JPWO2015151518A1 - Binder composition for lithium ion secondary battery electrode, slurry composition for lithium ion secondary battery electrode, electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

An object of the present invention is to provide a lithium ion secondary battery electrode binder composition that can produce a lithium ion secondary battery with low internal resistance and is excellent in both productivity and binding properties. . The binder composition for a lithium ion secondary battery electrode of the present invention comprises 10-80% by mass of an unsaturated acid lithium salt (monomer a), 5-40% by mass of an unsaturated acid (monomer b), It contains a polymer obtained by polymerizing a monomer composition containing 10 to 85% by mass of an α, β-unsaturated nitrile (monomer c), and a dispersion medium.

Description

  The present invention relates to a binder composition for a lithium ion secondary battery electrode, 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 provided with the electrical power collector and the electrode compound-material layer formed on the electrical power collector. The electrode mixture layer is made of, for example, a slurry composition obtained by dispersing a binder composition containing a polymer as a binder and an electrode active material in a dispersion medium such as an organic solvent or water. It is formed by coating on top and drying to bind an electrode active material or the like with a polymer.
Therefore, in order to achieve further performance improvement of the lithium ion secondary battery, attempts have been made to improve the binder composition and the slurry composition used for forming the electrode.

  Specifically, it has been proposed to use a binder composition containing a polymer containing a plurality of monomer units in a specific ratio for the production of an electrode such as a lithium ion battery. For example, Patent Document 1 includes 80 to 99.9% by weight of a repeating unit derived from a monomer containing a nitrile group and is derived from an ethylenically unsaturated compound such as a vinyl monomer having a carboxylic acid group. To improve the stability of the binder composition and the slurry composition prepared using the binder composition by including in the binder composition as a binder a polymer containing 0.1 to 20% by weight of repeating units. In addition, it has been reported that the cycle characteristics of a secondary battery produced using the binder composition can be improved.

International Publication No. 2012/091001

  However, in the synthesis of the polymer contained in the conventional binder composition, a large amount of polymerization reaction product is precipitated during the polymerization reaction due to the use of many monomers containing nitrile groups. The polymerization reaction tends to stop at an early stage. Therefore, the conversion rate of the monomer into the polymer (polymerization conversion rate) is as low as 70% at the highest, the material cost is high, and the post-treatment (for example, filtration) for removing the remaining monomer There has been a manufacturing problem that the processing becomes difficult.

  In addition, in the conventional binder composition, for example, when the amount of the vinyl monomer having a carboxylic acid group is increased in order to increase the binding property as a polymer, the polymerization reaction product aggregates during the polymerization reaction. There was another manufacturing problem.

  Furthermore, the conventional binder composition has room for improvement in that the internal resistance of a lithium ion secondary battery produced using the binder composition is high.

Accordingly, an object of the present invention is to provide a binder composition for a lithium ion secondary battery electrode that can produce a lithium ion secondary battery with low internal resistance and is excellent in both productivity and binding properties. And Another object of the present invention is to provide a slurry composition for a lithium ion secondary battery electrode that can prepare an electrode for a lithium ion secondary battery that has low internal resistance and excellent peel strength. Furthermore, an object of the present invention is to provide an electrode for a lithium ion secondary battery having low internal resistance and excellent peel strength.
Another object of the present invention is to provide a lithium ion secondary battery with low internal resistance.

  The present inventors have intensively studied for the purpose of solving the above problems. The inventors of the present invention can prepare a polymer obtained by polymerizing a monomer composed of a specific compound at a specific ratio with a high binding property and high productivity, and also with lithium ions. It has been found that when used in the production of a secondary battery, the internal resistance can be reduced, and the present invention has been completed.

  That is, the present invention aims to advantageously solve the above-mentioned problems, and the binder composition for lithium ion secondary battery electrodes of the present invention comprises an unsaturated acid lithium salt (monomer a) 10. Polymerization of a monomer composition containing -80 mass%, unsaturated acid (monomer b) 5-40 mass%, and α, β-unsaturated nitrile (monomer c) 10-85 mass% And a dispersion medium. In this way, polymerization is performed using a lithium salt of an unsaturated acid (monomer a), an unsaturated acid (monomer b), and an α, β-unsaturated nitrile (monomer c) in a predetermined ratio. Thus, a polymer having a high binding property and a binder composition for a lithium ion secondary battery electrode containing the polymer can be prepared with high productivity. And according to the binder composition containing the said polymer, a lithium ion secondary battery with low internal resistance can be manufactured.

  Here, in the binder composition for a lithium ion secondary battery electrode of the present invention, the α, β-unsaturated nitrile (monomer c) is preferably acrylonitrile. This is because when the α, β-unsaturated nitrile (monomer c) is acrylonitrile, the mechanical strength and oxidation resistance of the resulting polymer can be improved.

  Moreover, this invention aims at solving the said subject advantageously, The slurry composition for lithium ion secondary battery electrodes of this invention is the binder composition for lithium ion secondary battery electrodes mentioned above, and An electrode active material is included. Thus, according to the slurry composition for lithium ion secondary battery electrodes containing the binder composition for lithium ion secondary battery electrodes described above, the electrode for lithium ion secondary batteries having excellent peel strength and low internal resistance. Can be prepared.

  Moreover, it is preferable that the slurry composition for lithium ion secondary battery electrodes of this invention further contains polymers other than the polymer mentioned above. By including a polymer other than the above-mentioned polymer in the slurry composition for lithium ion secondary battery electrodes, the adhesion between the electrode mixture layer and the current collector and the output characteristics of the resulting lithium ion secondary battery are improved. It is because it becomes possible to make it.

  Furthermore, in the slurry composition for a lithium ion secondary battery electrode of the present invention, the polymer other than the above-described polymer is preferably a fluorine-containing polymer. By including the fluorine-containing polymer in the slurry composition for lithium ion secondary battery electrodes, it is possible to further improve the adhesion between the electrode mixture layer and the current collector and the output characteristics of the resulting lithium ion secondary battery. This is because it becomes possible.

  And this invention aims at solving the said subject advantageously, The electrode for lithium ion secondary batteries of this invention is prepared using the slurry composition for lithium ion secondary battery electrodes mentioned above. The electrode mixture layer is provided on a current collector. Such an electrode for a lithium ion secondary battery has a low internal resistance and an excellent peel strength.

  And this invention aims at solving the said subject advantageously, The lithium ion secondary battery of this invention is equipped with a positive electrode, a negative electrode, electrolyte solution, and a separator, At least one of the said positive electrode and negative electrode Is an electrode for a lithium ion secondary battery as described above. Such a lithium ion secondary battery has a low internal resistance.

ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery with low internal resistance can be manufactured, and the binder composition for lithium ion secondary battery electrodes which is excellent in both productivity and binding property can be provided. . Moreover, according to this invention, the slurry composition for lithium ion secondary battery electrodes which can prepare the electrode for lithium ion secondary batteries which is low in internal resistance and excellent in peel strength can be provided. Furthermore, according to the present invention, an electrode for a lithium ion secondary battery having low internal resistance and excellent peel strength can be provided.
Moreover, according to this invention, a lithium ion secondary battery with low internal resistance can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the binder composition for lithium ion secondary battery electrodes of the present invention can be used when preparing a slurry composition for lithium ion secondary battery electrodes. And the slurry composition for lithium ion secondary battery electrodes of this invention is prepared using the binder composition for lithium ion secondary battery electrodes and electrode active material of this invention, and manufactures the electrode of a lithium ion secondary battery. Used when. Moreover, the electrode for lithium ion secondary batteries of this invention can be manufactured using the slurry composition for lithium ion secondary battery electrodes of this invention. Furthermore, the lithium ion secondary battery of the present invention is characterized by using the electrode for a lithium ion secondary battery of the present invention.

(Binder composition for lithium ion secondary battery electrode)
The binder composition for a lithium ion secondary battery electrode of the present invention comprises 10-80% by mass of an unsaturated acid lithium salt (monomer a), 5-40% by mass of an unsaturated acid (monomer b), It contains a polymer obtained by polymerizing a monomer composition containing 10 to 85% by mass of an α, β-unsaturated nitrile (monomer c), and a dispersion medium. Moreover, the binder composition for lithium ion secondary battery electrodes of this invention may contain other components other than the said polymer and a dispersion medium arbitrarily.

<Polymer>
When the polymer contained in the binder composition for a lithium ion secondary battery electrode of the present invention is produced using the binder composition, the polymer contained in the electrode mixture layer in the produced electrode (for example, It is a component which can hold | maintain so that electrode active materials, such as a positive electrode active material and a negative electrode active material, may not detach | leave from an electrode compound material layer.
The polymer contained in the binder composition for a lithium ion secondary battery electrode of the present invention includes, as monomers, a lithium salt of an unsaturated acid (monomer a) and an unsaturated acid (monomer b). And a monomer composition containing α, β-unsaturated nitrile (monomer c) in a predetermined ratio. In addition, the monomer composition may optionally contain a monomer other than the above monomers (hereinafter sometimes referred to as “other monomers”).
Here, in the polymer contained in the binder composition for a lithium ion secondary battery electrode of the present invention, a unit derived from a lithium salt of an unsaturated acid (monomer a) and an unsaturated acid (monomer b) The lithium ion in the unit derived from the lithium salt of the unsaturated acid is coordinated with a part of the acid group in the unit derived from the unsaturated acid. Bond to form a cross-linked structure. And by such a crosslinked structure, the mechanical strength and electrolytic solution resistance as a polymer are improved. As a result, the obtained polymer can exhibit excellent binding properties, and when used in the production of a lithium ion secondary battery, the battery characteristics of the lithium ion secondary battery (for example, cycle characteristics and high temperature storage characteristics). ) Can be improved.
Moreover, since the polymer which the binder composition for lithium ion secondary battery electrodes of this invention contains contains the unit derived from the lithium salt (monomer a) of an unsaturated acid, lithium ion conductivity is made. Are better. Therefore, if a binder composition containing a polymer is used, the internal resistance of the electrode and the lithium ion secondary battery can be reduced.
Further, in the synthesis of the polymer contained in the binder composition for a lithium ion secondary battery electrode of the present invention, the presence of a lithium salt (anionic component) derived from the lithium salt of the unsaturated acid (monomer a) is reduced. Electric repulsion occurs. Therefore, even when the unsaturated acid (monomer b) is used to increase the binding property of the polymer, it is possible to avoid the aggregation of the polymerization reaction product during the polymerization reaction. In the synthesis of the above polymer, as monomers, lithium salt of unsaturated acid (monomer a), unsaturated acid (monomer b), and α, β-unsaturated nitrile (monomer) Since c) is used in combination, it is possible to suppress the precipitation of the polymerization reaction product during the polymerization reaction and to greatly improve the conversion rate of the monomer to the polymer (polymerization conversion rate). In view of these points, the above-described polymer and the binder composition for a lithium ion secondary battery electrode of the present invention containing the polymer can be easily subjected to post-treatment for removing the remaining monomer or In addition, it can be made unnecessary, and the manufacturing cost can be reduced, so that it can be prepared with high productivity. As apparent from the above, in the present invention, it is important that the monomer composition contains the monomer a from the time of polymerization. The effect described above cannot be obtained by lithium-chlorinating the unit derived from the monomer b after polymerization.

  Hereafter, each monomer contained in the monomer composition used for preparation of the polymer which the binder composition for lithium ion secondary battery electrodes of this invention contains is explained in full detail.

[Lithium salt of unsaturated acid (monomer a)]
The monomer composition needs to contain at least a lithium salt of an unsaturated acid (monomer a).
Here, among the unsaturated acid salts, the lithium salt of the unsaturated acid is an essential component, for example, using only other salts such as a sodium salt of an unsaturated acid and a potassium salt of an unsaturated acid. If the lithium salt of a saturated acid is not used, the resulting polymer inhibits lithium ion migration (for example, insertion into and desorption from the electrode active material) in the lithium ion secondary battery. This is because the solubility in an organic solvent such as N-methylpyrrolidone tends to be relatively low, and the desired effect (for example, improvement in battery performance) cannot be obtained.

The lithium salt of the unsaturated acid is not particularly limited, and examples thereof include a lithium salt of an unsaturated carboxylic acid, a lithium salt of an unsaturated sulfonic acid, and a lithium salt of an unsaturated phosphonic acid. Among these, as the lithium salt of an unsaturated acid, it is preferable to use a lithium salt of an unsaturated carboxylic acid or a lithium salt of an unsaturated sulfonic acid. The lithium salt of unsaturated carboxylic acid and lithium salt of unsaturated sulfonic acid are easy to obtain and have high polymerization reactivity. Therefore, if these lithium salts are used, the productivity of the binder composition can be further increased. Because you can. Moreover, since the lithium salt of unsaturated carboxylic acid and the lithium salt of unsaturated sulfonic acid have a high degree of dissociation of lithium ions, the internal resistance of the lithium ion secondary battery can be further reduced by using these lithium salts. Because you can.
Here, as the lithium salt of the unsaturated carboxylic acid, lithium salt of α, β-unsaturated monocarboxylic acid such as acrylic acid, methacrylic acid, crotonic acid; α, β such as maleic acid, fumaric acid, and itaconic acid -Lithium salt of unsaturated dicarboxylic acid; lithium salt of partially esterified product of α, β-unsaturated polyvalent carboxylic acid such as monomethyl maleate and monoethyl itaconate; unresolved such as oleic acid, linoleic acid, linolenic acid, rumenic acid Examples include lithium salts of saturated fatty acids.
Examples of the lithium salt of unsaturated sulfonic acid include vinyl sulfonic acid, o-styrene sulfonic acid, m-styrene sulfonic acid, p-styrene sulfonic acid, and 2-acrylamido-2-methylpropane sulfonic acid (AMPS). Examples thereof include lithium salts and various substitutes thereof.
Further, examples of the lithium salt of unsaturated phosphonic acid include lithium salts such as vinylphosphonic acid, o-styrenephosphonic acid, m-styrenephosphonic acid, and p-styrenephosphonic acid, and various substitutes thereof. .
In addition, the monomer composition may contain the lithium salt of one type of unsaturated acid independently, and may contain the lithium salt of two or more types of unsaturated acid in arbitrary ratios.
Here, as the lithium salt of the unsaturated acid described above, from the viewpoint of further increasing the dissociation of lithium ions and further reducing the internal resistance of the lithium ion secondary battery, lithium acrylate, lithium methacrylate, and p-styrene. Lithium sulfonate is particularly preferred.
As the lithium salt of the unsaturated acid, for example, a commercially available lithium salt of an unsaturated acid can be used, and an unsaturated acid and a basic lithium compound such as lithium hydroxide monohydrate or lithium carbonate. What was prepared by making it react with can also be used.

  And in this invention, although content of the lithium salt of the unsaturated acid in a monomer composition needs to be 10 mass% or more, it is preferable that it is 15 mass% or more. When the content of the lithium salt of the unsaturated acid in the monomer composition is less than 10% by mass, the polymerization stability cannot be maintained at a high level, and the polymerization reaction product aggregates during the polymerization reaction, resulting in high productivity. This is because a polymer cannot be prepared. The content of the lithium salt of the unsaturated acid in the monomer composition needs to be 80% by mass or less, preferably 60% by mass or less, and 50% by mass or less. Is more preferable. When the content of the lithium salt of the unsaturated acid in the monomer composition is more than 80% by mass, sufficient flexibility is not imparted to the resulting polymer, and the binding property is lowered. This is because, when a lithium ion secondary battery is manufactured by winding the electrode prepared by using the electrode, electrode breakage or the like may occur, which may make it difficult to manufacture the battery.

[Unsaturated acid (monomer b)]
Moreover, a monomer composition needs to contain an unsaturated acid (monomer b) at least.

The unsaturated acid is not particularly limited, and examples thereof include unsaturated carboxylic acids, unsaturated sulfonic acids, and unsaturated phosphonic acids. Among these, as the unsaturated acid, it is preferable to use an unsaturated carboxylic acid or an unsaturated sulfonic acid. This is because unsaturated carboxylic acid and unsaturated sulfonic acid are easily available, and can improve the adhesion between the electrode mixture layer and the current collector by increasing the binding property of the polymer.
Here, examples of the unsaturated carboxylic acid include α, β-unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; α, β-unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; Examples include partially esterified products of α, β-unsaturated polyvalent carboxylic acids such as monomethyl maleate and monoethyl itaconate; unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and rumenic acid.
Examples of the unsaturated sulfonic acid include vinyl sulfonic acid, o-styrene sulfonic acid, m-styrene sulfonic acid, p-styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and these Various substitutes are exemplified.
Furthermore, examples of the unsaturated phosphonic acid include vinyl phosphonic acid, o-styrene phosphonic acid, m-styrene phosphonic acid, p-styrene phosphonic acid, and various substitutes thereof.
In addition, the monomer composition may contain one type of unsaturated acid independently, and may contain two or more types of unsaturated acids in arbitrary ratios.
Here, as the unsaturated acid described above, from the viewpoint of further improving the adhesion between the electrode mixture layer and the current collector, and further reducing the frequency or degree of polymerization reaction product aggregation during the polymerization reaction. Acrylic acid, methacrylic acid, p-styrene sulfonic acid and vinyl sulfonic acid are preferred, and acrylic acid and methacrylic acid are particularly preferred.
In addition, as said unsaturated acid, a commercially available unsaturated acid can also be used, for example, and what substituted a part of such commercially available unsaturated acid with the halogen etc. can also be used.

  And in this invention, although content of the unsaturated acid in a monomer composition needs to be 5 mass% or more, it is preferable that it is 10 mass% or more, and it is 15 mass% or more. It is more preferable. When the content of the unsaturated acid in the monomer composition is less than 5% by mass, a current collector and an electrode mixture are prepared when an electrode for a lithium ion battery is prepared using a binder composition containing the resulting polymer. This is because the adhesion to the layer cannot be sufficiently improved. Further, the content of the unsaturated acid in the monomer composition is required to be 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less. . This is because if the content of the unsaturated acid in the monomer composition exceeds 40% by mass, the polymerization reaction product cannot be effectively prevented from aggregating during the polymerization reaction. Moreover, it is because there exists a possibility that the lithium ion conductivity of a polymer may fall and the internal resistance of an electrode and a lithium ion secondary battery may rise.

[Α, β-unsaturated nitrile (monomer c)]
Further, the monomer composition needs to contain at least an α, β-unsaturated nitrile (monomer c).

The α, β-unsaturated nitrile is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, and various substitutes thereof.
In addition, the monomer composition may contain one kind of α, β-unsaturated nitrile alone, or may contain two or more kinds of α, β-unsaturated nitriles in an arbitrary ratio.
Here, as the above-mentioned α, β-unsaturated nitrile, acrylonitrile or methacrylonitrile is preferable, and acrylonitrile is more preferable, from the viewpoint of ensuring the mechanical strength and oxidation resistance of the obtained polymer at a high level. . By ensuring the mechanical strength and oxidation resistance of the polymer at a high level, the polymer can exhibit good binding properties and have good battery characteristics (for example, high temperature) for lithium ion secondary batteries. Cycle characteristics and high-temperature storage characteristics).
As the α, β-unsaturated nitrile, for example, a commercially available α, β-unsaturated nitrile can be used, and a part of the commercially available α, β-unsaturated nitrile is substituted with halogen or the like. It is also possible to use what has been done.

  In the present invention, the content of the α, β-unsaturated nitrile in the monomer composition needs to be 10% by mass or more, preferably 20% by mass or more, more preferably It is 30 mass% or more, More preferably, it is 35 mass% or more. If the content of α, β-unsaturated nitrile in the monomer composition is less than 10% by mass, the resulting polymer has insufficient mechanical strength, and the adhesion between the current collector and the electrode mixture layer This is because the battery characteristics (for example, high temperature cycle characteristics and high temperature storage characteristics) of the lithium ion secondary battery may be deteriorated. Further, the content of α, β-unsaturated nitrile in the monomer composition is required to be 85% by mass or less, preferably 75% by mass or less, and more preferably 70% by mass or less. It is. If the content of α, β-unsaturated nitrile in the monomer composition is more than 85% by mass, a sufficiently high polymerization conversion rate may not be achieved, and the resulting polymer becomes excessively hard. This is because it becomes difficult to produce a lithium ion secondary battery electrode and a lithium ion secondary battery using the polymer.

[Other monomers]
Furthermore, the monomer composition can optionally contain a monomer other than the monomers described above (other monomers). The other monomer is not particularly limited. For example, when a homopolymer having a weight average molecular weight of more than 10,000 is formed, the monomer having a glass transition point Tg of the homopolymer below room temperature (single monomer Isomer d).

[[Monomer d]]
When the monomer composition contains the monomer d, the flexibility of the resulting polymer can be improved and high binding properties can be ensured.
The monomer composition may contain one kind of monomer d alone or may contain two or more kinds of monomers d in any ratio.

Here, as the monomer d, when a homopolymer having a weight average molecular weight of more than 10,000 is formed, the glass transition point Tg of the homopolymer is less than room temperature, preferably less than 0 ° C., more preferably If it is a monomer which will be less than -20 degreeC, it will not specifically limit, For example, (meth) acrylic acid ester is mentioned. Examples of such (meth) acrylic acid esters include (meth) acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, and butyl (meth) acrylate.
In the present specification, “(meth) acryl” in (meth) acrylic acid ester and the like refers to acryl and / or methacryl.

  In the present invention, the content of the monomer d in the monomer composition is preferably 70% by mass or less, more preferably 45% by mass or less, and 20% by mass or less. Is more preferable. By making the content of monomer d 70% by mass or less, a sufficient amount of units derived from the lithium salt of unsaturated acid, unsaturated acid and α, β-unsaturated nitrile in the polymer is secured, This is because the intended effect of using the polymer can be obtained.

[Preparation of polymer]
And the polymer which the binder composition for lithium ion secondary battery electrodes of this invention contains is not specifically limited, Each monomer (monomer a, monomer b, monomer c) mentioned above And other monomers) in the above-described proportions, for example, by polymerizing in an aqueous solvent.
In the above monomer composition, when the monomer a (lithium salt of unsaturated acid) is a compound obtained by subjecting the monomer b (unsaturated acid) to lithium chloride, it is particularly limited. The monomer composition precursor containing the monomer b, the monomer c, and optionally other monomers is prepared, and the monomer in the monomer composition precursor A monomer composition may be prepared by lithium-chlorinating a part of the body b with a basic lithium compound to form a monomer a. In this case, the content of monomer b in the monomer composition precursor is lithium chloride based on the amount of monomer a and monomer b to be included in the monomer composition. Thus, the total amount of the monomer b to be monomer a and the amount of monomer b to be contained in the monomer composition may be used.

Here, the production method of the polymer is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used.
As the polymerization method, 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.

And in manufacture of a polymer, since the polymer composition mentioned above is used, the polymerization conversion ratio of a monomer can be 90% or more, preferably 95% or more. Therefore, since the residual amount of each monomer after the polymerization reaction is greatly reduced, the post-treatment of the residual monomer can be made easy or unnecessary, and the material cost is further reduced.
The polymer produced as described above is a unit derived from the monomer contained in the monomer composition used for the polymerization, and the presence of each monomer in the monomer composition. It is included in the same ratio as the ratio.

<Dispersion medium>
The binder composition for a lithium ion secondary battery electrode of the present invention contains a dispersion medium. Here, the dispersion medium may be an aqueous solvent used when producing the polymer, or an organic solvent. Specifically, when the aqueous dispersion of a polymer obtained by polymerizing a monomer composition in an aqueous solvent is used as a binder composition as it is, the dispersion medium is water or an aqueous solution used for the polymerization. An aqueous solvent may be used. Further, for example, when the monomer composition is polymerized in an aqueous solvent and then the aqueous solvent is replaced with an organic solvent to obtain a binder composition, the organic solvent may be used. The organic solvent is not particularly limited, and examples thereof include N-methylpyrrolidone (NMP), acetonitrile, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, and ethylenediamine. . In addition, as a dispersion medium, an organic solvent is preferable and N-methylpyrrolidone (NMP) is more preferable.
And the binder composition for secondary battery electrodes of this invention may contain one type of solvent independently as the said dispersion medium, and may contain two or more types of solvents by arbitrary ratios.

<Other ingredients>
The binder composition for a lithium ion secondary battery electrode of the present invention may contain known optional components that can be blended in the binder composition in addition to the components described above. Moreover, residues, such as a polymerization initiator used for superposition | polymerization of a polymer, may be included.

(Slurry composition for lithium ion secondary battery electrode)
The slurry composition for lithium ion secondary battery electrodes of the present invention includes the above-described binder composition for lithium ion secondary battery electrodes and an electrode active material. And in the slurry composition for lithium ion secondary battery electrodes of this invention, the polymer which the slurry composition for lithium ion secondary battery electrodes contains functions as at least one part of a binder. By using such a slurry composition for a lithium ion secondary battery electrode, it is possible to provide an electrode for a lithium ion secondary battery having excellent peel strength and low internal resistance, and for the lithium ion secondary battery. A lithium ion secondary battery using an electrode and having low internal resistance can be provided.
Here, the slurry composition for a lithium ion secondary battery electrode of the present invention optionally includes a conductive material and a binder composition contained in the binder composition for the lithium ion secondary battery electrode and the electrode active material. It may contain a polymer other than the polymer, other optional additives, and the like.

<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. Hereinafter, the electrode active materials (positive electrode active material, negative electrode active material) used in the slurry composition for lithium ion secondary battery electrodes of the present invention will be described in detail.

[Positive electrode active material]
As a positive electrode active material mix | blended with the slurry composition of this invention, the known positive electrode active material used in the positive electrode of a lithium ion secondary battery can be used, without being specifically limited. Specifically, as the positive electrode active material, a compound containing a transition metal, for example, a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and a transition metal, or the like can be used. In addition, as a transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo etc. are mentioned, for example.

Here, as the transition metal oxide, for example, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , amorphous Examples include MoO ₃ , amorphous V ₂ O ₅ , and amorphous V ₆ O ₁₃ .
The transition metal sulfide, TiS _2, TiS _3, such as an amorphous MoS _2, FeS, and the like.
Examples of the composite metal oxide of lithium and transition metal include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure. It is done.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), Co—Ni—Mn lithium-containing composite oxide, and Ni—Mn. Examples include a lithium-containing composite oxide of -Al, a lithium-containing composite oxide of Ni-Co-Al, and a solid solution of LiMaO ₂ and Li ₂ MbO ₃ . Examples of the solid solution of LiMaO ₂ and Li ₂ MbO ₃ include xLiMaO _2. (1-x) Li ₂ MbO ₃ . Here, x represents a number satisfying 0 <x <1, Ma represents one or more transition metals having an average oxidation state of 3+, and Mb represents one or more transition metals having an average oxidation state of 4+. Represent.
In this specification, the “average oxidation state” indicates an average oxidation state of the “one or more transition metals”, and is calculated from the molar amount and valence of the transition metal. For example, when “one or more transition metals” is composed of 50 mol% Ni ²⁺ and 50 mol% Mn ⁴⁺ , the average oxidation state of “one or more transition metals” is (0. 5) × (2 +) + (0.5) × (4 +) = 3+

Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and compounds in which a part of Mn of lithium manganate (LiMn ₂ O ₄ ) is substituted with another transition metal. Is mentioned. A specific example is Li _s [Mn _{2 -t} Mc _t ] O ₄ . Here, Mc represents one or more transition metals having an average oxidation state of 4+. Specific examples of Mc include Ni, Co, Fe, Cu, and Cr. T represents a number satisfying 0 <t <1, and s represents a number satisfying 0 ≦ s ≦ 1. As the positive electrode active material, a lithium-excess spinel compound represented by Li _{1 + x} Mn _2−x O ₄ (0 <X <2) can also be used.

Examples of the lithium-containing composite metal oxide having an olivine type structure include olivine type phosphorus represented by Li _y MdPO ₄ such as olivine type lithium iron phosphate (LiFePO ₄ ) and olivine type lithium manganese phosphate (LiMnPO ₄ ). An acid lithium compound is mentioned. Here, Md represents one or more transition metals having an average oxidation state of 3+, and examples thereof include Mn, Fe, and Co. Y represents a number satisfying 0 ≦ y ≦ 2. Furthermore, in the olivine-type lithium phosphate compound represented by Li _y MdPO ₄ , Md may be partially substituted with another metal. Examples of the metal that can be substituted include Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo.

Among the above, from the viewpoint of improving the cycle characteristics and initial capacity of the secondary battery using the positive electrode formed using the slurry composition, lithium-containing cobalt oxide (LiCoO ₂ ), Co—Ni— as the positive electrode active material. It is preferable to use a lithium-containing composite oxide of Mn or olivine type lithium iron phosphate (LiFePO ₄ ).

Further, from the viewpoint of increasing the capacity of a lithium ion secondary battery using a positive electrode formed using the slurry composition, it is preferable to use a positive electrode active material containing at least one of Mn and Ni as the positive electrode active material. . Specifically, from the viewpoint of increasing the capacity of the lithium ion secondary battery, LiNiO ₂ , LiMn ₂ O ₄ , a lithium-excess spinel compound, LiMnPO ₄ , Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ , Li [ Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ , LiNi _0.5 Mn _1.5 O ₄ etc. are preferably used as the positive electrode active material, LiNiO ₂ , Lithium-excess spinel compound, Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ , Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O _2, etc. Is more preferably used as the positive electrode active material, and Li [Ni _0.5 Co _0.2 Mn _0.3 ] O ₂ is particularly preferably used as the positive electrode active material.
The particle size and specific surface area of the positive electrode active material are not particularly limited and can be the same as those of conventionally used positive electrode active materials.

  Here, when the slurry composition for a lithium ion secondary battery electrode of the present invention is used for a positive electrode, the content of the positive electrode active material in the slurry composition is not particularly limited. For example, the solid content of the slurry composition Preferably it is 90 to 98 mass parts per 100 mass parts. By setting the content of the positive electrode active material within this range, it is possible to improve the capacity of the lithium ion secondary battery while setting the internal resistance of the positive electrode for the lithium ion secondary battery to an appropriate level.

[Negative electrode active material]
As a negative electrode active material mix | blended with the slurry composition of this invention, the known negative electrode active material used in the negative electrode of a lithium ion secondary battery can be used, without being specifically limited. Specifically, a material that can occlude and release lithium is usually used as the negative electrode active material. Examples of the material that can occlude and release lithium include a carbon-based negative electrode active material, a metal-based negative electrode active material, and a negative electrode active material obtained by combining these materials.

[[Carbon-based negative electrode active material]]
The carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of inserting lithium (also referred to as “dope”). Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials. Is mentioned.

Here, examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. It is done.
Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like.
Examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.

  Moreover, as a graphite material, graphite (graphite), such as natural graphite and artificial graphite, is mentioned, for example.

[[Metal negative electrode active material]]
The metal-based negative electrode active material is an active material containing a metal, and usually contains an element capable of inserting lithium in the structure, and the theoretical electric capacity per unit mass when lithium is inserted is 500 mAh / g or more. Is an active material. Examples of the metal active material include lithium metal and a single metal capable of forming a lithium alloy (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn). , Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof.

  Among metal-based negative electrode active materials, an active material containing silicon (silicon-based negative electrode active material) is preferable. This is because the capacity of the lithium ion secondary battery can be increased by using the silicon-based negative electrode active material.

Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, SiO, SiO _x , and a composite of a Si-containing material obtained by coating or combining a Si-containing material with conductive carbon and conductive carbon. Etc. In addition, these silicon type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more types.

  Examples of the alloy containing silicon include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing a rare earth element such as tin and yttrium.

SiO _x is a compound containing at least one of SiO and SiO ₂ and Si, and x is usually 0.01 or more and less than 2. Then, SiO _x, for example, can be formed by using a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO _x can be prepared by heat-treating SiO, optionally in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, in an atmosphere containing an organic gas and / or vapor after grinding and mixing SiO and optionally a polymer.

  As a composite of Si-containing material and conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing, for example, an organic gas and / or steam. Can be mentioned. In addition, a method of coating the surface of the SiO particles by a chemical vapor deposition method using an organic gas, a method of forming composite particles (granulation) of the SiO particles and graphite or artificial graphite by a mechanochemical method, etc. It can also be obtained by a known method.

  The particle size and specific surface area of the negative electrode active material are not particularly limited, and can be the same as those of conventionally used negative electrode active materials.

  Here, when the slurry composition for lithium ion secondary battery electrodes of the present invention is used for a negative electrode, the content of the negative electrode active material in the slurry composition is not particularly limited. For example, the solid content of the slurry composition Preferably it is 90 to 98 mass parts per 100 mass parts. By setting the content of the negative electrode active material in this range, it is possible to improve the capacity of the lithium ion secondary battery while setting the internal resistance of the negative electrode for the lithium ion secondary battery to an appropriate level.

<Binder composition>
In the electrode mixture layer of the electrode for a lithium ion secondary battery prepared using the slurry composition for a lithium ion secondary battery electrode, the polymer contained in the binder composition described above is used as at least a part of the binder. Function.
And the slurry composition for lithium ion secondary battery electrodes of this invention is the above-mentioned binder composition for lithium ion secondary battery electrodes, for example per 100 mass parts of electrode active materials in solid content equivalent amount, Preferably it is 0. .1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass. By setting the content of the binder composition within this range, it is possible to improve the output characteristics of the lithium ion secondary battery while obtaining desired effects such as reduction of the internal resistance of the electrode for the lithium ion secondary battery. .

<Conductive material>
The conductive material is for ensuring electrical contact between the electrode active materials. The conductive material is not particularly limited, and a known conductive material can be used. Specifically, for example, as a conductive material for a positive electrode of a lithium ion secondary battery, conductive carbon materials such as acetylene black, ketjen black (registered trademark), carbon black, and graphite; fibers of various metals, foils, etc. Can be used. Among these, 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, the conductive material is acetylene. Black, ketjen black (registered trademark), carbon black, and graphite are preferably used, and acetylene black and ketjen black (registered trademark) are particularly preferably used.

  In addition, although the compounding quantity of the electrically conductive material in the slurry composition for lithium ion secondary battery positive electrodes of this invention is not specifically limited, For example, per 100 mass parts of positive electrode active materials, Preferably they are 1 mass part or more and 5 mass parts or less. is there. If the blending amount of the conductive material is too small, sufficient electrical contact between the electrode active materials cannot be ensured, and sufficient electrical characteristics of the lithium ion secondary battery cannot be ensured. On the other hand, when the amount of the conductive material is too large, the stability of the slurry composition is lowered and the density of the electrode mixture layer in the electrode is lowered, so that the capacity of the lithium ion secondary battery cannot be sufficiently increased. .

<Other polymers>
Here, the slurry composition for a lithium ion secondary battery electrode of the present invention includes, as a binder, a polymer other than the polymer (hereinafter referred to as “other heavy metals”) in addition to the polymer contained in the binder composition described above. May be referred to as “union”). By including the above-mentioned other polymer in the slurry composition for lithium ion secondary battery electrodes, the adhesion between the electrode mixture layer and the current collector is further improved, and the output characteristics of the obtained secondary battery are improved. It is because it becomes possible to make it.

  Examples of other polymers include fluorine-containing polymers and acrylonitrile polymers. Examples of the fluorine-containing polymer include polymers containing 30% by mass or more of vinylidene fluoride units, such as polyvinylidene fluoride. The acrylonitrile polymer includes heavy polymers containing more than 85% by mass of acrylonitrile units. Copolymers such as polyacrylonitrile are mentioned. Among these, a fluorine-containing polymer is more preferable from the viewpoint of further improving the adhesion between the electrode mixture layer and the current collector and further improving the output characteristics of the lithium ion secondary battery.

  In addition, when the slurry composition for lithium ion secondary battery electrodes of the present invention contains a polymer (other polymer) other than the polymer contained in the binder composition, the content of the other polymer is as follows: Although not particularly limited, the total amount of the above-described binder composition corresponding to the solid content and the other polymer is preferably 10% by mass to 90% by mass, more preferably 20% by mass to 80% by mass. It is. By setting the content of the other polymer within this range, the adhesion between the electrode mixture layer and the current collector can be further improved, and the output characteristics of the lithium ion secondary battery can be further improved. Can do.

<Other additives>
In addition to the above components, the slurry composition for lithium ion secondary battery electrodes of the present invention includes, for example, a viscosity modifier such as a reinforcing material, an antioxidant, a thickener, a surfactant, a dispersant, and an electrolytic solution. It may contain components such as an electrolytic solution additive having a function of suppressing the above. As these other additives, known ones can be used, for example, those described in International Publication No. 2012/036260 and those described in JP 2012-204303 A can be used.

<Preparation of slurry composition for lithium ion secondary battery electrode>
The slurry composition for a lithium ion secondary battery electrode of the present invention can be prepared by dissolving or dispersing the above components in an organic solvent. Specifically, the above components and the organic solvent are mixed using a blender 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, or a fill mix. Thus, a slurry composition can be prepared.
In addition, as an organic solvent, the organic solvent which the binder composition contains may be used as it is, and an organic solvent may be added when preparing a slurry composition. Further, the mixing of each of the above components and the organic solvent can usually be performed in the range of room temperature to 80 ° C. for 10 minutes to several hours.

(Electrode for lithium ion secondary battery)
The electrode for a lithium ion secondary battery of the present invention comprises an electrode mixture layer prepared using the slurry composition for a lithium ion secondary battery electrode obtained as described above on a current collector. The electrode mixture layer contains at least the electrode active material and the polymer described above. In addition, each component such as an electrode active material contained in the electrode mixture layer is contained in the slurry composition for lithium ion secondary battery electrodes of the present invention. The abundance ratio is the same as the preferred abundance ratio of each component in the slurry composition for a lithium ion secondary battery electrode of the present invention. Since the electrode for lithium ion secondary batteries of the present invention uses the binder composition of the present invention, it has high peel strength and low internal resistance.

<Manufacture of electrodes for lithium ion secondary batteries>
The electrode for a lithium ion secondary battery of the present invention was applied on the current collector by, for example, applying the slurry composition for a lithium ion secondary battery electrode obtained as described above on the current collector. It is obtained by drying a slurry composition for a lithium ion secondary battery electrode. That is, the electrode for a lithium ion secondary battery is obtained, for example, through a slurry composition coating process and a slurry composition drying process.

[Coating process]
It does not specifically limit as a method of apply | coating the said slurry composition for lithium ion secondary battery electrodes on a collector, A well-known method can be used. As a specific 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, the current collector to which the slurry composition is applied is not particularly limited as long as it is a material having electrical conductivity and electrochemical durability. From the viewpoint of heat resistance, the current collector is preferably made of metal, such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. Among them, for example, aluminum is particularly preferable for the positive electrode, and copper is preferable for the negative electrode. One type of current collector material may be used alone, or two or more types may be used in combination at any ratio.

[Drying process]
The 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 hot air, hot air, low-humidity air, vacuum drying, irradiation with infrared rays, electron beams, or the like. The drying method by 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 pressurization treatment can improve the adhesion between the electrode mixture layer and the current collector and reduce the porosity of the electrode.

  Moreover, a powder molding method is mentioned as an example of another manufacturing method of the electrode for lithium ion secondary batteries of this invention. The powder molding method refers to preparing a slurry composition for producing an electrode for a lithium ion secondary battery, preparing composite particles containing an electrode active material from the slurry composition, and using the composite particles as a current collector This is a production method for obtaining an electrode for a lithium ion secondary battery by forming an electrode mixture layer by supplying the material onto the surface and further rolling and forming as desired. At this time, as the slurry composition, the same slurry composition as described above can be used.

(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 lithium ion secondary battery electrode of the present invention is used for at least one of the positive electrode and the negative electrode. Since the lithium ion secondary battery of the present invention uses the above-described electrode for a lithium ion secondary battery, it has a low internal resistance.

<Electrode>
As described above, the electrode for a lithium ion secondary battery of the present invention is used as at least one of a positive electrode and a negative electrode. That is, the positive electrode of the lithium ion secondary battery of the present invention may be an electrode for a lithium ion secondary battery of the present invention, the negative electrode may be another known negative electrode, and the negative electrode of the lithium ion secondary battery of the present invention is the main electrode. The electrode for a lithium ion secondary battery of the invention, the positive electrode may be another known positive electrode, and both the positive electrode and the negative electrode of the lithium ion secondary battery of the invention are for the lithium ion secondary battery of the invention It may be an electrode.

<Electrolyte>
As an electrolytic solution for a lithium ion secondary battery, for example, a nonaqueous electrolytic solution in which a supporting electrolyte is dissolved in a nonaqueous solvent is used. As the supporting electrolyte, a lithium salt is usually 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 that are easily soluble in a solvent and exhibit a high degree of dissociation are preferable. One of these may be used alone, or two or more of these may be used in combination at any ratio. Since the lithium ion conductivity increases as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

  The non-aqueous solvent is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of non-aqueous solvents include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC); and 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; Among these, carbonates are preferable because they have a high dielectric constant and a wide stable potential region. A non-aqueous solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, you may contain an additive in electrolyte solution. Examples of the additive include carbonate compounds such as vinylene carbonate (VC). An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Further, as an electrolytic solution other than the above, for example, a polymer electrolyte such as polyethylene oxide or polyacrylonitrile; a gel polymer electrolyte obtained by impregnating the polymer electrolyte with an electrolytic solution; an inorganic solid electrolyte such as LiI or Li ₃ N; Also good.

<Separator>
As a separator, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these, from the viewpoint of reducing the overall thickness of the separator and increasing the electrode active material ratio in the lithium ion secondary battery to increase the capacity per volume, polyolefin resins (polyethylene, polypropylene, A microporous film made of polybutene or polyvinyl chloride is preferred.

<Method for producing lithium ion secondary battery>
As a specific manufacturing method of 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 shape of the battery. The method of inject | pouring electrolyte solution into a container and sealing is mentioned. Further, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the secondary battery may be any of 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 the following examples, as one aspect of the present invention, the lithium ion secondary battery electrode binder composition of the present invention was used only for the positive electrode to produce a lithium ion secondary battery.
In the examples and comparative examples, the polymerization conversion rate of the monomer, the peel strength of the positive electrode for the lithium ion secondary battery, and the low temperature characteristics, the high temperature storage characteristics and the high temperature cycle characteristics of the lithium ion secondary batteries are as follows. Used and evaluated.

<Polymerization conversion rate of monomer>
When preparing the monomer composition, the total weight of each monomer (total weight of charged monomers), the total weight of deionized water (charged water weight), and all the raw materials charged in the autoclave The total weight (total weight of raw materials charged) was precisely weighed.
Moreover, when it superposed | polymerized using a monomer composition, first, some polymerization reaction products obtained were extract | collected, and the weight (polymerization reaction product weight before drying) was precisely weighed. Next, the collected weight reaction product was dried in a hot air dryer at a temperature of 120 ° C. for 1 hour, and its weight (polymerization reaction product weight after drying) was weighed again. Here, (weight of polymerization reaction product after drying) ÷ (weight of polymerization reaction product before drying) × 100 was calculated and used as the solid content rate (%) of the polymerization reaction product.
And, [(total weight of charged raw material) × (solid content ratio of weight reaction product) − {(total weight of charged raw material) − (weight of charged water) − (total weight of charged monomer)}] ÷ (charged monomer Total weight) × 100 was calculated and used as the monomer polymerization conversion rate (%).

<Peel strength of positive electrode for lithium ion secondary battery>
The prepared positive electrode was cut into a rectangle having a width of 1.0 cm and a length of 10 cm to obtain a test piece. Then, a cellophane tape was attached to the surface of the test piece on the positive electrode mixture layer side. At this time, the cellophane tape defined in JIS Z1522 was used. Then, the stress when the test piece was peeled from the one end side toward the other end side at a speed of 50 mm / min with the cellophane tape fixed to the test stand was measured. The measurement was performed 10 times, the average value of the stress was determined, and this was taken as the peel strength (N / m), and evaluated according to the following criteria. The higher the peel strength, the better the binding property of the binding material, and the higher the adhesion of the positive electrode mixture layer to the current collector.
A: Peel strength is 30 N / m or more B: Peel strength is 20 N / m or more and less than 30 N / m C: Peel strength is 10 N / m or more and less than 20 N / m D: Peel strength is less than 10 N / m

<Low temperature characteristics of lithium ion secondary battery>
In order to evaluate the low temperature characteristics of the produced lithium ion secondary battery, the IV resistance was measured as follows. After charging to 50% of SOC (State Of Charge: Charging Depth) at 1C (C is a numerical value expressed by rated capacity (mA) / 1 hour (h)) in an atmosphere of −10 ° C., 50% of SOC is reduced. Charging for 15 seconds and discharging for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C as the center, respectively, and the battery voltage after 15 seconds in each case (charging side and discharging side) The slope was determined as IV resistance (Ω) (IV resistance during charging and IV resistance during discharging). The obtained IV resistance value (Ω) was evaluated according to the following criteria. The smaller the IV resistance value, the smaller the internal resistance and the better the low temperature characteristics.
A: IV resistance is 10Ω or less B: IV resistance is more than 10Ω and 15Ω or less C: IV resistance is more than 15Ω and 20Ω or less D: IV resistance is more than 20Ω

<High temperature storage characteristics of lithium ion secondary batteries>
About the produced lithium ion secondary battery, after charging to 4.3V by a 0.1 C constant current method in 25 degreeC environment, it stored at 80 degreeC for 100 hours. The open circuit voltage (hereinafter referred to as “OCV”) before the start of storage at 80 ° C. and the OCV of the cell after storage for 100 hours at 80 ° C. are measured, and at 80 ° C. relative to the OCV before the start of storage at 80 ° C. The ratio of OCV after storage for 100 hours was calculated as the OCV maintenance rate, and evaluated according to the following criteria. It shows that it is excellent in a high temperature storage characteristic, ie, a lifetime characteristic, so that an OCV maintenance factor is large.
A: OCV maintenance rate is 99.0% or more B: OCV maintenance rate is 98.5% or more and less than 99.0% C: OCV maintenance rate is 98.0% or more and less than 98.5% D: OCV maintenance rate is 98 Less than 0.0%

<High-temperature cycle characteristics of lithium ion secondary batteries>
The manufactured lithium ion secondary battery was charged to 4.2 V by a constant current method of 1.0 C in a 45 ° C. atmosphere and discharged to 3.0 V, and this operation was repeated 100 cycles. Charge / discharge capacity retention ratio (%) expressed by the ratio of the electric capacity at the end of 100 cycles and the electric capacity at the end of 5 cycles ((electric capacity at the end of 100 cycles / electric capacity at the end of 5 cycles) × 100) ) Was calculated and evaluated according to the following criteria. It shows that it is excellent in high temperature cycling characteristics, so that charging / discharging capacity retention rate is large.
A: Charge / discharge capacity retention is 95% or more B: Charge / discharge capacity retention is 90% or more and less than 95% C: Charge / discharge capacity retention is 85% or more and less than 90% D: Charge / discharge capacity retention is less than 85%

Example 1
<Preparation of monomer composition>
In an autoclave equipped with a stirrer, add 30 parts of methacrylic acid, 300 parts of deionized water, and 7.3 parts of lithium hydroxide monohydrate and stir for 10 minutes. An aqueous solution containing 16 parts of lithium methacrylate as monomer a and 15 parts of methacrylic acid as monomer b was obtained. Next, 69 parts of acrylonitrile as the monomer c was added to the obtained aqueous solution to prepare a monomer composition.

<Preparation of binder composition for lithium ion secondary battery electrode>
To the monomer composition obtained as described above, 0.5 part of potassium persulfate as a polymerization initiator was added, and the atmosphere was replaced with nitrogen and maintained at 70 ° C. for 3 hours and at 85 ° C. for 3 hours for polymerization. To obtain a uniform aqueous dispersion containing the polymer.
To 100 parts of this aqueous dispersion (solid content: 24.75 parts), 350 parts of N-methylpyrrolidone (NMP) was added to evaporate water under reduced pressure and evaporate 40.62 parts of NMP to produce lithium ions. A binder composition for a secondary battery electrode (solid content concentration: 8%) was obtained.
Table 1 shows the composition of the prepared monomer composition and the polymerization conversion rate when the above polymer is polymerized.

<Preparation of slurry composition for positive electrode of lithium ion secondary battery>
100 parts LiCoO ₂ (manufactured by Nippon Chemical Industry Co., Ltd., product name: Cellseed C-10N) as the positive electrode active material, 2 parts acetylene black as the conductive material, and the binder composition prepared as described above corresponding to the solid content 1 part was added, and N-methylpyrrolidone was further added so that the viscosity would be 4000 to 5000 mPa · s, and then mixed with a planetary mixer to prepare a slurry composition for a positive electrode of a lithium ion secondary battery.

<Preparation of positive electrode for lithium ion secondary battery>
The positive electrode slurry composition was applied to an aluminum foil having a thickness of 18 μm, dried at 120 ° C. for 3 hours, and then roll pressed to obtain a positive electrode having a positive electrode mixture layer having a thickness of 50 μm. The peel strength of the obtained positive electrode was evaluated. The results are shown in Table 1.

<Preparation of negative electrode for lithium ion secondary battery>
98 parts of graphite having a volume average particle diameter of 20 μm as a negative electrode active material and a specific surface area of 4.2 m ² / g, 40% by mass aqueous dispersion of styrene-butadiene copolymer as a binder (manufactured by Nippon Zeon Co., Ltd., BM-400B) 1.0 part (corresponding to solid content) and 1.0 part (corresponding to solid content) of sodium salt of carboxymethylcellulose as a viscosity modifier are mixed, and water is added and mixed with a planetary mixer. A negative electrode slurry composition was prepared. This negative electrode slurry composition was applied to one side of a copper foil having a thickness of 10 μm, dried at 110 ° C. for 3 hours, and then roll-pressed to obtain a negative electrode having a negative electrode mixture layer having a thickness of 60 μm.

<Production of laminated cell type lithium ion secondary battery>
A battery container was produced using a laminate film made of an aluminum sheet and a polypropylene resin covering both surfaces thereof. Next, the electrode mixture layer was removed from the ends of each of the positive electrode and the negative electrode, and a portion where the copper foil or aluminum foil was exposed was formed. A Ni tab was welded to the portion where the aluminum foil of the positive electrode was exposed, and a Cu tab was welded to the portion where the copper foil of the negative electrode was exposed. The obtained tabbed positive electrode and tabbed negative electrode were stacked with a separator made of a microporous film made of polyethylene interposed therebetween. The direction of the surface of the electrode was such that the surface on the positive electrode mixture layer side of the positive electrode and the surface on the negative electrode mixture layer side of the negative electrode face each other. The stacked electrodes and separator were wound and stored in the battery container. Subsequently, an electrolytic solution was injected here. As the electrolytic solution, a solution prepared by dissolving LiPF ₆ to a concentration of 1 mol / L in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1: 2 at 25 ° C. is used. It was.
Next, the laminate film was sealed to produce a laminate cell type secondary battery which is the lithium ion secondary battery of the present invention. The resulting laminated cell type secondary battery was evaluated for low temperature characteristics, high temperature storage characteristics, and high temperature cycle characteristics. The results are shown in Table 1.

(Examples 2 and 3)
As in Example 1, except that the amounts of methacrylic acid, lithium hydroxide monohydrate and acrylonitrile were changed during preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1. Then, a binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced, and various evaluations were performed. The results are shown in Table 1.

Example 4
The amount of acrylonitrile was changed during the preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1, and butyl acrylate as the monomer d (with a weight average molecular weight of 10 , More than 1,000 homopolymers Tg = −54 ° C. or less) was added to the monomer composition so that the content of monomer d was as shown in Table 1, and was the same as in Example 1. The electrode binder composition, the positive electrode slurry composition, the positive electrode, the negative electrode, and the secondary battery were prepared and produced, and various evaluations were performed. The results are shown in Table 1.

(Example 5)
A binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced in the same manner as in Example 1 except that the monomer composition prepared as described below was used. Various evaluations were made. The results are shown in Table 1.
<Preparation of monomer composition>
In an autoclave equipped with a stirrer, 29.78 parts of acrylic acid, 300 parts of deionized water, and 8.6 parts of lithium hydroxide monohydrate are added and stirred for 10 minutes. Chlorinated to obtain an aqueous solution containing 16 parts of lithium acrylate as monomer a and 15 parts of acrylic acid as monomer b. Next, 69 parts of acrylonitrile as the monomer c was added to the obtained aqueous solution to prepare a monomer composition.

(Examples 6 and 7)
As in Example 5, except that the amount of acrylic acid, lithium hydroxide monohydrate and acrylonitrile was changed during preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1. Then, a binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced, and various evaluations were performed. The results are shown in Table 1.

(Example 8)
The amount of acrylonitrile was changed during the preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1, and butyl acrylate as the monomer d was changed to the monomer d. A binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared in the same manner as in Example 5 except that the content was as shown in Table 1 and added to the monomer composition. Preparation, production, and various evaluations were performed. The results are shown in Table 1.

Example 9
A binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced in the same manner as in Example 1 except that the monomer composition prepared as described below was used. Various evaluations were made. The results are shown in Table 1.
<Preparation of monomer composition>
In an autoclave equipped with a stirrer, 16 parts of lithium p-styrenesulfonate (LiSS, manufactured by Tosoh Organic Chemical Co., Ltd.) as monomer a, 15 parts of methacrylic acid as monomer b, acrylonitrile as monomer c 69 parts and 300 parts of deionized water were added and mixed to prepare a monomer composition.

(Examples 10 and 11)
As in Example 9, except that the amounts of p-styrene sulfonate, methacrylic acid and acrylonitrile were changed during preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1. Then, a binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced, and various evaluations were performed. The results are shown in Table 1.

(Example 12)
The amount of acrylonitrile was changed during the preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1, and butyl acrylate as the monomer d was changed to the monomer d. A binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared in the same manner as in Example 9 except that the content was as shown in Table 1 and added to the monomer composition. Preparation, production, and various evaluations were performed. The results are shown in Table 1.

(Example 13)
The blending amount of the binder composition is 0.5 parts corresponding to the solid content, and polyvinylidene fluoride (PVDF) (manufactured by Kureha Chemical Industry Co., Ltd., product name: KF # 7208) as the other polymer is 0.00. A slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced in the same manner as in Example 1 except that only 5 parts were further blended, and various evaluations were performed. The results are shown in Table 1.

(Comparative Example 1)
Except having used the monomer composition prepared as follows and the binder composition for lithium ion secondary battery electrodes, it carried out similarly to Example 1, and the binder composition for electrodes, the slurry composition for positive electrodes, and the positive electrode A negative electrode and a secondary battery were prepared and manufactured, and various evaluations were performed. The results are shown in Table 1.
<Preparation of monomer composition>
A monomer composition was prepared by adding 15 parts of methacrylic acid as monomer b, 85 parts of acrylonitrile as monomer c, and 300 parts of deionized water to an autoclave equipped with a stirrer.
<Preparation of binder composition for lithium ion secondary battery electrode>
To the monomer composition obtained as described above, 0.5 part of potassium persulfate as a polymerization initiator was added, and the atmosphere was replaced with nitrogen and maintained at 70 ° C. for 3 hours and at 85 ° C. for 3 hours for polymerization. To obtain an aqueous dispersion containing coarse particles of a heterogeneous polymer.
1 part of aluminum sulfate was added to this aqueous dispersion, and the solid content was washed twice by filtration using water to obtain a solid polymer. To 24.75 parts of this polymer, 350 parts of N-methylpyrrolidone (NMP) was added to evaporate water under reduced pressure and to evaporate 40.62 parts of NMP to obtain a binder composition for lithium ion secondary battery electrodes. (Solid content concentration: 8%) was obtained.

(Comparative Examples 2 and 3)
As in Example 1, except that the amounts of methacrylic acid, lithium hydroxide monohydrate and acrylonitrile were changed during preparation of the monomer composition so that the composition of the monomer composition was as shown in Table 1. Then, a binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced, and various evaluations were performed. The results are shown in Table 1.

(Comparative Example 4)
A binder composition for an electrode, a slurry composition for a positive electrode, a positive electrode, a negative electrode, and a secondary battery were prepared and produced in the same manner as in Example 1 except that the monomer composition prepared as described below was used. Various evaluations were made. The results are shown in Table 1.
<Preparation of monomer composition>
In an autoclave equipped with a stirrer, 27.26 parts of methacrylic acid, 300 parts of deionized water, and 6.8 parts of sodium hydroxide are placed, stirred for 10 minutes, and a part of methacrylic acid is sodium chloride with sodium hydroxide. An aqueous solution containing 16 parts of sodium acid and 15 parts of methacrylic acid was obtained. Next, 69 parts of acrylonitrile was added to the obtained aqueous solution to prepare a monomer composition.

From Examples 1 to 13 in Table 1, the polymer can be polymerized at a conversion rate of 99% or more by using a monomer composition containing monomer a to monomer c in a predetermined ratio. In addition, by using a binder composition containing such a polymer, the peel strength of the lithium ion secondary battery electrode and the low temperature characteristics, high temperature storage characteristics and high temperature cycle characteristics of the lithium ion secondary battery are aligned at a high level. You can see that
In particular, Examples 1 to 12 show that various characteristics can be further improved by adjusting the contents of monomer a to monomer c in the monomer composition.
On the other hand, in Comparative Example 1 of Table 1, since the monomer composition does not contain monomer a and the content of monomer c is large, the polymerization conversion is remarkably low, and during polymerization, It can be seen that the polymerization reaction product aggregates. Moreover, it turns out that the lithium ion secondary battery manufactured using the binder composition of Comparative Example 1 has high internal resistance and deteriorated high-temperature storage characteristics and high-temperature cycle characteristics.
Moreover, in Comparative Example 2 of Table 1, since the monomer composition contains the monomer a excessively, sufficient flexibility is not imparted to the resulting polymer, and the content of the monomer b Therefore, the peel strength cannot be maintained. It can also be seen that the high-temperature storage characteristics and the high-temperature cycle characteristics are deteriorated due to the excessive inclusion of monomer a and the low content of monomer c.
In Comparative Example 3 of Table 1, the monomer composition contains monomer a, but the content of monomer b and monomer c is outside the predetermined range, so the lithium ion of the polymer It can be seen that the conductivity and oxidation resistance are lowered, and the high-temperature storage characteristics and the high-temperature cycle characteristics of the lithium ion secondary battery produced using the binder composition of Comparative Example 3 are deteriorated.
Further, in Comparative Example 4 of Table 1, since a sodium salt is used instead of the lithium salt of the unsaturated acid, the internal resistance of the lithium ion secondary battery is increased, and the high temperature storage characteristics and the high temperature cycle characteristics are deteriorated. You can see that

  In addition, when preparing the slurry composition for lithium ion secondary battery electrodes from Examples 1 and 13 in Table 1, a polymerized polymer was obtained using a monomer composition containing monomers a to c at a predetermined ratio. It can be seen that various characteristics can be improved even when a polymer other than the polymer, for example, a fluorine-containing polymer, is blended in addition to the binder composition containing the coalescence.

ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery with low internal resistance can be manufactured, and the binder composition for lithium ion secondary battery electrodes which is excellent in both productivity and binding property can be provided. .
Moreover, according to this invention, the slurry composition for lithium ion secondary battery electrodes which can prepare the electrode for lithium ion secondary batteries which is low in internal resistance and excellent in peel strength can be provided.
Furthermore, according to the present invention, an electrode for a lithium ion secondary battery having low internal resistance and excellent peel strength can be provided.
Moreover, according to this invention, a lithium ion secondary battery with low internal resistance can be provided.

Claims (7)

  Lithium salt of unsaturated acid (monomer a) 10 to 80% by mass, unsaturated acid (monomer b) 5 to 40% by mass, α, β-unsaturated nitrile (monomer c) 10 to 10% The binder composition for lithium ion secondary battery electrodes containing the polymer formed by superposing | polymerizing the monomer composition containing 85 mass%, and a dispersion medium.   The binder composition for a lithium ion secondary battery electrode according to claim 1, wherein the α, β-unsaturated nitrile (monomer c) is acrylonitrile.   The slurry composition for lithium ion secondary battery electrodes containing the binder composition for lithium ion secondary battery electrodes of Claim 1 or 2, and an electrode active material.   The slurry composition for a lithium ion secondary battery electrode according to claim 3, further comprising a polymer other than the polymer.   The slurry composition for a lithium ion secondary battery electrode according to claim 4, wherein the polymer other than the polymer is a fluorine-containing polymer.   The electrode for lithium ion secondary batteries provided with the electrode compound-material layer prepared using the slurry composition for lithium ion secondary battery electrodes as described in any one of Claims 3-5 on a collector.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein at least one of the positive electrode and the negative electrode is the electrode for a lithium ion secondary battery according to claim 6.