binder in the electrode mixture layer in the same manner as the water-soluble chitosan compound while interacting with the water-soluble chitosan compound as described above. is there. The particulate polymer is usually water-insoluble and is present dispersed in a dispersion medium such as water. In the present invention, the polymer (excluding the chitosan compound) is “water-insoluble” when the temperature is 25 ° C. and 0.5 g of the polymer is dissolved in 100 g of water, the insoluble content is 80 mass. It means to become more than%.

  Here, the composition of the particulate polymer is not particularly limited, and may be appropriately changed according to the type of electrode (positive electrode or negative electrode) formed using the slurry composition. However, even when the slurry composition is used for any electrode, the particulate polymer preferably contains an acidic group-containing monomer unit. The particulate polymer containing an acidic group-containing monomer unit interacts well with the water-soluble chitosan compound, and can further enhance the peel strength of the electrode while further improving the coating properties of the slurry composition. It is. Hereinafter, the acidic group-containing monomer unit will be described first, and then the monomer unit other than the acidic group-containing monomer unit is divided into a case where the slurry composition is used for the positive electrode and a case where the slurry composition is used for the negative electrode. explain.

[Acid group-containing monomer unit]
Examples of the acidic group-containing monomer that can form an acidic group-containing monomer unit include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, and a monomer having a phosphoric acid group. Can be mentioned. In the present invention, the monomer having an acidic group is included in the acidic group-containing monomer even if it has a functional group other than the acidic group (for example, an amide group or a hydroxyl group). To do.

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and dicarboxylic acid. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.
Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropane sulfone. Acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like. In the present invention, “(meth) allyl” means allyl and / or methallyl.
Examples of the monomer having a phosphoric acid group include phosphoric acid-2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate. Can be mentioned. In the present invention, “(meth) acryloyl” means acryloyl and / or methacryloyl.

  Among these, the acidic group-containing monomer is a monomer having a carboxylic acid group from the viewpoint of further improving the coating property of the slurry composition, the peel strength of the electrode, and the cycle characteristics of the lithium ion secondary battery. Are preferred, acrylic acid, methacrylic acid and itaconic acid are more preferred, and itaconic acid is even more preferred. Moreover, an acid group containing monomer may be used individually by 1 type, and may be used in combination of 2 or more types. For example, as an acidic group-containing monomer, a monomer having a carboxylic acid and a monomer having a sulfonic acid group can be used in combination.

  And, the content ratio of the acidic group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, It is more preferably 0.5% by mass or more, further preferably 1.5% by mass or more, more preferably 10% by mass or less, and even more preferably 7% by mass or less. More preferably, it is at most mass%. If the content ratio of the acidic group-containing monomer unit in the particulate polymer is 0.1% by mass or more, the coating property of the slurry composition, the peel strength of the electrode, and the cycle characteristics of the lithium ion secondary battery If it is 10% by mass or less, an excessive increase in viscosity due to aggregation between the particulate polymers can be suppressed, and the coatability of the slurry composition can be further improved. Manufacturing stability and storage stability can be ensured.

[Preferable composition of particulate polymer for positive electrode use]
The particulate polymer (positive particulate polymer) in the positive electrode slurry composition is preferably a particulate polymer (acrylic polymer) containing a (meth) acrylic acid ester monomer unit. The monomer units contained in the acrylic polymer as the particulate polymer for the positive electrode include an acidic group-containing monomer monomer unit and a (meth) acrylate monomer unit, ) Acrylonitrile monomer unit, fluorine-containing (meth) acrylic acid ester monomer unit, and the like. The acrylic polymer may contain monomer units other than these.

-Acrylic polymer (particulate polymer for positive electrode)-
Examples of the (meth) acrylate monomer that can form a (meth) acrylate monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, Alkyl acrylates such as isobutyl acrylate, n-pentyl acrylate, isopentyl 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 Relate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate Methacrylic acid alkyl esters such as glycidyl methacrylate; and the like. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferable from the viewpoint of imparting sufficient flexibility to the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types. In the present invention, among (meth) acrylate monomers, those containing fluorine are distinguished from (meth) acrylate monomers as fluorine-containing (meth) acrylate monomers. Shall.

  The content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer is preferably 20% by mass or more when the total repeating unit in the particulate polymer is 100% by mass. , 40% by mass or more, more preferably 50% by mass or more, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer is 20% by mass or more, the electrode can be given flexibility and cracking of the electrode can be suppressed, and 90% by mass or less. If so, the mechanical strength and peel strength of the electrode can be ensured.

  Examples of the (meth) acrylonitrile monomer that can form a (meth) acrylonitrile monomer unit include acrylonitrile and methacrylonitrile. Among these, acrylonitrile is preferable from the viewpoint of increasing the mechanical strength while further improving the peel strength of the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the (meth) acrylonitrile monomer unit in the particulate polymer is preferably 3% by mass or more when the total repeating unit in the particulate polymer is 100% by mass. The content is more preferably at least mass%, more preferably at most 40 mass%, and even more preferably at most 30 mass%. If the content ratio of the (meth) acrylonitrile monomer unit in the particulate polymer is 3% by mass or more, the mechanical strength can be increased while further improving the peel strength of the electrode, and 40% by mass or less. If so, the electrode flexibility can be secured and cracking of the electrode can be suppressed.

  Fluorine-containing (meth) acrylic acid ester monomers that can form fluorine-containing (meth) acrylic acid ester monomer units include (meth) acrylic acid 2,2,2-trifluoroethyl, (meth) acrylic acid β- (perfluorooctyl) ethyl, 2,2,3,3-tetrafluoropropyl (meth) acrylate, 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, (meth) 1H, 1H, 9H-perfluoro-1-nonyl acrylate, 1H, 1H, 11H-perfluoroundecyl (meth) acrylate, perfluorooctyl (meth) acrylate, trifluoromethyl (meth) acrylate, ( Meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzoo Shi] 2-hydroxypropyl, etc. (meth) acrylic acid perfluoroalkyl ester. Among these, 2,2,2-trifluoroethyl methacrylate is preferable from the viewpoint of suppressing the deterioration of the particulate polymer due to charge and discharge and further improving the cycle characteristics of the lithium ion secondary battery. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  And the content rate of the fluorine-containing (meth) acrylic acid ester monomer unit in a particulate polymer is 0.1 mass% or more when the total repeating unit in a particulate polymer is 100 mass%. It is preferably 1% by mass or more, and more preferably 10% by mass or less. When the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the particulate polymer is within the above range, the polymerization stability and storage stability of the particulate polymer are improved. In addition, while further improving the peel strength of the electrode, it is possible to sufficiently suppress the deterioration of the particulate polymer due to charge / discharge, and to exhibit more excellent cycle characteristics in the lithium ion secondary battery.

[Preferred composition of particulate polymer in negative electrode application]
As the particulate polymer in the slurry composition for negative electrode (particulate polymer for negative electrode), an acrylic polymer and a polymer containing an aliphatic conjugated diene monomer unit (conjugated diene polymer) are preferable. From the viewpoint of improving the peel strength, an acrylic polymer is preferred.

-Acrylic polymer (particulate polymer for negative electrode)-
The monomer unit contained in the acrylic polymer as the particulate polymer for the negative electrode includes an acid group-containing monomer unit, a (meth) acrylic acid ester monomer unit, and a (meth) acrylonitrile monomer. Units, aromatic vinyl monomer units, amide group-containing monomer units, and the like. The acrylic polymer may contain monomer units other than these.

  Examples of the (meth) acrylic acid ester monomer that can form a (meth) acrylic acid ester monomer unit include those described above in “Acrylic polymer (particulate polymer for positive electrode)”. Among these, 2-ethylhexyl acrylate and butyl acrylate are preferable from the viewpoint of imparting sufficient flexibility to the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer is preferably 20% by mass or more when the total repeating unit in the particulate polymer is 100% by mass. , 40% by mass or more, more preferably 50% by mass or more, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the content ratio of the (meth) acrylic acid ester monomer unit in the particulate polymer is 20% by mass or more, the electrode can be given flexibility and cracking of the electrode can be suppressed, and 90% by mass or less. If so, the mechanical strength and peel strength of the electrode can be ensured.

  Examples of the (meth) acrylonitrile monomer that can form a (meth) acrylonitrile monomer unit include those described above under “Acrylic polymer (particulate polymer for positive electrode)”. Among these, acrylonitrile is preferable from the viewpoint of increasing the mechanical strength while further improving the peel strength of the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

The content ratio of the (meth) acrylonitrile monomer unit in the particulate polymer is preferably 0.5% by mass or more when the total repeating unit in the particulate polymer is 100% by mass. The content is more preferably 1% by mass or more, more preferably 20% by mass or less, and even more preferably 15% by mass or less.
If the content ratio of the (meth) acrylonitrile monomer unit in the particulate polymer is 0.5 mass% or more, the mechanical strength can be increased while further improving the peel strength of the electrode, and 20 mass. If it is made into% or less, the softness | flexibility of an electrode can be ensured and the crack of an electrode can be suppressed.

  Examples of the aromatic vinyl monomer that can form an aromatic vinyl monomer unit include styrene, α-methylstyrene, vinyl toluene, and divinylbenzene. Among these, styrene is preferable from the viewpoint of increasing the mechanical strength of the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content of the aromatic vinyl monomer unit in the particulate polymer is preferably 5% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, preferably 10% by mass. % Or more, more preferably 20% by mass or less, and even more preferably 15% by mass or less. If the content of the aromatic vinyl monomer unit in the particulate polymer is 5% by mass or more, mechanical strength can be imparted to the electrode, and if it is 20% by mass or less, the flexibility of the electrode is increased. It can be ensured and cracking of the electrode can be suppressed.

  Examples of the amide group-containing monomer that can form an amide group-containing monomer unit include acrylamide and methacrylamide. Among these, acrylamide is preferable from the viewpoint of further improving the peel strength of the electrode and the cycle characteristics of the lithium ion secondary battery. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the amide group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, The content is more preferably 1% by mass or more, more preferably 5% by mass or less, and even more preferably 3% by mass or less. If the content ratio of the amide group-containing monomer unit in the particulate polymer is within the above range, the peel strength of the electrode and the cycle characteristics of the lithium ion secondary battery can be further improved.

-Conjugated diene polymer (particulate polymer for negative electrode)-
The conjugated diene polymer is a polymer containing an aliphatic conjugated diene monomer unit as described above. In the present invention, the aliphatic conjugated diene monomer unit includes those hydrogenated by hydrogenation. Specific examples of the conjugated diene polymer include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl / aliphatic conjugated diene copolymers such as styrene-butadiene polymer (SBR); acrylonitrile-butadiene. Examples thereof include vinyl cyanide-conjugated diene copolymers such as a base polymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like. Among these, aromatic vinyl / aliphatic conjugated diene copolymers such as styrene-butadiene-based polymers (SBR) are preferable. Hereinafter, an aromatic vinyl / aliphatic conjugated diene copolymer will be described as an example.

  The monomer units contained in the aromatic vinyl / aliphatic conjugated diene copolymer as the particulate polymer for the negative electrode include acidic group-containing monomer units, aromatic vinyl monomer units, and aliphatic conjugated diene units. In addition to the monomer unit, a hydroxyl group-containing monomer unit may be mentioned. The aromatic vinyl / aliphatic conjugated diene copolymer may contain monomer units other than these.

―Aromatic vinyl monomer unit―
Examples of the aromatic vinyl monomer that can form an aromatic vinyl monomer unit include those described above in “Acrylic polymer (particulate polymer for negative electrode)”. Among these, styrene is preferable from the viewpoint of increasing the mechanical strength of the electrode. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  And the content ratio of the aromatic vinyl monomer unit in the particulate polymer is preferably 40% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, and 50% by mass. % Or more, more preferably 60% by mass or more, further preferably 85% by mass or less, more preferably 80% by mass or less, and 70% by mass or less. Is more preferable. If the content of the aromatic vinyl monomer unit in the particulate polymer is 40% by mass or more, mechanical strength can be imparted to the electrode, and if it is 85% by mass or less, the flexibility of the electrode is improved. It can be ensured and cracking of the electrode can be suppressed.

-Aliphatic conjugated diene monomer unit-
Examples of the aliphatic conjugated diene monomer that can form an aliphatic conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, Examples include 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. Among these, 1,3-butadiene is preferable. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the aliphatic conjugated diene monomer unit in the particulate polymer is preferably 10% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, and 20 More preferably, it is more preferably 30% by mass or more, further preferably 55% by mass or less, more preferably 50% by mass or less, and 40% by mass or less. More preferably. If the content of the aliphatic conjugated diene monomer unit in the particulate polymer is 10% by mass or more, flexibility can be imparted to the electrode, and if it is 55% by mass or less, the peel strength of the electrode and The cycle characteristics of the lithium ion secondary battery can be ensured.

-Hydroxyl group-containing monomer unit-
Examples of the hydroxyl group-containing monomer that can form a hydroxyl group-containing monomer unit include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3- Examples include chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. It is done. Among these, 2-hydroxyethyl acrylate is preferable. Moreover, these may be used individually by 1 type and may be used in combination of 2 or more types.

  The content ratio of the hydroxyl group-containing monomer unit in the particulate polymer is preferably 0.1% by mass or more when the total repeating unit in the particulate polymer is 100% by mass, It is more preferably 0.5% by mass or more, more preferably 3% by mass or less, and even more preferably 2% by mass or less. When the content ratio of the hydroxyl group-containing monomer unit in the particulate polymer is within the above range, the production stability and storage stability of the particulate polymer can be ensured.

[Preparation method of particulate polymer]
The particulate polymer can be produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent. Moreover, you may hydrogenate by a known method as needed. Here, in the present invention, the content ratio of each monomer in the monomer composition can be determined according to the content ratio of the monomer units (repeating units) in the particulate polymer.

The aqueous solvent is not particularly limited as long as the particulate polymer can be dispersed in a particulate state, and water may be used alone or a mixed solvent of water and another solvent may be used.
The polymerization mode is not particularly limited, and any mode such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used.
And generally used emulsifiers, dispersants, polymerization initiators, polymerization aids and the like used for the polymerization can be used, and the amount used is also generally used.
In the preparation of the particulate polymer, an aqueous dispersion of the particulate polymer containing the preservative may be obtained by adding a preservative described later into the polymerization system. And the said aqueous dispersion can be used for preparation of a slurry composition.

[Properties of particulate polymer]
The tetrahydrofuran (THF) insoluble content of the particulate polymer is preferably 80% by mass or more, and more preferably 90% by mass or more. It is estimated that the THF-insoluble content is approximately proportional to the amount of insoluble content in the electrolyte solution. For this reason, if THF insoluble content is 80 mass% or more, it is thought that elution to the electrolyte solution of a particulate polymer can be suppressed and battery characteristics, such as cycling characteristics, can be improved. In addition, THF insoluble matter can be measured using the method as described in Unexamined-Japanese-Patent No. 2013-051076.

  The glass transition temperature of the particulate polymer is preferably −40 ° C. or higher, preferably 50 ° C. or lower, more preferably 0 ° C. or lower. When the glass transition temperature of a particulate polymer is the said range, the softness | flexibility and adhesiveness of an electrode compound-material layer can be improved, and the peel strength of an electrode can be improved further. The glass transition temperature of the polymer can be measured according to JIS K7121.

  Further, the volume average particle diameter of the particulate polymer is preferably 50 nm or more, more preferably 80 nm or more, preferably 400 nm or less, and more preferably 250 nm or less. When the volume average particle diameter of the particulate polymer is within the above-mentioned range, the particulate polymer can be sufficiently adsorbed on the surface of the electrode active material, so that the particulate polymer accompanies the movement of the electrode active material. Can follow and move. As a result, single migration by any one of the electrode active material and the particulate polymer is suppressed, and battery characteristics such as cycle characteristics can be sufficiently ensured. The volume average particle size of the particulate polymer is determined by measuring the particle size distribution (volume basis) of the particulate polymer using a laser diffraction / scattering particle size distribution measuring device for the aqueous dispersion containing the particulate polymer. The particle diameter can be determined so that the cumulative volume calculated from the small diameter side is 50%.

[Blend polymer content]
And the compounding quantity of the particulate polymer in a slurry composition is although it does not specifically limit, It is preferable that it is 0.5 mass part or more per 100 mass parts of electrode active materials mentioned later, and it is 1 mass part or more. Is more preferably 4 parts by mass or less, and more preferably 3 parts by mass or less. If the slurry composition contains 0.5 parts by mass or more of the particulate polymer per 100 parts by mass of the electrode active material, the coating properties of the slurry composition and the peel strength of the electrode are further increased, and the cycle characteristics of the lithium ion secondary battery Is further improved. On the other hand, if the slurry composition contains 4 parts by mass or less of the particulate polymer per 100 parts by mass of the electrode active material, the rate characteristics of the lithium ion secondary battery will not be excessively lowered.

  In addition, the blending ratio of the particulate polymer and the water-soluble chitosan compound in the slurry composition is not particularly limited, but is a value calculated by dividing the blending amount of the water-soluble chitosan compound by the blending amount of the particulate polymer. The (water-soluble chitosan / particulate polymer ratio) is preferably 0.02 or more, more preferably 0.03 or more, and preferably 5 or less, more preferably 3 or less. Preferably, it is 1 or less, more preferably 0.1 or less. If the water-soluble chitosan / particulate polymer ratio is within the above-mentioned range, the water-soluble chitosan compound and the particulate polymer interact well, and the coating properties of the slurry composition can be further improved.

<Electrode active material>
The electrode active material is a substance that transfers electrons in the electrodes (positive electrode and negative electrode) of the lithium ion secondary battery.

[Positive electrode active material]
As the positive electrode active material, a material that can occlude and release lithium is usually used. Specifically, the positive electrode active material for the lithium ion secondary battery is not particularly limited, and lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide ( LiNiO _2), lithium-containing composite oxide of Co-Ni-Mn (Li ( Co Mn Ni) O 2), lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, In olivine type lithium iron phosphate (LiFePO ₄ ), olivine type lithium manganese phosphate (LiMnPO ₄ ), Li ₂ MnO ₃ —LiNiO ₂ solid solution, Li _{1 + x} Mn _2−x O ₄ (0 <X <2) Examples include known positive electrode active materials such as lithium-rich spinel compounds, Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ , LiNi _0.5 Mn _1.5 O _4. The Among these, olivine type lithium iron phosphate and lithium manganate are preferable, and olivine type lithium iron phosphate is more preferable. In addition, the compounding quantity and particle size of a positive electrode active material are not specifically limited, It can be made to be the same as that of the positive electrode active material used conventionally.

[Negative electrode active material]
As the negative electrode active material of the lithium ion secondary battery, a material that can occlude and release lithium is usually used. Specifically, the negative electrode active material for the lithium ion secondary battery is not particularly limited, and includes coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, pyrolytic vapor-grown carbon fiber, and phenol resin. Carbon-based negative electrode active materials such as fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, furfuryl alcohol resin fired bodies (PFA), hard carbon, natural graphite, artificial graphite; silicon (Si), alloys containing silicon Non-carbon-based negative electrode active materials such as a composite of Si-containing material and conductive carbon obtained by coating or combining SiO, SiOx, and Si-containing material with conductive carbon. Of these, natural graphite and artificial graphite are preferable. In addition, the compounding quantity and particle size of a negative electrode active material are not specifically limited, It can be made to be the same as that of the negative electrode active material used conventionally.

<Preservative>
Here, the slurry composition of the present invention preferably contains a preservative. By including a preservative in the slurry composition, it is possible to suppress the decay of the water-soluble chitosan compound, and it is possible to suppress an excessive decrease in viscosity and white turbidity of the slurry composition. Specifically, examples of the preservative include known preservatives such as isothiazoline compounds and 2-bromo-2-nitro-1,3-propanediol. Here, the isothiazoline-based compound is not particularly limited, and examples thereof include those described in JP2013-211246A, JP2005-097474A, and JP2013-206624A. In addition, a preservative may be used individually by 1 type and may be used in combination of 2 or more types.

  And the compounding quantity of the antiseptic | preservative in a slurry composition is although it does not specifically limit, It is preferable that it is 0.01 mass part or more per 100 mass parts of electrode active materials, and it is more preferable that it is 0.1 mass part or more. Preferably, it is 0.3 parts by mass or more, more preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and further preferably 1 part by mass or less. If the slurry composition contains the preservative in an amount within the above range, the water-soluble chitosan compound can be sufficiently prevented from decaying and excessive viscosity reduction and cloudiness of the slurry composition can be suppressed.

<Conductive material>
Moreover, it is preferable that the slurry composition of this invention contains a electrically conductive material. The conductive material is for ensuring electrical contact between the electrode active materials. As the conductive material, carbon black (for example, acetylene black, ketjen black (registered trademark), furnace black, etc.), graphite, carbon fiber, carbon flake, and ultra-short carbon fiber (for example, carbon nanotube or vapor grown carbon) Conductive carbon materials such as fibers); fibers and foils of various metals can be used. Among them, as the conductive material, carbon black is preferable, and acetylene black is more preferable. These can be used alone or in combination of two or more.

  And the compounding quantity of the electrically conductive material in a slurry composition is although it does not specifically limit, It is preferable that it is 1 mass part or more per 100 mass parts of electrode active materials, and it is preferable that it is 10 mass parts or less. If the slurry composition includes the conductive material in an amount within the above range, a good conductive path is formed in the electrode mixture layer prepared using the slurry composition, and the slurry composition was used particularly for the positive electrode. In this case, battery characteristics such as rate characteristics of the lithium ion secondary battery can be improved.

<Other ingredients>
In addition to the above components, the slurry composition of the present invention may contain components such as a reinforcing material, a leveling agent, a viscosity modifier, and an electrolytic solution additive. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

<Preparation of slurry composition>
The slurry composition of the present invention can be prepared by dissolving or dispersing the above components in a dispersion medium such as water. Specifically, the above components and the dispersion medium are mixed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crushed crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a fill mix, etc. Thus, a slurry composition can be prepared.

<Properties of slurry composition>
The solid content concentration of the slurry composition obtained as described above is preferably 48% by mass or more and 57% by mass or less. When the solid content concentration of the slurry composition is within the above range, the drying efficiency when preparing the electrode mixture layer by removing the dispersion medium from the slurry composition can be increased. Moreover, since the slurry composition of the present invention contains a water-soluble chitosan compound and a particulate polymer as described above, an excellent coating can be obtained even when the solid content concentration is relatively high as described above. Demonstrate workability.

  And it is preferable that the viscosity of a slurry composition is 3600 mPa * s or more and 5000 mPa * s or less. If the viscosity of the slurry composition is within the above-mentioned range, the coating properties will be good, holes due to air entrainment at the time of slurry composition preparation, coating unevenness will be sufficiently suppressed, and an electrode mixture having a uniform thickness A layer can be formed. The “viscosity” of the slurry composition for a lithium ion secondary battery electrode is a viscosity measured using a single cylindrical rotational viscometer (B-type viscometer). It can be measured using the method described in the examples.

(Electrode for lithium ion secondary battery)
The electrode for lithium ion secondary batteries of this invention is equipped with a collector and the electrode compound-material layer formed on the collector. And the electrode compound-material layer is formed using the said slurry composition for lithium ion secondary battery electrodes, and can be specifically formed by drying the said slurry composition. That is, the electrode mixture layer in the lithium ion secondary battery electrode of the present invention comprises a dried product of the lithium ion secondary battery electrode slurry composition, and usually contains the water-soluble chitosan compound and the particulate weight. It contains a coalescence and the electrode active material, and optionally contains the preservative, the conductive material, and the other components. When the particulate polymer described above contains a crosslinkable monomer unit, the particulate polymer is crosslinked during the drying of the slurry composition or during a heat treatment optionally performed after drying. (That is, the electrode mixture layer in the electrode for a lithium ion secondary battery may contain a crosslinked product of the particulate polymer described above). In addition, the suitable abundance ratio of each component contained in the electrode mixture layer is the same as the preferred abundance ratio of each component in the slurry composition.
And since the electrode for lithium ion secondary batteries of this invention is manufactured using the slurry composition of this invention, it is excellent in peel strength. And if the said electrode is used, the lithium ion secondary battery excellent in battery characteristics, such as cycling characteristics, will be obtained.

<Method for producing electrode for lithium ion secondary battery>
The lithium ion secondary battery electrode of the present invention includes, for example, a step of applying the above-described slurry composition on the current collector (application step), and a drying of the slurry composition applied on the current collector. And a step of forming an electrode mixture layer on the current collector (drying step).

[Coating process]
The method for applying the slurry composition onto 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 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, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. In addition, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[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. Thus, by drying the slurry composition on the current collector, an electrode mixture layer is formed on the current collector, and a lithium ion secondary battery electrode including the current collector and the electrode mixture layer is obtained. be able to.
Note that after the drying step, the electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. The adhesion between the electrode mixture layer and the current collector can be improved by the pressure treatment.

(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 uses the electrode for a lithium ion secondary battery of the present invention as at least one of the positive electrode and the negative electrode. And since the lithium ion secondary battery of this invention is equipped with the electrode for lithium ion secondary batteries of this invention, it is excellent in battery characteristics, such as cycling characteristics.

<Electrode>
Here, the electrode other than the above-described electrode for the lithium ion secondary battery that can be used for the lithium ion secondary battery of the present invention is not particularly limited and is used for the production of a lithium ion secondary battery. Known electrodes can be used. Specifically, as an electrode other than the above-described electrode for a lithium ion secondary battery, an electrode formed by forming an electrode mixture layer on a current collector using a known production method can be used.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte for the lithium ion secondary battery, for example, a lithium salt is used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Of these, 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 ethyl methyl 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 these, carbonates are preferably used because they have a high dielectric constant and a wide stable potential region.
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. In addition, known additives such as fluoroethylene carbonate and ethyl methyl sulfone can 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 thickness of the separator as a whole can be reduced, thereby increasing the ratio of the electrode active material in the lithium ion secondary battery and increasing the capacity per volume. A microporous membrane made of a resin of the type (polyethylene, polypropylene, polybutene, 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 lithium ion secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

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.
In Examples and Comparative Examples, the viscosity and coating property of the slurry composition, the peel strength of the electrode, and the cycle characteristics of the lithium ion secondary battery were measured and evaluated by the following methods.

<Viscosity of slurry composition>
According to JISZ8803: 1991, it was measured with a B-type viscometer (25 ° C., rotation speed = 60 rpm, spindle shape: 4), and the value 60 seconds after the start of measurement was taken as the viscosity of the slurry composition.
<Coating property of slurry composition>
The produced electrode for a lithium ion secondary battery was cut out, and 12 test pieces having a size of 0.5 m ² were prepared. Then, the electrode mixture layer of the test piece is observed with a scanning electron microscope (the interface between the electrode mixture layer and the current collector is magnification: 5000 to 10000 times, and other portions are magnifications of 300 to 5000 times), and the slurry composition The number of test pieces having holes and uneven coating on the surface of the electrode mixture layer surface and the interface between the electrode mixture layer and the current collector due to air entrainment during the preparation of the product was counted and evaluated according to the following criteria. It shows that a slurry composition is excellent in coating property, so that there are few holes by air entrainment and coating unevenness.
A: Holes and coating unevenness due to air entrainment are not observed in all 12 sheets.
B: Holes and / or coating unevenness due to air entrainment are observed in 1 to 2 of 12 sheets.
C: Holes and / or coating unevenness due to air entrainment are observed on 3 to 4 of 12 sheets.
D: Holes due to air entrainment and / or uneven coating are observed on 5 or more of 12 sheets.
<Peel strength of electrode>
The produced electrode for a lithium ion secondary battery was cut into a rectangle having a length of 100 mm and a width of 10 mm to obtain a test piece, and a cellophane tape (specified in JIS Z1522) was formed on the surface of the electrode mixture layer with the surface having the electrode mixture layer facing down. The stress was measured when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled off (the cellophane tape was fixed to the test stand). The measurement was performed 3 times, the average value was calculated | required, this was made into peel strength, and the following references | standards evaluated. It shows that it is excellent in the adhesiveness of an electrode compound-material layer and an electrical power collector, so that the value of peel strength is large.
A: Peel strength is 20 N / m or more B: Peel strength is 15 N / m or more and less than 20 N / m C: Peel strength is less than 15 N / m <Cycle characteristics of lithium ion secondary battery>
The produced lithium ion secondary battery was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, under an environment of 25 ° C., charging and discharging operations were performed by charging to 4.2 V by a low current method of 0.5 C and discharging to 3.0 V, and an initial capacity C0 was measured. Furthermore, this lithium ion secondary battery was charged and discharged in the same manner as described above 200 times (200 cycles) in an environment of 60 ° C., and the capacity C1 after 200 cycles was measured.
For the cycle characteristics (high-temperature cycle characteristics), a capacity retention ratio ΔC represented by ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. It shows that it is excellent in cycling characteristics, so that the value of this capacity | capacitance maintenance factor (DELTA) C is high.
A: Capacity maintenance ratio ΔC is 85% or more B: Capacity maintenance ratio ΔC is 80% or more and less than 85% C: Capacity maintenance ratio ΔC is less than 80%

Example 1
<Preparation of particulate polymer for positive electrode>
In a 5 MPa pressure vessel with a stirrer, 4 parts of itaconic acid as an acidic group-containing monomer, 74 parts of 2-ethylhexyl acrylate as a (meth) acrylic acid ester monomer, 20 parts of acrylonitrile as a (meth) acrylonitrile monomer 2 parts of 2,2,2-trifluoroethyl methacrylate as the fluorine-containing (meth) acrylic acid ester monomer, 1 part of sodium dodecylbenzenesulfonate as the surfactant, and 0.8 parts of potassium persulfate as the polymerization initiator And 150 parts of ion-exchanged water were added and sufficiently stirred. Then, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion reached 96%, the reaction was stopped by cooling. Subsequently, after removing the unreacted monomer by heating under reduced pressure, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a desired positive electrode particulate polymer (acrylic polymer).
<Preparation of slurry composition for positive electrode of lithium ion secondary battery>
In a planetary mixer with a disper, 100 parts of olivine type lithium iron phosphate (LiFePO ₄ ) as a positive electrode active material, 2 parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, water-soluble chitosan 0.1 part of compound 1 (derived from α-type chitin, degree of deacetylation: 85%, residual ratio in water solubility test: 10% by mass) is added and mixed with stirring for 10 minutes, and solid content concentration is 83 with ion-exchanged water. % And then mixed at 25 ° C. for 60 minutes. To the obtained mixture, 2 parts of an aqueous dispersion containing the positive electrode particulate polymer (solid content concentration adjusted to 40%) was added in an amount corresponding to the solid content, and then the solid content concentration was adjusted to 53% with ion-exchanged water. It was adjusted. In addition to the mixture containing the positive electrode particulate polymer, an antiseptic X (product name: Activide (registered trademark) LA5008, the antiseptic X is 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one and 2-bromo-2-nitro-1,3-propanediol, each containing 3.7: 1.3: 8 (mass ratio). 0.5 equivalent amount was added and mixed to prepare a slurry composition for a positive electrode of a lithium ion secondary battery (solid content concentration: 53%, pH: 5.0). The slurry composition was evaluated for viscosity and coatability. The results are shown in Table 1.
<Preparation of positive electrode for lithium ion secondary battery>
An aluminum foil with a thickness of 20 μm was prepared as a current collector. And the obtained slurry composition was apply | coated to the single side | surface of aluminum foil with the comma coater, it was made to dry, and the positive electrode original fabric was obtained. In this drying, the aluminum foil provided with the coating film is transported in an oven at 60 ° C. for 2 minutes at a speed of 0.5 m / min, and then further heated in an oven at 120 ° C. for 2 minutes. went. The obtained positive electrode fabric was rolled by a roll press to obtain a positive electrode for a lithium ion secondary battery having a positive electrode mixture layer thickness of 100 μm. The peel strength of this positive electrode was evaluated. The results are shown in Table 1.
<Preparation of particulate polymer for negative electrode>
In a 5 MPa pressure vessel equipped with a stirrer, 33.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as an acidic group-containing monomer, 62 parts of styrene as an aromatic vinyl monomer, 1 part of 2-hydroxyethyl acrylate as a hydroxyl group-containing monomer, 0.4 part of sodium dodecylbenzenesulfonate as a surfactant, 0.5 part of potassium persulfate as a polymerization initiator, and 150 parts of ion-exchanged water, Stir well. Then, it heated to 50 degreeC and superposition | polymerization was started. The reaction was stopped by cooling when the polymerization conversion reached 96%. Subsequently, after removing the unreacted monomer by heating under reduced pressure, it was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a desired negative electrode particulate polymer (conjugated diene polymer).
<Preparation of slurry composition for negative electrode of lithium ion secondary battery>
In a planetary mixer with a disper, 100 parts of artificial graphite as a negative electrode active material, 1 part of a 2% aqueous solution of carboxymethyl cellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener, and an ion Exchange water was mixed to adjust the solid concentration to 65%, and then mixed at 25 ° C. for 60 minutes. Subsequently, it adjusted with ion-exchange water so that solid content concentration might be 60%, and also mixed for 15 minutes at 25 degreeC. Thereafter, 2 parts of an aqueous dispersion containing the above particulate polymer for negative electrode and ion-exchanged water were added to the obtained mixed liquid, and further mixed for 10 minutes. This was defoamed under reduced pressure to prepare a negative electrode slurry composition (solid content concentration: 53%) having good fluidity.
<Preparation of negative electrode for lithium ion secondary battery>
A copper foil having a thickness of 20 μm was prepared as a current collector. And the obtained slurry composition was apply | coated to the single side | surface of copper foil with the comma coater, it was made to dry, and the negative electrode original fabric was obtained. In this drying, the copper foil provided with the coating film is conveyed in an oven at 60 ° C. at a rate of 0.5 m / min for 2 minutes, and then further heated in an oven at 120 ° C. for 2 minutes. went. The obtained negative electrode original fabric was rolled with a roll press to obtain a negative electrode for a lithium ion secondary battery having a negative electrode mixture layer thickness of 80 μm.
<Preparation of separator for lithium ion secondary battery>
A single-layer polypropylene separator (“CELGARD (registered trademark) 2500” manufactured by Celgard) was cut into a 5 cm × 5 cm square.
<Manufacture of lithium ion secondary batteries>
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained above was cut into a 4 cm × 4 cm square and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. The square separator obtained above was disposed on the positive electrode mixture layer of the positive electrode. Furthermore, the negative electrode obtained above was cut into a square of 4.2 cm × 4.2 cm, and this was arranged on the separator so that the surface on the negative electrode mixture layer side faces the separator. Furthermore, electrolyte (solvent: EC / DEC / vinylene carbonate (volume ratio at 25 ° C.) = 40.0 / 58.5 / 1.5, electrolyte: LiPF _{6 at} a concentration of 1 M, relative dielectric constant (25 ° C.): 36 0.5, viscosity (25 ° C.): 1.2 mPa · s) was injected so that no air remained. Thereafter, in order to seal the opening of the aluminum packaging material exterior, heat sealing was performed at 150 ° C. to close the aluminum packaging material exterior, and a lithium ion secondary battery was obtained. The cycle characteristics were evaluated using the obtained lithium ion secondary battery. The results are shown in Table 1.

(Examples 2-3, 13)
Except having changed the kind and ratio of the monomer to be used as shown in Table 1 at the time of preparing the particulate polymer for the positive electrode, in the same manner as in Example 1, the positive electrode slurry composition, the negative electrode slurry composition, A positive electrode, a negative electrode, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Examples 4-6, 11)
In the same manner as in Example 1, except that the following water-soluble chitosan compounds 2 to 5 were used in place of the water-soluble chitosan compound 1 when preparing the positive electrode slurry composition, the positive electrode slurry composition and the negative electrode slurry were used. A composition, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.
Water-soluble chitosan compound 2 (derived from β-type chitin, degree of deacetylation: 85%, residue ratio in water-soluble test: 10% by mass)
Water-soluble chitosan compound 3 (derived from γ-type chitin, degree of deacetylation: 80%, residue ratio in water-soluble test: 10% by mass)
Water-soluble chitosan compound 4 (derived from α-type chitin, degree of deacetylation: 92%, residue ratio in water-soluble test: 4% by mass)
Water-soluble chitosan compound 5 (derived from α-type chitin, degree of deacetylation: 75%, residue ratio in water-soluble test: 40% by mass)

(Examples 7 to 10)
The positive electrode slurry composition, the positive electrode, the negative electrode, and the lithium ion secondary were prepared in the same manner as in Example 6 except that the amount of the water-soluble chitosan compound 4 was changed as shown in Table 1 when preparing the positive electrode slurry composition. A battery was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 12)
Example except that 0.1 part of water-soluble chitosan compound 1 and 0.5 part of preservative X were added in place of 1 part of carboxymethylcellulose sodium salt corresponding to the solid content during preparation of the slurry composition for negative electrode In the same manner as in Example 1, a positive electrode slurry composition, a negative electrode slurry composition, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. (That is, the positive electrode slurry composition used for evaluation of viscosity and coatability and the positive electrode used for evaluation of peel strength were both produced in the same manner as in Example 1.)

(Example 14)
In the preparation of the positive electrode slurry composition, 0.1 part of the water-soluble chitosan compound 1 and 0.5 part of the preservative X were not added, but carboxymethylcellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) 2 A positive electrode slurry composition and a positive electrode were produced in the same manner as in Example 1 except that 1 part of a% aqueous solution was added corresponding to the solid content.
In addition, in preparing the negative electrode slurry composition, 0.1 part of water-soluble chitosan compound 1 and 0.5 part of preservative X were added instead of 1 part of carboxymethylcellulose sodium salt corresponding to the solid content. Produced a slurry composition for a negative electrode and a negative electrode in the same manner as in Example 1. The viscosity and coatability of the obtained negative electrode slurry composition and the peel strength of the negative electrode were evaluated. The results are shown in Table 1.
And the lithium ion secondary battery was produced similarly to Example 1 except having used the said positive electrode and negative electrode, and the cycling characteristics were evaluated. The results are shown in Table 1.

(Example 15)
A negative electrode slurry composition, a positive electrode slurry composition, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 14 except that the negative electrode particulate polymer obtained as described below was used. Produced. Then, the viscosity and coatability of the negative electrode slurry composition, the peel strength of the negative electrode, and the cycle characteristics of the lithium ion secondary battery were evaluated. The results are shown in Table 1.
<Preparation of particulate polymer for negative electrode>
In a 5 MPa pressure vessel with a stirrer, 3 parts of itaconic acid as an acidic group-containing monomer, 31 parts of 2-ethylhexyl acrylate, 23 parts of methyl methacrylate and 25 parts of butyl acrylate as a (meth) acrylic acid ester monomer, (meth) 3 parts of acrylonitrile as the acrylonitrile monomer, 13 parts of styrene as the aromatic vinyl monomer, 2 parts of acrylamide as the amide group-containing monomer, 0.4 part of sodium dodecylbenzenesulfonate as the surfactant, and excess as the polymerization initiator 0.5 parts of potassium sulfate and 150 parts of ion exchange water were added and stirred sufficiently. Then, it heated to 50 degreeC and superposition | polymerization was started. The reaction was stopped by cooling when the polymerization conversion reached 96%. Next, after removing the unreacted monomer by heating under reduced pressure, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a desired negative electrode particulate polymer (acrylic polymer).

(Comparative Example 1)
A positive electrode slurry composition and a positive electrode were prepared as follows. Other than that was carried out similarly to Example 1, and produced the slurry composition for negative electrodes, the negative electrode, and the lithium ion secondary battery. Then, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of slurry composition for positive electrode of lithium ion secondary battery>
Place 100 parts of olivine type lithium iron phosphate (LiFePO ₄ ) as a positive electrode active material and 2 parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material in a planetary mixer with a disper for 10 minutes. The mixture was stirred and mixed, and further adjusted to a solid content concentration of 83% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. To the obtained mixture, 2 parts of an aqueous dispersion containing the positive electrode particulate polymer obtained in Example 1 (solid content concentration adjusted to 40%) was added in an amount corresponding to the solid content, and then solidified with ion-exchanged water. The partial concentration was adjusted to 53%. In addition to the mixture containing the positive electrode particulate polymer, an antiseptic X (product name: Activide (registered trademark) LA5008, the antiseptic X is 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one and 2-bromo-2-nitro-1,3-propanediol, each containing 3.7: 1.3: 8 (mass ratio). An aqueous composition (solid content concentration: 53%, pH: 5.0) was prepared by adding 0.5 in an amount corresponding to the minute and mixing. To this aqueous composition, N-methyl-2-pyrrolidone (NMP) having the same mass as the positive electrode active material was added, and water was removed azeotropically at 60 ° C. under reduced pressure. Next, 0.1 part of water-insoluble chitosan compound 6 (derived from α-type chitin, degree of deacetylation: 70%, residue ratio in water solubility test: 60% by mass) is added so that the solid content concentration becomes 53%. NMP was added to to prepare a solvent-based positive electrode slurry composition. In this slurry composition, the acrylic polymer was dissolved in NMP and was not in the form of particles (that is, the positive electrode slurry composition of Comparative Example 1 did not contain a “particulate” polymer). ).
<Preparation of positive electrode for lithium ion secondary battery>
A positive electrode for a lithium ion secondary battery having a positive electrode mixture layer thickness of 100 μm was obtained in the same manner as in Example 1 except that the solvent-based positive electrode slurry composition described above was used.

(Comparative Example 2)
When preparing the slurry composition for the positive electrode, in place of the water-soluble chitosan compound 1, the water-insoluble chitosan compound 6 (derived from α-type chitin, degree of deacetylation: 70%, residue ratio in water solubility test: 60% by mass) A positive electrode slurry composition, a positive electrode, a negative electrode, and a lithium ion secondary battery were produced in the same manner as in Example 1 except that was used, and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
A positive electrode slurry composition, a positive electrode, a negative electrode, and a lithium ion secondary battery were prepared in the same manner as in Example 1 except that the particulate polymer was not added during the preparation of the positive electrode slurry composition. And evaluated. The results are shown in Table 1.

In Table 1 shown below,
“LFP” indicates olivine-type lithium iron phosphate (LiFePO ₄ ),
“GR” indicates artificial graphite,
“IA” indicates itaconic acid,
“AN” stands for acrylonitrile,
“2EHA” refers to 2-ethylhexyl acrylate,
“MMA” indicates methyl methacrylate,
“BA” represents butyl acrylate,
“TFEM” refers to 2,2,2-trifluoroethyl methacrylate,
“BD” indicates 1,3-butadiene,
“ST” indicates styrene,
“HEA” represents hydroxyethyl acrylate,
“AAm” indicates acrylamide,
“AcB” indicates acetylene black,
“CMC-Na” represents carboxymethylcellulose sodium salt.

From Table 1, in Examples 1-15 using the slurry composition for lithium ion secondary battery electrodes containing a water-soluble chitosan compound, a particulate polymer, and an electrode active material, the applicability of the slurry composition was ensured. However, it can be seen that an electrode having excellent peel strength and a lithium ion secondary battery having excellent cycle characteristics can be obtained.
Further, from Table 1, a slurry composition containing a non-particulate polymer as a binder and containing a water-insoluble chitosan compound, a slurry composition containing a water-insoluble chitosan compound, and no particulate polymer. In Comparative Examples 1 to 3 each using the slurry composition, it is understood that the coating property of the slurry composition cannot be secured, and the peel strength of the electrode and the cycle characteristics of the lithium ion secondary battery are deteriorated.

ADVANTAGE OF THE INVENTION According to this invention, it can provide the slurry composition for lithium ion secondary battery electrodes which can form the electrode for lithium ion secondary batteries which has favorable coating property and is excellent in peel strength.
Moreover, according to this invention, the lithium ion secondary battery which is excellent in the electrode for lithium ion secondary batteries excellent in peel strength, and cycling characteristics can be provided.

Claims (9)

  A slurry composition for a lithium ion secondary battery electrode, comprising a water-soluble chitosan compound, a particulate polymer, and an electrode active material.   The slurry composition for a lithium ion secondary battery electrode according to claim 1, wherein the particulate polymer contains an acid group-containing monomer unit in an amount of 0.1 mass% to 10 mass%.   The slurry composition for lithium ion secondary battery electrodes according to claim 1 or 2, wherein the particulate polymer contains 20% by mass or more and 90% by mass or less of a (meth) acrylic acid ester monomer unit.   The slurry composition for lithium ion secondary battery electrodes in any one of Claims 1-3 in which the said particulate polymer contains 3 to 40 mass% of (meth) acrylonitrile monomer units.   The lithium ion secondary battery electrode according to any one of claims 1 to 4, wherein the particulate polymer contains 0.1 mass% or more and 10 mass% or less of a fluorine-containing (meth) acrylate monomer unit. Slurry composition.   Furthermore, the slurry composition for lithium ion secondary battery electrodes in any one of Claims 1-5 containing a preservative.   Furthermore, the slurry composition for lithium ion secondary battery electrodes in any one of Claims 1-6 containing a electrically conductive material.   The electrode for lithium ion secondary batteries which has an electrode compound-material layer obtained using the slurry composition for lithium ion secondary battery electrodes in any one of Claims 1-7. A positive electrode, a negative electrode, an electrolyte and a separator;
The lithium ion secondary battery whose at least one of the said positive electrode and a negative electrode is an electrode for lithium ion secondary batteries of Claim 8.